ESRL/PSD reanalysis-1 (R1) data plots (including the AAM plots) have updated through May 23rd as of this writing. Hopefully the Global Wind Oscillation (GWO) phase space plot will be soon.
With the exception of eastern Indonesia, tropical SSTs remain generally quite warm across the Eastern Hemisphere. The most exceptional positive SST anomalies are over the western Indian Ocean having magnitudes of ~2C and totals in excess of 30C. The west central Pacific warmth continues to hang around (along with its positive anomaly horseshoe pattern into the extratropics) with magnitudes of ~1C (down to ~200m) and totals ~30C. Weakening cool anomalies are still present along the equatorial cold tongue east of the date line while the tropical Atlantic remains “luke warm”. Recent surface westerly wind anomalies have led to some moderation of the tropical east Pacific negative anomalies. Whether or not the colder subsurface anomalies (~minus 3-4C ~100m/140W per TAO data) can be upwelled along with any further development of La-Nina depends on the subseasonal events to be discussed.
Now comes some of the fun discussing recent subseasonal atmospheric activities. It is unfortunate we have not been afforded the opportunity to have a dedicated web page effort to illustrate with graphics the appropriate level of science discussions like these requires. The latter is only fair to meteorology and the users. There is much additional diagnostic information that can and must be incorporated into any forecast process for ~weeks 1-4. Kindly stated, recent numerical model performance and official week 1 forecast products issued last week for the current trough digging into the western USA is yet another example where weather-climate linkage information within the GSDM framework would have helped. There was a consensus our current western USA trough would be progressive, which is not going to happen. In order to use numerical models intelligently a detailed and disciplined understanding of the weather-climate situation requiring rigorous daily monitoring is a must, no exceptions!!! The issue of expressing these predictions probabilistically for the benefit of the users is also another matter needing far more attention.
During late April and ~May 11th there was a weak then strong positive global mountain-negative frictional torque index cycle. The latter had a global signal of ~plus 40 Hadleys for the mountain torque, which was roughly 45 days after the big event during early April. It is kind of “funny” how the intraseasonal time scale works into this. What all this means is dynamical processes involving the (tilts of the) midlatitude synoptic eddies interacting with global north-south mountain massifs are adding anomalous zonal mean westerly flow to particularly the subtropical atmospheres of both hemispheres. The May 11th variation contributed to a global AAM time tendency of at least plus 40 Hadleys.
So, where am I going here? I have discussed in past postings ~10-30 day variability involving the tropical convective forcing and mountain-frictional torques. These atmospheric variations have been occurring since at least mid February, within a base state generally fluxing (transporting) AAM out of the subtropics into the midlatitudes (GSDM Stage 1). The transports are the largest contributor to the earth-atmosphere AAM budget. Having both the Indian Ocean and west Pacific Ocean tropical convective forcing occurring “at the same time” has loosely supported a GSDM Stage 4-1 base state, but with at times significant orbits in phase space as seen on the GWO plot. Monitoring these orbits has added some additional week-2 predictability (over the models) to the barrage of western USA troughs seen this spring. The dynamics for this are complicated, but this is where thinking in terms of forcing-response-feedbacks with subsequent interactions is needed. I think we have just gone through another large orbit in GWO phase space, with the above contributing to it.
The additional anomalous subtropical westerly flow (~5-10m/s at 200mb) and interactions with the synoptic eddies forced the dynamical tropical convective signal into the Western Hemisphere about a week-10 days ago. Possibly involving the seasonal cycle including the Eastern Hemisphere monsoon systems, I think this dynamical signal has developed into a true Madden-Julian Oscillation (MJO). The Wheeler phase space plot strongly supports this assertion, as do phase speed computations of recent OLRA anomalies (~3.5m/s). Full disk satellite imagery has shown a rapid increase of intense tropical convection across the warm waters of the Indian Ocean, centered ~5N/60E. There is sporadic convection across the west central Pacific while thunderstorm clusters linger across Africa and roughly northern South America.
I think the weather-climate situation is solidly in GSDM Stage 4. Anomalous zonal mean easterly flow of ~5m/s at 200mb has developed throughout the tropical atmosphere. Twin upper tropospheric subtropical anticyclones remain across the Western Hemisphere (linked to the subtropical jet across the southern USA), but are slowly progressing into Africa and the Indian Ocean. As of May 23rd the AAM time tendency was ~minus 30 Hadleys which included a contribution from a negative East Asian mountain torque. The anomalous Rossby wave train tied to that torque was one of my reasons for thinking late last week that a slower and deeper western USA trough was more probable this week.
Besides the upper tropospheric zonal mean zonal wind anomalies across the tropical and subtropical atmospheres, there are also zonal mean anomalous easterlies ~35N and 30S, with anomalous westerlies poleward. In fact, at 60N these westerly anomalies have been recently ~plus 15m/s at 200mb, and there is evidence that some of this westerly flow goes back to poleward propagation off the equator from the strong December 2006 MJO event. In any case, this gives some reason to the recent observed midlatitude split flows.
This writing is already far too long. I think the global weather-climate situation will be in GSDM Stage 1 by week 2 as the MJO moves slowly east. I am still unclear about the timing and intensity of this new MJO; however, I speculate its centroid will be ~100-120E by the end of week 2. A trade wind surge downstream from this MJO may "revive" La-Nina development. Both the Indian and Southeast Asian monsoon regions should be active, while the west Pacific remains a “wild card”, as it has for several years. Models are finally starting to pick up not only on the slower and deeper western USA trough (developing into a closed low) for week 1, but even the much stronger system starting ~ day 10. The week 1 trough will be more of a heavy rainfall producer for the Plains and Mississippi Valley while the week 2 system may result in widespread severe storms across the central part of the country including tornadoes. Other ramifications should be apparent. During weeks 3-4 the situation evolve into GSDM Stage 2.
Appendix
An experimental phase space plot of the GSDM (depicting a Global Wind Oscillation (GWO)) utilizing normalized relative AAM time 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 not be able to write another posting until next Monday (6/4) due to covering various shifts.
Ed Berry
Monday, May 28, 2007
Friday, May 25, 2007
Update
Reanalysis-1 (R1) data woes still continue meaning ESRL/PSD AAM plots have not updated since May 11th (as well as the GWO phase space plot). Work on resolving this problem is occurring as I type.
I will not post a discussion today since I had to cover an operational shift. I do plan on issuing a discussion on Monday, 5/28.
However, I did have time to do some monitoring, and there is little change from my thoughts given in the May 22nd Blog discussion. The tropical convective dynamical signal is centered ~0/60W and there is now a zonal wave number 1 spatial pattern to the 200mb velocity potential field. Tropical convective forcing is increasing across the Indian Ocean just south of the equator. By the end of week 2 the dynamical signal should be well into the Eastern Hemisphere supporting strong convection from the warm Indian Ocean perhaps into the Indo-China region (including onset of the Indian Monsoon). Suppression may be prevalent across the west central Pacific. In fact, there may be some truth to what the Wheeler phase space plot is already depicting. A true MJO may be developing, or at least a spatially coherent region of tropical forcing and circulation response.
I think the global weather-climate state is solidly in GSDM Stage 4 given increasing easterly flow across the upper tropospheric tropical/subtropical atmospheres and relative AAM becoming negative (per operational plot). Tied to what may be a negative East Asian mountain torque, a baroclinic wave packet coming off that continent is interacting with a downstream Rossby wave train. A probable solution is a slower and deeper western USA trough early next week and some models are beginning to capture that. During week 2, the strong North Pacific jet shown by most models is likely to be transient as the tropical forcing intensifies across the Eastern Hemisphere. I favor an evolution toward GSDM Stage 1 increasing the probability of yet another unseasonably strong western USA trough by 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, 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 plan on writing a posting 5/28. Also, since I have to cover additional shifts next week, the posting after that is likely to be the following Monday, 6/4.
Ed Berry
I will not post a discussion today since I had to cover an operational shift. I do plan on issuing a discussion on Monday, 5/28.
However, I did have time to do some monitoring, and there is little change from my thoughts given in the May 22nd Blog discussion. The tropical convective dynamical signal is centered ~0/60W and there is now a zonal wave number 1 spatial pattern to the 200mb velocity potential field. Tropical convective forcing is increasing across the Indian Ocean just south of the equator. By the end of week 2 the dynamical signal should be well into the Eastern Hemisphere supporting strong convection from the warm Indian Ocean perhaps into the Indo-China region (including onset of the Indian Monsoon). Suppression may be prevalent across the west central Pacific. In fact, there may be some truth to what the Wheeler phase space plot is already depicting. A true MJO may be developing, or at least a spatially coherent region of tropical forcing and circulation response.
I think the global weather-climate state is solidly in GSDM Stage 4 given increasing easterly flow across the upper tropospheric tropical/subtropical atmospheres and relative AAM becoming negative (per operational plot). Tied to what may be a negative East Asian mountain torque, a baroclinic wave packet coming off that continent is interacting with a downstream Rossby wave train. A probable solution is a slower and deeper western USA trough early next week and some models are beginning to capture that. During week 2, the strong North Pacific jet shown by most models is likely to be transient as the tropical forcing intensifies across the Eastern Hemisphere. I favor an evolution toward GSDM Stage 1 increasing the probability of yet another unseasonably strong western USA trough by 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, 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 plan on writing a posting 5/28. Also, since I have to cover additional shifts next week, the posting after that is likely to be the following Monday, 6/4.
Ed Berry
Tuesday, May 22, 2007
Atmosphere Lacks Discipline
Reanalysis-1 (R1) data woes still continue meaning ESRL/PSD AAM plots have not updated since May 11th (as well as the GWO phase space plot).
There has been no significant change to the distribution of global tropical SSTs discussed in my May 18th posting (please review for details). La-Nina development during the next 3-6 months still remains a possibility.
The tropical convective forcing dynamical signal is well into the Western Hemisphere (WH). It is centered ~0/80W and is moving east at around 10m/s or roughly 7-8 deg long/day. Enhanced convection extends from the East Pacific ITCZ all the way into west central Africa. This signal has some projection onto a convectively coupled Kelvin wave. However, it is only a component of strong tropical-extratropical interactions that have occurred during the past few weeks. These interactions included the global mountain-frictional torque index cycle earlier this month within a general envelope of 20-30 day atmospheric variability.
Full disk satellite imagery not only shows the enhanced tropical convection across the WH, but also a loose consolidation of forcing centered ~5-10N/140E. The latter extends from eastern Indonesia into portions of the central Pacific. The Indian Ocean remains suppressed. However, strong enhancement is spreading across equatorial Africa as I type, and the Indian Ocean could become active much sooner than I think given the warm SSTs in that region.
It has been a real struggle trying to monitor these fast modes of tropical/extratropical variability and interactions. There has been no recent MJO signal, and as shown by the GWO phase space plot, our base state has been orbiting around GSDM Stage 1 since mid February. These orbits have come from competing tropical forcing from the East Indian and west Pacific Oceans, as well as mountain-frictional torque index cycles. Interactions with the mid-latitude synoptic eddies have maintained a loose AAM transport signal of fluxing momentum out of the subtropics into the mid-latitudes hence persisting a GSDM Stage 1 base state. Some of the past week 2-3 predictability “successes” for the USA have come from daily monitoring the GWO and AAM transport signals.
Most recently there has been the issue of whether or not an early onset to the Indian Monsoon would occur. In past discussions I have felt that was probable. However, per yearly ESRL/PSD time-latitude sections of OLRA, there was already enhanced convection across the Indian Ocean and portions of India at this time. Currently we have suppression there. My feeling is the current WH dynamical signal will be the catalyst needed to lead to the onset of the Indian Monsoon. Extrapolation would be in ~2 weeks, possibly much sooner given current satellite trends. However, my concerns about the warm west Pacific remain and a resumption of forcing from ~0/80-150E extending into the Southeast Asian monsoon region may occur by ~week 3 instead. Whatever does happen is unclear to me.
Animations of upper tropospheric vector wind anomalies shows twin tropical anticyclones centered ~80W as part of the WH dynamical signal. Even larger twin subtropical anticyclones are present ~150-160E (anomalies ~40m/s at 150mb) directly linked to the west Pacific convection locally forced by the warm SSTs. A strong Rossby wave energy dispersion across the North Pacific from these anticyclones is contributing to the present digging western USA trough. Not only have I struggled with the degree of amplification of this trough, but so have the models.
200mb zonal mean zonal wind anomalies (a good proxy for vertically integrated tropospheric AAM) remain above average throughout both the subtropical (~5m/s) and midlatitude (~10m/s) atmospheres of both hemispheres. Anomalous upper tropospheric subtropical easterly flow is returning to the Eastern Hemisphere and the recent extended North Pacific jet (for this time of year) is collapsing. Just how much easterly flow returns to the tropics and subtropics may have some dependency on the magnitude of the Indian Monsoon. If the west Pacific forcing continues to be an important component to the weather-climate system going into boreal summer, above average zonal mean tropical/subtropical westerly flow may be probable. My own feeling is the latter will have an influence. If so, speculation suggests a possible negative factor for Atlantic tropical cyclone development.
I think the weather-climate system is in a GSDM Stage 3-4 situation. I think Stage 4 is probable by week 2 and then Stage 1 afterwards. However, unlike much this past winter and spring, uncertainty is much higher than average. After an active week 1 for especially the Rockies and Plains, there should be a break by around the middle of next week. I like the solution offered by the ESRL/PSD ensemble suggesting more anomalous troughs particularly across the southwestern states starting ~day 10. Afterwards, a general western states trough and southeast USA ridge pattern is the most probable solution I can offer, especially by week 3. This would target the Northern Plains and Upper Mississippi Valley with rounds of MCS activity including severe storms and heavy rainfall, while intense heat occurs across the Deep South.
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 post an update this Friday.
Ed Berry
There has been no significant change to the distribution of global tropical SSTs discussed in my May 18th posting (please review for details). La-Nina development during the next 3-6 months still remains a possibility.
The tropical convective forcing dynamical signal is well into the Western Hemisphere (WH). It is centered ~0/80W and is moving east at around 10m/s or roughly 7-8 deg long/day. Enhanced convection extends from the East Pacific ITCZ all the way into west central Africa. This signal has some projection onto a convectively coupled Kelvin wave. However, it is only a component of strong tropical-extratropical interactions that have occurred during the past few weeks. These interactions included the global mountain-frictional torque index cycle earlier this month within a general envelope of 20-30 day atmospheric variability.
Full disk satellite imagery not only shows the enhanced tropical convection across the WH, but also a loose consolidation of forcing centered ~5-10N/140E. The latter extends from eastern Indonesia into portions of the central Pacific. The Indian Ocean remains suppressed. However, strong enhancement is spreading across equatorial Africa as I type, and the Indian Ocean could become active much sooner than I think given the warm SSTs in that region.
It has been a real struggle trying to monitor these fast modes of tropical/extratropical variability and interactions. There has been no recent MJO signal, and as shown by the GWO phase space plot, our base state has been orbiting around GSDM Stage 1 since mid February. These orbits have come from competing tropical forcing from the East Indian and west Pacific Oceans, as well as mountain-frictional torque index cycles. Interactions with the mid-latitude synoptic eddies have maintained a loose AAM transport signal of fluxing momentum out of the subtropics into the mid-latitudes hence persisting a GSDM Stage 1 base state. Some of the past week 2-3 predictability “successes” for the USA have come from daily monitoring the GWO and AAM transport signals.
Most recently there has been the issue of whether or not an early onset to the Indian Monsoon would occur. In past discussions I have felt that was probable. However, per yearly ESRL/PSD time-latitude sections of OLRA, there was already enhanced convection across the Indian Ocean and portions of India at this time. Currently we have suppression there. My feeling is the current WH dynamical signal will be the catalyst needed to lead to the onset of the Indian Monsoon. Extrapolation would be in ~2 weeks, possibly much sooner given current satellite trends. However, my concerns about the warm west Pacific remain and a resumption of forcing from ~0/80-150E extending into the Southeast Asian monsoon region may occur by ~week 3 instead. Whatever does happen is unclear to me.
Animations of upper tropospheric vector wind anomalies shows twin tropical anticyclones centered ~80W as part of the WH dynamical signal. Even larger twin subtropical anticyclones are present ~150-160E (anomalies ~40m/s at 150mb) directly linked to the west Pacific convection locally forced by the warm SSTs. A strong Rossby wave energy dispersion across the North Pacific from these anticyclones is contributing to the present digging western USA trough. Not only have I struggled with the degree of amplification of this trough, but so have the models.
200mb zonal mean zonal wind anomalies (a good proxy for vertically integrated tropospheric AAM) remain above average throughout both the subtropical (~5m/s) and midlatitude (~10m/s) atmospheres of both hemispheres. Anomalous upper tropospheric subtropical easterly flow is returning to the Eastern Hemisphere and the recent extended North Pacific jet (for this time of year) is collapsing. Just how much easterly flow returns to the tropics and subtropics may have some dependency on the magnitude of the Indian Monsoon. If the west Pacific forcing continues to be an important component to the weather-climate system going into boreal summer, above average zonal mean tropical/subtropical westerly flow may be probable. My own feeling is the latter will have an influence. If so, speculation suggests a possible negative factor for Atlantic tropical cyclone development.
I think the weather-climate system is in a GSDM Stage 3-4 situation. I think Stage 4 is probable by week 2 and then Stage 1 afterwards. However, unlike much this past winter and spring, uncertainty is much higher than average. After an active week 1 for especially the Rockies and Plains, there should be a break by around the middle of next week. I like the solution offered by the ESRL/PSD ensemble suggesting more anomalous troughs particularly across the southwestern states starting ~day 10. Afterwards, a general western states trough and southeast USA ridge pattern is the most probable solution I can offer, especially by week 3. This would target the Northern Plains and Upper Mississippi Valley with rounds of MCS activity including severe storms and heavy rainfall, while intense heat occurs across the Deep South.
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 post an update this Friday.
Ed Berry
Friday, May 18, 2007
Stage 3 Orbit -- Update
Reanalysis-1 (R1) data woes continue meaning ESRL/PSD AAM plots have not updated since May 11th.
The spatial distribution of global tropical SSTs remain similar to at least a week ago. Notable anomalies include the 1-2C warmth across the western Indian Ocean/Arabian Sea and west central Pacific, the latter as part of a horseshoe pattern into the extratropics. SST totals are ~30C for the former and ~29C across the latter. The equatorial cold tongue still has ~minus 1-3C anomalies down to about 200m with the coldest of ~-4C at 140W/100m (per TAO buoy data). However, the recent west Pacific westerly wind burst (WWB) may have initiated an oceanic downwelling Kelvin wave since at least plus 1C subsurface anomalies (~100m) are spreading east across the date line as I type. This situation could disrupt an evolution towards La-Nina. In any case, we have a warm west Pacific and cold east Pacific, only adding complexity.
The coupling of the recent global positive mountain-negative (decreasing) frictional torque index cycle and eastward shift of tropical forcing into the west central Pacific not only contributed to the strong WWB, but also added more westerly flow to the subtropical atmospheres than expected. Physical mechanisms for this coupling include upper tropospheric Rossby wave energy dispersion into the equatorial central Pacific from the East Asian topography and an upwelling convectively coupled Kelvin wave interacting with the Andes Mountains.
200mb zonal mean zonal wind anomalies of ~5m/s are present ~15S and 25N with even stronger anomalous westerly flow across the upper midlatitudes of both hemispheres. At least for the Northern Hemisphere, the roughly 5-10m/s anomalous zonal mean westerly flow centered ~45N goes back to poleward propagation off the equator tied to the December 2006 strong MJO event. It is possible these anomalous branches of westerly flow will combine during the next few weeks.
Full disk satellite imagery shows tropical convective forcing slowly increasing across the warm Indian Ocean and Arabian Sea while weakly hanging around the Bay of Bengal into western Indonesia. Only 2 tropical cyclones remain of the once intense west Pacific forcing. There is no MJO signal. In fact, since early April convectively coupled Kelvin waves have been the only eastward propagating modes within loosely a base state having both East Indian and west central-South Pacific Ocean tropical forcing. Currently there is one moving through the Western Hemisphere with another (the one that hit the Andes mountains) helping to excite the Indian Ocean convection. Could this be the “wave of the future” in what I have dubbed as a “new world atmosphere” in past discussions?
I think GSDM Stage 3 best describes the weather-climate situation. If updated, I suspect the Global Wind Oscillation (GWO) phase space plot would be orbiting toward Stage 3 similar to early April. I do think the tropical convective forcing across the Indian Ocean into western Indonesia/Southeast Asia will become dominate during the next few weeks. One contribution is a probable early onset of the Indian monsoon. The GWO should orbit toward GSDM Stage 4 then 1 later this month into early June.
My broken record predictions of probable occurrences of stormy patterns across the Rockies and Plains, attendant temperature extremes, etc., shifting north with the seasonal cycle, remains unchanged. I suspect most models are a bit too progressive with the western and central USA trough for early-mid next week. However, per issues discussed it will not persist for ~5 days across the western states as I thought a week ago. However, recall that week-2 ensemble means from all operational centers valid next week were predicting strong ridge conditions across the USA, which is not likely. There will be widespread severe storms and heavy rainfall across the central USA with this trough. The magnitude is still unclear.
By next weekend much of the central and east may have cooler than normal temperatures while the west coast starts to heat up. I think it is probable for more unseasonably strong troughs to impact the Pacific Northwest into the Plains later week 2 and week 3 with the return of GSDM Stage 4-1. In fact, monitoring will be needed to see if this situation becomes persistent for more than a few days. Weather ramifications should be obvious by now.
Appendix
An experimental phase space plot of the GSDM (depicting a global wind oscillation) 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 sometime during Monday-Wednesday next week.
Ed Berry
The spatial distribution of global tropical SSTs remain similar to at least a week ago. Notable anomalies include the 1-2C warmth across the western Indian Ocean/Arabian Sea and west central Pacific, the latter as part of a horseshoe pattern into the extratropics. SST totals are ~30C for the former and ~29C across the latter. The equatorial cold tongue still has ~minus 1-3C anomalies down to about 200m with the coldest of ~-4C at 140W/100m (per TAO buoy data). However, the recent west Pacific westerly wind burst (WWB) may have initiated an oceanic downwelling Kelvin wave since at least plus 1C subsurface anomalies (~100m) are spreading east across the date line as I type. This situation could disrupt an evolution towards La-Nina. In any case, we have a warm west Pacific and cold east Pacific, only adding complexity.
The coupling of the recent global positive mountain-negative (decreasing) frictional torque index cycle and eastward shift of tropical forcing into the west central Pacific not only contributed to the strong WWB, but also added more westerly flow to the subtropical atmospheres than expected. Physical mechanisms for this coupling include upper tropospheric Rossby wave energy dispersion into the equatorial central Pacific from the East Asian topography and an upwelling convectively coupled Kelvin wave interacting with the Andes Mountains.
200mb zonal mean zonal wind anomalies of ~5m/s are present ~15S and 25N with even stronger anomalous westerly flow across the upper midlatitudes of both hemispheres. At least for the Northern Hemisphere, the roughly 5-10m/s anomalous zonal mean westerly flow centered ~45N goes back to poleward propagation off the equator tied to the December 2006 strong MJO event. It is possible these anomalous branches of westerly flow will combine during the next few weeks.
Full disk satellite imagery shows tropical convective forcing slowly increasing across the warm Indian Ocean and Arabian Sea while weakly hanging around the Bay of Bengal into western Indonesia. Only 2 tropical cyclones remain of the once intense west Pacific forcing. There is no MJO signal. In fact, since early April convectively coupled Kelvin waves have been the only eastward propagating modes within loosely a base state having both East Indian and west central-South Pacific Ocean tropical forcing. Currently there is one moving through the Western Hemisphere with another (the one that hit the Andes mountains) helping to excite the Indian Ocean convection. Could this be the “wave of the future” in what I have dubbed as a “new world atmosphere” in past discussions?
I think GSDM Stage 3 best describes the weather-climate situation. If updated, I suspect the Global Wind Oscillation (GWO) phase space plot would be orbiting toward Stage 3 similar to early April. I do think the tropical convective forcing across the Indian Ocean into western Indonesia/Southeast Asia will become dominate during the next few weeks. One contribution is a probable early onset of the Indian monsoon. The GWO should orbit toward GSDM Stage 4 then 1 later this month into early June.
My broken record predictions of probable occurrences of stormy patterns across the Rockies and Plains, attendant temperature extremes, etc., shifting north with the seasonal cycle, remains unchanged. I suspect most models are a bit too progressive with the western and central USA trough for early-mid next week. However, per issues discussed it will not persist for ~5 days across the western states as I thought a week ago. However, recall that week-2 ensemble means from all operational centers valid next week were predicting strong ridge conditions across the USA, which is not likely. There will be widespread severe storms and heavy rainfall across the central USA with this trough. The magnitude is still unclear.
By next weekend much of the central and east may have cooler than normal temperatures while the west coast starts to heat up. I think it is probable for more unseasonably strong troughs to impact the Pacific Northwest into the Plains later week 2 and week 3 with the return of GSDM Stage 4-1. In fact, monitoring will be needed to see if this situation becomes persistent for more than a few days. Weather ramifications should be obvious by now.
Appendix
An experimental phase space plot of the GSDM (depicting a global wind oscillation) 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 sometime during Monday-Wednesday next week.
Ed Berry
Monday, May 14, 2007
Like Dealing with the Devil (It's complicated!)
The spatial pattern of Eastern Hemisphere tropical SSTs remains relatively unchanged with warmth across the Indian Ocean-cool Indonesia and warm west central Pacific. Largest anomalies and totals persist over the west central Indian Ocean into the Arabian Sea with magnitudes of plus 1-2C and greater than 30C respectively. Cooling continues along the equator east of the date line with values of at least minus 2C west of South America. Negative subsurface anomalies of at least minus 3C exist down to ~100m but positive anomalies greater than 1C down to ~300m are present west of the date line. A strong surface westerly wind burst (WWB) centered ~150-160E on the equator has been in progress for at least the past 5 days. There is some possibility for a downwelling oceanic Kelvin wave to develop as a response and transport some of this warm water to the east during the next few months. This is an example of why development of La-Nina is still a bit of an open question.
The Eastern Hemisphere tropical convective forcing loosely mirrors the SST distribution. One intense region remains relatively stationary ~0/100E while extending into the Bay of Bengal (including Tropical Cyclone 01B) and Southeast Asia while another area is over the west central Pacific. Overall, since the strong MJO event back in December 2006-January 2007, these 2 regions have been the dominate source of tropical forcing (equatorial Africa and tropical South America have been episodic). In fact, this behavior goes all the way back to the winter of 2001-2002. With the exception of the weak-moderate MJO during February, we have observed ~10-30 day excursions of tropical convection into the west central and South Pacific while forcing has loosely persisted ~90-120E.
Possibly related to the seasonal cycle, since late February I think there has been a close relationship between the eastward excursions of tropical convection into the west Pacific and a global mountain-frictional torque index cycle. The latter is a component of the GSDM having a broad periodicity of 10-60 days and is related to familiar teleconnection patterns such as the PNA (see WB (2007) for details). The point is while west Pacific tropical forcing has added anomalous westerly flow to the subtropics there has also been an additional source from the East Asian topography (for our purposes). These contributions have allowed extensions of the East Asian/North Pacific jet within an overall GSDM Stage 1 base state having tropical forcing across the East Indian Ocean. The jet extensions have contributed to the barrage of anomalously strong troughs into the western USA and associated extreme weather impacts. Numerical models have struggled predicting these situations especially for weeks 2-3.
The orbits around GSDM Stage 1 seen on the phase plot of the global wind oscillation (hopefully the most recent plot will be available soon) have been related to the above. Per reanalysis data plots through May 11th the global mountain torque is ~plus 30 Hadleys with the largest coming from the Andes Mountains (linked to a recent convectively coupled Kelvin wave) with a lesser component from East Asia. Global AAM tendency is ~plus 20 Hadleys meaning once again our overall GSDM Stage 1 base state is being perturbed with anomalous subtropical westerly flow. In fact, zonal mean westerly flow at 200mb is at least plus 5m/s throughout the subtropical atmospheres of both hemispheres.
I suspect the global wind oscillation signal is currently ~GSDM Stage 1.5. I do think there will be another orbit perhaps close to Stage 4 before going back to Stage 1. In any case, AAM transports have become strongly poleward (due to the tilts of the synoptic eddies) across the Northern Hemisphere since ~May 1st. A sink has developed ~35N with a source ~55N. The transport signal is largest contribution of the AAM budget, and in this case will maintain ~GSDM Stage 1. In fact, the only real difference between now and back ~December 1st, 2006, is the northward shift of this signal with the seasonal cycle.
During the next few weeks I think the tropical convection will increase in coverage across the Eastern Hemisphere including the Indian Ocean from ~40-120E (with a contribution from the currently very active convection across Africa). An early onset to the Indian monsoon is probable. Flare-ups will continue across the west Pacific. I remain firm on my predictions of more strong troughs to impact the western USA starting next week. The models are “all over the place” on catching up to the atmosphere and synoptic details are unclear. I think this situation may persist into June shifting northwest with the seasonal cycle. Probable weather ramifications include exceptional outbreaks of severe storms again across the Plains and early summertime heat across the Deep South and portions of the East.
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
Recent data issues have caused availability problems with this plot. My apologies.
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 post an update this Friday.
Ed Berry
The Eastern Hemisphere tropical convective forcing loosely mirrors the SST distribution. One intense region remains relatively stationary ~0/100E while extending into the Bay of Bengal (including Tropical Cyclone 01B) and Southeast Asia while another area is over the west central Pacific. Overall, since the strong MJO event back in December 2006-January 2007, these 2 regions have been the dominate source of tropical forcing (equatorial Africa and tropical South America have been episodic). In fact, this behavior goes all the way back to the winter of 2001-2002. With the exception of the weak-moderate MJO during February, we have observed ~10-30 day excursions of tropical convection into the west central and South Pacific while forcing has loosely persisted ~90-120E.
Possibly related to the seasonal cycle, since late February I think there has been a close relationship between the eastward excursions of tropical convection into the west Pacific and a global mountain-frictional torque index cycle. The latter is a component of the GSDM having a broad periodicity of 10-60 days and is related to familiar teleconnection patterns such as the PNA (see WB (2007) for details). The point is while west Pacific tropical forcing has added anomalous westerly flow to the subtropics there has also been an additional source from the East Asian topography (for our purposes). These contributions have allowed extensions of the East Asian/North Pacific jet within an overall GSDM Stage 1 base state having tropical forcing across the East Indian Ocean. The jet extensions have contributed to the barrage of anomalously strong troughs into the western USA and associated extreme weather impacts. Numerical models have struggled predicting these situations especially for weeks 2-3.
The orbits around GSDM Stage 1 seen on the phase plot of the global wind oscillation (hopefully the most recent plot will be available soon) have been related to the above. Per reanalysis data plots through May 11th the global mountain torque is ~plus 30 Hadleys with the largest coming from the Andes Mountains (linked to a recent convectively coupled Kelvin wave) with a lesser component from East Asia. Global AAM tendency is ~plus 20 Hadleys meaning once again our overall GSDM Stage 1 base state is being perturbed with anomalous subtropical westerly flow. In fact, zonal mean westerly flow at 200mb is at least plus 5m/s throughout the subtropical atmospheres of both hemispheres.
I suspect the global wind oscillation signal is currently ~GSDM Stage 1.5. I do think there will be another orbit perhaps close to Stage 4 before going back to Stage 1. In any case, AAM transports have become strongly poleward (due to the tilts of the synoptic eddies) across the Northern Hemisphere since ~May 1st. A sink has developed ~35N with a source ~55N. The transport signal is largest contribution of the AAM budget, and in this case will maintain ~GSDM Stage 1. In fact, the only real difference between now and back ~December 1st, 2006, is the northward shift of this signal with the seasonal cycle.
During the next few weeks I think the tropical convection will increase in coverage across the Eastern Hemisphere including the Indian Ocean from ~40-120E (with a contribution from the currently very active convection across Africa). An early onset to the Indian monsoon is probable. Flare-ups will continue across the west Pacific. I remain firm on my predictions of more strong troughs to impact the western USA starting next week. The models are “all over the place” on catching up to the atmosphere and synoptic details are unclear. I think this situation may persist into June shifting northwest with the seasonal cycle. Probable weather ramifications include exceptional outbreaks of severe storms again across the Plains and early summertime heat across the Deep South and portions of the East.
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
Recent data issues have caused availability problems with this plot. My apologies.
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 post an update this Friday.
Ed Berry
Friday, May 11, 2007
Update on the Return
Shift work obligations and data issues preclude a complete discussion. I will try to be more comprehensive Monday-Wednesday next week.
There is no change from my thinking as discussed on 5/8. Global tropical SSTs remain similar and any development of La-Nina is still a monitoring issue. There has been a rapid coherent eastward shift of tropical convective forcing across the Eastern Hemisphere which does project onto a convectively coupled Kelvin wave. The centroid of this forcing is ~0/140E having recent 3-day OLRA less than minus 70 W/m**2. In fact, a surface westerly wind burst is accompanying this convection and may adversely impact development toward a cold event. This recent eastward shift has some similarities to the behavior of the tropical convective forcing seen during late March-early April. Tropical forcing also remains active across the Indian Ocean and even the South Pacific.
I think we are headed for a transient GSDM Stage 2 response for the early-mid part of next week (also seen during the first part of April), and most models have captured this evolution. As both the NWS/CPC and SPC forecasts show, probable weather impacts include heavy rainfall and severe storms focusing on the central-northern Plains and Upper Mississippi Valley.
However, I also think there will remain the issue of two regions of Eastern Hemisphere tropical convective forcing, the Indian Ocean and the west central Pacific (along with other matters). This favors a GSDM Stage 4-1 response meaning more western USA troughs interacting with above average subtropical jets. Hence I disagree with many week-2 ensemble means from various operational centers and recent official forecasts derived from them suggesting ridge conditions across the USA for that period. Shifted northwest, I am holding the line of resumption of exceptionally active weather for the Rockies and Plains perhaps starting as early as next weekend and continuing into week 3 (~19 May – June 1). Ramifications include more severe storms and flooding rainfall for the central and northern Plains, summertime heat across the Southeast and cool conditions with heavy snowfall for the Rockies. Recent ensemble numerical models have been starting to trend toward this prediction.
Appendix
An experimental phase space plot of the GSDM (depicting a global wind oscillation) 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 sometime Monday-Wednesday next week.
Ed Berry
There is no change from my thinking as discussed on 5/8. Global tropical SSTs remain similar and any development of La-Nina is still a monitoring issue. There has been a rapid coherent eastward shift of tropical convective forcing across the Eastern Hemisphere which does project onto a convectively coupled Kelvin wave. The centroid of this forcing is ~0/140E having recent 3-day OLRA less than minus 70 W/m**2. In fact, a surface westerly wind burst is accompanying this convection and may adversely impact development toward a cold event. This recent eastward shift has some similarities to the behavior of the tropical convective forcing seen during late March-early April. Tropical forcing also remains active across the Indian Ocean and even the South Pacific.
I think we are headed for a transient GSDM Stage 2 response for the early-mid part of next week (also seen during the first part of April), and most models have captured this evolution. As both the NWS/CPC and SPC forecasts show, probable weather impacts include heavy rainfall and severe storms focusing on the central-northern Plains and Upper Mississippi Valley.
However, I also think there will remain the issue of two regions of Eastern Hemisphere tropical convective forcing, the Indian Ocean and the west central Pacific (along with other matters). This favors a GSDM Stage 4-1 response meaning more western USA troughs interacting with above average subtropical jets. Hence I disagree with many week-2 ensemble means from various operational centers and recent official forecasts derived from them suggesting ridge conditions across the USA for that period. Shifted northwest, I am holding the line of resumption of exceptionally active weather for the Rockies and Plains perhaps starting as early as next weekend and continuing into week 3 (~19 May – June 1). Ramifications include more severe storms and flooding rainfall for the central and northern Plains, summertime heat across the Southeast and cool conditions with heavy snowfall for the Rockies. Recent ensemble numerical models have been starting to trend toward this prediction.
Appendix
An experimental phase space plot of the GSDM (depicting a global wind oscillation) 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 sometime Monday-Wednesday next week.
Ed Berry
Tuesday, May 08, 2007
Exceptionally Active Weather for USA Probable Weeks 2-3
The spatial distribution of global tropical SSTs features warmth across the Indian Ocean-cool Indonesia-warm west central into South Pacific. Locations across the equatorial Pacific east of ~170W are again cooling while the Atlantic remains generally warm. Anomaly magnitudes are roughly 0.5-1C but near 2C just west of South America and portions of the equatorial Atlantic. SST totals remain ~30C across both the Indian and west Pacific basins and recently the east Pacific ~10N. Subsurface anomalies ~minus 3-4C remain along the equator around 130-140W at 100m within a cool reservoir down to ~200m from the west coast of South America to the date line. Development of La-Nina remains a monitoring issue but is appearing more likely.
Tropical convective forcing has become quite intense centered around 0/140E while extending in a west-northwest to east-southeast band from the Bay of Bengal into the South Pacific. This represents a fairly rapid eastward shift from a week ago. I attribute this change to strong complex interactions with the extratropics including a weak-moderate positive global and East Asian mountain torque during late April. This behavior is similar to what happened around April 1st, but much weaker. For instance, the global mountain torque around April 1st was ~plus 45 Hadleys while only 15 Haldeys recently. In any case, since about mid-February we have seen ~10-30 day variations involving global mountain torques, East Asia jet extensions and transient eastward shifts of tropical forcing across the Eastern Hemisphere. This has been in what we feel is a base state best described as GSDM Stage 1, and is seen from the quasi-phase space plot per link in the Appendix. Stated another way, the global wind has been oscillating (orbiting in phase space) around GSDM Stage 1, with the largest late March-late April. I see no reason for this end for at least weeks 2-3.
Zonal mean upper tropospheric westerly flow has increased slightly throughout the tropical and subtropical atmospheres, with anomalies ~2-5m/s. I expect this anomalous westerly flow will propagate to the midlatitudes and contribute to yet another intensification of the East Asian/North Pacific jet weeks 2-3. As already supported by full disk satellite and wind animation trends, tropical convective forcing should become more robust across the Indian Ocean weeks 2-3 while remaining active in other regions like the west Pacific. For the lower 48 states (my focus in these writings) this all suggests more strong troughs interacting with subtropical jets impacting the western USA ~forecast days 10-25.
The probable weather ramifications would be similar to what has already occurred several times since late February. A difference is for the general southwest flow storm track across the Plains to be farther northwest. Thus exceptional outbreaks of severe storms may again occur across the Plains perhaps starting by around next weekend.
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 post an update this Friday while having to cover operational shifts.
Ed Berry
Tropical convective forcing has become quite intense centered around 0/140E while extending in a west-northwest to east-southeast band from the Bay of Bengal into the South Pacific. This represents a fairly rapid eastward shift from a week ago. I attribute this change to strong complex interactions with the extratropics including a weak-moderate positive global and East Asian mountain torque during late April. This behavior is similar to what happened around April 1st, but much weaker. For instance, the global mountain torque around April 1st was ~plus 45 Hadleys while only 15 Haldeys recently. In any case, since about mid-February we have seen ~10-30 day variations involving global mountain torques, East Asia jet extensions and transient eastward shifts of tropical forcing across the Eastern Hemisphere. This has been in what we feel is a base state best described as GSDM Stage 1, and is seen from the quasi-phase space plot per link in the Appendix. Stated another way, the global wind has been oscillating (orbiting in phase space) around GSDM Stage 1, with the largest late March-late April. I see no reason for this end for at least weeks 2-3.
Zonal mean upper tropospheric westerly flow has increased slightly throughout the tropical and subtropical atmospheres, with anomalies ~2-5m/s. I expect this anomalous westerly flow will propagate to the midlatitudes and contribute to yet another intensification of the East Asian/North Pacific jet weeks 2-3. As already supported by full disk satellite and wind animation trends, tropical convective forcing should become more robust across the Indian Ocean weeks 2-3 while remaining active in other regions like the west Pacific. For the lower 48 states (my focus in these writings) this all suggests more strong troughs interacting with subtropical jets impacting the western USA ~forecast days 10-25.
The probable weather ramifications would be similar to what has already occurred several times since late February. A difference is for the general southwest flow storm track across the Plains to be farther northwest. Thus exceptional outbreaks of severe storms may again occur across the Plains perhaps starting by around next weekend.
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 post an update this Friday while having to cover operational shifts.
Ed Berry
Wednesday, May 02, 2007
Stuck
Weekly mean sea surface temperatures (SST) remain well above average across the Indian Ocean and weakly so over the west Pacific with magnitudes ~0.5-1C. SSTs greater than 30C are present from the Indian Ocean into the Bay of Bengal, decreasing to ~29C across the central and South Pacific. In response to increasing trades, negative SST anomalies have been strengthening around the equatorial date line while persisting west of South America. In the subsurface negative temperature anomalies of 3-4C remain at ~100 meters depth along the east Pacific cold tongue. There is still uncertainty about the intensity of any upcoming cold event, particularly since SSTs have also cooled to below normal around Indonesia. The latter is reminiscent of last fall, when we had a similar warm-cool-warm distribution of Eastern Hemisphere tropical SSTs.
The MJO signal remains incoherent. A few weeks ago I thought this mode of tropical convective variability would emerge across the Indian Ocean by now. Even though fairly intense convection is centered ~0/100E, MJO evolution appears less likely for the next 1-2 weeks. Full disk satellite imagery and other monitoring tools show that enhanced tropical rainfall has persisted across much of the eastern Indian Ocean for about the last week (OLRA ~minus 50-70 W/m**2). More recently a separate but weaker region of enhancement has developed over the west central Pacific. This mirrors the SST distribution discussed above. However, I think we are in a stationary or slowly evolving situation which is focusing the most intense forcing around 100E. Meanwhile, much faster tropical modes such as convectively coupled Kelvin waves and interactions with the extratropics are leading to flare-ups across other regions including the west Pacific.
Zonal mean easterly wind flow anomalies of ~5m/s continue over much of the equatorial and subtropical atmospheres helping to keep the global relative AAM low (~1.5 standard deviations below the reanalysis climatology). However, recently the global AAM tendency has become positive, reaching about 15 Hadleys. I attribute that to a positive East Asian mountain torque forced by a Rossby wave energy dispersion (RWD) and also an equatorial source forced by west Pacific tropical convection. This RWD has arced from north Asia into the central Pacific during the last 5-7 days while interacting not only with the tropical forcing at 100E, but also from the west Pacific. This RWD will lead to a strong western USA trough by the upcoming weekend, as shown by the numerical models. An enhanced probability of more western states troughs by this time was suggested in my April 20th posting.
The global circulation remains in GSDM Stage 1, and unless the character of the tropical forcing discussed above changes, we should roughly remain in that state for at least weeks 1-2. Stated another way, the global wind signal may orbit in phase space tilted toward GSDM Stage 1. If this situation persists through the rest of this month, I think it is more probable for a La-Nina to develop. For example, stationary tropical convective forcing across the Indian Ocean/Indonesia favors strong trades across the central and eastern equatorial Pacific, allowing upwelling of the colder subsurface waters currently present. For weeks 1-3, I think there will be another respite in the stormy regime across the USA by around the middle of next week, only to resume by week 3 but somewhat shifted northwest.
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. My next posting will not be until next week.
Ed Berry and Klaus Weickmann
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