Global tropical SSTs remain above average with exceptions of coolness around Indonesia and more importantly the equatorial east Pacific. Magnitudes are ~0.5-1.5 C. Subsurface anomalies as low as minus 4.0C exist down to about 100m at 140W per TAO buoy array data with cool anomalies down to about 200m at the equatorial date line. Total SSTs are generally near or above 30C across the Indian Ocean and from the west central-South Pacific. It is still unclear whether or not a La-Nina is developing since May is a seasonally critical month.
Tropical convective forcing is getting better organized ~90-120E. Monitoring tools including the Wheeler phase space plot suggest a MJO may be developing in that region. The latter has been discussed as a possibility in recent posts. Other clusters of intense tropical thunderstorm activity remain across the South Pacific and equatorial Africa. A convectively coupled Kelvin wave, possibly forced by the extratropics a week ago, is supporting the activity across Africa. This forcing may contribute to additional enhanced rainfall across the equatorial Indian Ocean into Indonesia week 1. Whether or not a coherent eastward shift of tropical convection occurs across the Eastern Hemisphere afterwards remains to be seen. However, those with interests in that region should be concerned about excessive rainfall and possibly Bay of Bengal tropical cyclone development for at least weeks 1-2.
GSDM Stage 0.5 still best describes the current-weather climate situation. An evolution to ~ Stage 1.5 may occur during the next few weeks particularly if a MJO develops. Zonal mean easterly wind flow anomalies of ~5m/s loosely exist across the equatorial and subtropical atmospheres with magnitudes as high as 10m/s around 25N. Global relative AAM tendency is still weakly negative while actual AAM is a good 1 standard deviation below the R1 climatology as of April 25th (~1.5 sigma including the stratosphere presumably due to the easterly QBO phase). There are also indications of flux convergence of AAM ~40-50N in the presence of a developing sink across the northern subtropics. In fact, this flux convergence of AAM transport has been shifting northward during the last couple of weeks, probably related to the seasonal cycle.
Much of the USA (the CONUS has generally been my focus in these postings) has been through a very active period this past week. After a brief respite, this situation is probable to return. Particularly with the week-2 ensemble means from various operational centers, there is a lot of model spread in regard to the locations of troughs, ridges, possible so-called omega blocking north of the Great Lakes, etc., etc., etc.. These are the situations where an understanding of the weather-climate situation from rigorous daily monitoring utilizing tools such as the GSDM is needed to make an intelligent evaluation of all other numerical, statistical, etc., tools to formulate week 1-2 (week 1-4?) predictions. I view this procedure as a complete forecast process to provide the best possible information to sophisticated users.
Probablistically, more deep troughs and closed lows in the Rockies are likely by week 2 (pattern shifting slowly north). These lows should eject northeast into the mid and upper Mississippi Valley having the kind of impacts (warm sector severe thunderstorms and snowstorms across the Rockies) already observed for the past several weeks. Heavy rainfall and strong storms may start across the Southern Plains by early next week with the remnants of a subtropical jet. By week 2 the Rockies and Plains should experience exceptionally active May weather. I do think a blocking GSDM Stage 1 USA pattern is a possibility for week 2. Other ramifications may include excessive warmth across the Deep South with cool conditions across the Northeast. This situation should slowly shift east week 3.
Appendix
An experimental phase space plot of the GSDM utilizing normalized relative AAM tendency (Y-axis) and normalized relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg
These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to write an update sometime next week while on travel.
Ed Berry
Friday, April 27, 2007
Monday, April 23, 2007
Stage 0.5 Update
There is no change to the discussion I issued on 4/20. Upper tropospheric zonal mean easterly wind flow anomalies are increasing throughout the tropical and subtropical atmospheres with much of that coming from the Eastern Hemisphere. In fact, anomalous twin subtropical anticyclones are becoming quite robust from Africa into Indonesia. Global relative atmospheric angular momentum (AAM) tendency remains at ~minus 20 Hadleys as of April 21st per reanalyis data (R1) with actual AAM about 1 standard deviation below the 1968-1997 R1 climatology.
We expect the tropical convective forcing to further respond to these wind signals starting this week and especially week 2. Anomalous rainfall should become noticeable from the equatorial Indian Ocean to Indonesia from ~80-120E while the South Pacific forcing weakens. Full-disk satellite imagery supports this trend. Whether or not this convection shifts east as a MJO afterwards is unclear. However, the multivariate Wheeler phase space plot suggests a MJO projection may be developing across the Indian Ocean. It is possible this convection may just persist in that region of the Eastern Hemisphere.
Our interpretation is GSDM Stage 0.5 best describes the global weather-climate situation (see link below). We think the global circulation will be in ~Stage 1.5 by the end of week 2. Signals are mixed whether or not a La-Nina is developing, and May is a critical transition month.
As discussed on 4/20, equatorial westerlies currently across the East Pacific will contribute to another North Pacific jet extension by early next week (which many ensembles do show) and then slam the western USA with more strong troughs starting later week 2. Thus after the current active period for much of the USA ends, there should be a respite. However, exceptionally active May weather looks probable later week 2 into possibly week 4 (shifted slightly north from April). Most readers should know the ramifications of strong mobile western states troughs and a southwest flow storm track on the Plains during May. For instance, several rounds of severe local storms on the Plains, late season snowstorms across the Rockies and summertime heat across the Deep South are probable.
Appendix
An experimental phase space plot of the GSDM utilizing normalized relative AAM tendency (Y-axis) and normalized relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg
These are probabilistic statements, and work is ongoing to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to write an update by Thursday or Friday this week. I am on lots of travel and have to cover operational shifts.
Ed Berry
We expect the tropical convective forcing to further respond to these wind signals starting this week and especially week 2. Anomalous rainfall should become noticeable from the equatorial Indian Ocean to Indonesia from ~80-120E while the South Pacific forcing weakens. Full-disk satellite imagery supports this trend. Whether or not this convection shifts east as a MJO afterwards is unclear. However, the multivariate Wheeler phase space plot suggests a MJO projection may be developing across the Indian Ocean. It is possible this convection may just persist in that region of the Eastern Hemisphere.
Our interpretation is GSDM Stage 0.5 best describes the global weather-climate situation (see link below). We think the global circulation will be in ~Stage 1.5 by the end of week 2. Signals are mixed whether or not a La-Nina is developing, and May is a critical transition month.
As discussed on 4/20, equatorial westerlies currently across the East Pacific will contribute to another North Pacific jet extension by early next week (which many ensembles do show) and then slam the western USA with more strong troughs starting later week 2. Thus after the current active period for much of the USA ends, there should be a respite. However, exceptionally active May weather looks probable later week 2 into possibly week 4 (shifted slightly north from April). Most readers should know the ramifications of strong mobile western states troughs and a southwest flow storm track on the Plains during May. For instance, several rounds of severe local storms on the Plains, late season snowstorms across the Rockies and summertime heat across the Deep South are probable.
Appendix
An experimental phase space plot of the GSDM utilizing normalized relative AAM tendency (Y-axis) and normalized relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg
These are probabilistic statements, and work is ongoing to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to write an update by Thursday or Friday this week. I am on lots of travel and have to cover operational shifts.
Ed Berry
Friday, April 20, 2007
Orbiting in GSDM Phase Space
Shift work obligations and upcoming travel for at least the next 2 weeks will impact the timeliness and completeness of these discussions, including this writing. However, my thinking from 4/17 remains unchanged. Zonal mean anomalous upper tropospheric easterly wind flow continues to increase throughout the tropical and subtropical atmospheres. Magnitudes are ~5m/s contributing to a negative global relative atmospheric angular momentum (AAM) tendency of about minus 15 Hadleys as of 4/18. Twin upper tropospheric subtropical anticyclones are becoming better established over the Eastern Hemisphere and actual relative AAM is approaching 1 standard deviation below the 1968-1997 NCEP/NCAR reanalysis climatology.
A fairly large region of enhanced tropical convective forcing extends from eastern Indonesia into the South Pacific. This rainfall has been locally forced by warm SSTs and interactions with the extratropics. Upper tropospheric Western Hemisphere westerly wind flow anomalies across the Pacific have been a response, and have contributed to the southern USA subtropical jet. This region of tropical convection is slowly moving east-southeast enhancing the South Pacific Convergence Zone (SPCZ). Meanwhile, monitoring tools suggest a struggling dynamical signal from the equatorial Atlantic into the Indian Ocean.
I think the global circulation remains in GSDM Stage 4, and it now appears probable to me it will stay roughly in that phase plane until the above mentioned dynamical signal becomes robust. In fact, the trajectory shown on the referenced plot in the Appendix may do ~1-2 circles before we finally get a MJO sometime in May. My feeling is those equatorial westerlies discussed above will contribute to another extended North Pacific jet by week 2 (which many ensembles have picked up) and then slam the western USA with more strong troughs by weeks 3-4. Thus after an active week 1 for much of the USA, week 2 should be relatively tranquil followed by exceptionally active May weather weeks 3-4 (shifted slightly north from April). Most readers should know the ramifications of strong mobile western states troughs and a southwest flow storm track on the Plains during May. For instance, several rounds of severe local storms on the Plains, late season snowstorms across the Rockies and summertime heat across the Deep South would be probable.
Appendix
An experimental phase space plot of the GSDM utilizing normalized relative AAM tendency (Y-axis) and normalized relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg
These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I should be able to write an update by late next week.
Ed Berry
A fairly large region of enhanced tropical convective forcing extends from eastern Indonesia into the South Pacific. This rainfall has been locally forced by warm SSTs and interactions with the extratropics. Upper tropospheric Western Hemisphere westerly wind flow anomalies across the Pacific have been a response, and have contributed to the southern USA subtropical jet. This region of tropical convection is slowly moving east-southeast enhancing the South Pacific Convergence Zone (SPCZ). Meanwhile, monitoring tools suggest a struggling dynamical signal from the equatorial Atlantic into the Indian Ocean.
I think the global circulation remains in GSDM Stage 4, and it now appears probable to me it will stay roughly in that phase plane until the above mentioned dynamical signal becomes robust. In fact, the trajectory shown on the referenced plot in the Appendix may do ~1-2 circles before we finally get a MJO sometime in May. My feeling is those equatorial westerlies discussed above will contribute to another extended North Pacific jet by week 2 (which many ensembles have picked up) and then slam the western USA with more strong troughs by weeks 3-4. Thus after an active week 1 for much of the USA, week 2 should be relatively tranquil followed by exceptionally active May weather weeks 3-4 (shifted slightly north from April). Most readers should know the ramifications of strong mobile western states troughs and a southwest flow storm track on the Plains during May. For instance, several rounds of severe local storms on the Plains, late season snowstorms across the Rockies and summertime heat across the Deep South would be probable.
Appendix
An experimental phase space plot of the GSDM utilizing normalized relative AAM tendency (Y-axis) and normalized relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg
These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I should be able to write an update by late next week.
Ed Berry
Tuesday, April 17, 2007
GSDM Stage 4
A horseshoe pattern of slightly warmer than normal SSTs (~.5-1.0C) still extends from the far west Pacific into the subtropical date line regions. Globally, the only significant but weak cool anomalies are those along the equatorial east Pacific east of ~150W. However, subsurface magnitudes as low as minus 4C remain down to depths of around 200m and will need to be monitored for the possibility of La-Nina. Large expanses of 29C and warmer total SST cover much of the Indian Ocean and from around Indonesia into the South Pacific.
Since the weak MJO during February and the large negative tendency of relative AAM of ~minus 40 Hadleys around the middle of that month, weather-climate signals have been difficult to diagnose. However, forced by warm west Pacific SSTs and interactions with the extratropics, intense flare-ups of tropical convection have occurred ~every 10-20 days. The envelope of this forcing loosely shifted east from ~120E on about March 19th to 160W by around April 2nd. At least 2 well-defined Rossby wave energy dispersions linked to this forcing arced across the North American and Atlantic extratropics into Asia. These resulted in strong positive global mountain torques (in excess of 30 Hadleys) with a large contribution from East Asia. A response was for large upper tropospheric zonal mean westerly wind anomalies across the northern subtropical atmosphere with magnitudes greater than 10m/s. This occurred from a combination of poleward propagating zonal mean westerly wind flow anomalies off the equator forced by the convection and the positive mountain torques.
Regionally, 4 intensifications of the East Asia jet into the North Pacific occurred since late February. However, the strongest (anomalies in excess of 30m/s) were just after March 20th and about a week ago, directly linked to the strong East Asia mountain torque. The latter is actually a faster component of the GSDM we term as a mountain-frictional torque index cycle, where surface friction works to remove atmospheric westerly flow (global frictional torque currently around minus 10 Hadleys). These jet intensifications have contributed to periods of extremely stormy and high-impact weather across much of the USA.
I think all of the above is a situation where the atmosphere is exhibiting fairly rapid subseasonal variations while dynamically working to maintain a slowly evolving La-Nina base state. We are now at the point where the SSTs and the extratropics are leading to a reorganization of the tropical forcing across the Eastern Hemisphere. Specifically, per animations of upper tropospheric wind fields anomalous twin anticyclones are developing ~120-140E as a response to the strong convection while a weak dynamical signal remains around Africa. It is unclear how strong the latter will become. However, anomalous zonal mean easterly flow is developing across the subtropical atmospheres and global relative AAM tendency is again strongly negative as are the mountain and frictional torques.
I think we are solidly in GSDM Stage 4. Tropical convective forcing currently extends from the Indian Ocean into the west Pacific, just south of the equator. Other pockets of are also across equatorial Africa and South America (with twin anticyclones). My feeling is for the tropical convection to get better organized and consolidated from Africa into the Indian Ocean roughly by the end of week 2, while other SST forced convection remains across the west Pacific. Later week 2 into week 3, the dynamical signal discussed above may project onto a MJO.
With good initial condition information, most ensembles show an exceptionally active storm track with several western USA troughs/closed lows through at least day 10. Not discussed above is the possibility of our GSDM Stage 4 situation being nearly stationary for ~1-2 weeks (not favorable for west coast upwelling) before evolving into Stage 1. In any case, I offer that this active pattern (above climatology) may persist well into May, weeks 3-4. Thus locations such as the Plains States may have several rounds of severe thunderstorms while the Northern Rockies and Northern Plains experience late season snowstorms.
Appendix
An experimental phase space plot of the GSDM utilizing relative AAM tendency (Y-axis) and relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_040507_95d.gif
These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will attempt an update this Friday.
Ed Berry
Since the weak MJO during February and the large negative tendency of relative AAM of ~minus 40 Hadleys around the middle of that month, weather-climate signals have been difficult to diagnose. However, forced by warm west Pacific SSTs and interactions with the extratropics, intense flare-ups of tropical convection have occurred ~every 10-20 days. The envelope of this forcing loosely shifted east from ~120E on about March 19th to 160W by around April 2nd. At least 2 well-defined Rossby wave energy dispersions linked to this forcing arced across the North American and Atlantic extratropics into Asia. These resulted in strong positive global mountain torques (in excess of 30 Hadleys) with a large contribution from East Asia. A response was for large upper tropospheric zonal mean westerly wind anomalies across the northern subtropical atmosphere with magnitudes greater than 10m/s. This occurred from a combination of poleward propagating zonal mean westerly wind flow anomalies off the equator forced by the convection and the positive mountain torques.
Regionally, 4 intensifications of the East Asia jet into the North Pacific occurred since late February. However, the strongest (anomalies in excess of 30m/s) were just after March 20th and about a week ago, directly linked to the strong East Asia mountain torque. The latter is actually a faster component of the GSDM we term as a mountain-frictional torque index cycle, where surface friction works to remove atmospheric westerly flow (global frictional torque currently around minus 10 Hadleys). These jet intensifications have contributed to periods of extremely stormy and high-impact weather across much of the USA.
I think all of the above is a situation where the atmosphere is exhibiting fairly rapid subseasonal variations while dynamically working to maintain a slowly evolving La-Nina base state. We are now at the point where the SSTs and the extratropics are leading to a reorganization of the tropical forcing across the Eastern Hemisphere. Specifically, per animations of upper tropospheric wind fields anomalous twin anticyclones are developing ~120-140E as a response to the strong convection while a weak dynamical signal remains around Africa. It is unclear how strong the latter will become. However, anomalous zonal mean easterly flow is developing across the subtropical atmospheres and global relative AAM tendency is again strongly negative as are the mountain and frictional torques.
I think we are solidly in GSDM Stage 4. Tropical convective forcing currently extends from the Indian Ocean into the west Pacific, just south of the equator. Other pockets of are also across equatorial Africa and South America (with twin anticyclones). My feeling is for the tropical convection to get better organized and consolidated from Africa into the Indian Ocean roughly by the end of week 2, while other SST forced convection remains across the west Pacific. Later week 2 into week 3, the dynamical signal discussed above may project onto a MJO.
With good initial condition information, most ensembles show an exceptionally active storm track with several western USA troughs/closed lows through at least day 10. Not discussed above is the possibility of our GSDM Stage 4 situation being nearly stationary for ~1-2 weeks (not favorable for west coast upwelling) before evolving into Stage 1. In any case, I offer that this active pattern (above climatology) may persist well into May, weeks 3-4. Thus locations such as the Plains States may have several rounds of severe thunderstorms while the Northern Rockies and Northern Plains experience late season snowstorms.
Appendix
An experimental phase space plot of the GSDM utilizing relative AAM tendency (Y-axis) and relative AAM (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_040507_95d.gif
These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will attempt an update this Friday.
Ed Berry
Friday, April 13, 2007
Snowed In
My next posting will be delayed to about next Tuesday (4/17) thanks to complications caused by a (thunder) snowstorm attributable to our GSDM Stage 3-4 regime. My thinking from the 4/11 posting remains unchanged. Tropical convective forcing is getting better organized across the Eastern Hemisphere including central Africa, the equatorial Indian Ocean ~80E and the west Pacific ~150E. We will need to monitor where this forcing consolidates. My suspicion is from ~60-120E during week 2, then possibly shift east as a MJO. I think the circulation will evolve into GSDM Stage 4 by week 2 then Stage 1 afterwards. An exceptionally active regime emphasizing the Rockies and Plains weeks 1-3 is probable. This may include several rounds of severe thunderstorms across the Plains later week 2 - week 3.
Ed Berry
Ed Berry
Wednesday, April 11, 2007
Rebirth of the MJO revisited
The spatial distribution of global tropical SSTs remains similar to 4/5, the date of my last posting. A horseshoe pattern of weak-moderate warmth centered at roughly 0/155E (anomalies ~.5-1C) continues while total SST of 29-30C extend from near the Philippines into the South Pacific. Recent surface westerly wind anomalies have disrupted the cooling along the equatorial cold tongue east of 150W. SSTs remain above average across most of the Indian Ocean, with totals around 29-30C, as well as the tropical Atlantic.
There is not much change in my thinking from the 4/5 posting. Global relative atmosphere angular momentum (AAM) is now weakly above average. The recent strong positive AAM tendency of ~40 Hadleys did more to overcome strong zonal mean easterly wind anomalies than actually contributing to zonal mean westerly wind flow anomalies. However, there have been other dynamical feed-back processes tied to past Rossby wave energy dispersions from west central Pacific tropical forcing. Also, AAM transports linked to the synoptic eddies have led to a zonal mean flux convergence of westerly momentum at around 35N. A response has been for strong zonal mean westerly wind anomalies; for example, ~10m/s at 200mb from 30-40N. A very strong positive global mountain torque (with contributions from east Asia and North America) of more than 40 Hadleys as of 4/8 per reanalysis data plots is helping to maintain the strong midlatitude westerly flow. I think the latter is part of a global mountain-frictional torque index cycle, one of the components of the GSDM. The above would offer some attribution to the current strong and baroclinically active extended jet extending from South Asia into the central USA.
The main highlight about the tropical convective forcing is the increase observed over the warm Indian Ocean SSTs during the past 5-7 days. Animations of upper tropospheric daily mean vector wind totals and anomalies suggest jet streak dynamics with the anomalous subtropical twin cyclones ~100E are helping to initiate this convection. In fact, water vapor satellite imagery shows westerly flow from this Indian Ocean convection interacting with the strong North Pacific jet. Other enhanced convection remains across the west central Pacific and portions of tropical Africa and South America.
Velocity potential fields and multivariate EOF tools such as the Wheeler phase space plot clearly show a Western Hemisphere dynamical signal. Upper tropospheric vector wind animations also present a signal of Western Hemisphere anomalous twin subtropical anticyclones. This signal is already starting to return into the Eastern Hemisphere, and I think it will do so weeks 2-3. My probabilistic thought would be to see a consolidation of the tropical forcing ~60-120E during this time and possibly project onto a MJO. Even if the latter does not occur (yet), those with global interests should be concerned about heavy rainfall from the Indian Ocean into possibly the west central Pacific weeks 2-3. Furthermore, there may be an increased risk of tropical cyclones across the Bay of Bengal and perhaps portions of the west Pacific during this time.
I think GSDM Stage 3 best describes the weather-climate situation, but only as a faster variation within a low AAM base state since mid-February. In fact, an experimental phase space plot of relative AAM tendency (Y-axis) and relative AAM (X-axis) at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_040507_95d.gif
supports this notion.
I think AAM tendency will become negative “soon” followed by a decrease of AAM. I would expect ~GSDM Stage 4 by week 2 followed by Stage 1 afterwards. As most models are showing, this means a very active pattern for most of the USA week 1. This emphasis should shift west and north weeks 2-3. However, many week-2 ensemble means suggest a trough to also linger along the east coast, which is reasonable given shorter wavelengths. This does not bode well for enhanced west coast upwelling.
Please note: These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will attempt a brief update this Friday.
Ed Berry
There is not much change in my thinking from the 4/5 posting. Global relative atmosphere angular momentum (AAM) is now weakly above average. The recent strong positive AAM tendency of ~40 Hadleys did more to overcome strong zonal mean easterly wind anomalies than actually contributing to zonal mean westerly wind flow anomalies. However, there have been other dynamical feed-back processes tied to past Rossby wave energy dispersions from west central Pacific tropical forcing. Also, AAM transports linked to the synoptic eddies have led to a zonal mean flux convergence of westerly momentum at around 35N. A response has been for strong zonal mean westerly wind anomalies; for example, ~10m/s at 200mb from 30-40N. A very strong positive global mountain torque (with contributions from east Asia and North America) of more than 40 Hadleys as of 4/8 per reanalysis data plots is helping to maintain the strong midlatitude westerly flow. I think the latter is part of a global mountain-frictional torque index cycle, one of the components of the GSDM. The above would offer some attribution to the current strong and baroclinically active extended jet extending from South Asia into the central USA.
The main highlight about the tropical convective forcing is the increase observed over the warm Indian Ocean SSTs during the past 5-7 days. Animations of upper tropospheric daily mean vector wind totals and anomalies suggest jet streak dynamics with the anomalous subtropical twin cyclones ~100E are helping to initiate this convection. In fact, water vapor satellite imagery shows westerly flow from this Indian Ocean convection interacting with the strong North Pacific jet. Other enhanced convection remains across the west central Pacific and portions of tropical Africa and South America.
Velocity potential fields and multivariate EOF tools such as the Wheeler phase space plot clearly show a Western Hemisphere dynamical signal. Upper tropospheric vector wind animations also present a signal of Western Hemisphere anomalous twin subtropical anticyclones. This signal is already starting to return into the Eastern Hemisphere, and I think it will do so weeks 2-3. My probabilistic thought would be to see a consolidation of the tropical forcing ~60-120E during this time and possibly project onto a MJO. Even if the latter does not occur (yet), those with global interests should be concerned about heavy rainfall from the Indian Ocean into possibly the west central Pacific weeks 2-3. Furthermore, there may be an increased risk of tropical cyclones across the Bay of Bengal and perhaps portions of the west Pacific during this time.
I think GSDM Stage 3 best describes the weather-climate situation, but only as a faster variation within a low AAM base state since mid-February. In fact, an experimental phase space plot of relative AAM tendency (Y-axis) and relative AAM (X-axis) at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_040507_95d.gif
supports this notion.
I think AAM tendency will become negative “soon” followed by a decrease of AAM. I would expect ~GSDM Stage 4 by week 2 followed by Stage 1 afterwards. As most models are showing, this means a very active pattern for most of the USA week 1. This emphasis should shift west and north weeks 2-3. However, many week-2 ensemble means suggest a trough to also linger along the east coast, which is reasonable given shorter wavelengths. This does not bode well for enhanced west coast upwelling.
Please note: These are probabilistic statements, which we will try to quantify in future posts. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will attempt a brief update this Friday.
Ed Berry
Thursday, April 05, 2007
Rebirth of the MJO?
The most robust signal of global tropical SSTs are the cool anomalies east of about 150W along the equatorial cold tongue, with magnitudes as low as minus 3C. Negative anomalies of at least minus 4C remain down to ~200m extending to about the date line. The positive SST anomalies across the west central and South Pacific have cooled significantly during the past week due to recent intense rainfall and tropical cyclone activity. Anomaly magnitudes are only ~.5C with totals ~28-29C. Similar SSTs also exist across the equatorial Atlantic Ocean, and the equatorial Indian Ocean remains quite warm with SSTs ~29-30C. It is still unclear to me if the coupled ocean-atmosphere (and other processes) system is evolving toward La-Nina since May is a critical month.
The weather-climate situation remains very complicated meaning most (not all) signals are weak. Careful daily monitoring within the GSDM framework is a must for any week 1-4 predictions. Short course is the extended North Pacific jet of roughly 2 weeks ago contributed to an eastward shift of the most intense tropical convection from ~120E to 160E in a period of about a week. This forcing has since weakened with only “pockets” of convection hanging around central-eastern Indonesia into the central Pacific, northern South America, west central Africa and the central Indian Ocean. The latter is a component of the slow westward drift of the tropical forcing from the South Pacific which started around mid-January.
The most robust signals remain the global relative atmospheric angular momentum (AAM) and its tendency, keeping in mind the zonal mean contributions. Animations of upper tropospheric winds during the last week-10 days present some rapid but interesting behaviors. As the tropical forcing moved into the west central Pacific Rossby wave energy dispersion led to ridge amplification along the USA west coast and a deep central North American trough. Additionally, weak upper tropospheric zonal mean westerly wind anomalies (~5m/s or less at 200mb) have developed throughout the tropical and subtropical atmospheres, while exhibiting poleward propagation. The dynamics responsible for these processes have resulted in a global AAM daily mean positive tendency of ~40 Hadleys on April 2nd (reanalysis plots are 5-day averages). The magnitude of this tendency is roughly equal to the negative event observed back in mid-February.
Does this mean we have had a GSDM Stage 2 response and are headed for Stage 3, or are we seeing a perturbation in a slowly evolving GSDM Stage 1 base state possibly linked to a developing La-Nina? I continue to advocate the latter. While there is likely to be a “spike” in global relative AAM during the next few days (how much is unclear), that is all I think it will be. Several diagnostics including velocity potential and even the multivariate EOF Wheeler phase space plot tell me there is a developing dynamical signal across the Western Hemisphere. I think this signal will come back into the Eastern Hemisphere and it is probable that MJO tropical convection will appear across the warm Indian Ocean sometime week 2-3. This would argue for another negative AAM tendency and an overall persistence of a low AAM GSDM Stage 1 regime.
As most ensembles are capturing, another extended North Pacific jet episode is highly probable starting this weekend leading to strong troughs that will first slam into the USA west coast. This situation is likely to weaken coastal upwelling along the California coast, at least in the short-term. These troughs are then likely to move into the Rockies and Plains. This means the April cold regime now affecting the Upper Mississippi Valley into the Northeast should moderate early next week. Going well into next week and possibly through week 3, much of the lower 48 states may be in for an exceptionally stormy regime, centered on the Rockies and Plains. In fact, understanding the seasonal cycle, events similar to the period of the last couple of weeks of December 2006 and the last half of February 2007 may be probable.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I continue to have travel. It is likely I will not be able to do another posting until around 4/11. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
The weather-climate situation remains very complicated meaning most (not all) signals are weak. Careful daily monitoring within the GSDM framework is a must for any week 1-4 predictions. Short course is the extended North Pacific jet of roughly 2 weeks ago contributed to an eastward shift of the most intense tropical convection from ~120E to 160E in a period of about a week. This forcing has since weakened with only “pockets” of convection hanging around central-eastern Indonesia into the central Pacific, northern South America, west central Africa and the central Indian Ocean. The latter is a component of the slow westward drift of the tropical forcing from the South Pacific which started around mid-January.
The most robust signals remain the global relative atmospheric angular momentum (AAM) and its tendency, keeping in mind the zonal mean contributions. Animations of upper tropospheric winds during the last week-10 days present some rapid but interesting behaviors. As the tropical forcing moved into the west central Pacific Rossby wave energy dispersion led to ridge amplification along the USA west coast and a deep central North American trough. Additionally, weak upper tropospheric zonal mean westerly wind anomalies (~5m/s or less at 200mb) have developed throughout the tropical and subtropical atmospheres, while exhibiting poleward propagation. The dynamics responsible for these processes have resulted in a global AAM daily mean positive tendency of ~40 Hadleys on April 2nd (reanalysis plots are 5-day averages). The magnitude of this tendency is roughly equal to the negative event observed back in mid-February.
Does this mean we have had a GSDM Stage 2 response and are headed for Stage 3, or are we seeing a perturbation in a slowly evolving GSDM Stage 1 base state possibly linked to a developing La-Nina? I continue to advocate the latter. While there is likely to be a “spike” in global relative AAM during the next few days (how much is unclear), that is all I think it will be. Several diagnostics including velocity potential and even the multivariate EOF Wheeler phase space plot tell me there is a developing dynamical signal across the Western Hemisphere. I think this signal will come back into the Eastern Hemisphere and it is probable that MJO tropical convection will appear across the warm Indian Ocean sometime week 2-3. This would argue for another negative AAM tendency and an overall persistence of a low AAM GSDM Stage 1 regime.
As most ensembles are capturing, another extended North Pacific jet episode is highly probable starting this weekend leading to strong troughs that will first slam into the USA west coast. This situation is likely to weaken coastal upwelling along the California coast, at least in the short-term. These troughs are then likely to move into the Rockies and Plains. This means the April cold regime now affecting the Upper Mississippi Valley into the Northeast should moderate early next week. Going well into next week and possibly through week 3, much of the lower 48 states may be in for an exceptionally stormy regime, centered on the Rockies and Plains. In fact, understanding the seasonal cycle, events similar to the period of the last couple of weeks of December 2006 and the last half of February 2007 may be probable.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I continue to have travel. It is likely I will not be able to do another posting until around 4/11. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
Friday, March 30, 2007
GSDM Stage 1 Perturbed
The west Pacific SST horseshoe of warmth remains; however, anomalies are weakening due to recent days of intense tropical rainfall. Magnitudes are generally 0.5-1C with SSTs ~29-30C, with the warmest waters now around 10S/160W as of March 29th. Conversely, the equatorial Indian Ocean continues to slowly warm due to suppression (with the exception of a tropical cyclone in the South Indian Ocean) with SST totals and anomalies comparable to the west Pacific warm pool. Cooling along the equatorial east Pacific cold tongue has again intensified this past week with negative anomalies ~minus 1-3C east of 140W and at least minus 4C in the subsurface. These colder than normal waters extend down to roughly 200m at the date line per latest TAO buoy data. Whether or not La-Nina is evolving is an open question (recall May 2003); however, it is not unusual to see “pulses” of cooling if this is the case.
Hard times continue trying to understand the tropical convective forcing, and there is a seasonal cycle consideration to remember. There is no coherent MJO dynamical signal. Most significant behavior during the last 10 days has been an eastward shift of intense (OLRA ~ minus 50-70 W/m**2) forcing from ~120E to 160E just south of the equator. I maintain this is a transient event linked to very complicated tropical-extratropical interactions. These can only be reasonably understood observationally from disciplined detailed daily monitoring of fields such as animations of upper and lower tropospheric wind fields utilizing the GSDM framework. Some of these interactions include last week’s extension of the North Pacific jet shifting this forcing to the east, possibly reinforced by feedbacks from the extratropics including a strong positive East Asian mountain torque.
Full disk satellite imagery already shows the west Pacific tropical forcing drifting west and northwest, and the coherent modes Hovmollers suggest a weak projection on the convectively coupled Rossby mode. In fact, a tropical cyclone may develop out of this region north of the equator during the next few days per JTWC. Weaker forcing (diurnal cycle understood) also persists across northwest South America, west central Africa and ~0/120E.
Our best weather-climate signal remains global relative AAM including the zonal mean contributions. This quantity is a good diagnostic measure of the character and evolution of the global and zonal mean circulation anomalies. Relative AAM continues at around 1.5 standard deviations below the 1968-1997 reanalysis data climatology, and its tendency has been weak for the last couple of weeks. Furthermore, zonal mean upper tropospheric easterly wind anomalies remain at around 5m/s throughout much of the tropical and subtropical atmospheres. These easterlies are contributing to a zonal mean sink of AAM ~20N while flux convergence of its transports occur ~35N. All of these observations are consistent with a GSDM Stage 1 base state (most probable during a La-Nina) that has been around since at least late February.
Given the warm Indian Ocean SSTs, feedbacks from our low AAM regime and the slow westward shift of tropical forcing back to 120E discussed on 3/27, we need to monitor for the development of intense tropical convection across the Indian Ocean into Indonesia sometime weeks 2-3. In the meantime, the transient SPCZ convection discussed above has generated enough anomalous (~20-30m/s at 150mb on 3/29) upper tropospheric equatorial westerly wind flow over the east Pacific to perturb our GSDM Stage 1 state toward Stage 2 for week 1. In fact, animations of daily mean upper tropospheric vector wind anomalies show well defined twin tropical anticyclones at 160E as of 3/29. These anticyclones are already interacting with Rossby wave energy dispersion (RWD) processes from Asia to North America, including the ridge building into Alaska and the developing downstream trough across western Canada. It is possible the models may be underestimating the impacts of this trough onto the Rockies and Plains early-mid next week given the large circulation anomalies tied to this RWD and the complex dynamics. Overall, as shown by most ensemble numerical models, a colder regime is probable for the eastern two-thirds of the USA for at least week 1.
My thoughts for weeks 2-3 remain the same. I speculate whatever “renegade” North Pacific jet that does come out may lead to a similar evolution of synoptic events that was observed during the last 7-10 days. If the tropical convective scenario discussed above does occur, a shift back to a GSDM Stage 4-1 would be most probable by sometime week 3 (April 14-20). Although models do not predict the evolution of tropical convection very well after week 1, the NCEP week 2 ensemble mean total precipitation forecast lends loose support to renewed Indian Ocean convection. The latter is likely a SST response. This would lead to a renewed active pattern for much of the western and central USA, including severe local storms across the Plains. Careful monitoring will be needed to see if Eastern Hemisphere tropical forcing eventually develops into a MJO.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I am unclear when I will be able to another discussion next week due to travel. We are also working on a weather-climate discussion for the ESRL/PSD MJO web site, which will hopefully be posted during the next couple of weeks. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
Hard times continue trying to understand the tropical convective forcing, and there is a seasonal cycle consideration to remember. There is no coherent MJO dynamical signal. Most significant behavior during the last 10 days has been an eastward shift of intense (OLRA ~ minus 50-70 W/m**2) forcing from ~120E to 160E just south of the equator. I maintain this is a transient event linked to very complicated tropical-extratropical interactions. These can only be reasonably understood observationally from disciplined detailed daily monitoring of fields such as animations of upper and lower tropospheric wind fields utilizing the GSDM framework. Some of these interactions include last week’s extension of the North Pacific jet shifting this forcing to the east, possibly reinforced by feedbacks from the extratropics including a strong positive East Asian mountain torque.
Full disk satellite imagery already shows the west Pacific tropical forcing drifting west and northwest, and the coherent modes Hovmollers suggest a weak projection on the convectively coupled Rossby mode. In fact, a tropical cyclone may develop out of this region north of the equator during the next few days per JTWC. Weaker forcing (diurnal cycle understood) also persists across northwest South America, west central Africa and ~0/120E.
Our best weather-climate signal remains global relative AAM including the zonal mean contributions. This quantity is a good diagnostic measure of the character and evolution of the global and zonal mean circulation anomalies. Relative AAM continues at around 1.5 standard deviations below the 1968-1997 reanalysis data climatology, and its tendency has been weak for the last couple of weeks. Furthermore, zonal mean upper tropospheric easterly wind anomalies remain at around 5m/s throughout much of the tropical and subtropical atmospheres. These easterlies are contributing to a zonal mean sink of AAM ~20N while flux convergence of its transports occur ~35N. All of these observations are consistent with a GSDM Stage 1 base state (most probable during a La-Nina) that has been around since at least late February.
Given the warm Indian Ocean SSTs, feedbacks from our low AAM regime and the slow westward shift of tropical forcing back to 120E discussed on 3/27, we need to monitor for the development of intense tropical convection across the Indian Ocean into Indonesia sometime weeks 2-3. In the meantime, the transient SPCZ convection discussed above has generated enough anomalous (~20-30m/s at 150mb on 3/29) upper tropospheric equatorial westerly wind flow over the east Pacific to perturb our GSDM Stage 1 state toward Stage 2 for week 1. In fact, animations of daily mean upper tropospheric vector wind anomalies show well defined twin tropical anticyclones at 160E as of 3/29. These anticyclones are already interacting with Rossby wave energy dispersion (RWD) processes from Asia to North America, including the ridge building into Alaska and the developing downstream trough across western Canada. It is possible the models may be underestimating the impacts of this trough onto the Rockies and Plains early-mid next week given the large circulation anomalies tied to this RWD and the complex dynamics. Overall, as shown by most ensemble numerical models, a colder regime is probable for the eastern two-thirds of the USA for at least week 1.
My thoughts for weeks 2-3 remain the same. I speculate whatever “renegade” North Pacific jet that does come out may lead to a similar evolution of synoptic events that was observed during the last 7-10 days. If the tropical convective scenario discussed above does occur, a shift back to a GSDM Stage 4-1 would be most probable by sometime week 3 (April 14-20). Although models do not predict the evolution of tropical convection very well after week 1, the NCEP week 2 ensemble mean total precipitation forecast lends loose support to renewed Indian Ocean convection. The latter is likely a SST response. This would lead to a renewed active pattern for much of the western and central USA, including severe local storms across the Plains. Careful monitoring will be needed to see if Eastern Hemisphere tropical forcing eventually develops into a MJO.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I am unclear when I will be able to another discussion next week due to travel. We are also working on a weather-climate discussion for the ESRL/PSD MJO web site, which will hopefully be posted during the next couple of weeks. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
Tuesday, March 27, 2007
Hard Times
Above average SSTs remain centered around 0/150E and continue to have a horseshoe distribution pattern into both hemispheres. Anomalies are ~0.5-1C having total SSTs of 29-30C with the warmest centered at roughly 5-10S/170E. These SSTs have cooled a bit during the last week as a response to enhanced rainfall in that region. Weak-moderate warm anomalies continue to exist across much of the equatorial Indian and north tropical Atlantic Oceans. In fact, suppression of tropical convection has allowed SSTs across the Indian Ocean to warm by about 0.5C over the past week. The equatorial east Pacific remains moderately cool east of 120W with negative anomalies as low as -4C down to roughly 200m.
Understanding the current tropical convective forcing is about as difficult as it can get. There is no coherent MJO dynamical signal, and these are the situations where additional understanding beyond linear MJO (and linear dynamics) thinking is needed. The strongest tropical convective forcing globally is centered ~5-10S/165E, in the region of warm SSTs. In fact, three-day averaged OLRA are at least minus 50-70 W/m**2 (including Hurricane Becky) and the Wheeler multivariate MJO index even projects this convection as a MJO as of March 26th. The latter is a response to the baroclinic vertical wind structure with this convection. For example, there are weak anomalous twin upper tropospheric tropical anticylones with cross-equatorial southerly flow (with lower level opposite wind flows) around the date line.
As discussed on my last Friday posting (3/23), the enhancement of the North Pacific jet helped to shift tropical convection into the southwest Pacific. I believe that additional dynamical forcing tied to a strong East Asian mountain torque around March 20th (~20 Hadleys with a global torque of 30 Hadleys) contributed to maintaining this jet and the SPCZ convection. Other weaker tropical forcing persists over northwest South America with respectable thunderstorm activity across west central Africa.
However, another region of now relatively weak tropical convection remains centered at roughly 0/120E. This is actually a westward shift out of the South Pacific from mid-January, and continues to be the most important tropical forcing to impact the global circulation. A response is that global relative AAM remains about 1.5 standard deviations below the 1968-1997 reanalysis data climatology, reflective of loosely deep zonal mean easterly flow throughout much of the tropical and subtropical atmospheres (~5m/s anomalies). I think this is a slowly evolving component and may be part of a coupled process involving a transition to La-Nina. The role of the seasonal cycle needs to be remembered, particularly around May. GSDM Stage 1 continues to define the current weather-climate/global circulation, which is consistent with La-Nina. Summing up, our strongest weather-climate signal remains global relative AAM while the subseasonal evolution of the tropical forcing is unclear. I can only offer the following speculation.
Discussion in past postings has addressed the fairly rapid subtropical variations (~10-15 days as seen from the global AAM tendency time series) within this GSDM Stage 1 base state. There are fairly symmetric anomalous wave trains across the subtropical atmospheres of both hemispheres, including twin upper tropospheric cyclones across the east Pacific and Indian Oceans. These are actually generating anomalous equatorial westerly flow that I think will locally interact with the subtropics. I also suspect tropical convection will increase across the warm Indian Ocean SSTs during the next 2-3 weeks once the twin cyclones in that region move east. A weak eastward propagating dyamical signal from the southwest Pacific may also arrive there. By weeks 3-4 tropical forcing may become very intense around 90-120E. The gist is there may be a shift toward GSDM Stage 1-2 by week 2 and then perhaps a GSDM Stage 4-1 response afterwards.
Needless to say, forecast confidence after week 1 is very low. I like the increasing number of solutions being displayed by most ensembles through around days 5-7. Blocking developing across Alaska is highly probable since I can already see this process, linked to the 120E tropical forcing, from animations of daily mean 150mb and 250mb vector wind anomalies. This will allow wave breaking troughs to develop across the central Pacific hence supporting a ridge off the USA west coast and a downstream central North American trough. This suggests a colder and wetter regime for much of the northern and central USA in the wake of the present western states trough. Daily monitoring will be needed in regard to the amplitude of these features, particularly for upwelling concerns off the California coast and southward penetration of Arctic air into the Northern Rockies and Plains. Afterwards, my thought would be for this regime to shift west and north, going back into an active (above climatology) spring pattern for especially the Plains by week 3. Careful monitoring will be needed to see if the Eastern Hemisphere tropical forcing eventually develops into a MJO.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another (hopefully shorter) discussion this Friday. We are also working on a weather-climate discussion for the ESRL/PSD MJO web site, which will hopefully be posted during the next couple of weeks. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
Understanding the current tropical convective forcing is about as difficult as it can get. There is no coherent MJO dynamical signal, and these are the situations where additional understanding beyond linear MJO (and linear dynamics) thinking is needed. The strongest tropical convective forcing globally is centered ~5-10S/165E, in the region of warm SSTs. In fact, three-day averaged OLRA are at least minus 50-70 W/m**2 (including Hurricane Becky) and the Wheeler multivariate MJO index even projects this convection as a MJO as of March 26th. The latter is a response to the baroclinic vertical wind structure with this convection. For example, there are weak anomalous twin upper tropospheric tropical anticylones with cross-equatorial southerly flow (with lower level opposite wind flows) around the date line.
As discussed on my last Friday posting (3/23), the enhancement of the North Pacific jet helped to shift tropical convection into the southwest Pacific. I believe that additional dynamical forcing tied to a strong East Asian mountain torque around March 20th (~20 Hadleys with a global torque of 30 Hadleys) contributed to maintaining this jet and the SPCZ convection. Other weaker tropical forcing persists over northwest South America with respectable thunderstorm activity across west central Africa.
However, another region of now relatively weak tropical convection remains centered at roughly 0/120E. This is actually a westward shift out of the South Pacific from mid-January, and continues to be the most important tropical forcing to impact the global circulation. A response is that global relative AAM remains about 1.5 standard deviations below the 1968-1997 reanalysis data climatology, reflective of loosely deep zonal mean easterly flow throughout much of the tropical and subtropical atmospheres (~5m/s anomalies). I think this is a slowly evolving component and may be part of a coupled process involving a transition to La-Nina. The role of the seasonal cycle needs to be remembered, particularly around May. GSDM Stage 1 continues to define the current weather-climate/global circulation, which is consistent with La-Nina. Summing up, our strongest weather-climate signal remains global relative AAM while the subseasonal evolution of the tropical forcing is unclear. I can only offer the following speculation.
Discussion in past postings has addressed the fairly rapid subtropical variations (~10-15 days as seen from the global AAM tendency time series) within this GSDM Stage 1 base state. There are fairly symmetric anomalous wave trains across the subtropical atmospheres of both hemispheres, including twin upper tropospheric cyclones across the east Pacific and Indian Oceans. These are actually generating anomalous equatorial westerly flow that I think will locally interact with the subtropics. I also suspect tropical convection will increase across the warm Indian Ocean SSTs during the next 2-3 weeks once the twin cyclones in that region move east. A weak eastward propagating dyamical signal from the southwest Pacific may also arrive there. By weeks 3-4 tropical forcing may become very intense around 90-120E. The gist is there may be a shift toward GSDM Stage 1-2 by week 2 and then perhaps a GSDM Stage 4-1 response afterwards.
Needless to say, forecast confidence after week 1 is very low. I like the increasing number of solutions being displayed by most ensembles through around days 5-7. Blocking developing across Alaska is highly probable since I can already see this process, linked to the 120E tropical forcing, from animations of daily mean 150mb and 250mb vector wind anomalies. This will allow wave breaking troughs to develop across the central Pacific hence supporting a ridge off the USA west coast and a downstream central North American trough. This suggests a colder and wetter regime for much of the northern and central USA in the wake of the present western states trough. Daily monitoring will be needed in regard to the amplitude of these features, particularly for upwelling concerns off the California coast and southward penetration of Arctic air into the Northern Rockies and Plains. Afterwards, my thought would be for this regime to shift west and north, going back into an active (above climatology) spring pattern for especially the Plains by week 3. Careful monitoring will be needed to see if the Eastern Hemisphere tropical forcing eventually develops into a MJO.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another (hopefully shorter) discussion this Friday. We are also working on a weather-climate discussion for the ESRL/PSD MJO web site, which will hopefully be posted during the next couple of weeks. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
Friday, March 23, 2007
Renegade North Pacific Jet
Above average SSTs still persist across the tropical west central Pacific with the warmest centered ~ 5S/165E having magnitudes of 1-2C and actual SSTs ~30C. Weak-moderate warm anomalies are also present across much of the equatorial Indian and north tropical Atlantic Oceans. The equatorial east Pacific remains moderately cool east of 120W with negative anomalies as low as -4C down to roughly 200m.
The tropical forcing discussed on my March 20th posting has loosely separated into 2 regions. One area remains quasi-stationary ~0/120E while another region has moved into the warm waters of the southwest Pacific centered at roughly 5-10S/170E. The former region continues to have the strongest interactions with the extratropics while the latter may be a response to the transient strong Pacific jet stream embedded within the low relative AAM, GSDM Stage 1.
We speculate that a Rossby wave energy dispersion from west Pacific forcing last week contributed to the snow storm for the USA northeast. Animations of 150mb and 250mb daily mean vector wind anomalies suggest that both tropical forcing present across Indonesia and a strong east Asian mountain torque of roughly 20 Hadleys (30 Hadleys globally) combined to add more westerly flow to the Pacific subtropics. Now there is an intense jet across the North Pacific having anomalies of at least 30-40 m/s. This feature is “out running” the tropical forcing back at 120E, and perhaps shifting the convection east across the southwest Pacific. In fact, according to the coherent modes Hovmollers, the convection across the southwest Pacific projects onto a Kelvin wave.
The future evolution of the tropical forcing still remains unclear. However, for at least the next 1-3 weeks, the most important convection to impact the extratropics should remain quasi-stationary centered in the region of 120E (consistent with a low AAM regime) while the southwest Pacific has episodic flare-ups. The strong North Pacific jet is transient. As most models show, this jet should amplify a strong trough across the western USA by early next week. For weeks 2-3, given persistence of GSDM Stage 1, ridge amplification across the central and east Pacific into Alaska with more troughs impacting the western and central states is probable. This is an active pattern for the Rockies and Plains favorable for late season snowstorms and outbreaks of severe thunderstorms with individual synoptic baroclinic cyclones. Careful monitoring will be needed to see if the Eastern Hemisphere tropical forcing develops into a MJO, and if the current cooling of the tropical east Pacific develops into a La-Nina.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion next Tuesday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
The tropical forcing discussed on my March 20th posting has loosely separated into 2 regions. One area remains quasi-stationary ~0/120E while another region has moved into the warm waters of the southwest Pacific centered at roughly 5-10S/170E. The former region continues to have the strongest interactions with the extratropics while the latter may be a response to the transient strong Pacific jet stream embedded within the low relative AAM, GSDM Stage 1.
We speculate that a Rossby wave energy dispersion from west Pacific forcing last week contributed to the snow storm for the USA northeast. Animations of 150mb and 250mb daily mean vector wind anomalies suggest that both tropical forcing present across Indonesia and a strong east Asian mountain torque of roughly 20 Hadleys (30 Hadleys globally) combined to add more westerly flow to the Pacific subtropics. Now there is an intense jet across the North Pacific having anomalies of at least 30-40 m/s. This feature is “out running” the tropical forcing back at 120E, and perhaps shifting the convection east across the southwest Pacific. In fact, according to the coherent modes Hovmollers, the convection across the southwest Pacific projects onto a Kelvin wave.
The future evolution of the tropical forcing still remains unclear. However, for at least the next 1-3 weeks, the most important convection to impact the extratropics should remain quasi-stationary centered in the region of 120E (consistent with a low AAM regime) while the southwest Pacific has episodic flare-ups. The strong North Pacific jet is transient. As most models show, this jet should amplify a strong trough across the western USA by early next week. For weeks 2-3, given persistence of GSDM Stage 1, ridge amplification across the central and east Pacific into Alaska with more troughs impacting the western and central states is probable. This is an active pattern for the Rockies and Plains favorable for late season snowstorms and outbreaks of severe thunderstorms with individual synoptic baroclinic cyclones. Careful monitoring will be needed to see if the Eastern Hemisphere tropical forcing develops into a MJO, and if the current cooling of the tropical east Pacific develops into a La-Nina.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion next Tuesday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Tuesday, March 20, 2007
GSDM Stage 1
This discussion will be “short and sweet”. The distribution of global tropical SSTs remains similar to that discussed on my posting last Friday (3/16/07). The horseshoe pattern of warmth persists across the west central Pacific with anomalies of ~1-2C and 29-31C actual SSTs while similar cool SST anomalies exist along the equator from 150W to South America. The latter have actually cooled a bit during the last few days while colder anomalies ~2-4C persist in the subsurface down to roughly 200m.
Tropical convective forcing is getting better organized across the Eastern Hemisphere centered at about 0/120E. Latest 3-day averaged OLRA are ~minus 50-70W/m**2. Other pockets of enhancement still remain across the South Pacific, Brasil and equatorial Africa. The dynamical MJO signal discussed in my last posting has lost coherence. The future evolution of the tropical convection is unclear. Based on its current position around 120-130E and the existing low AAM circulation anomalies, we speculate that convection will remain quasi-stationary or shift slightly west over the next one to two weeks. Kelvin waves excited by the convection should also help excite transient convective episodes over the west Pacific. This complicated picture may all be part of a slow process of the atmosphere transitioning to a more pronounced La-Nina base state.
GSDM Stage 1 (most probable during La-Nina) still best describes the current weather-climate situation. It is probable this situation will persist for at least the next 2-3 weeks. Relative atmospheric angular momentum (AAM) remains well below the 1968-1997 reanalysis data climatology at ~1.5 standard deviations. For the Pacific-North American sector, more strong troughs are expected for the western USA with a southwest flow storm track across the Plains probable at least into early April. This pattern is favorable for late season snowstorms across portions of the Rockies and northern/central High Plains with a greater than climatology risk for severe local storms across the Plains and Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion this Friday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Tropical convective forcing is getting better organized across the Eastern Hemisphere centered at about 0/120E. Latest 3-day averaged OLRA are ~minus 50-70W/m**2. Other pockets of enhancement still remain across the South Pacific, Brasil and equatorial Africa. The dynamical MJO signal discussed in my last posting has lost coherence. The future evolution of the tropical convection is unclear. Based on its current position around 120-130E and the existing low AAM circulation anomalies, we speculate that convection will remain quasi-stationary or shift slightly west over the next one to two weeks. Kelvin waves excited by the convection should also help excite transient convective episodes over the west Pacific. This complicated picture may all be part of a slow process of the atmosphere transitioning to a more pronounced La-Nina base state.
GSDM Stage 1 (most probable during La-Nina) still best describes the current weather-climate situation. It is probable this situation will persist for at least the next 2-3 weeks. Relative atmospheric angular momentum (AAM) remains well below the 1968-1997 reanalysis data climatology at ~1.5 standard deviations. For the Pacific-North American sector, more strong troughs are expected for the western USA with a southwest flow storm track across the Plains probable at least into early April. This pattern is favorable for late season snowstorms across portions of the Rockies and northern/central High Plains with a greater than climatology risk for severe local storms across the Plains and Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion this Friday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Friday, March 16, 2007
Recap on the Complexity
Tropical west Pacific SSTs still remain above average in a horseshoe pattern centered on 155E with anomalies ~0.5-1.5C and actual temperatures from 29-31C. There has also been some warming across portions of the equatorial Indian Ocean with positive anomalies ~0.5-1C and SSTs near 30C. Below normal SSTs remain from the north coast of Australia to the equator, with anomalies ~1.0C. With the exception of the equatorial Pacific ~120W, eastern hemisphere tropical SSTs are weakly positive. While the negative anomalies along the central equatorial Pacific cold tongue are currently minimal, colder subsurface anomalies remain down to roughly 200m. The latter are important for possible La-Nina development.
Largely forced by the warm SSTs, favorable upper tropospheric winds and Rossby wave energy propagation from the extratropics, tropical convective forcing remains loosely organized centered ~0/140E. This area extends from the central Indian Ocean into the South Pacific. However, the convection in this region is not a large departure from climatology. There is still evidence from various fields such as animations of daily mean 150mb vector wind anomalies and velocity potential Hovmollers that a weak dynamical signal is moving through the Western Hemisphere. I think it is centered at roughly 0/60W and moving east at about 10 deg long/day. We expect this signal to come back into the Eastern Hemisphere sometime during week 2, and allow the tropical convective forcing to increase from Africa to the warming SSTs of the Indian Ocean. We may see the third MJO since late last fall evolve in that region by late week 2 or 3.
GSDM Stage 1 best describes the current weather-climate situation. Relative atmospheric angular momentum (AAM) remains well below the 1968-1997 reanalysis data climatology at ~1.5 standard deviations. The global tropical and subtropical atmospheres are dominated by zonal mean easterly wind anomalies with magnitudes of 5-10m/s. The fast dynamical signal discussed above should reinforce what is already a low AAM regime during the week 2-3 time frame. Synoptically, the most probable response across the Pacific North American sector would be for a discontinuous retrogression of existing circulation anomalous by at least 20-30 degrees of longitude. This means the ridge currently over the western North America should redevelop ~150W.
Even with the above reasoning, forecast uncertainty for weeks 2-3 remains very high. If a coherent MJO develops across the Indian Ocean by week 3, forecast confidence in subseasonal outlooks may improve. Most models forecast a fairly strong trough to impact the west coast early next week and then shift into the Rockies and Plains afterwards. It is possible this first trough may “split” with northern and southern stream developments during the course of its evolution. In fact, recent signals of AAM transports would support this possibility. Afterwards, a more “classic” GSDM Stage 1 springtime active pattern for the western and central USA may emerge for weeks 2-3. This would argue for late season snowstorms across portions of the Rockies and northern/central High Plains with a greater than climatology risk for severe local storms across the Plains and Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion next Tuesday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Largely forced by the warm SSTs, favorable upper tropospheric winds and Rossby wave energy propagation from the extratropics, tropical convective forcing remains loosely organized centered ~0/140E. This area extends from the central Indian Ocean into the South Pacific. However, the convection in this region is not a large departure from climatology. There is still evidence from various fields such as animations of daily mean 150mb vector wind anomalies and velocity potential Hovmollers that a weak dynamical signal is moving through the Western Hemisphere. I think it is centered at roughly 0/60W and moving east at about 10 deg long/day. We expect this signal to come back into the Eastern Hemisphere sometime during week 2, and allow the tropical convective forcing to increase from Africa to the warming SSTs of the Indian Ocean. We may see the third MJO since late last fall evolve in that region by late week 2 or 3.
GSDM Stage 1 best describes the current weather-climate situation. Relative atmospheric angular momentum (AAM) remains well below the 1968-1997 reanalysis data climatology at ~1.5 standard deviations. The global tropical and subtropical atmospheres are dominated by zonal mean easterly wind anomalies with magnitudes of 5-10m/s. The fast dynamical signal discussed above should reinforce what is already a low AAM regime during the week 2-3 time frame. Synoptically, the most probable response across the Pacific North American sector would be for a discontinuous retrogression of existing circulation anomalous by at least 20-30 degrees of longitude. This means the ridge currently over the western North America should redevelop ~150W.
Even with the above reasoning, forecast uncertainty for weeks 2-3 remains very high. If a coherent MJO develops across the Indian Ocean by week 3, forecast confidence in subseasonal outlooks may improve. Most models forecast a fairly strong trough to impact the west coast early next week and then shift into the Rockies and Plains afterwards. It is possible this first trough may “split” with northern and southern stream developments during the course of its evolution. In fact, recent signals of AAM transports would support this possibility. Afterwards, a more “classic” GSDM Stage 1 springtime active pattern for the western and central USA may emerge for weeks 2-3. This would argue for late season snowstorms across portions of the Rockies and northern/central High Plains with a greater than climatology risk for severe local storms across the Plains and Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion next Tuesday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Tuesday, March 13, 2007
Regrouping or What?
SSTs remain warm in a horseshoe pattern centered on 0/150E and extend to just southwest of Hawaii as well as into the South Pacific. Anomalies are ~plus 0.5-1.0C with actual SSTs from 29-30C. Other weak-moderate positive tropical SST anomalies are also present across portions of the Indian Ocean, far eastern Pacific and the North Tropical Atlantic. Negative anomalies of roughly 0.5-1.0C are present from Indonesia into Northern Australia as the result of recent tropical cyclone and heavy precipitation activity. Cool anomalies of ~0.5C also remain on the equator from about 120-150W with colder subsurface values down to 200m at the date line per latest TAO data. The latter may be attributable to a developing La-Nina. If one does develop, we expect the cooling to occur in “steps” related to forcing from subseasonal events.
Resolving the situation with the tropical convective forcing is difficult and about as tough as it gets in terms of uncertainty. A very weak dynamical signal with the recent weak-moderate MJO remains around 90W and appears to be stalling just west of South America. Tropical convection has also tried to get better organized ~0/140-150E for the past several days, largely forced by the warm SSTs in that region and favorable upper level winds. A Rossby wave energy dispersion from the Southern Hemisphere extratropics has led to an increase in upper tropospheric easterly wind anomalies across the west central Pacific. The locally strengthened upper level divergence is providing a source of lift for additional thunderstorm activity.
Animations of 150mb daily mean vector wind anomalies suggest twin subtropical anticyclones redeveloping ~150E. However, whether or not this convection will then shift east toward the warm SSTs as a MJO-like signal is unclear. Currently, a component actually shifting northwest from the west Pacific toward the Philippines is only complicating matters. Furthermore, should a strong eastward shift occur, the bulk of the forcing will stay south of the equator given the cool east Pacific SSTs and the time of year.
The uncertainty in the near term tropical convective forcing is not present in all circulation fields. Global relative atmospheric angular momentum (AAM) remains low at about -1.5 sigma anomaly. A large contribution is coming from the northern subtropical atmosphere centered ~25N. Zonal mean easterly wind anomalies at 200mb are from 5-10m/s in that region, having propagated off the equator starting back in mid February tied to the recent MJO. There have been a couple of episodes of weak positive global AAM tendency since then (~10 Hadleys), partly linked to variations involving mountain and frictional torques in addition to the MJO dynamical signal moving into the Western Hemisphere. For the latter, weak upper tropospheric westerly wind anomalies developed along the Western Hemisphere equator and are interacting with a subtropical wave train currently moving through South Asia.
A very strong storm system is currently pounding Tibet and northern India, part of the wave energy dispersion along the South Asian wave train. As this system interacts with the west central Pacific convection, an extension of the East Asia Jet (EAJ) is probable. Synoptically, this translates to the current trough just east of Japan moving east toward western North America while the upstream system replaces it. This was a possibility discussed in my March 9th posting, and most models predict this situation starting around next Tuesday. However, details remain very unclear. Nevertheless, there is hope for at least one IOP for the American River Basin HMT project with this system. This trough should then move into the Rockies and Plains during week 2 increasing the probability of high impact weather.
Afterwards, for weeks 2-3, uncertainty remains very high. I would think a GSDM Stage 1 base state (consistent with La-Nina) is most probable to persist, with subseasonal variations. Considering the seasonal cycle more strong troughs for particularly the Rockies and Plains while ridge amplification occurs across the central/east Pacific would be expected. However, if the tropical forcing shifts east along the equator to the date line (and/or a strong central Pacific flare-up occurs), the circulation could quickly transition to Stage 3.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion this Friday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Resolving the situation with the tropical convective forcing is difficult and about as tough as it gets in terms of uncertainty. A very weak dynamical signal with the recent weak-moderate MJO remains around 90W and appears to be stalling just west of South America. Tropical convection has also tried to get better organized ~0/140-150E for the past several days, largely forced by the warm SSTs in that region and favorable upper level winds. A Rossby wave energy dispersion from the Southern Hemisphere extratropics has led to an increase in upper tropospheric easterly wind anomalies across the west central Pacific. The locally strengthened upper level divergence is providing a source of lift for additional thunderstorm activity.
Animations of 150mb daily mean vector wind anomalies suggest twin subtropical anticyclones redeveloping ~150E. However, whether or not this convection will then shift east toward the warm SSTs as a MJO-like signal is unclear. Currently, a component actually shifting northwest from the west Pacific toward the Philippines is only complicating matters. Furthermore, should a strong eastward shift occur, the bulk of the forcing will stay south of the equator given the cool east Pacific SSTs and the time of year.
The uncertainty in the near term tropical convective forcing is not present in all circulation fields. Global relative atmospheric angular momentum (AAM) remains low at about -1.5 sigma anomaly. A large contribution is coming from the northern subtropical atmosphere centered ~25N. Zonal mean easterly wind anomalies at 200mb are from 5-10m/s in that region, having propagated off the equator starting back in mid February tied to the recent MJO. There have been a couple of episodes of weak positive global AAM tendency since then (~10 Hadleys), partly linked to variations involving mountain and frictional torques in addition to the MJO dynamical signal moving into the Western Hemisphere. For the latter, weak upper tropospheric westerly wind anomalies developed along the Western Hemisphere equator and are interacting with a subtropical wave train currently moving through South Asia.
A very strong storm system is currently pounding Tibet and northern India, part of the wave energy dispersion along the South Asian wave train. As this system interacts with the west central Pacific convection, an extension of the East Asia Jet (EAJ) is probable. Synoptically, this translates to the current trough just east of Japan moving east toward western North America while the upstream system replaces it. This was a possibility discussed in my March 9th posting, and most models predict this situation starting around next Tuesday. However, details remain very unclear. Nevertheless, there is hope for at least one IOP for the American River Basin HMT project with this system. This trough should then move into the Rockies and Plains during week 2 increasing the probability of high impact weather.
Afterwards, for weeks 2-3, uncertainty remains very high. I would think a GSDM Stage 1 base state (consistent with La-Nina) is most probable to persist, with subseasonal variations. Considering the seasonal cycle more strong troughs for particularly the Rockies and Plains while ridge amplification occurs across the central/east Pacific would be expected. However, if the tropical forcing shifts east along the equator to the date line (and/or a strong central Pacific flare-up occurs), the circulation could quickly transition to Stage 3.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion this Friday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Friday, March 09, 2007
Details are Important
Not much change has occurred with the tropical sea surface temperatures (SSTs) since my posting on Tuesday (3/6). While equatorial Pacific SSTs remain cool east of 150W (~minus 1-2C), warm anomalies are still present across the west central into the South Pacific. The latter are roughly 0.5-1C extending to depths of about 100m with actual SSTs varying from 29-31C. Only weak anomalies exist to the west.
There are at least 2 important regions of tropical convective forcing. One is nearly stationary centered around 10S/120E, and may be part of a slower process linked to a transition from El-Nino to La-Nina. The other is the dynamical signal with the MJO ~15-20S/160W. About 10 days ago these regions consolidated, and there were at least 2-3 tropical cyclones in the area of Australia left in the wake.
An important point is that a MJO signal remains. In fact, this signal can be traced back to late January 2007 in the near equatorial velocity potential Hovmollers courtesy of CPC. The signal is weakening especially in the convective field while it continues to evolve as expected in the upper level wind field (see below). The convective field now has multiple regions of tropical forcing with well defined anomalous twin upper tropospheric subtropical anticyclones near 120E and also near 160W (but mainly south of the equator).
At this time upper tropospheric zonal mean anomalous easterly flow continues to propagate poleward through the northern subtropical atmosphere, with magnitudes of ~10m/s around 25N (as a response to the MJO). This has contributed to a -2 sigma global relative angular momentum anomaly. Locally, there are weak upper tropospheric equatorial westerly wind anomalies starting to interact with the subtropics.
The MJO dynamical signal is moving east at about 10 deg long/day, and it may re-emerge into the Eastern Hemisphere by late week 2 or week 3. During this time zonal mean westerly flow should increase throughout the northern subtropics possibly allowing the East Asian Jet to undercut the recent blocking across the North Pacific. Convective flare-ups from the west central-South Pacific are also probable while a stationary convective signal may remain near 120E. Forecast uncertainty remains tremendously high after week 1 but I think we will see persistence of a GSDM Stage 1 anomaly pattern.
I think the models have a reasonable handle on week1 across the lower 48 states with ridge amplification just off the west coast and a central and eventually eastern states trough. This will keep the western states relatively warm and dry with cooler and wetter weather for the central and east USA. However, while I did underestimate in recent posts the impacts from the subtropical easterlies discussed above, I do think there will be more strong troughs to impact the western USA by late week 2 into week 3. The latter is most probable during GSDM Stage 1, and also during seasonal transition into spring. In fact, should the tropical convective forcing become quite intense across the Eastern Hemisphere during week 3 (leading to MJO #3 since December 2006?) with central Pacific flare-ups, an active regime for the USA may persist well into April.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion next Tuesday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
There are at least 2 important regions of tropical convective forcing. One is nearly stationary centered around 10S/120E, and may be part of a slower process linked to a transition from El-Nino to La-Nina. The other is the dynamical signal with the MJO ~15-20S/160W. About 10 days ago these regions consolidated, and there were at least 2-3 tropical cyclones in the area of Australia left in the wake.
An important point is that a MJO signal remains. In fact, this signal can be traced back to late January 2007 in the near equatorial velocity potential Hovmollers courtesy of CPC. The signal is weakening especially in the convective field while it continues to evolve as expected in the upper level wind field (see below). The convective field now has multiple regions of tropical forcing with well defined anomalous twin upper tropospheric subtropical anticyclones near 120E and also near 160W (but mainly south of the equator).
At this time upper tropospheric zonal mean anomalous easterly flow continues to propagate poleward through the northern subtropical atmosphere, with magnitudes of ~10m/s around 25N (as a response to the MJO). This has contributed to a -2 sigma global relative angular momentum anomaly. Locally, there are weak upper tropospheric equatorial westerly wind anomalies starting to interact with the subtropics.
The MJO dynamical signal is moving east at about 10 deg long/day, and it may re-emerge into the Eastern Hemisphere by late week 2 or week 3. During this time zonal mean westerly flow should increase throughout the northern subtropics possibly allowing the East Asian Jet to undercut the recent blocking across the North Pacific. Convective flare-ups from the west central-South Pacific are also probable while a stationary convective signal may remain near 120E. Forecast uncertainty remains tremendously high after week 1 but I think we will see persistence of a GSDM Stage 1 anomaly pattern.
I think the models have a reasonable handle on week1 across the lower 48 states with ridge amplification just off the west coast and a central and eventually eastern states trough. This will keep the western states relatively warm and dry with cooler and wetter weather for the central and east USA. However, while I did underestimate in recent posts the impacts from the subtropical easterlies discussed above, I do think there will be more strong troughs to impact the western USA by late week 2 into week 3. The latter is most probable during GSDM Stage 1, and also during seasonal transition into spring. In fact, should the tropical convective forcing become quite intense across the Eastern Hemisphere during week 3 (leading to MJO #3 since December 2006?) with central Pacific flare-ups, an active regime for the USA may persist well into April.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion next Tuesday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Tuesday, March 06, 2007
Not What I Expected
Tropical sea surface temperatures continue to cool across the equatorial Pacific Ocean while weak-moderate positive anomalies remain from the west central to the South Pacific. In fact, negative temperature anomalies as low as -2C have recently been observed at around 120W per TAO buoy data, extending to depths of at least 200m. An evolution to La-Nina is looking more probable.
The dynamical signal with the MJO continues to propagate east at roughly 5m/s (4 deg long/day) toward the west central and South Pacific per diagnostic monitoring tools and satellite imagery. For instance, as of March 5th the Wheeler index suggests this signal to be at ~160E. We prefer to describe the recent eastward shift as part of a weather-climate or subseasonal event. These typically consist of multiple time scales, one of which is the MJO but others of which are less oscillatory.
Tropical convective forcing has also been getting better organized from the central Indian Ocean to Indonesia during the last few days, centered at about 10S/120E. Hovmoller plots of both total and anomalous OLR suggest this forcing may become a stationary possibly linked to a developing cold event. The global circulation has responded accordingly with anomalous zonal mean easterly flow propagating off the equator into the subtropical atmosphere particularly for the Northern Hemisphere (magnitudes ~minus 10m/s for the latter). Global relative AAM remains very low at about 2 standard deviations below the 1968-1997 reanalysis climatology with its tendency at roughly minus 10 Hadleys. The recent peak of AAM tendency to plus 10 Hadleys was the result of the subseasonal signal discussed above.
As predicted, GSDM Stage 1 best describes the current global circulation. However, regionally from the Asian to North American sector the distribution of circulation anomalies has become very complicated. Animations of daily mean 150mb and 250mb vector wind anomalies show twin anticyclones centered around 115E with downstream troughs near the date line. However, there are also residual anomalies linked to past forcing from the tropical west Pacific including those across the Arctic. From a synoptic view point the ridge that is most probable to be centered ~140-150W in this situation has been split in two; one portion is at the date line with the other over western North America. Most ensemble means (not details) suggested this possibility 7-10 days ago. There is some hint from recent model runs for current Gulf of Alaska trough to slowly move east and southeast into western North America during the next couple of weeks. My own thought a week ago was for an enhanced probability for this process to happen sooner and farther south than the models were showing, allowing a resumption of an active regime for much of the country. This appears less likely in the immediate future.
Whatever the case over the next 7-10 days, I think forecast uncertainty for a week 2-3 prediction for the USA is very high, despite what appears to be good model agreement of a low amplitude trough across western North America and a northward displaced storm track. In fact, I think it probable that a strong synoptic scale trough will impact the western and central USA with the extreme weather typical of GSDM Stage 1 during weeks 2-3. This would mean at least one prominent “southwest flow cyclonic baroclinic event” across the Plains similar to the 2 recent events. Until then, a rather benign weather pattern with warm and dry across the southern states and a bit unsettled across the north can be expected.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion this Friday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
The dynamical signal with the MJO continues to propagate east at roughly 5m/s (4 deg long/day) toward the west central and South Pacific per diagnostic monitoring tools and satellite imagery. For instance, as of March 5th the Wheeler index suggests this signal to be at ~160E. We prefer to describe the recent eastward shift as part of a weather-climate or subseasonal event. These typically consist of multiple time scales, one of which is the MJO but others of which are less oscillatory.
Tropical convective forcing has also been getting better organized from the central Indian Ocean to Indonesia during the last few days, centered at about 10S/120E. Hovmoller plots of both total and anomalous OLR suggest this forcing may become a stationary possibly linked to a developing cold event. The global circulation has responded accordingly with anomalous zonal mean easterly flow propagating off the equator into the subtropical atmosphere particularly for the Northern Hemisphere (magnitudes ~minus 10m/s for the latter). Global relative AAM remains very low at about 2 standard deviations below the 1968-1997 reanalysis climatology with its tendency at roughly minus 10 Hadleys. The recent peak of AAM tendency to plus 10 Hadleys was the result of the subseasonal signal discussed above.
As predicted, GSDM Stage 1 best describes the current global circulation. However, regionally from the Asian to North American sector the distribution of circulation anomalies has become very complicated. Animations of daily mean 150mb and 250mb vector wind anomalies show twin anticyclones centered around 115E with downstream troughs near the date line. However, there are also residual anomalies linked to past forcing from the tropical west Pacific including those across the Arctic. From a synoptic view point the ridge that is most probable to be centered ~140-150W in this situation has been split in two; one portion is at the date line with the other over western North America. Most ensemble means (not details) suggested this possibility 7-10 days ago. There is some hint from recent model runs for current Gulf of Alaska trough to slowly move east and southeast into western North America during the next couple of weeks. My own thought a week ago was for an enhanced probability for this process to happen sooner and farther south than the models were showing, allowing a resumption of an active regime for much of the country. This appears less likely in the immediate future.
Whatever the case over the next 7-10 days, I think forecast uncertainty for a week 2-3 prediction for the USA is very high, despite what appears to be good model agreement of a low amplitude trough across western North America and a northward displaced storm track. In fact, I think it probable that a strong synoptic scale trough will impact the western and central USA with the extreme weather typical of GSDM Stage 1 during weeks 2-3. This would mean at least one prominent “southwest flow cyclonic baroclinic event” across the Plains similar to the 2 recent events. Until then, a rather benign weather pattern with warm and dry across the southern states and a bit unsettled across the north can be expected.
Please note: These are probabilistic statements, which we will try to quantify in future posts. I am on TDY at ESRL/PSD with the HMT project until April 3rd. I will try to post another discussion this Friday. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry and Klaus Weickmann
Friday, March 02, 2007
Brief Update -- Global models may perform like the recent global markets
The dynamical signal with the MJO is centered at ~10S/140E per several monitoring tools including the multivariate EOF Wheeler index and animations of circulation anomalies. Rough calculations of its phase speed give me anywhere from 5-8m/s depending on what variable you use; for example, velocity potential or OLRA. In any case, this recent MJO event has been a very difficult one to monitor and understand. In fact, I think what has happened during the past week is a consolidation between the MJO dynamical signal and westward propagating convection associated with west Pacific SST boundary forcing. The latter is a slower process that started about mid-January 2007 and may be part of the evolution of a transition from El-Nino to La-Nina.
My point in this short writing is I do not think the global models have “much of a clue” of the responses to the above. Global relative AAM tendency is ~plus 10-15 Hadleys per reanalysis data with much of that signal coming from the equatorial and subtropical atmospheres of the Western Hemisphere. Contributions are from the tropical forcing crossing Indonesia and an increase in the global frictional torque (while global relative AAM remains ~minus 2 sigma). I think the global circulation is trending toward GSDM Stage 2. This argues for ridge amplification across the eastern Pacific (~140W given seasonal cycle) during the next few weeks, most likely week 2. The global models (ensembles) do not depict this very well. They generally want to persist a trough across the Gulf of Alaska downstream of the central Pacific blocking.
I would not want to be a person investing money banking on “good” global model performance during the next few weeks. A decline in, for example, the skill of week-2 ensemble model means going into the middle of this month, appears probable (similar to the recent global markets?). Sources would include not only the excitation of a west Pacific wavetrain forced by Rossby wave energy dispersion tied to the east Indonesia/west Pacific tropical forcing, but also seasonal transition. My thought would be for the Gulf of Alaska trough to dig southeast along the USA west coast (impacting ARB) during week 2, then shift into the Rockies leading to a resumption of a stormy regime for much of the USA. This would be similar to recently observed, but with an Arctic cold air source. If this MJO signal stalls, say ~150E, then shifts back to west, this regime may persist for a period longer than 1 synoptic event.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I will try to post a more complete discussion ~Tuesday next week while at ESRL/PSD. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
My point in this short writing is I do not think the global models have “much of a clue” of the responses to the above. Global relative AAM tendency is ~plus 10-15 Hadleys per reanalysis data with much of that signal coming from the equatorial and subtropical atmospheres of the Western Hemisphere. Contributions are from the tropical forcing crossing Indonesia and an increase in the global frictional torque (while global relative AAM remains ~minus 2 sigma). I think the global circulation is trending toward GSDM Stage 2. This argues for ridge amplification across the eastern Pacific (~140W given seasonal cycle) during the next few weeks, most likely week 2. The global models (ensembles) do not depict this very well. They generally want to persist a trough across the Gulf of Alaska downstream of the central Pacific blocking.
I would not want to be a person investing money banking on “good” global model performance during the next few weeks. A decline in, for example, the skill of week-2 ensemble model means going into the middle of this month, appears probable (similar to the recent global markets?). Sources would include not only the excitation of a west Pacific wavetrain forced by Rossby wave energy dispersion tied to the east Indonesia/west Pacific tropical forcing, but also seasonal transition. My thought would be for the Gulf of Alaska trough to dig southeast along the USA west coast (impacting ARB) during week 2, then shift into the Rockies leading to a resumption of a stormy regime for much of the USA. This would be similar to recently observed, but with an Arctic cold air source. If this MJO signal stalls, say ~150E, then shifts back to west, this regime may persist for a period longer than 1 synoptic event.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I will try to post a more complete discussion ~Tuesday next week while at ESRL/PSD. The WB (2007) paper on the GSDM has been published in the February issue of MWR.
Ed Berry
Tuesday, February 27, 2007
MJO or not?
The distribution of global tropical SSTs remains similar to about a week ago. This includes general warmth from the Indian Ocean toward the central and South Pacific while cooling continues along the equatorial cold tongue east of 150W. However, recent tropical cyclone activity has led to a negative SST tendency across the South Indian Ocean while positive tendencies are present across the central and South Pacific.
After the recent burst of intense tropical cyclone activity across the South Indian Ocean, a renewed organization of the tropical forcing is occurring centered ~10S/120-140E. General enhancement is present in a west-northwest to east-southeast oriented band roughly 10 deg wide from ~5S/90E to ~15S/160E which does include the SPCZ. I continue to maintain that this forcing is tied to a decent MJO signal. Monitoring tools such as the Wheeler index, velocity potential and animations of 150mb, 250mb and surface daily mean vector wind anomalies support my contention. Care must be taken to remember that it is not only the convective signal which defines a MJO, but also the winds (the multivariate EOF Wheeler technique considers this). The atmosphere is a dynamical system that consists of forcing, response and feedback processes all the time, and the MJO is just one of those components. About 10-20% of the tropical variability can be explained by the MJO, which only adds importance to diagnosing that signal when it is present.Care must also be taken to understand the details of tools utilized to interpret various modes of subseasonal variability. For instance, the Wheeler technique can be unrepresentative when there are multiple regions of tropical forcing.
I think the dynamical signal with the MJO is centered ~10S/100E, which does not have to be at the same location of the enhanced tropical convection. The global circulation has strongly responded with features such as twin upper tropospheric subtropical anticyclones across Africa and the Indian Ocean and downstream cyclones just east of the date line. Circulation anomalies are starting to reverse in the lower troposphere; for instance, there are westerly wind anomalies just north of Australia. This is a signal of a tropical baroclinic mode. Finally, zonal mean easterly wind anomalies remain ~good 5m/s throughout the tropical and subtropical atmospheres and global relative AAM is at least 2 standard deviations below normal per reanalysis data/climatology. The circulation has been in GSDM Stage 4 for roughly the past week, and GSDM Stage 1 appears probable during the next 1-3 weeks.
A serious question for weeks 1-3+ predictions is how far east is this MJO signal going to propagate? Our thought has been for this particular event to be truncated (linked to a possible transition to La-Nina) meaning it may not get by roughly Indonesia. In the presence of periodic flare-ups across the central/South Pacific, I am going to continue that feeling. This means the East Asian Jet (EAJ) will remain retracted and more troughs are probable to impact the west coast into the Plains. Should the convection come out to the date line, then the EAJ would be expected to expand east.
Most models have now captured the recent EAJ retraction and I do agree with the notion of trough development from the Alaska into the East Pacific during week 1. That would favor a less active pattern for much of the USA after the upcoming Plains storm development, consistent with the “lull” I have discussed in past postings. I think that will change during week 2 and continue week 3. Initially, heavy precipitation should spread southward along the USA west coast, including the ARB region (for the Hydrometeorological Testbed Project). Troughs would then be expected to move through the Rockies leading to baroclinic storm development on the Plains with an Arctic cold air source. The latter has been somewhat lacking with our past active situation.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I may not be able to post another discussion until early next week (~Tuesday) due to travel and shift work obligations. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
After the recent burst of intense tropical cyclone activity across the South Indian Ocean, a renewed organization of the tropical forcing is occurring centered ~10S/120-140E. General enhancement is present in a west-northwest to east-southeast oriented band roughly 10 deg wide from ~5S/90E to ~15S/160E which does include the SPCZ. I continue to maintain that this forcing is tied to a decent MJO signal. Monitoring tools such as the Wheeler index, velocity potential and animations of 150mb, 250mb and surface daily mean vector wind anomalies support my contention. Care must be taken to remember that it is not only the convective signal which defines a MJO, but also the winds (the multivariate EOF Wheeler technique considers this). The atmosphere is a dynamical system that consists of forcing, response and feedback processes all the time, and the MJO is just one of those components. About 10-20% of the tropical variability can be explained by the MJO, which only adds importance to diagnosing that signal when it is present.Care must also be taken to understand the details of tools utilized to interpret various modes of subseasonal variability. For instance, the Wheeler technique can be unrepresentative when there are multiple regions of tropical forcing.
I think the dynamical signal with the MJO is centered ~10S/100E, which does not have to be at the same location of the enhanced tropical convection. The global circulation has strongly responded with features such as twin upper tropospheric subtropical anticyclones across Africa and the Indian Ocean and downstream cyclones just east of the date line. Circulation anomalies are starting to reverse in the lower troposphere; for instance, there are westerly wind anomalies just north of Australia. This is a signal of a tropical baroclinic mode. Finally, zonal mean easterly wind anomalies remain ~good 5m/s throughout the tropical and subtropical atmospheres and global relative AAM is at least 2 standard deviations below normal per reanalysis data/climatology. The circulation has been in GSDM Stage 4 for roughly the past week, and GSDM Stage 1 appears probable during the next 1-3 weeks.
A serious question for weeks 1-3+ predictions is how far east is this MJO signal going to propagate? Our thought has been for this particular event to be truncated (linked to a possible transition to La-Nina) meaning it may not get by roughly Indonesia. In the presence of periodic flare-ups across the central/South Pacific, I am going to continue that feeling. This means the East Asian Jet (EAJ) will remain retracted and more troughs are probable to impact the west coast into the Plains. Should the convection come out to the date line, then the EAJ would be expected to expand east.
Most models have now captured the recent EAJ retraction and I do agree with the notion of trough development from the Alaska into the East Pacific during week 1. That would favor a less active pattern for much of the USA after the upcoming Plains storm development, consistent with the “lull” I have discussed in past postings. I think that will change during week 2 and continue week 3. Initially, heavy precipitation should spread southward along the USA west coast, including the ARB region (for the Hydrometeorological Testbed Project). Troughs would then be expected to move through the Rockies leading to baroclinic storm development on the Plains with an Arctic cold air source. The latter has been somewhat lacking with our past active situation.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I may not be able to post another discussion until early next week (~Tuesday) due to travel and shift work obligations. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
Friday, February 23, 2007
MJO and Atmospheric Angular Momentum (AAM) - Reprisal
There is not much “new” information I can add to my posting from 2/20. SSTs generally continue the trend of cooling along the equatorial cold tongue while above average warmth remains from the South Indian Ocean into Indonesia. Above average SSTs also linger from the equatorial date line into the South Pacific. A transition from El-Nino to La-Nina must be monitored during the upcoming months. Such a transition could have implications for the upcoming Atlantic hurricane season.
Tropical convective forcing continues to get better organized across the Eastern Hemisphere. Remembering that we have a slowly evolving situation, many monitoring and diagnostic tools suggest that at least a weak-moderate signal of the MJO is present centered ~10S/80-90E. The development of at least 3 tropical cyclones across the South Indian Ocean during the past week is a response. I think this MJO signal has “stalled”, and that may be part of the evolutionary process of transitioning from El-Nino to La-Nina.
As of February 19th, ESRL/PSD reanalysis data plots of global AAM tendency were still ~minus 50 Hadleys. Contributions were from large negative global mountain and frictional torques as well as deep zonal mean anomalous easterly flow (~5-10m/s) throughout the tropical and subtropical atmospheres. A trade wind surge from the South Pacific into the South Indian Ocean is currently lessening the negative frictional torque and I suspect this may become positive during the next week or so. Finally, about a week ago the general pattern, observed since ~December 1st 2006, of westerly flow being transported out of the subtropics into the northern extratropics resumed. The latter is a characteristic of La-Nina situations and is described by Stage 1 of the GSDM.
I think we are still in GSDM Stage 4 (due to the very large negative global AAM tendency) and it is probable the global circulation will evolve into Stage 1 during the next 1-3 weeks. The East Asian Jet (EAJ) retracted significantly during the past week and it should stay that way. In fact, as some ensemble members and week-2 means show, there may be a surge of cold air into the east Pacific during that period due to this retraction. However, to me this would only be one of those “lulls” for much of the USA (except, of course, the west coast) in an otherwise stormy regime with an Arctic cold air source. What may persist this situation would be a “stationary MJO signal” ~100-120E while flare-ups of convection occur from the west central into the South Pacific. Rossby wave energy dispersions tied to the MJO signal would favor western USA troughs that would subsequently interact with subtropical jets forced by the central/South Pacific signal. My outlook from now through March 2007 posted on February 20th remains unchanged.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I will try to post another update on about next Tuesday. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
Tropical convective forcing continues to get better organized across the Eastern Hemisphere. Remembering that we have a slowly evolving situation, many monitoring and diagnostic tools suggest that at least a weak-moderate signal of the MJO is present centered ~10S/80-90E. The development of at least 3 tropical cyclones across the South Indian Ocean during the past week is a response. I think this MJO signal has “stalled”, and that may be part of the evolutionary process of transitioning from El-Nino to La-Nina.
As of February 19th, ESRL/PSD reanalysis data plots of global AAM tendency were still ~minus 50 Hadleys. Contributions were from large negative global mountain and frictional torques as well as deep zonal mean anomalous easterly flow (~5-10m/s) throughout the tropical and subtropical atmospheres. A trade wind surge from the South Pacific into the South Indian Ocean is currently lessening the negative frictional torque and I suspect this may become positive during the next week or so. Finally, about a week ago the general pattern, observed since ~December 1st 2006, of westerly flow being transported out of the subtropics into the northern extratropics resumed. The latter is a characteristic of La-Nina situations and is described by Stage 1 of the GSDM.
I think we are still in GSDM Stage 4 (due to the very large negative global AAM tendency) and it is probable the global circulation will evolve into Stage 1 during the next 1-3 weeks. The East Asian Jet (EAJ) retracted significantly during the past week and it should stay that way. In fact, as some ensemble members and week-2 means show, there may be a surge of cold air into the east Pacific during that period due to this retraction. However, to me this would only be one of those “lulls” for much of the USA (except, of course, the west coast) in an otherwise stormy regime with an Arctic cold air source. What may persist this situation would be a “stationary MJO signal” ~100-120E while flare-ups of convection occur from the west central into the South Pacific. Rossby wave energy dispersions tied to the MJO signal would favor western USA troughs that would subsequently interact with subtropical jets forced by the central/South Pacific signal. My outlook from now through March 2007 posted on February 20th remains unchanged.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I will try to post another update on about next Tuesday. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
Tuesday, February 20, 2007
MJO and Atmospheric Angular Momentum
Tropical SSTs remain roughly 0.5-1.0C above average over much of the South Indian Ocean as well as around the equatorial date line into the South Pacific. Actual SSTs are generally in the 29-30C range across these regions. Significant cool anomalies are now being observed by the TAO buoy array around 0/120W with magnitudes of about minus 1C. Values as low as minus 6C at ~50m deep have been recently observed across this region. The latter is the result of an upwelling oceanic Kelvin wave from the December 2006 MJO and may be contributing to a transition from El-Nino to La-Nina.
Full disk satellite imagery and other monitoring tools depict intense tropical convection across several regions of the globe. These include South Africa, the South Indian Ocean, the north coast of Australia into the South Pacific and much of Brasil. This is a rather complicated situation; however, a slowly evolving dynamical signal projecting onto the MJO is emerging currently centered ~10S/80E. Statistical tools such as the multivariate EOF Wheeler technique and empirical methods such as the time-filtered coherent modes Hovmollers support this notion. Furthermore, a rough phase speed computation of the convective envelope gives me about 4 m/s (3 deg long/day), consistent with a MJO.
There is also strong diagnostic support that a MJO signal is developing across the Eastern Hemisphere. Recall there was an intense flare-up of tropical convection across the warm South Pacific SSTs during about the middle of January. Through interactions with the Southern Hemisphere extratropics, a dynamical signal moved east to intensify convection across South Africa. It is this forcing that has now shifted into the South Indian Ocean. The global circulation has responded strongly to this redistribution of tropical forcing, with, for example, the tendency of global relative atmospheric angular momentum (AAM) down to about minus 50 Hadleys as of February 17th per re-analysis data! There are also other contributions to this tendency such as the current “negative phase” of a mountain-frictional torque index cycle. This is largest magnitude of a negative AAM tendency signal in at least a year and in itself represents an extreme weather-climate event. What is even more interesting is this negative AAM tendency is after the positive maximum of ~30 Hadleys around January 10th (roughly 50 days ago).
The point is westerly flow is being removed from the atmosphere by the earth and the spatial rearrangement of the tropical forcing has contributed to it. Furthermore, if one more carefully understands the time and space scales of what was first adding westerly flow to the atmosphere, early January, then the current removal of it, there is consistency with the MJO time scale. Currently zonal mean anomalous easterly flow prevails throughout the tropical and subtropical atmospheres with magnitudes of ~5-10m/s. Additionally, there are anomalous twin upper tropospheric subtropical anticyclones developing across the Indian Ocean with downstream cyclones and surface wind anomalies that are generally opposite. This means we already have a tropical baroclinic mode as a response to the developing MJO convection.
To me it is not a matter of whether there is a MJO, it is simply how strong will it be during the next several weeks. I do think the eastward movement of this MJO is going to be truncated (not get past roughly Indonesia) given recent SST trends. I also think our west central-South Pacific signal will continue with roughly 10-15 day flare-ups and assist with enhancing the climatologically strong southern USA subtropical jet.
We are currently in GSDM Stage 4 and it is probable to go into Stage 1 during the next 2-3 weeks (with at times strong subtropical jets). More models and their ensembles have become supportive of my past feelings about particularly the western and central portions of the USA going into an active regime. The ensemble means do struggle with differing solutions (along with a lot of spread) after about day 10. This is not at all a surprise to me given the abrupt shifts is circulation anomalies as measured by AAM tendency. With variations in amplitude including “lulls”, I think this regime may mature during March, especially if the tropical forcing becomes more persistent around 120E in the presence of the central and South Pacific signal.
As stated in my February 16th posting, we should several troughs first impact the west coast and then move northeast across the Plains (loosely – already starting). The western states will cool while the east warms. Arctic air may initially build up across Alaska (due to blocking west of the state) and then come into the western/central states during early March. March 2007 may be exceptionally active (above climatology) with heavy rain/severe storms across the Deep South into the east while late winter/early spring blizzards pound much of the Rockies into the Plains/Upper Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I will try to post at least a short update this Friday. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
Full disk satellite imagery and other monitoring tools depict intense tropical convection across several regions of the globe. These include South Africa, the South Indian Ocean, the north coast of Australia into the South Pacific and much of Brasil. This is a rather complicated situation; however, a slowly evolving dynamical signal projecting onto the MJO is emerging currently centered ~10S/80E. Statistical tools such as the multivariate EOF Wheeler technique and empirical methods such as the time-filtered coherent modes Hovmollers support this notion. Furthermore, a rough phase speed computation of the convective envelope gives me about 4 m/s (3 deg long/day), consistent with a MJO.
There is also strong diagnostic support that a MJO signal is developing across the Eastern Hemisphere. Recall there was an intense flare-up of tropical convection across the warm South Pacific SSTs during about the middle of January. Through interactions with the Southern Hemisphere extratropics, a dynamical signal moved east to intensify convection across South Africa. It is this forcing that has now shifted into the South Indian Ocean. The global circulation has responded strongly to this redistribution of tropical forcing, with, for example, the tendency of global relative atmospheric angular momentum (AAM) down to about minus 50 Hadleys as of February 17th per re-analysis data! There are also other contributions to this tendency such as the current “negative phase” of a mountain-frictional torque index cycle. This is largest magnitude of a negative AAM tendency signal in at least a year and in itself represents an extreme weather-climate event. What is even more interesting is this negative AAM tendency is after the positive maximum of ~30 Hadleys around January 10th (roughly 50 days ago).
The point is westerly flow is being removed from the atmosphere by the earth and the spatial rearrangement of the tropical forcing has contributed to it. Furthermore, if one more carefully understands the time and space scales of what was first adding westerly flow to the atmosphere, early January, then the current removal of it, there is consistency with the MJO time scale. Currently zonal mean anomalous easterly flow prevails throughout the tropical and subtropical atmospheres with magnitudes of ~5-10m/s. Additionally, there are anomalous twin upper tropospheric subtropical anticyclones developing across the Indian Ocean with downstream cyclones and surface wind anomalies that are generally opposite. This means we already have a tropical baroclinic mode as a response to the developing MJO convection.
To me it is not a matter of whether there is a MJO, it is simply how strong will it be during the next several weeks. I do think the eastward movement of this MJO is going to be truncated (not get past roughly Indonesia) given recent SST trends. I also think our west central-South Pacific signal will continue with roughly 10-15 day flare-ups and assist with enhancing the climatologically strong southern USA subtropical jet.
We are currently in GSDM Stage 4 and it is probable to go into Stage 1 during the next 2-3 weeks (with at times strong subtropical jets). More models and their ensembles have become supportive of my past feelings about particularly the western and central portions of the USA going into an active regime. The ensemble means do struggle with differing solutions (along with a lot of spread) after about day 10. This is not at all a surprise to me given the abrupt shifts is circulation anomalies as measured by AAM tendency. With variations in amplitude including “lulls”, I think this regime may mature during March, especially if the tropical forcing becomes more persistent around 120E in the presence of the central and South Pacific signal.
As stated in my February 16th posting, we should several troughs first impact the west coast and then move northeast across the Plains (loosely – already starting). The western states will cool while the east warms. Arctic air may initially build up across Alaska (due to blocking west of the state) and then come into the western/central states during early March. March 2007 may be exceptionally active (above climatology) with heavy rain/severe storms across the Deep South into the east while late winter/early spring blizzards pound much of the Rockies into the Plains/Upper Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. I will try to post at least a short update this Friday. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
Friday, February 16, 2007
Resurrection Update
I have been on travel this past week meaning this posting will be not as complete. Hopefully I will be able to post a better discussion around Tuesday next week.
Per full disk satellite imagery and monitoring tools, I think a renewed moist phase of the MJO is evolving from South Africa into the South Indian Ocean. The possibility of this development was offered in my January 30th posting based on the scientific principles utilized to derive our GSDM, including responses from the rapid weakening of warm ENSO.
The centroid of this convection was at ~10S/60E and extended east to about western Indonesia. Other sporadic tropical convection continued across the South Pacific and South America. SSTs are about plus 1C (at least 29C) over much of the South Indian Ocean and these warm waters will contribute to a lot of CAPE to our developing MJO. I suspect this MJO will become more robust ~90-110E by late week 2/early week 3.
The global circulation is already responding with features such as twin upper tropospheric subtropical anticyclones ~60E and downstream twin cyclones. In fact, the cyclone just north of India tied to this MJO contributed to a recent extended period of extreme cold/wet weather in that region. Upper tropospheric easterly wind anomalies are increasing throughout the tropical and subtropical atmospheres and the tendency of global relative atmospheric angular momentum is about minus 15 Hadleys. The latter is still decreasing with a contribution coming from a strong negative frictional torque (~15 Hadleys) that began about 2 weeks ago. I think we are in Stage 4 of the GSDM and it is probable we will go into Stage 1 during the next 2-3 weeks. There will also remain periodic forcing from the South Pacific that may enhance a climatologically strong subtropical jet.
My feelings about particularly the western and central portions of the USA going into an active pattern for the next few weeks remain unchanged. In fact, I think this regime may mature going into March. We should several troughs first impact the west coast and then move east-northeast across the Plains (loosely). The western states will cool while the east warms. Arctic air may initially build up across Alaska (due to blocking west of the state) and then come into the western/central states during early March. March 2007 may be exceptionally active (above climatology) with (for example) heavy rain/severe storms across the Deep South into the east while late winter/early spring blizzards pound much of the Rockies into the Plains/Upper Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
Per full disk satellite imagery and monitoring tools, I think a renewed moist phase of the MJO is evolving from South Africa into the South Indian Ocean. The possibility of this development was offered in my January 30th posting based on the scientific principles utilized to derive our GSDM, including responses from the rapid weakening of warm ENSO.
The centroid of this convection was at ~10S/60E and extended east to about western Indonesia. Other sporadic tropical convection continued across the South Pacific and South America. SSTs are about plus 1C (at least 29C) over much of the South Indian Ocean and these warm waters will contribute to a lot of CAPE to our developing MJO. I suspect this MJO will become more robust ~90-110E by late week 2/early week 3.
The global circulation is already responding with features such as twin upper tropospheric subtropical anticyclones ~60E and downstream twin cyclones. In fact, the cyclone just north of India tied to this MJO contributed to a recent extended period of extreme cold/wet weather in that region. Upper tropospheric easterly wind anomalies are increasing throughout the tropical and subtropical atmospheres and the tendency of global relative atmospheric angular momentum is about minus 15 Hadleys. The latter is still decreasing with a contribution coming from a strong negative frictional torque (~15 Hadleys) that began about 2 weeks ago. I think we are in Stage 4 of the GSDM and it is probable we will go into Stage 1 during the next 2-3 weeks. There will also remain periodic forcing from the South Pacific that may enhance a climatologically strong subtropical jet.
My feelings about particularly the western and central portions of the USA going into an active pattern for the next few weeks remain unchanged. In fact, I think this regime may mature going into March. We should several troughs first impact the west coast and then move east-northeast across the Plains (loosely). The western states will cool while the east warms. Arctic air may initially build up across Alaska (due to blocking west of the state) and then come into the western/central states during early March. March 2007 may be exceptionally active (above climatology) with (for example) heavy rain/severe storms across the Deep South into the east while late winter/early spring blizzards pound much of the Rockies into the Plains/Upper Mississippi Valley.
Please note: These are probabilistic statements, which we will try to quantify in future posts. My next 1 month period at ESRL/PSD with the HMT project will be from 3/4-4/3. The WB (2007) paper on the GSDM has been published in this month’s issue of MWR.
Ed Berry
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