Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
The spatial distribution of global tropical SST anomalies still resembles a mature warm event, with positive values across the western Indian Ocean and along the equator from ~170E-South America and cool readings around Indonesia particularly south of the equator. Magnitudes as low as ~minus 2C and lower were observed north of Australia on 26 October while ~plus 2C just east of the equatorial date line and west of South America (keep in mind the seasonal cycle of SSTs). The SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific remains, and is best defined across the Southern Hemisphere with values ~minus 1-2C.
SSTs of 30C and warmer cover much of the equatorial date line region while ~29-29.5C waters are present across the central Indian Ocean and around both sides of Central America. Weak positive SST anomalies cover most of the tropical Atlantic with actual temperatures ~28-29C.
There is some evidence that the warm-cool-warm SSTs discussed above have shifted ~10 degrees east during the last week or so. The recent surface westerly wind event (WWE) with anomalies in excess of 10m/s (westerly anomalies still remain along and east of the date line) has apparently excited another oceanic Kelvin wave which is propagating toward the east Pacific. Anomalies as high as plus 4C down ~150m at 170W were observed per recent TAO array buoy data. This oceanic Kelvin wave along with an advective component from the anomalous westerly flow may be helping to shift the SST distribution to the east.
The WWE tied to the recent MJO helped to strengthen our warm ENSO. At this point I see 2 ocean basins with warm SSTs, the central equatorial Indian Ocean and the date line. There are folks that will call the former a positive phase of the Indian Ocean Dipole (IOD) and others which feel this SST distribution is consistent with a warm event (I feel the latter). Whatever the case, I try to understand the weather-climate situation from a dynamical forcing-response-feedback perspective, and I think I can see physically how this whole SST situation evolved starting around March 2006 (too long to discuss here). The point is both of these warm ocean basins (and other oceanic regions) are currently impacting the circulation and will continue to do so.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Full disk satellite imagery and other monitoring tools (coherent modes Hovmollers, velocity potential/OLRA animations, etc.) suggest the dynamical signal with the MJO has returned to the Eastern Hemisphere and was located ~60E. The phase speed of this signal has slowed considerably and its magnitude has significantly weakened. Tropical convective forcing has been increasing across much of the central Indian Ocean and in a band from the South Pacific toward the Philippines (with Tropical Cyclone Cimaron). Enhanced convection has recently been propagating east-southeast along the South Pacific Convergence Zone (SPCZ) (weakly projecting onto a convectively coupled Kelvin wave) while also shifting back toward the Philippines. In fact, the recent pattern of Indian Ocean enhancement-Indonesian suppression- west Pacific enhancement is less robust than a week ago.
My own thought is we may see some consolidation of the tropical convective forcing ~ 10-15N/90-120E during the next 1-2 weeks (north of the cool SSTs). However, flare-ups across both the Indian Ocean and especially the date line/South Pacific region may occur “any time”. Illustrations of this kind of behavior are the weather-climate events during past 4 weeks or so which we hope to detail in another weather-climate discussion for the ESRL/PSD MJO web page.
Briefly, as the dynamical signal with the MJO interacted with the warm date line SSTs during late September and early October, a Rossby wave energy dispersion (RWD) occurred across the PNA sector leading to a deep trough across the Great Lakes and North Atlantic blocking by around 12-14 October (recall the Buffalo, NY snow event). There were subsequent RWDs from the North Atlantic blocking which interacted with other wave packets moving across Asia. These helped to re-invigorate the date line tropical convection through their enhanced divergent upper tropospheric outflows all while the MJO signal was moving through the Western Hemisphere, by about 15 October. Among other responses, there was a central/east tropical Pacific basin wide surface westerly wind event with anomalies well in excess of 10m/s which helped to strengthen the warm ENSO. To me, this is a situation of tropics forcing extratropics (including from the MJO and ENSO in this case) and then extratropics forcing back (with properly phased wave trains) to maintain an “equilibrium weather-climate situation” through the interactions of multiple time scales.
A “repeat” of the above recently occurred about 5 days ago with another flare-up of date line tropical forcing (~every 20 days for a time-scale?) which led to intense baroclinic storm development from the central/southern Rockies to the eastern part of the USA. A difference is the MJO signal had re-emerged into the Eastern Hemisphere (and weakened). The models did struggle with the synoptic details of this storm (which was responsible for a blizzard across eastern Colorado and possibly more than 2 dozen tornadoes across Southwest Kansas).
Is the recent intensification of the Indian Ocean convection going to “disrupt this feedback loop?” Has this latest MJO caused our warm event to (finally) peak? Are we going to see 2 (or more) regions of tropical forcing with the Indian Ocean convection (eventually spreading east inconsideration of the SSTs?) becoming dominate at some point? Will there be another coherent MJO signal? These are just some of the issues that are unclear.
Evidence of circulation impacts from the variability of the date line tropical forcing can also be seen from plots of the earth-atmosphere AAM budget available from ESRL/PSD (using the re-analysis data and its 1968-97 climatology). Loosely, around 1 October global relative AAM tendency was positive with positive global mountain and frictional torques. That all reversed by about the middle of this month only to recently become positive (magnitudes ~10-20 Hadleys). Global relative AAM has lagged by roughly 10 days.
There has also been poleward propagation of zonal mean westerly wind anomalies into both the midlatitude and subtropical atmospheres of the Northern Hemispheres with anomalies ~5-10m/s at 200mb linked to the tropical forcing. Animations of both 150mb and 250mb daily mean vector wind anomalies show the presence of anomalous twin subtropical anticyclones across the Western Hemisphere coming back into the Indian Ocean while a separate pair persists near the date line. The former have been associated with the MJO signal while the latter is at least partly from ENSO. There is a well defined subtropical jet (STJ) extending from the date line pair (as also seen from full-disk satellite water vapor imagery) with additional enhancement from the anticyclones downstream. Anomalies with this STJ have been in excess of 25 m/s at 150mb at times.
Overall we have a weather-climate situation I would offer is best described by GSDM Stage 4 but with additional complexity due to the date line tropical forcing. I have been terming the latter as a signal due to the current warm phase of ENSO throughout this discussion. However, in reality I think there may be even slower time scales involved with this along with “other processes”, in addition to ENSO.
To summarize, I think we have 1) a warm event (plus a global warming signal whose cause is unclear?), 2) possibly an increasing role of the Indian Ocean SSTs, 3) the MJO signal which may become very weak, 4) 20-30 day tropical convective variability, 5) some evidence of mountain-frictional torque index cycle variations (not discussed – may be linked to (4)), fast RWDs, baroclinic wave packets and all sorts of other white noise, and 6) seasonal cycle issues.
The latter (6) may involve just how sensitive the response across the Asia-PNA sector will become to tropical convective forcing (or lack of) as the climatological strengthening of the East Asian Jet (EAJ) occurs. For instance, if we do get into a situation of 2 regions of tropical forcing (with suppression, say around the Philippines), the response may become GSDM Stage 1 with STJs through late December. Afterwards, as both the convection and EAJ shift south, enhanced convection across the central Pacific may become dominate and lead to GSDM Stage 3 by sometime in January. We will see.
In what follows, I am leaning toward my notion of consolidation of the tropical forcing during weeks 1-2 per above. Afterwards, I think it is unclear to offer anything statistically useful without additional tools. Confidence remains as low as it can ever get making week 1-3 predictions in this weather-climate situation. This is why detailed disciplined daily monitoring is critical.
Week 1 (28 October – 3 November 2006): GSDM Stage 4 with additional forcing from the central Pacific appears probable. The models are generally consistent with mid/upper tropospheric trough development across the east Pacific (~140W) with a downstream ridge along the west coast and subsequent eastern states trough by early next week. I see no reason to differ given the central Pacific twin subtropical anticyclones. At some point I would expect the westerly flow to increase across East Asia as trough development occurs there. This should allow the east Pacific trough to approach the west coast going into week 2.
This situation is generally dry for most of the country with warm conditions across the western states and cool for the east (not all the unusual for this time of year). The Pacific Northwest should have increasing opportunities for rainfall. There may also be opportunities for rainfall across the Deep South at times tied to the STJ.
Week 2 (4-10 November 2006): GSDM Stage 1 with an above average STJ may be most probable. At this point particularly the Pacific Northwest may receive substantial precipitation, which could spread slowly south. Depending on how far inland the trough gets, cooler and wetter weather may become more likely for the portions of the Rockies. The rest of the country may see above normal temperatures.
Week 3 (11-17November 2006): Unclear; however, an eastward progression of the situation discussed for week 2 would be reasonable if there is any truth to it.
Climatologically this is still the dry time of the year for Southwest Kansas. The recent storm/rain event was a pleasant “surprise (other than the tornadoes depending on your perspective)”. Week 1 looks generally dry with near-below normal temperatures (on average). Dryness may continue well into week 2 while temperatures may warm to well above average. Jet streaks along the STJ could give us at least a minor precipitation surprise by then. An active regime may return for this part of the world week 3 (for this time of year).
I will be on travel to ESRL/PSD next week so I do not know when there will be another posting on this Blog (perhaps a short one ~ middle of next week). We do have plans to write another weather-climate discussion for the ESRL/PSD MJO web page to hopefully post by the end of November. Please see the Appendix.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
Friday, October 27, 2006
Sunday, October 22, 2006
Update on What Goes Around Gets Messy -- written 10/21/06
This posting will be very brief. I hope to do a more complete effort late this upcoming week after I have completed covering overnight shifts (~10/26-27/06). Please see other postings for all web links.
The spatial distribution of global tropical SSTs are consistent with a mature warm ENSO. Strong westerly wind anomalies (~10m/s) and actual westerlies remain across the equatorial date line region. In fact, TAO buoy data suggest a downwelling oceanic Kelvin wave has developed east of the date line and is moving east along the equatorial cold tongue. We will see how robust this warm event gets (there is always uncertainty in many different aspects). At this point odds would favor above normal surface temperatures for especially the north central states during DJF and JFM (see CPC outlooks). However, please remember these are seasonal mean indications and this does not at all rule out possibilities of extreme cold episodes along with other forms of high impact severe winter weather for the northern or any portions of the USA.
The dynamical signal with the MJO is moving into the Eastern Hemisphere while SST boundary forced tropical convection slowly increases across the central Indian Ocean and west Pacific (per full disk satellite imagery). Three-day mean charts of OLRA indicate enhanced rainfall is present just south of the equator ~60E, 160E-160W including the SPCZ and from much of northern South America into the Atlantic ITCZ. Anomalous upper tropospheric twin tropical/subtropical anticyclones (with lower level westerly anomalies – baroclinic response) accompany these 3 regions, particularly for the MJO dynamical signal.
Re-analysis data plots from ESRL/PSD shows global relative AAM tendency has become strongly negative (as of 10/18) with a magnitude of ~ minus 25 Hadleys. Both the global mountain and frictional torques are contributing. Zonal mean easterly wind anomalies are replacing westerly anomalies throughout the tropical and subtropical atmospheres while existing westerly anomalies propagate into the midlatitudes of both hemispheres. In this type of situation a synoptician is going to see a tendency for troughs and ridges to become northeast-southwest oriented across the Northern Hemisphere along with features such as anticyclonically wave breaking (AWB) “upper level lows”. These tilts will contribute to AAM being fluxed poleward from the tropics into eventually the midlatitudes.
GSDM Stage 4 best describes the current weather-climate situation. The future evolution of the tropical convective forcing is unclear, including if there will be another MJO. My own thought is we may see some consolidation of the tropical forcing across the Eastern Hemisphere during the next 1-3 weeks, perhaps around 10N/90-120E to the north of the cool Indonesian SSTs. While this may be occurring, the date line region and even the SPCZ may continue experience tropical convective flare-ups (there are still the ~20-30 day tropical convective variability and convectively coupled Kelvin waves going on). Locations such as the South Indian Ocean-Bay of Bengal and west central and South Pacific may be vulnerable to tropical cyclone development (and we need to watch the Caribbean and even the North Atlantic for especially hybrids). During weeks 2-3 GSDM Stage 1 with subtropical jets may be most probable particularly for the Asia-PNA sector. This would suggest western North America to become increasingly at risk to strong synoptic-scale troughs while an active storm track develops across the Plains possibly going well into November. Most readers should be familiar what all this means in terms of weather particularly if a cold air source evolves during November.
Ed Berry
The spatial distribution of global tropical SSTs are consistent with a mature warm ENSO. Strong westerly wind anomalies (~10m/s) and actual westerlies remain across the equatorial date line region. In fact, TAO buoy data suggest a downwelling oceanic Kelvin wave has developed east of the date line and is moving east along the equatorial cold tongue. We will see how robust this warm event gets (there is always uncertainty in many different aspects). At this point odds would favor above normal surface temperatures for especially the north central states during DJF and JFM (see CPC outlooks). However, please remember these are seasonal mean indications and this does not at all rule out possibilities of extreme cold episodes along with other forms of high impact severe winter weather for the northern or any portions of the USA.
The dynamical signal with the MJO is moving into the Eastern Hemisphere while SST boundary forced tropical convection slowly increases across the central Indian Ocean and west Pacific (per full disk satellite imagery). Three-day mean charts of OLRA indicate enhanced rainfall is present just south of the equator ~60E, 160E-160W including the SPCZ and from much of northern South America into the Atlantic ITCZ. Anomalous upper tropospheric twin tropical/subtropical anticyclones (with lower level westerly anomalies – baroclinic response) accompany these 3 regions, particularly for the MJO dynamical signal.
Re-analysis data plots from ESRL/PSD shows global relative AAM tendency has become strongly negative (as of 10/18) with a magnitude of ~ minus 25 Hadleys. Both the global mountain and frictional torques are contributing. Zonal mean easterly wind anomalies are replacing westerly anomalies throughout the tropical and subtropical atmospheres while existing westerly anomalies propagate into the midlatitudes of both hemispheres. In this type of situation a synoptician is going to see a tendency for troughs and ridges to become northeast-southwest oriented across the Northern Hemisphere along with features such as anticyclonically wave breaking (AWB) “upper level lows”. These tilts will contribute to AAM being fluxed poleward from the tropics into eventually the midlatitudes.
GSDM Stage 4 best describes the current weather-climate situation. The future evolution of the tropical convective forcing is unclear, including if there will be another MJO. My own thought is we may see some consolidation of the tropical forcing across the Eastern Hemisphere during the next 1-3 weeks, perhaps around 10N/90-120E to the north of the cool Indonesian SSTs. While this may be occurring, the date line region and even the SPCZ may continue experience tropical convective flare-ups (there are still the ~20-30 day tropical convective variability and convectively coupled Kelvin waves going on). Locations such as the South Indian Ocean-Bay of Bengal and west central and South Pacific may be vulnerable to tropical cyclone development (and we need to watch the Caribbean and even the North Atlantic for especially hybrids). During weeks 2-3 GSDM Stage 1 with subtropical jets may be most probable particularly for the Asia-PNA sector. This would suggest western North America to become increasingly at risk to strong synoptic-scale troughs while an active storm track develops across the Plains possibly going well into November. Most readers should be familiar what all this means in terms of weather particularly if a cold air source evolves during November.
Ed Berry
Tuesday, October 17, 2006
ENSO and Complexity Making a Comeback
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
The spatial distribution of global tropical SST anomalies continues to resemble a mature warm event, with positive values across the western Indian Ocean and along the equator from ~140E-South America with cool readings around Indonesia particularly south of the equator. In fact, the SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific is quite well defined. Anomalies are generally from 1-2C with magnitudes around 3C along the East Pacific cold tongue, extending to depths of ~200m around the date line. SSTs of 29C and warmer cover much of the equatorial date line region, the central Indian Ocean and both sides of Central America. Weak positive SST anomalies cover most of the tropical Atlantic with actual temperatures ~28-29C.
SST and SST anomaly tendencies during the past week or so have reinforced the spatial distribution discussed above. Magnitudes have been ~plus .5-1C, with the warming along the equatorial cold tongue the result of a basin-wide surface westerly wind event whose anomalies have exceeded 10m/s (more said below). At this point our warm event has become better defined during the past 1-2 weeks. I have expressed concern in past writings this event may have already peaked. Whether or not this is the case, is unclear to me, as is the future for this warm ENSO (there are seasonal cycle issues). Whatever the case, the SSTs linked to this ENSO evolution have already impacted synoptic variability across North America since at least June 2006, and are doing so as I type.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Per coherent modes and velocity potential Hovmollers (and other monitoring tools), the dynamical signal with the MJO is in the Western Hemisphere ~0/60W having a phase speed of ~10-15m/s. The MJO signal typically propagates eastward much faster across the Western Hemisphere due to less air/sea coupling with cooler SSTs (loosely acting like a Kelvin wave enhancing upper tropospheric divergence). Full disk satellite imagery shows quite a bit of convective enhancement centered on northern South America with OLRAs ~minus 50-90W/m**2. The recent heavy rainfall across the USA Deep South had a contribution from this MJO signal as the result of a local enhancement of the subtropical jet (STJ) via complex interactions with the extratropics.
Well defined twin upper tropospheric subtropical anticyclones are present around 90-120W (including the Gulf of Mexico) with wind speed anomalies ~20-30m/s per animations of 150mb daily mean vector wind anomalies. Additionally, Rossby wave energy is dispersing into the extratropics of both hemispheres leading to, for example, a negative projection onto the North Atlantic Oscillation (NAO).
Full disk satellite imagery also shows tropical convection increasing across the west central Pacific centered ~0/150-160E as well as the equatorial Indian Ocean ~60E, while strong suppression remains across Indonesia with positive values of OLRA in excess of 70 W/m**2 ~0/100E. This spatial pattern of enhancement-suppression-enhancement across the Eastern Hemisphere would be expected from the SSTs, with the former termed by some folks as a positive phase of the Indian Ocean Dipole (IOD) and the latter due to ENSO. It is typical to see a warm western Indian Ocean during a mature warm ENSO, and I like to understand climate variability as dynamical processes involving forcing-response-feedbacks (and so on) globally interacting with regional behaviors, etc.
After reaching a positive maximum of ~20 Hadleys (reanalysis data climatology from 1968-1997) just before October 1st, the global tendency of relative AAM has dropped to ~minus 10 Hadleys as of October 14th. As expected with a MJO, this positive AAM tendency started along/just south of the equator ~ September 18th, and has coherently propagated poleward into both hemispheres, particularly across the Northern Hemisphere (currently around 40N). A time-latitude section of 200mb zonal mean zonal wind anomalies loosely shows this poleward propagation, with westerly anomalies currently ~5-10m/s centered at about 30N (one level as opposed to a vertical integral).
After roughly October 1st there was relative AAM flux divergence from about 45N (sink) leading to flux convergence near 30N (source; we are looking at divergence of the AAM transports), again consistent with the dynamical signal of the MJO moving into the Western Hemisphere. This redistribution of AAM helped to weaken the midlatitude flow while increasing the westerly flow across the subtropics (including the STJ). A forecaster looking at a polar stereographic projection map of 250mb total vector winds (for example) would have observed a split flow pattern along the North American West Coast at times during this period as a response.
The point is using monitoring tools such as AAM tendencies and transports allows some understanding of the recent increases of the zonal mean westerly flow throughout the subtropical and midlatitude atmospheres. Through tropical-extratropical interactions involving the midlatitude synoptic eddies (reader needs to think about this) not only have we seen the central and east Pacific basin wide surface westerly wind event (discussed above), there has also been a strengthening of the North Pacific jet over the last 1-2 weeks, the latter having seven-day mean anomalies of ~20m/s. For the USA the result has been recent PNA responses (from Rossby wave energy dispersions -- index sign depends on location of features; one weakness of it) and an enhanced STJ all contributing to recent cool outbreaks for the central states and heavy rain for the Deep South. Please see our recent weather-climate discussion dated August 18th as an example to interpret some of these behaviors (link below).
The enhanced surface westerlies across the north tropical Pacific Ocean basin for at least the past 1-2 weeks has brought the global frictional torque down to around minus 20 Hadleys, and the global mountain torque is also starting to decline (see ESRL/PSD plots for details). GSDM Stage 2 would best describe the weather-climate situation from roughly October 1-14 (at times tilting toward Stage 3), with a loose GSDM Stage 4 the last few days. Animations of 150mb and 250mb daily mean vector wind anomalies once again present a strong signal of anomalous twin tropical/subtropical anticyclones around 160E tied to the tropical convective flare-up in that region (with well defined twin cyclones ~90E tied to the suppression; this is a baroclinic process). A Rossby wave energy dispersion is in progress and will lead to another PNA. This has some similarities to what occurred around October 8th, except the MJO dynamical signal is now in the Western Hemisphere, as opposed to the west Pacific. In fact, upper tropospheric easterly wind anomalies of ~20-30m/s at 150mb have been appearing across the equatorial east Pacific during the last few days, having more consistency with Stage 4 as opposed to Stage 2. This all suggests a retrogression of existing circulation anomalies during the next few days or so across the northern extratropics particularly from Asia-North America (“bottom line”).
To summarize, I think we have 1) a warm event (with the understanding of Indian Ocean-Pacific SSTs) whose future evolution still remains unclear (but likely to persist into 2007), 2) at least a moderate MJO signal moving across the Western Hemisphere, 3) intensifying tropical convective forcing from the Indian Ocean, 4) a mountain-frictional torque index cycle, 5) baroclinic wave packets/fast Rossby wave energy dispersions interacting with the west central Pacific tropical forcing, and 6) seasonal cycle issues.
There are other matters I am unclear about such as any sub-monthly component involving the mountain torque and other faster modes of tropical convective variability. The future of the MJO even after week 1 is also unclear. I do think the dominant forcing from the tropics is coming from the west central Pacific, and it may not just be a warm ENSO signal. The SSTs are also cool across the tropical northwest Pacific (opposite of last year) and the evolution of this whole “SST situation” is anything but trivial to understand. It would be interesting to see how well coupled GCMs would simulate these SST events since the start of this year.
In any case, we must also remember the suppression from Indonesia also has circulation impacts, and I can easily see Indian Ocean tropical forcing disrupting events across the west Pacific. The statistical models (Wheeler phase space technique, for example) bring the dynamical signal well into the Eastern Hemisphere (~60-80E) by about day 10, and I think that is reasonable. My own thoughts is there may be 2 well defined regions of enhanced tropical convection during week 2, the Indian Ocean and west central Pacific, while the Western Hemisphere becomes suppressed. During week 3 there may be some consolidation of the 2 regions north of the cool SSTs across Indonesia. Confidence in any scientifically defensible statistically useful prediction particularly beyond week 1 is as low as it gets. This is the real world!
Week 1 (18-24 October 2006): I think a loose rendition of GSDM Stage 2 is most probable, but roughly 5-10 degrees farther west (for the USA) than about a week ago. This would mean a trough ~100W with a large amplitude ridge just off the USA west coast possibly into Alaska. Nearly all models are predicting some version of this response since the Rossby wave energy dispersion discussed above should be in the initial conditions. This means a much cooler than normal regime for a good part of the country especially the central and north central states. The warm locations may be the West Coast and Florida. One surge of cool air is occurring as I type, with another due by this weekend per operational NCEP GFS (and other models).
I have a bit of concern for this second surge of cool air. The jet streak that will contribute to it (interacting with “everything else”) may involve the remnants of Typhoon Soulik. The baroclinic development which ensures on the Plains by this weekend may begin with amplification of the trough a bit farther west into the central Rockies. That may suggest more robust cyclogenesis across the Mid/Upper Mississippi Valley. Even though moisture will be relatively limited, a “decent” snow event is not out of the realm of possibilities for locations such as Iowa into the Great Lakes (latter including lake effect). Other effects on the weather should be apparent.
The Tropical North Atlantic may remain suppressed for tropical cyclone activity. There is always the concern for hybrids this time of year and I could also see a period of upper tropospheric easterlies across the tropical Atlantic, latter perhaps allowing a window of opportunity for development. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information. Active regions for tropical cyclones may include the west central Pacific and even the Bay of Bengal, particularly weeks 2-3.
Week 2 (25-31 October 2006): If the west Pacific is “calling the shots”, then similar to week 1 except for the usual synoptic variations of amplitude.
Week 3 (1-7 November 2006): I can envision possibilities (like anyone else), but let us just say “unclear” for now.
Climatologically this is the dry time of the year for Southwest Kansas. Other than one or two minor episodes of precipitation, week 1 looks generally cool and dry. There is a small possibility of a “surprise” this weekend. I would expect week 2 to remain generally dry with roughly seasonable temperatures (on average!). Even though not discussed for week 3, opportunities for precipitation may increase for this part of the world should “STJ activity” become more robust.
Since I continue to have to cover lots of shifts (including mids), I may not be able to update this Blog until late next week. We do have plans to write another weather-climate discussion for the ESRL/PSD MJO web page to hopefully post by the end of November. Please see the Appendix.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), along with all the other issuances, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
The spatial distribution of global tropical SST anomalies continues to resemble a mature warm event, with positive values across the western Indian Ocean and along the equator from ~140E-South America with cool readings around Indonesia particularly south of the equator. In fact, the SST horse shoe pattern of cool surrounding warm anomalies (would be reversed for a cold event) across the tropical Indo-Pacific is quite well defined. Anomalies are generally from 1-2C with magnitudes around 3C along the East Pacific cold tongue, extending to depths of ~200m around the date line. SSTs of 29C and warmer cover much of the equatorial date line region, the central Indian Ocean and both sides of Central America. Weak positive SST anomalies cover most of the tropical Atlantic with actual temperatures ~28-29C.
SST and SST anomaly tendencies during the past week or so have reinforced the spatial distribution discussed above. Magnitudes have been ~plus .5-1C, with the warming along the equatorial cold tongue the result of a basin-wide surface westerly wind event whose anomalies have exceeded 10m/s (more said below). At this point our warm event has become better defined during the past 1-2 weeks. I have expressed concern in past writings this event may have already peaked. Whether or not this is the case, is unclear to me, as is the future for this warm ENSO (there are seasonal cycle issues). Whatever the case, the SSTs linked to this ENSO evolution have already impacted synoptic variability across North America since at least June 2006, and are doing so as I type.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Per coherent modes and velocity potential Hovmollers (and other monitoring tools), the dynamical signal with the MJO is in the Western Hemisphere ~0/60W having a phase speed of ~10-15m/s. The MJO signal typically propagates eastward much faster across the Western Hemisphere due to less air/sea coupling with cooler SSTs (loosely acting like a Kelvin wave enhancing upper tropospheric divergence). Full disk satellite imagery shows quite a bit of convective enhancement centered on northern South America with OLRAs ~minus 50-90W/m**2. The recent heavy rainfall across the USA Deep South had a contribution from this MJO signal as the result of a local enhancement of the subtropical jet (STJ) via complex interactions with the extratropics.
Well defined twin upper tropospheric subtropical anticyclones are present around 90-120W (including the Gulf of Mexico) with wind speed anomalies ~20-30m/s per animations of 150mb daily mean vector wind anomalies. Additionally, Rossby wave energy is dispersing into the extratropics of both hemispheres leading to, for example, a negative projection onto the North Atlantic Oscillation (NAO).
Full disk satellite imagery also shows tropical convection increasing across the west central Pacific centered ~0/150-160E as well as the equatorial Indian Ocean ~60E, while strong suppression remains across Indonesia with positive values of OLRA in excess of 70 W/m**2 ~0/100E. This spatial pattern of enhancement-suppression-enhancement across the Eastern Hemisphere would be expected from the SSTs, with the former termed by some folks as a positive phase of the Indian Ocean Dipole (IOD) and the latter due to ENSO. It is typical to see a warm western Indian Ocean during a mature warm ENSO, and I like to understand climate variability as dynamical processes involving forcing-response-feedbacks (and so on) globally interacting with regional behaviors, etc.
After reaching a positive maximum of ~20 Hadleys (reanalysis data climatology from 1968-1997) just before October 1st, the global tendency of relative AAM has dropped to ~minus 10 Hadleys as of October 14th. As expected with a MJO, this positive AAM tendency started along/just south of the equator ~ September 18th, and has coherently propagated poleward into both hemispheres, particularly across the Northern Hemisphere (currently around 40N). A time-latitude section of 200mb zonal mean zonal wind anomalies loosely shows this poleward propagation, with westerly anomalies currently ~5-10m/s centered at about 30N (one level as opposed to a vertical integral).
After roughly October 1st there was relative AAM flux divergence from about 45N (sink) leading to flux convergence near 30N (source; we are looking at divergence of the AAM transports), again consistent with the dynamical signal of the MJO moving into the Western Hemisphere. This redistribution of AAM helped to weaken the midlatitude flow while increasing the westerly flow across the subtropics (including the STJ). A forecaster looking at a polar stereographic projection map of 250mb total vector winds (for example) would have observed a split flow pattern along the North American West Coast at times during this period as a response.
The point is using monitoring tools such as AAM tendencies and transports allows some understanding of the recent increases of the zonal mean westerly flow throughout the subtropical and midlatitude atmospheres. Through tropical-extratropical interactions involving the midlatitude synoptic eddies (reader needs to think about this) not only have we seen the central and east Pacific basin wide surface westerly wind event (discussed above), there has also been a strengthening of the North Pacific jet over the last 1-2 weeks, the latter having seven-day mean anomalies of ~20m/s. For the USA the result has been recent PNA responses (from Rossby wave energy dispersions -- index sign depends on location of features; one weakness of it) and an enhanced STJ all contributing to recent cool outbreaks for the central states and heavy rain for the Deep South. Please see our recent weather-climate discussion dated August 18th as an example to interpret some of these behaviors (link below).
The enhanced surface westerlies across the north tropical Pacific Ocean basin for at least the past 1-2 weeks has brought the global frictional torque down to around minus 20 Hadleys, and the global mountain torque is also starting to decline (see ESRL/PSD plots for details). GSDM Stage 2 would best describe the weather-climate situation from roughly October 1-14 (at times tilting toward Stage 3), with a loose GSDM Stage 4 the last few days. Animations of 150mb and 250mb daily mean vector wind anomalies once again present a strong signal of anomalous twin tropical/subtropical anticyclones around 160E tied to the tropical convective flare-up in that region (with well defined twin cyclones ~90E tied to the suppression; this is a baroclinic process). A Rossby wave energy dispersion is in progress and will lead to another PNA. This has some similarities to what occurred around October 8th, except the MJO dynamical signal is now in the Western Hemisphere, as opposed to the west Pacific. In fact, upper tropospheric easterly wind anomalies of ~20-30m/s at 150mb have been appearing across the equatorial east Pacific during the last few days, having more consistency with Stage 4 as opposed to Stage 2. This all suggests a retrogression of existing circulation anomalies during the next few days or so across the northern extratropics particularly from Asia-North America (“bottom line”).
To summarize, I think we have 1) a warm event (with the understanding of Indian Ocean-Pacific SSTs) whose future evolution still remains unclear (but likely to persist into 2007), 2) at least a moderate MJO signal moving across the Western Hemisphere, 3) intensifying tropical convective forcing from the Indian Ocean, 4) a mountain-frictional torque index cycle, 5) baroclinic wave packets/fast Rossby wave energy dispersions interacting with the west central Pacific tropical forcing, and 6) seasonal cycle issues.
There are other matters I am unclear about such as any sub-monthly component involving the mountain torque and other faster modes of tropical convective variability. The future of the MJO even after week 1 is also unclear. I do think the dominant forcing from the tropics is coming from the west central Pacific, and it may not just be a warm ENSO signal. The SSTs are also cool across the tropical northwest Pacific (opposite of last year) and the evolution of this whole “SST situation” is anything but trivial to understand. It would be interesting to see how well coupled GCMs would simulate these SST events since the start of this year.
In any case, we must also remember the suppression from Indonesia also has circulation impacts, and I can easily see Indian Ocean tropical forcing disrupting events across the west Pacific. The statistical models (Wheeler phase space technique, for example) bring the dynamical signal well into the Eastern Hemisphere (~60-80E) by about day 10, and I think that is reasonable. My own thoughts is there may be 2 well defined regions of enhanced tropical convection during week 2, the Indian Ocean and west central Pacific, while the Western Hemisphere becomes suppressed. During week 3 there may be some consolidation of the 2 regions north of the cool SSTs across Indonesia. Confidence in any scientifically defensible statistically useful prediction particularly beyond week 1 is as low as it gets. This is the real world!
Week 1 (18-24 October 2006): I think a loose rendition of GSDM Stage 2 is most probable, but roughly 5-10 degrees farther west (for the USA) than about a week ago. This would mean a trough ~100W with a large amplitude ridge just off the USA west coast possibly into Alaska. Nearly all models are predicting some version of this response since the Rossby wave energy dispersion discussed above should be in the initial conditions. This means a much cooler than normal regime for a good part of the country especially the central and north central states. The warm locations may be the West Coast and Florida. One surge of cool air is occurring as I type, with another due by this weekend per operational NCEP GFS (and other models).
I have a bit of concern for this second surge of cool air. The jet streak that will contribute to it (interacting with “everything else”) may involve the remnants of Typhoon Soulik. The baroclinic development which ensures on the Plains by this weekend may begin with amplification of the trough a bit farther west into the central Rockies. That may suggest more robust cyclogenesis across the Mid/Upper Mississippi Valley. Even though moisture will be relatively limited, a “decent” snow event is not out of the realm of possibilities for locations such as Iowa into the Great Lakes (latter including lake effect). Other effects on the weather should be apparent.
The Tropical North Atlantic may remain suppressed for tropical cyclone activity. There is always the concern for hybrids this time of year and I could also see a period of upper tropospheric easterlies across the tropical Atlantic, latter perhaps allowing a window of opportunity for development. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information. Active regions for tropical cyclones may include the west central Pacific and even the Bay of Bengal, particularly weeks 2-3.
Week 2 (25-31 October 2006): If the west Pacific is “calling the shots”, then similar to week 1 except for the usual synoptic variations of amplitude.
Week 3 (1-7 November 2006): I can envision possibilities (like anyone else), but let us just say “unclear” for now.
Climatologically this is the dry time of the year for Southwest Kansas. Other than one or two minor episodes of precipitation, week 1 looks generally cool and dry. There is a small possibility of a “surprise” this weekend. I would expect week 2 to remain generally dry with roughly seasonable temperatures (on average!). Even though not discussed for week 3, opportunities for precipitation may increase for this part of the world should “STJ activity” become more robust.
Since I continue to have to cover lots of shifts (including mids), I may not be able to update this Blog until late next week. We do have plans to write another weather-climate discussion for the ESRL/PSD MJO web page to hopefully post by the end of November. Please see the Appendix.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), along with all the other issuances, has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
Wednesday, October 11, 2006
Weather-Climate Update
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings, and this one will be short due to shift work obligations.
SSTs have changed little since my posting on October 6th. There is some evidence that the current warm phase of ENSO is peaking.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
The dynamical signal with the MJO is propagating through the Western Hemisphere, with a phase speed of 10-15m/s based on Hovmollers of velocity potential and OLRA. This is an increase from about 2 weeks ago, and is typical when the MJO signal moves into the Western Hemisphere. Full disk satellite imagery suggests the dynamical signal is centered around 0/80W. Surface westerly wind anomalies of 10-20m/s have propagated northward from the equatorial date line region and have contributed to anomalous westerly flow across much of the North Pacific at ~30N during the last few days. The latter was theresult of 2 tropical convective flare-ups and westerly wind events during the last 10-14 days, and has been associated with tropical cyclone activity across the West Pacific. In fact, there is a signal in the global AAM tendency of the tropical convective flare-ups associated with the MJO.
In the upper troposphere, 200mb zonal mean zonal wind anomalies of ~5m/s are presently centered ~20N, and there is evidence of meridional symmetry. Additionally, some linkage between the anomalous zonal mean westerly flows throughout the subtropical and midlatitude atmospheres has occurred during the last few days. Loosely, GSDM Stage 2 (tilted toward Stage 3) best describes the weather-climate situation during the past week. This has impacted the USA in the form of the currently strong positive phase of the Pacific-North American teleconnection (PNA). A major cold outbreak (for this time of year) into the North Central states is occurring as a response.
Strong suppression exists across much of the Eastern Hemisphere while convection remains perhaps coupled to the warm SSTs just west of date line, oriented north-south across the equator over the 29C and greater SSTs. The latter region has been weakening after the development of Tropical Cyclone Soulik. Most of the tropical convective enhancement is along the East Pacific ITCZ (where SSTs are also warm) into the South Atlantic Convergence Zone (SACZ) and spreading into the tropical North Atlantic ITCZ. This activity is associated with "wavy" upper tropospheric westerly wind anomalies that normally develop downstream of tropical forcing over the Eastern Hemisphere.
My thoughts are for the dynamical signal to propagate into the Eastern Hemisphere by the week 2-3 time frame, and reinvigorate the tropical convection across much of the Indian Ocean (where are SSTs are also quite warm with anomalies ~plus 0.5-1C over greater than 29C water). SST boundary forced tropical convection would also be expected to continue just west of the date line. A rendition of GSDM Stage 4-1 may be probable during weeks 2-3, loosely suggesting a retrogression of existing circulation anomalies with the continuation of subtropical jets. Many numerical ensemble prediction systems are capturing this scenario for much of the northern extratropics for week 2.
Ramifications would include the possibility of an anomalously deep trough across the western USA (with a subtropical jet), along with a strong southwest flow storm track across the Plains and central portions of the country. While synoptic details are unclear (ex., the magnitude of any baroclinic cyclogenesis), there exists the possibility of an early season major winter-like storm for the Central and Northern Rockies (there will be a cold air source). Meanwhile, severe local storms and widespread rainfall (some heavy) would be possible for locations from the Plains into the Upper Mississippi/Ohio Valleys and Great Lakes states. Other weather anomalies from this type of pattern should be well known by now.
I hope to post a more complete discussion roughly a week from today.
Ed Berry
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM and additional components.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
We hope to post another writing on the ESRL/PSD MJO web site within the next 4-6 weeks.
SSTs have changed little since my posting on October 6th. There is some evidence that the current warm phase of ENSO is peaking.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
The dynamical signal with the MJO is propagating through the Western Hemisphere, with a phase speed of 10-15m/s based on Hovmollers of velocity potential and OLRA. This is an increase from about 2 weeks ago, and is typical when the MJO signal moves into the Western Hemisphere. Full disk satellite imagery suggests the dynamical signal is centered around 0/80W. Surface westerly wind anomalies of 10-20m/s have propagated northward from the equatorial date line region and have contributed to anomalous westerly flow across much of the North Pacific at ~30N during the last few days. The latter was theresult of 2 tropical convective flare-ups and westerly wind events during the last 10-14 days, and has been associated with tropical cyclone activity across the West Pacific. In fact, there is a signal in the global AAM tendency of the tropical convective flare-ups associated with the MJO.
In the upper troposphere, 200mb zonal mean zonal wind anomalies of ~5m/s are presently centered ~20N, and there is evidence of meridional symmetry. Additionally, some linkage between the anomalous zonal mean westerly flows throughout the subtropical and midlatitude atmospheres has occurred during the last few days. Loosely, GSDM Stage 2 (tilted toward Stage 3) best describes the weather-climate situation during the past week. This has impacted the USA in the form of the currently strong positive phase of the Pacific-North American teleconnection (PNA). A major cold outbreak (for this time of year) into the North Central states is occurring as a response.
Strong suppression exists across much of the Eastern Hemisphere while convection remains perhaps coupled to the warm SSTs just west of date line, oriented north-south across the equator over the 29C and greater SSTs. The latter region has been weakening after the development of Tropical Cyclone Soulik. Most of the tropical convective enhancement is along the East Pacific ITCZ (where SSTs are also warm) into the South Atlantic Convergence Zone (SACZ) and spreading into the tropical North Atlantic ITCZ. This activity is associated with "wavy" upper tropospheric westerly wind anomalies that normally develop downstream of tropical forcing over the Eastern Hemisphere.
My thoughts are for the dynamical signal to propagate into the Eastern Hemisphere by the week 2-3 time frame, and reinvigorate the tropical convection across much of the Indian Ocean (where are SSTs are also quite warm with anomalies ~plus 0.5-1C over greater than 29C water). SST boundary forced tropical convection would also be expected to continue just west of the date line. A rendition of GSDM Stage 4-1 may be probable during weeks 2-3, loosely suggesting a retrogression of existing circulation anomalies with the continuation of subtropical jets. Many numerical ensemble prediction systems are capturing this scenario for much of the northern extratropics for week 2.
Ramifications would include the possibility of an anomalously deep trough across the western USA (with a subtropical jet), along with a strong southwest flow storm track across the Plains and central portions of the country. While synoptic details are unclear (ex., the magnitude of any baroclinic cyclogenesis), there exists the possibility of an early season major winter-like storm for the Central and Northern Rockies (there will be a cold air source). Meanwhile, severe local storms and widespread rainfall (some heavy) would be possible for locations from the Plains into the Upper Mississippi/Ohio Valleys and Great Lakes states. Other weather anomalies from this type of pattern should be well known by now.
I hope to post a more complete discussion roughly a week from today.
Ed Berry
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM and additional components.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
We hope to post another writing on the ESRL/PSD MJO web site within the next 4-6 weeks.
Friday, October 06, 2006
MJO is for Real; Large Uncertainty Remains for the Future of our Warm Event
Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings.
The spatial distribution of global tropical sea surface temperature (SST) anomalies has not changed significantly since our last posting on September 26th. Positive anomalies persist (keep in mind the seasonal cycle) across the central Indian Ocean and from the date line to the west coast of South America, with weekly mean values ~plus .5-1.0C (around plus 2C west of South America). Above average SSTs also remain from the Caribbean into much of the Tropical North Atlantic Ocean. Below normal SSTs are still present from about 90-150E within 25-30 degrees of the equator. Actual SSTs of 29C and greater continue over the central Indian Ocean, from east of the Philippines to the South Pacific centered ~160E and on “both sides” of Central America. A recent development since the last posting has been a decided cooling (~minus .5-1.0C) of equatorial SSTs from around the date line to near the west coast of South America, as well as portions of the Tropical Northwest Pacific.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and
remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Since about September 1st, tropical convective forcing has been coherently propagating eastward west of the date line, generally along and north of the equator. This forcing “originated” around Africa, and while undergoing some complex variations, its propagation speed has remained around 4-5 m/s (3-4 deg long/day). Monitoring tools such as the Wheeler phase diagram and coherent modes Hovmollers indicate this region of enhanced tropical rainfall projects onto a Madden-Julian Oscillation (MJO), and I agree. In fact, I would consider it at least a moderate MJO for this time of year.
On about September 28th this MJO consolidated with a Rossby mode over the warm SSTs near 10-15N/155E, leading to an intense convective flare-up with negative OLR anomalies of at least minus 90W/m**2. Centered near 155E, there was an upstream (downstream) westerly wind burst (trade wind surge) on the equator with wind speed anomalies of at least 5m/s (leading to anomalous convergence). The anomalous westerlies did shift off the equator into both hemispheres, and “led” to some enhancement along the SPCZ as well. A reinvigoration of both convection and anomalous surface westerlies occurred near the equatorial date line a couple of days ago.
Current full disk satellite imagery shows the tropical convective forcing with the MJO extending from equatorial date line to near 15N/140E. There is also other enhancement across the North Tropical East Pacific ITCZ due to at least one convectively coupled Kelvin wave emanating from the MJO, as well as a flare-up around the Bay of Bengal. Strong suppression exists from far east Africa into the most of the Indian Ocean.
Anomalous upper tropospheric westerlies across the Western Hemisphere have been one of the responses to the MJO. Per animations of daily mean 150mb vector wind anomalies, there have been at least 2 “wavy” bands, with one across the equatorial atmosphere (moving into Africa) and the other extending from ~10N/180 into the western portion of the USA (leading to the current heavy precipitation across portions of the Southwest). Anomalies have been ~15-25m/s. Per time-latitude section of 200mb zonal mean zonal wind anomalies, westerly anomalies ~5m/s have been present since about September 30th from 0-30N (with other zonal mean interhemispheric symmetry of anomalies).
As would be expected, based on the reanalysis data (and its 1968-1997 climatology), the tendency of global relative AAM is strongly positive with a magnitude of ~25 Hadleys. Much of that contribution (in the zonal mean) started just north of the equator about a week ago, and is currently shifting poleward. Both the global mountain and frictional torques remain positive (latter recently increasing due to the trades). The global AAM based on both the reanalysis and operational data sets is near average (but obviously increasing). The interested reader needs to look at the actual plots (from the ESRL/PSD web site) to grasp the important details of the distribution of zonal mean AAM anomalies as well as the torques and transports.
To summarize, I think we have 1) a weak warm event whose future evolution is unclear (perhaps in doubt), 2) at least a moderate MJO signal, 3) at least one convectively coupled Kelvin wave moving into the East Pacific as I type (which could “speed things up a lot”), 4) tropical convective forcing from the Indian Ocean Dipole, which is another SST boundary forced component that could become important once again, 5) a sub-monthly component involving the global mountain torque, 6) a baroclinic wave packet interacting with the west central/northwest Pacific tropical forcing (with distorted twin subtropical anticyclones) which is part of the GSDM Stage 2 process (not discussed) and 7) the usual lots and lots of white noise.
There are two points I want make having given the above very brief background on the current weather-climate situation. First, the anomalously cool SSTs around Indonesia have been expanding eastward for about the past week-10 days while the SSTA tendency has been negative along the equatorial cold tongue. There has also been cooling across the Tropical Northwest Pacific particularly around the Philippines. This needs to be monitored! There are numerous scenarios that can be envisioned including the reflection of our recent oceanic Kelvin wave back to the west as an upwelling oceanic Rossby mode. This all means the future evolution of our current warm El-Nino is unclear, including the possibility it could weaken or even dissipate during the next few months.
The second point is I think we are transitioning into GSDM Stage 2 given the MJO and earth –atmosphere angular momentum budget situation. Most numerical models and their ensembles have generally captured this change. How long GSDM Stage 2 will persist is unclear. My thoughts for the MJO is that the dynamical signal will continue its movement into the Western Hemisphere (as currently shown by Hovmoller plots of 200mb velocity potential), increasing to around 10 deg long/day. The Western Hemisphere ITCZs are likely to become enhanced (including perhaps the SACZ). Tropical convection may persist around the date line and increase across Africa into the Indian Ocean. Thus a transition to GSDM Stage 3 and even Stage 4 may occur during weeks 2-3. My predictability confidence is about average for week 1 (everything considered!), then very low for weeks 2-3.
Week 1 (07 – 13 October 2006): GSDM Stage 2 is most probable. This will manifest itself as a large amplitude mid/upper tropospheric ridge along the west coast of North America into Alaska/western Canada and an anomalously deep trough around the Mississippi Valley. In fact, the NCEP GFS ensemble predicts ~minus 3 sigma 500mb height anomalies at tau 168hrs from 0000 UTC 6 October 2006 initial conditions. Thus below to well below normal temperatures are probable from the east slopes of the Rockies into much of the central and eastern parts of the country while the Pacific Northwest has very warm temperatures. In fact, widespread record low temperatures (at least) may occur across much of the north/central Plains into the Great Lakes states after areas such as the Front Range into the Great Lakes see their first “flakes of snow”.
Above average precipitation is probable generally east of the Mississippi River while the western third of the country is dry (after this weekend). Depending on the magnitude of the baroclinic development roughly the middle of next week, high winds are possible across much of the north central states along with a possibility of severe local storms along the cold front centered on the Ohio and Tennessee Valleys.
The Tropical North Atlantic looks to remain suppressed for tropical cyclone activity while the Central and East Pacific becomes more active. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (14 – 20 October 2006): The circulation may transition to GSDM Stage 3. For this time of year, we may see a relatively strong North Pacific Jet lead to a split flow pattern across much of North America (not the strong jet that may be seen during January, for example, during a warm event). This flow pattern will probably include a subtropical jet. Much of the lower 48 states should experience near-above normal temperatures, meaning a warming trend for the central and east (“Indian Summer”). Most of the country would also be dry. The East Pacific (along with the West and perhaps Central Pacific) may become (remain?) quite active with tropical cyclone activity, possibly spreading into the Southwest Caribbean (sooner?).
There is only one problem I have with the above. I have concern that the cool SSTs across the Tropical Northwest Pacific could lead to some persistence of the GSDM Stage 2 regime which evolves during week 1 (perhaps even retrograde it). There are a few numerical and statistical tools which imply this (without having much clue of the tropical convective forcing during week 2; it is coming from initial condition information).
Week 3 (21 – 27 October 2006): Unclear.
Overall, I do not see a wet period for Southwest Kansas through at least week 2. Some light precipitation is probable around Sunday Night into Monday and perhaps around the middle of next week. Cooler than normal temperatures look like a good bet during week 1, especially starting Monday. Temperatures may moderate to about normal week 2 (understanding daily variability). Monitoring will be needed to get a better sense for week 2 and beyond. For instance, if a 20-30 degree retrogression of the week 1 positive PNA pattern were to occur with a subtropical jet entering the Desert Southwest, a different outcome to the weather experienced than implied above is likely.
I will try to do an update to this blog next week. Please see the Appendix.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
The spatial distribution of global tropical sea surface temperature (SST) anomalies has not changed significantly since our last posting on September 26th. Positive anomalies persist (keep in mind the seasonal cycle) across the central Indian Ocean and from the date line to the west coast of South America, with weekly mean values ~plus .5-1.0C (around plus 2C west of South America). Above average SSTs also remain from the Caribbean into much of the Tropical North Atlantic Ocean. Below normal SSTs are still present from about 90-150E within 25-30 degrees of the equator. Actual SSTs of 29C and greater continue over the central Indian Ocean, from east of the Philippines to the South Pacific centered ~160E and on “both sides” of Central America. A recent development since the last posting has been a decided cooling (~minus .5-1.0C) of equatorial SSTs from around the date line to near the west coast of South America, as well as portions of the Tropical Northwest Pacific.
The following are links to ENSO discussions.
http://www.cdc.noaa.gov/people/klaus.wolter/MEI
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and
remember that official USA information on anything related to ENSO comes from CPC.
http://www.cpc.ncep.noaa.gov/products/predictions/90day/
Since about September 1st, tropical convective forcing has been coherently propagating eastward west of the date line, generally along and north of the equator. This forcing “originated” around Africa, and while undergoing some complex variations, its propagation speed has remained around 4-5 m/s (3-4 deg long/day). Monitoring tools such as the Wheeler phase diagram and coherent modes Hovmollers indicate this region of enhanced tropical rainfall projects onto a Madden-Julian Oscillation (MJO), and I agree. In fact, I would consider it at least a moderate MJO for this time of year.
On about September 28th this MJO consolidated with a Rossby mode over the warm SSTs near 10-15N/155E, leading to an intense convective flare-up with negative OLR anomalies of at least minus 90W/m**2. Centered near 155E, there was an upstream (downstream) westerly wind burst (trade wind surge) on the equator with wind speed anomalies of at least 5m/s (leading to anomalous convergence). The anomalous westerlies did shift off the equator into both hemispheres, and “led” to some enhancement along the SPCZ as well. A reinvigoration of both convection and anomalous surface westerlies occurred near the equatorial date line a couple of days ago.
Current full disk satellite imagery shows the tropical convective forcing with the MJO extending from equatorial date line to near 15N/140E. There is also other enhancement across the North Tropical East Pacific ITCZ due to at least one convectively coupled Kelvin wave emanating from the MJO, as well as a flare-up around the Bay of Bengal. Strong suppression exists from far east Africa into the most of the Indian Ocean.
Anomalous upper tropospheric westerlies across the Western Hemisphere have been one of the responses to the MJO. Per animations of daily mean 150mb vector wind anomalies, there have been at least 2 “wavy” bands, with one across the equatorial atmosphere (moving into Africa) and the other extending from ~10N/180 into the western portion of the USA (leading to the current heavy precipitation across portions of the Southwest). Anomalies have been ~15-25m/s. Per time-latitude section of 200mb zonal mean zonal wind anomalies, westerly anomalies ~5m/s have been present since about September 30th from 0-30N (with other zonal mean interhemispheric symmetry of anomalies).
As would be expected, based on the reanalysis data (and its 1968-1997 climatology), the tendency of global relative AAM is strongly positive with a magnitude of ~25 Hadleys. Much of that contribution (in the zonal mean) started just north of the equator about a week ago, and is currently shifting poleward. Both the global mountain and frictional torques remain positive (latter recently increasing due to the trades). The global AAM based on both the reanalysis and operational data sets is near average (but obviously increasing). The interested reader needs to look at the actual plots (from the ESRL/PSD web site) to grasp the important details of the distribution of zonal mean AAM anomalies as well as the torques and transports.
To summarize, I think we have 1) a weak warm event whose future evolution is unclear (perhaps in doubt), 2) at least a moderate MJO signal, 3) at least one convectively coupled Kelvin wave moving into the East Pacific as I type (which could “speed things up a lot”), 4) tropical convective forcing from the Indian Ocean Dipole, which is another SST boundary forced component that could become important once again, 5) a sub-monthly component involving the global mountain torque, 6) a baroclinic wave packet interacting with the west central/northwest Pacific tropical forcing (with distorted twin subtropical anticyclones) which is part of the GSDM Stage 2 process (not discussed) and 7) the usual lots and lots of white noise.
There are two points I want make having given the above very brief background on the current weather-climate situation. First, the anomalously cool SSTs around Indonesia have been expanding eastward for about the past week-10 days while the SSTA tendency has been negative along the equatorial cold tongue. There has also been cooling across the Tropical Northwest Pacific particularly around the Philippines. This needs to be monitored! There are numerous scenarios that can be envisioned including the reflection of our recent oceanic Kelvin wave back to the west as an upwelling oceanic Rossby mode. This all means the future evolution of our current warm El-Nino is unclear, including the possibility it could weaken or even dissipate during the next few months.
The second point is I think we are transitioning into GSDM Stage 2 given the MJO and earth –atmosphere angular momentum budget situation. Most numerical models and their ensembles have generally captured this change. How long GSDM Stage 2 will persist is unclear. My thoughts for the MJO is that the dynamical signal will continue its movement into the Western Hemisphere (as currently shown by Hovmoller plots of 200mb velocity potential), increasing to around 10 deg long/day. The Western Hemisphere ITCZs are likely to become enhanced (including perhaps the SACZ). Tropical convection may persist around the date line and increase across Africa into the Indian Ocean. Thus a transition to GSDM Stage 3 and even Stage 4 may occur during weeks 2-3. My predictability confidence is about average for week 1 (everything considered!), then very low for weeks 2-3.
Week 1 (07 – 13 October 2006): GSDM Stage 2 is most probable. This will manifest itself as a large amplitude mid/upper tropospheric ridge along the west coast of North America into Alaska/western Canada and an anomalously deep trough around the Mississippi Valley. In fact, the NCEP GFS ensemble predicts ~minus 3 sigma 500mb height anomalies at tau 168hrs from 0000 UTC 6 October 2006 initial conditions. Thus below to well below normal temperatures are probable from the east slopes of the Rockies into much of the central and eastern parts of the country while the Pacific Northwest has very warm temperatures. In fact, widespread record low temperatures (at least) may occur across much of the north/central Plains into the Great Lakes states after areas such as the Front Range into the Great Lakes see their first “flakes of snow”.
Above average precipitation is probable generally east of the Mississippi River while the western third of the country is dry (after this weekend). Depending on the magnitude of the baroclinic development roughly the middle of next week, high winds are possible across much of the north central states along with a possibility of severe local storms along the cold front centered on the Ohio and Tennessee Valleys.
The Tropical North Atlantic looks to remain suppressed for tropical cyclone activity while the Central and East Pacific becomes more active. Please see http://www.nhc.noaa.gov/ for the latest tropical cyclone information.
Week 2 (14 – 20 October 2006): The circulation may transition to GSDM Stage 3. For this time of year, we may see a relatively strong North Pacific Jet lead to a split flow pattern across much of North America (not the strong jet that may be seen during January, for example, during a warm event). This flow pattern will probably include a subtropical jet. Much of the lower 48 states should experience near-above normal temperatures, meaning a warming trend for the central and east (“Indian Summer”). Most of the country would also be dry. The East Pacific (along with the West and perhaps Central Pacific) may become (remain?) quite active with tropical cyclone activity, possibly spreading into the Southwest Caribbean (sooner?).
There is only one problem I have with the above. I have concern that the cool SSTs across the Tropical Northwest Pacific could lead to some persistence of the GSDM Stage 2 regime which evolves during week 1 (perhaps even retrograde it). There are a few numerical and statistical tools which imply this (without having much clue of the tropical convective forcing during week 2; it is coming from initial condition information).
Week 3 (21 – 27 October 2006): Unclear.
Overall, I do not see a wet period for Southwest Kansas through at least week 2. Some light precipitation is probable around Sunday Night into Monday and perhaps around the middle of next week. Cooler than normal temperatures look like a good bet during week 1, especially starting Monday. Temperatures may moderate to about normal week 2 (understanding daily variability). Monitoring will be needed to get a better sense for week 2 and beyond. For instance, if a 20-30 degree retrogression of the week 1 positive PNA pattern were to occur with a subtropical jet entering the Desert Southwest, a different outcome to the weather experienced than implied above is likely.
I will try to do an update to this blog next week. Please see the Appendix.
Appendix
The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).
http://www.cdc.noaa.gov/MJO/Predictions/wb2006.pdf
From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM.
Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Ed Berry
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