Saturday, December 27, 2008

Shifting Around in the Atmosphere’s Witches Brew

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”


Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.


http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml


The 91-day signal to noise ratio (snr) anomaly composites are being updated daily. There are still some map room issues that will hopefully be resolved soon. WB (2009), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.


These discussions are part of an experimental effort involving linking weather and climate. We are moving forward on having a one day workshop in Boulder tentatively planned for 24 February 2009 on the WB (2009) GWO. Details are still being worked out, and stay tuned for our announcement.


This is little overall substantial change to the spatial distribution of global SSTs. The warmest ocean waters extend from the extreme west central Pacific to ~10S/160E with totals ~30C and anomalies roughly 1C. There has been some recent cooling of Eastern Hemisphere tropical SSTs due to persistent enhanced rainfall (more said below).


Significant negative anomalies have evolved along the equatorial Pacific Ocean cold tongue, responding to (as was expected) the global ocean-land-atmosphere dynamical system being tilted toward La-Nina. Numerous past discussions have addressed a few of these important scientific matters. Magnitudes along the cold tongue are generally minus 1-1.5C, with totals well under 26C east of the 0/160W. At least from the subseasonal perspective, our La-Nina encore is anything but “weak, transient, still neutral, cannot happen because of the seasonal cycle (good eating for the Rottweiler!!!) , etc…………”


http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html


http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html


http://www.pmel.noaa.gov/tao/jsdisplay/


http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)


http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18).


http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif


The rest of this discussion is abbreviated due to “holiday constraints”. That said there is not much new additional information to offer to that already written since at least the 22 November 2008 posting.


The wind and tropical convective signals are getting better aligned as the quasi-stationary La-Nina base state matures. Tropical convective forcing has loosely consolidated ~5N/125E while extending from the equatorial Indian Ocean into the warm southwest Pacific. There has been some shifting around of components, including the recent excitation along the SPCZ. However, any real MJO signal is weak. I think the roughly 2 sigma projection (26 December) in octant 4 of WH (2004) phase space retaining the ENSO and interannual components is a response (really a computation) to the wind and convective signals syncing up. Phase 4 of the 250mb snr composite anomalies of psi (olr) reasonably depicts tropical circulation anomalies (convection).


Global relative AAM (through 25 December) has dipped to ~1 sigma below the R1 data climatology, the lowest since at least October. I do think this global signal will continue to decrease at least into next week. The various terms of the global and zonal mean AAM budget generally reflect our La-Nina. For instance, the global frictional torque and earth AAM are slightly positive, with zonal mean contributions coming from enhanced Northern Hemisphere trades and high surface pressures across the midlatitudes. The latter are a response of the current strong positive phase of a Branstator (2002) circumglobal teleconnection of anomalous ridges. Contributing to a well-defined interhemispheric meridional symmetry of zonal mean zonal wind anomalies, easterly wind flow is very intense across the subtropical atmospheres. In fact, zonal mean easterly wind flow anomalies ~30N (shifting south for the past several weeks) are roughly 10m/s.


The WB (2009) measure of the GWO may be “settling down” in octants 1-3 of phase space. However, whether or not that becomes a JFM seasonal mean is unclear. The roles of possible additional MJO variability and/or the southwest Pacific Ocean have already been discussed. However, I think some rendition of a superposition of tropical and extratropical circulation (rainfall) anomalies depicted by the 250mb snr composite psi (olr) anomaly plots for phases 3-4 of both the MJO and GWO are a possibility. That suggests a continued loose preference for an East Asian trough-central Pacific Ocean ridge-west and central North American trough.


There will be transient synoptic variations including those linked to fast GWO orbits. Case in point, the west coast ridge/eastern states trough predicted by many week-2 numerical model ensemble means is not unrealistic (a feedback in this case). What may be least likely is a JFM seasonal mean outcome of an extended and southward displaced North Pacific Ocean jet leading to a downstream split flow pattern and a tilt toward (such as) cold/wet across the Deep South of the USA (typical of GWO phase 7, El-Nino base state).


USA and international weather ramifications should be well understood by now. For example, continued excessive rainfall from most of Indonesia into portions of Australia “UFN”. Please see all the snr composites per ESRL/PSD GSDM web link for details. We are actually going into week-5 per the 22 November 2008 posting. It is interesting that what many define as a reverse or negative phase of the Pacific North American teleconnection pattern (-PNA/RNA) appears to be relaxing, at least for the time being. Stay tuned.


I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide, including official statements for tropical cyclones that may impact regions such as around Australia during the next several weeks. Episodes of global extreme weather events continue; for instance, the recent heat and flooding across portions of Brasil.


Appendix


Links to CPC and PSD ENSO discussions:


http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml


http://www.cdc.noaa.gov/people/klaus.wolter/MEI/


The following is a link to information about the stratosphere and other nice monitoring tools:


http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html


The following is a link to NCEP model verifications (surf around for lots more)


http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html .


The following is a link discussing recent global weather and related events:


http://www.wmo.ch/pages/mediacentre/news/index_en.html


These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.


The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the following link:


http://www.cdc.noaa.gov/map/clim/wb08_revised_final.pdf


In addition to the subseasonal snr composite anomaly plots, we hope near real-time discussions with “weather maps” will become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook! I plan on posting at least an abbreviated discussion the weekend of 3-4 January 2009.


Ed Berry

Friday, December 19, 2008

Sinking Deeper into La-Nina?

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”


Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.


http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml


The 91-day signal to noise ratio (snr) anomaly composites are being updated daily. There are still some map room issues that will hopefully be resolved soon. WB (2009), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.


These discussions are part of an experimental effort involving linking weather and climate. We are moving forward on having a one-day workshop in Boulder during about mid-February 2009 on the WB (2009) GWO. Hopefully details will be available next week (22-26 December).


The warmest SSTs globally still extend from northwest of Australia to the Dateline ~10-15S, with totals in excess of 30C and departures from climatology greater than 1C. However, significant cooling of equatorial central and eastern Pacific Ocean SSTs has occurred during the last 1-2 weeks, with nearly minus 1C anomalies across all Nino regions per 5-day averaged TAO buoy data. In fact, SSTs are ~minus 1.5C below normal at 0/160W, and anomalies colder than minus 5C are present at 125m depth/135W. The subsurface equatorial Pacific Ocean anomalies are now very similar to a year ago (steeper than normal thermocline).


Bottom line, this is the type of “Nino SST” response that has been anticipated by us since at least early October, in the presence of the global ocean-land-atmosphere dynamical system exhibiting La-Nina characteristics (with variations) arguably since December 2006. How much additional Nino cooling occurs is unclear; however, “my expectations (in terms of magnitude)” have already been exceeded.


http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html


http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html


http://www.pmel.noaa.gov/tao/jsdisplay/


http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)


http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18)


http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif


The wind and convective signals are once again are out of sync for at least the third time since October. Perhaps this is a characteristic for a “second year La-Nina”. Tropical convective forcing is somewhat disorganized, with enhancement focused on central Indonesia into northern Australia, tropical South America and South Africa. The latter is attempting to expand into the southwest Indian Ocean, and there is a strong flare-up over the southern Arabian Sea.


Updated through 18 December, the WH (2004) measure of the MJO shows a ~1.5 sigma projection in octant 7 of phase space; i.e., the west Pacific Ocean. Retaining the interannual and ENSO signals gives literally no projection. The latter is much more reasonable. The "artificial" west Pacific MJO signal is coming from the winds. The dynamics responsible for those winds are more accurately explained and properly represented by the WB (2009) measure of the GWO. I will only summarize below. Please see the AAM and other plots for details.


Since about mid September, with the important exceptions of two large ~3 sigma 20 to 30-day variations of the WB (2009) measure of the GWO, ~10-day orbits tilted toward low AAM have occurred. More generally, if a 90-day averaged location in phase space of the GWO is calculated, there would be a drift towards octants 8-1-2. The November orbit was slower, with a large excursion toward high AAM, and had better interactions with the tropics. There was considerable frictional dissipation of anomalous subtropical westerly wind flow during the November variation linked to extratropical storm track activity especially across the North Pacific Ocean.


In any case, the two large variations loosely involved first poleward AAM fluxes, then positive surface torques and finally interhemispheric positively phased subtropical wavetrains (Branstator (2002); +SWT). These +SWTs have had phase speeds of ~20-25m/s, and aligned by the base state have maintained the upper tropospheric zonally asymmetric wave 0/1 La-Nina distribution of tropical circulation anomalies consisting of twin Indian Ocean (Dateline) anticyclones (cyclones) that has been present since early October.


A strong poleward AAM transport signal (all part of eddy feedback processes from our quasi-stationary La-Nina global circulation state) appeared ~1 December (maximum transport ~40N) leading to a similar chain of events as described above. However, the response of the global surface torques was apparently “damped” suggestive of the current on-going weaker and faster GWO orbit through phases 8-1 to 4-5 then 8-1 behavior. The accompanying +SWT, however, is quite robust with wind speed anomalies ~40-60m/s at 250mb. In fact, with strong poleward AAM flux once again, similar to 2007-08 an interhemispheric positive phase of a Branstator (2002) circumglobal teleconnection meaning anomalous midlatitude ridges is back.


So, sparing anymore “Gone with the Wind”, I think our quasi-stationary La-Nina base state is continuing to mature. While currently just slightly below the R1 data climatology (through 17 December) after the plus 2 sigma November excursion, how low global AAM may drop is unclear. There is nice meridional symmetry of zonal mean zonal wind anomalies featuring equatorial westerlies, strong subtropical easterlies (5-10m/s at 200mb both hemispheres) then westerlies across the higher latitudes. It is probable this La-Nina situation will continue at least well into boreal spring (yes, more and more coupled models have been catching on, and other “organizations” are starting to “yield” a bit).


Responding to increasing regional scale divergence forced by +SWT, tropical convection is probable to increase across the Indian Ocean during the next 1-2 weeks. The details are unclear. However, by early January there should be a large region of intense to severe thunderstorm activity from roughly the equatorial Indian Ocean into Western Australia possibly focused ~5S/90-100E. Perhaps at that time the wind and convective signals will get back in sync, and “stay that way”.


Evolutionary behaviors depicted by phases 8-1-2-3 of the GWO 250mb snr composite psi anomalies are likely to represent the extratropical circulation at least through week-2. USA weather ramifications including the likelihood of additional extreme weather events should be “common knowledge” by now. For reasons, there is a bit of a historical maximum for significant/severe winter storm development to occur on the Plains during early January. We will see if that is the case for January 2009.


Speculating farther into next month, uncertainty increases because of seasonal cycle issues. I am still concerned that at least episodic events of enhanced convection across both the warm southwest Pacific and Indian Ocean/Australian regions may occur simultaneously. The role of MJO activity is uncertain. Bottom line, lack of MJO (additional MJO) variability may suggest a circulation tilt toward that shown by the snr 250mb psi composite anomalies for GWO phases 8-1-2 (3-4-5). On average JFM may see anomalous cold/wet (warmth/dryness) shifted toward the USA west coast into the Northern Plains (Deep Southeast), a slight westward displacement from 2007-08. There would still be an active southwest flow storm track across the Plains, but perhaps locations such as the Dakotas would have an increase of “the classic Great Plains blizzards from days back”. Finally, given recent behaviors, drought conditions (there is a multiyear component) may return to portions of the High Plains especially from west Texas into southwest Kansas.


Internationally, the 3 regions of enhanced tropical rainfall discussed above are likely to continue through week-1, with consolidation probable across the Indian Ocean into Western Australia at least weeks 2-3. Frontal thunderstorm activity may become quite intense across portions of Australia going into January. Regardless of the behavioral details, most of Indonesia and even the Philippines (at times) are likely to experience anomalous rainfall including severe thunderstorms and flooding “until further notice”.


The focus for tropical cyclone development may shift into the South Indian Ocean (TC Billy and Cinda understood) to the northwest coast of Australia during austral summer. In fact, an increase in that region to above climatology is possible during weeks 2-3. I would be surprised not to see at least one or two tropical cyclone developments along the SPCZ east of Australia into the South Pacific Islands during JFM given the very warm ocean temperatures. Please see the latest official tropical cyclone forecasts for all basins.


I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide. There has been an increase during the past week.


Appendix


Links to CPC and PSD ENSO discussions:


http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml


http://www.cdc.noaa.gov/people/klaus.wolter/MEI/


The following is a link to information about the stratosphere and other nice monitoring tools:


http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html


The following is a link to NCEP model verifications (surf around for lots more)


http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html .


The following is a link discussing recent global weather and related events:


http://www.wmo.ch/pages/mediacentre/news/index_en.html


These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.


The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the following link:


http://www.cdc.noaa.gov/map/clim/wb08_revised_final.pdf


In addition to the subseasonal snr composite anomaly plots, we hope near real-time discussions with “weather maps” will become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook! I plan on posting a discussion the weekend of 27-28 December.


Ed Berry

Saturday, December 13, 2008

Entering Week-3 of the “Extreme”

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”


Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.


http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml


The 91-day signal to noise ratio (snr) anomaly composites are being updated daily. There are still some map room issues that will hopefully be resolved soon. WB (2009), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.


These discussions are part of an experimental effort involving linking weather and climate. We are moving forward on having a one-day workshop in Boulder during February 2009 on the WB (2009) GWO. Details will be forthcoming.


The warmest ocean waters globally extend from central Indonesia to the north coast of Australia then into the southwest Pacific Ocean. SST totals are in excess of 30C with anomalies ~plus 1-2C. Negative anomalies along the equator from ~160E extending into all Nino regions persist, having magnitudes varying from 0.5-2C and totals generally well under 28C. In fact, latest 5-day averaged TAO buoy data shows ~minus 1C anomaly near 0/140W with roughly minus 5C at 125m depth. Overall, there is little change in the spatial pattern of global SSTs. The PDO is strongly negative; the tropical Atlantic Ocean remains warm, as does the southwest Indian Ocean.


Responding to the global atmospheric circulation, basin-wide cool SST conditions have been observed for at least the past month across all Nino regions. A recent disruption of the trades across the west central Pacific Ocean may have excited a downwelling oceanic Kelvin wave; and impacts from it, if any, are unclear.


http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html


http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html


http://www.pmel.noaa.gov/tao/jsdisplay/


http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)


http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18)


http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif


The wind and convective signals have shown some evidence of getting into sync during the last few weeks, as have the tropics and extratropics. However, they are still not lined up (GWO octant 1 verses MJO octant 4 in phase space – discussed below), and the interactions are exceptionally complicated. The dynamics of these processes are too difficult to discuss (at the level we are comfortable with) in a medium such as a blog. Only a few highlights are given in the following, and relevant material presented in my last few postings will not be repeated.


As was anticipated from monitoring the dynamics explained by the WB (2009) measure of the GWO (loosely stated), moist intense tropical convective forcing has reasonably consolidated ~0/110E extending from the southern Arabian Sea east-southeast into northern Australia. There is some “sputtering” tied to frontal activity across the warm southwest Indian and Pacific Oceans, while tropical South America and South Africa are at least climatologically active.


Retaining the interannual and ENSO signals, there is ~1 sigma MJO projection in octant 4 of WH (2004) phase space. In fact, phase 4 of the WH (2004) MJO snr 250mb psi composite anomaly plots reasonably depicts the current global tropical circulation. However, in my view there is currently no real coherent MJO signal of tropical convective forcing. We are observing a quasi-stationary La-Nina like component of the global ocean-land-atmosphere system. Furthermore, any notions about an active MJO signal in the west central Pacific are simply incorrect. A few techniques and tools suggest the latter. This type of misinterpretation serves as an example of what results when care is not taken to understand the dynamics of fundamental atmospheric processes including monitoring constant everyday non-linear interactions (yes, the Rottweiler is barking)! An overview and simplified brief attribution of “what recently happened” is given in the following paragraph.


Animations of various daily mean vector total and anomalous wind fields for the last 1-2 weeks do suggest strong tropical-extratropical interactions especially across the Eastern Hemisphere. As a response to the tropical forcing, twin upper tropospheric anticyclones redeveloped across the Indian Ocean. Poleward directed Rossby wave energy dispersions (RWDs) from the anticyclones, interacting with midlatitude wavetrains, resulted in the formation of anomalous twin upper tropospheric west central Pacific Ocean cyclones. This evolution was a re-invigoration of the zonally asymmetric wave 0/1 of La-Nina tropical circulation anomalies observed since at least early October. There was subsequent equatorial moist convective development forced by the twin cyclones, and even a weak westerly wind episode, leading to the above mentioned trade wind interruption. Leaving Tropical Cyclone (TC) Dolphin in the wake, the west Pacific Ocean trades are resuming and convection is disorganized.


Through 11 December the WB (2009) measure of the GWO had ~1 sigma projection in octant 1 of phase space. However, this data point is along a recent trajectory having a magnitude of 3 sigma at times. Making use of this GWO variation along with the 250mb snr psi composite anomaly plots (phases 7-8-1), this was one very important consideration to anticipate several weeks ago (before the models and official forecasts) the on-going retrogression of PNA circulation anomalies leading to a western USA trough. Additionally, the excursion toward “high AAM” has been the largest this year, and part of a trend to increase global westerly wind flow since March. Identifying the latter was one of my reasons when I suggested several months ago that while boreal cold seasons 2007-08 and 2008-09 may have similar circulation characteristics, an important difference may be greater zonal mean subtropical westerly wind flow this winter. So far, this speculation has been correct.


Global relative AAM has dipped to slightly below the R1 data climatology while its tendency remains weakly negative. Recent significant anomalous zonal mean westerly wind flow in the subtropical atmospheres has largely been removed through frictional dissipation especially across the North Pacific Ocean. Poleward fluxing of AAM with maximum divergence ~40-45N has continued since late November, and zonal mean anomalous easterly wind flow is getting re-established ~30-40N (5-10m/s at 200mb). The latter are actually part of an equatorward shift. Finally, the global mountain torque is ~minus 20 Hadleys while the global frictional torque may soon become positive (see plots for zonal mean contributions). The point, these and other components of the earth-atmosphere angular momentum budget that contribute to the WB (2009) measure of the GWO suggest a “resurgence of La-Nina”. However, I think it is unlikely to see the 2-3 sigma global La-Nina situations like that observed boreal spring 2008.


Phase 1 of the GWO 250mb snr psi composite anomaly plot best represents the extratropics. I still do think coupling in ~GWO and MJO phase 3 (La-Nina) is a possibility during the next few weeks, with perhaps variations in ~phases 3-5 for several weeks going into 2009. Loosely that translates to central/eastern Pacific Ocean ridging with western and central USA troughs. Of course, shifting around of anomalies across the PNA sector will occur due to unpredictable “synoptic noise/interruptions” (i.e.; for example, western ridge/eastern trough from time to time). Weather ramifications (should be easily understood by now), including the elevated risk for high impact events, can be seen from the corresponding snr composite anomaly temperature and psi plots.


The role of the anomalously warm Australian and southwest Pacific Ocean SSTs for the USA and globally will clarify (seasonal cycle) during the next several weeks. Typically the 29C and greater SSTs become “covered” with intense moist tropical convection starting around early January. Whether or not there will be a resumption of coherent eastward shifts of tropical forcing projecting onto bona fide MJOs is unclear. Speculation suggests a rendition of our La-Nina like state will continue through at least JFM, but with situations having anomalous subtropical jets and possibly even episodes of strong East Asian/North Pacific Ocean jets slamming the USA west coast.


Internationally, the focus for intense to severe tropical thunderstorm activity is probable to continue across the Eastern Hemisphere centered ~100-120E the next few weeks (shifting slowly south). Locations to be impacted include much of Indonesia and northern Australia. At least climatologically intense diurnal thunderstorm activity is likely for tropical South America and South Africa. In fact, the “La-Nina side” of the GWO/MJO OLR snr composite anomaly plots suggests enhancement shifting toward southern and western Brasil with time, while suppression may occur across the “Nordeste”.


The tropical cyclone hazard for both the west central Pacific Ocean (both sides of the equator), and the Indian Ocean/Australian basins is unclear. However, the greatest risk may be in the region of the South Indian Ocean toward Madagascar week-1 then shifting into the region of the northwest coast of Australia week-2 (TC Dolphin understood). Please see the latest official tropical cyclone forecasts for all basins.


I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide. For instance, anomalous cold Arctic air is finally building up in both Siberia (surface temperatures ~minus 70F) and western Canada. Arctic air from western Canada is plunging into the Northern Rockies as I type.


Appendix


Links to CPC and PSD ENSO discussions:


http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml


http://www.cdc.noaa.gov/people/klaus.wolter/MEI/


The following is a link to information about the stratosphere and other nice monitoring tools:


http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html


The following is a link to NCEP model verifications (surf around for lots more)


http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html .


The following is a link discussing recent global weather and related events:


http://www.wmo.ch/pages/mediacentre/news/index_en.html


These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.


The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the
following link:


http://www.cdc.noaa.gov/map/clim/wb08_revised_final.pdf


In addition to the subseasonal snr composite anomaly plots, we hope near real-time discussions with “weather maps” will become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook! I plan on posting a discussion the weekend of 19-21 December.


Ed Berry

Saturday, December 06, 2008

It is now “Weeks 2-5”; USA High Impact Weather Likely

The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”


Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.


http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml


The 91-day signal to noise ratio (snr) anomaly composites are again being updated daily. There are still some map room issues that will hopefully be resolved soon. WB (2009; likely not to be published until next year), part-1 of a 2 part paper where the GWO is formally introduced, is in press for MWR publication. There is a link in the Appendix to download the manuscript.


Please remember that these discussions are part of an experimental effort involving linking weather and climate. Until this effort is formalized at the national level, many important scientific issues we are easily well aware of cannot be addressed. Stated another way, it is nearly impossible for me to talk about “everything” in these postings, including offering attribution to unpredictable noise. Plans are moving forward to have a one-day workshop on the WB (2009) GWO concepts during February 2009 in Boulder. Stay tuned for details.


Like a broken record, the spatial pattern of global SSTs remains entrenched. There is a strong negative phase of the PDO (extratropics have a role) and the central and eastern equatorial Pacific Ocean has weakly responded to La-Nina. In fact, per latest TAO buoy data, negative subsurface anomalies ~minus 1-3C are present at roughly 150m depth east of 160W. The latter are similar to a year ago. Although recently weakened (more said below), strongly enhanced trades from the equatorial Pacific Ocean to Indonesia have been contributing to the cooling for nearly 2 months.


The warmest SSTs globally extend from north of Australia into the southwest Pacific Ocean, with totals ~29-30C and anomalies 1-2C. These SSTs have cooled during the last few days. Meanwhile, the Indian Ocean has been warming with totals nearing 29C and anomalies roughly plus 0.5C. There are several issues with these SSTs, and I hope to address a few below.


http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html


http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html


http://www.pmel.noaa.gov/tao/jsdisplay/


http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)


http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18).


http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif


The wind and convective signals are still out of sync (discussed in last 2 postings), and the dynamics as explained by WB (2009) measure of the GWO is “calling the shots”. The MJO signal is weak, in octant 4 of WH (2004) phase space leaving in the interannual component. Additionally, just as the La-Nina like global atmosphere has been forcing much of the tropical oceans for nearly 2 months, the extratropics have been forcing the tropics for at least the past couple of weeks. I can only wish that I could stop writing right here.


Moist tropical convective forcing has been getting better organized in the region of western Indonesia during the past week, currently centered ~0/100E per full disk satellite imagery. There is some frontal activity defining the SPCZ over those warm South Pacific waters while thunderstorm activity has been on the wane across tropical South America. Finally, activity is increasing across South Africa and starting to spread into the southwest Indian Ocean.


The Eastern Hemisphere tropical forcing has been evolving through a combination of more rapid westward shifting elements forced by the extratropics over the last couple weeks, along with slower processes involving consolidation. The latter have also involved westward shifts from the west Pacific Ocean particularly north of the equator. Regardless of the details, the concentration of moist tropical forcing into the region of ~80-120E particularly since mid-November is consistent with La-Nina. The WB (2009) measure of the GWO considers these types of behaviors.


The Western Hemisphere enhancement during the last ~2 weeks especially across tropical South America is relatively “easy” to link to the wind signal. In other words, monitoring animations of daily mean upper tropospheric vector wind anomalies one can follow Rossby wave energy dispersions (RWDs) through the extratropical and subtropical atmospheres enhancing regions if tropical rainfall. Loosely, there is some signal of these RWDs in the 250mb snr psi composite anomalies for GWO phases 6-7. However, I want to focus on the GWO and not offer attribution to “other things” using a means that is inefficient.


Since September, there have been 3 circuits in phase space of the WB (2009) measure of the GWO (recent two ~3 sigma), each succeeding event seemingly making a larger excursion toward “high AAM” having periods of roughly 30 days. The dynamical processes, loosely involving first poleward AAM transport by the eddies (through RWDs; the early October situation most robust) and then “responding” surface torques, have worked to increase global westerly wind flow anomalies. For example, during mid November RWDs from the anomalous upper tropospheric Dateline twin cyclones placed the wicked ridge from Hell along the USA west coast. Subsequently, there was an enhancement of the surface easterlies increasing the global frictional torque. Much of the global westerly wind flow anomaly has been in the equatorial and subtropical atmospheres having zonal mean magnitudes ~5-10m/s at 200mb.


As discussed in WB (2009), the GWO is an independent mode of subseasonal atmospheric variability. This boreal autumn may be a “clinic” demonstrating that to the “non-believers”. I think the September and October variations may have been “internal” to the extratropics (got to keep this simple!), while the most recent and on-going event is starting to involve the tropics (recall the above about the convection). Having my reasons, I think the seasonal cycle linked to the southward shift of zonal mean Northern Hemisphere westerlies is partly responsible. The latest evolution from phases 4-5 to 8 in GWO phase space has taken more than 2 weeks, much slower than the past two. The extended jet from East Asia ~25 November was a synoptic response. Put another way, we may finally be starting to see evidence that the wind and convective signals are coupling and that presumably may also be the case for the tropics and extratropics.


About 10 days ago, global relative AAM was ~2 standard deviations above the R1 data climatology (GWO1), the highest in about 2 years. Updated through 4 December, with minor variations both the global friction and mountain torques were strongly negative. The recent explosive north central Pacific Ocean cyclonic baroclinic development did a lot to contribute to a negative zonal mean frictional torque of ~2 Hadleys at 30N. This is an example of how the atmosphere eliminates anomalous westerly wind flow. The negative global mountain torque has involved an East Asia component, a response to anomalous surface low pressure that I can link to intensifying Eastern Hemisphere tropical forcing per above. The ongoing cold air outbreak from East Asia will not go into the deep tropics, and thus I do not think there will be a strong positive mountain torque from the Tibetan Plateau, etc.


The above paragraph is intended to offer a quick attribution to the large negative AAM tendency (GWO2), ~ 30 Hadleys, that has been expected, observed 4 December (averaging periods understood). Relative AAM is approaching the R1 data climatology. Also, particularly across the Northern Hemisphere AAM is once again fluxing poleward, with the maximum divergence ~40N.


Animations of upper tropospheric daily mean vector wind anomalies show twin tropical anticyclones getting better defined ~120E with downstream cyclones around the Dateline. While details are still complicated that will not be addressed here (ex., a well defined Northern Hemisphere positive phased subtropical wave train (Branstator (2002) is present), our zonally asymmetric wave-1 pattern of tropical circulation anomalies is returning. Phases 4-5 of the WH (2004) MJO snr psi composite anomaly plots reasonably depict tropical circulation anomalies.


I think the GWO signal is coming back into the Eastern Hemisphere as I type. Tropical convective forcing is probable to expand and intensify across much of the Indian Ocean and western Indonesia during the next 1-2 weeks. As the wind and convective signals sync up, global relative AAM is likely to decrease (well?) below the R1 data climatology. It is reasonable to offer that a superposition of circulation anomalies depicted by phase 3 (typical of La-Nina) of both the MJO and GWO snr psi composite anomaly plots may be observed by ~week-3. During this evolution the surface trades from east of Indonesia to the equatorial Pacific Ocean are likely to again increase. That may persist and possibly further cool the Nino SSTs.


The current retrogression of extratropical circulation anomalies across the Asia-North American sector, expected for at least the past 2-3 weeks (see past discussions), is directly tied to what appears to be the wind and convective signals syncing up. The relatively repeatable GWO variations have presented opportunities to offer reasonably successful statements of probabilistic predictions.


Typical during an orbit through phases 7-8-1-2 of GWO phase space, all global numerical models and their ensembles have struggled with their circulation forecasts, in this case capturing the on-going PNA retrogression. For example, about 2 weeks ago nearly all models were predicting the ridge from Hell to persist along the USA west coast "until further notice (UFN)”. The latter provided “motivation” for the discussion I wrote on 22 November. I again must emphasize not to rely on the numerical models alone when making subseasonal forecasts! A dynamical weather-climate linkage framework (ex., WB (2007, 2009)) that utilizes real-time data and diagnostics is a must as part of a complete more sophisticated forecast process.


Models have now generally caught on to what some would describe as a large amplitude reverse/negative phase of the PNA teleconnection by week-2. I think it is probable this situation may persist the rest of this month per above. As discussed in past postings, particularly weeks 2-4 there should be episodes of significant precipitation along the USA west coast associated with “cold” digging troughs, leading to an active southwest flow storm track across the Plains. Weather ramifications, including high impact blizzard conditions and intense thundersnow in the cold sectors and severe local storms in the warm sectors of synoptic lows, should be understood. Arctic air may become entrenched from the central and northern Rockies into the Plains while summer-like conditions are experienced over portions of the Deep South.


Whether or not JFM 2009 has similarities to JFM 2008 is unclear. At some point the warm southwest Pacific Ocean will become convectively active. Perhaps there may be a resumption of coherent (truncated?) MJOs and accompanying circulation shifts. I do have my suspicions, and stay tuned.


Internationally, locations focused on western Indonesia and generally from 80-120E along the equator appear to be in for an extended period of intense to severe thunderstorm activity. This enhanced rainfall will impact northern Australia with the seasonal southward shift. The tropical cyclone risk is unclear; however, as convection intensifies across the Indian Ocean, the risk for cyclones impacting Madagascar may increase. The southwest Pacific Ocean islands are likely to have enhanced rainfall at least week-1, and that whole region will be a “wild card” UFN. Generally seasonable tropical rainfall should return to Brasil and South America weeks 1-3, while enhanced thunderstorm activity occurs across South Africa at least week-1.


Please see the latest official tropical cyclone forecasts for all basins. I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide. For instance, there is an intense cold air outbreak currently impacting Japan.


Appendix


Links to CPC and PSD ENSO discussions:


http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml


http://www.cdc.noaa.gov/people/klaus.wolter/MEI/


The following is a link to information about the stratosphere and other nice monitoring tools:


http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html


The following is a link to NCEP model verifications (surf around for lots more)


http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html .


The following is a link discussing recent global weather and related events:


http://www.wmo.ch/pages/mediacentre/news/index_en.html


These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.


The WB (2007) paper on the GSDM has been published in the February issue of MWR. The first of a two-part paper, where WB formally introduce the GWO (WB (2009)), has been accepted for publication MWR. A pdf of the in press version can be downloaded from the following link:


http://www.cdc.noaa.gov/map/clim/wb08_revised_final.pdf


In addition to the subseasonal snr composite anomaly plots, we hope near real-time discussions with “weather maps” will become a routine part of the ESRL/PSD GSDM web site sometime soon. Part-2 of our GWO paper will discuss the latter. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook! I plan on posting a discussion the weekend of 13-14 December.


Ed Berry