Getting What was "Expected"???

Continuing data issues limit a complete discussion of the current global weather-climate situation. I will only be able to speculate about components involving the earth-atmosphere AAM budget (torques, transports, etc.) as well as the GWO.

Global tropical SSTs have been relatively “steady state” since my posting nearly 10 days ago. Very warm ocean waters (high heat content) extend from north of Australia into the South Pacific, having anomaly magnitudes in excess of 2C and totals greater than 30C especially ~10S. The latter have been shifting slowly south with the seasonal/annual cycle. SST anomalies remain well below normal in all Nino regions (~160E-South America), with magnitudes less than minus 3C extending to depths ~100m east of 140W. The weak oceanic Kelvin wave continues to propagate east at around 150m depth per latest 5-day averaged TAO buoy data having reached about 150W. Finally, monitoring suggests the convectively suppressed Indian Ocean is slowly warming while much of the tropical and North Atlantic Ocean remains warmer than climatology.

So what is the point to giving a quick overview of the global tropical SSTs, at least for this posting (see http://www.pmel.noaa.gov/tao/jsdisplay and other relevant links for details)? Although I can just offer speculation here not having objective data sets, the on-going circulation response cannot be attributed to El-Viejo alone. In fact, this is often (always?) the case where the ENSO variability is only a component. Simple monitoring of the global circulation for the last several years in itself demonstrates that Eastern Hemisphere/west Pacific Ocean warm pool SSTAs have had significant impacts onto the global circulation (including right now).

Strong-severe tropical convection currently extends from the central equatorial Indian Ocean east-southeast to just north of Australia into a southwestward shifted South Pacific Convergence Zone (SPCZ). The core of this tropical convective forcing is ~10S/130E, also shifting south with the seasonal cycle. Suppression exists across the region of the equatorial date line. OLR anomaly magnitudes are in excess of 50 W/m**2.

There is a significant MJO component to this tropical forcing, located in phase 5 per WH(2004) phase space plots updated through 29 December. However, as suggested in my last posting, atmosphere-ocean coupling involving the very warm SSTs north of Australia appears to have been in progress for at least the last week. Not only has the WH(2004) MJO signal slowed down, other plots such as Hovmollers of OLR/A and velocity potential suggest a recent stationary signal. However, I do think a relatively fast MJO dynamical signal will emerge into the Western Hemisphere during the next few weeks. Again, there is HUGE uncertainty about timing and other details.

Animations of upper tropospheric daily mean vector wind anomalies show the classic expected response given the spatial distribution of the tropical forcing discussed above. Twin subtropical anticyclones (cyclones) are centered ~110E (~date line) with anomaly magnitudes in excess of 40m/s for the equatorial Pacific westerlies. There have been several episodes of meridionally oriented Rossby wave energy dispersions (RWDs) into the extratropics tied to circulation features such as these for the last several weeks. For the PNA sector these RWDs have led to robust cyclonic circulation anomalies around Alaska poleward of a central Pacific Ocean anticyclone. Several strong troughs have impacted the USA west coast on into the Plains as a result, accompanied by high impact weather events including ice and snowstorms.

For the Asian-North American extratropics, this response fits ~phases 3-4 for the WB(200?) DJF MJO composite (a component of the GWO; publication is planned), but it is somewhat different for the tropics. The point is there are highly complex non-linear dynamical feedback processes involving the extratropics and particularly the synoptic eddies going on. For instance, during the last ~5 days a fast baroclinic wave packet tied to presumably a positive East Asian mountain torque (explained by the GWO) has been aimed at North America. This will lead to the west coast ridge amplification and anomalous cold for the central/eastern USA the models have been predicting. However, this is a transient event and when updated, all that is probable to be observed is at least one circuit around GWO phase 3 (old GSDM Stage 1).

The East Asian jet extension as a response to the positive mountain torque will strongly impact the USA west coast by the end of this upcoming week per all models. As shown by DJF GWO and MJO composites WB are working on, the MJO itself does not generate enough extratropical westerly wind flow to allow the East Asian jet to impact the USA west coast. A strong positive East Asian mountain torque needs to be involved, on average.

Uncertainty is huge where the global circulation goes from here, especially when lack of resources denies me much needed data sets (latter speaking for myself). I think GWO phase 3 best describes the current global weather-climate situation. As long as the tropical convective forcing stays coupled north of Australia, I do not think this subseasonal base state (La-Nina understood) will change. However, these coupling events have recently lasted ~2 weeks, and several tropical cyclones are developing/occurring with the convection. As mentioned above, I do think a MJO component will continue into the Western Hemisphere during the next several weeks. Support for this notion are an intense westerly wind burst (WWB) north of Australia heading into the South Pacific, as well as the strong upper tropospheric equatorial westerly wind flow anomalies also mentioned above. Whether or not this WWB will be close enough to the equator (may be too far south) to generate another downwelling oceanic Kelvin wave is unclear.

Similar to about the first half of December 2007, I suspect any larger GWO orbit through phases 5-8 that may occur ~mid/late January 2008 will be relatively fast. Hence, for the lower 48 states, weeks 2-3 may have similar weather to that observed during much of December. Delivery of Arctic airmasses will be limited as long as large cyclonic circulation anomalies persist near Alaska. Nevertheless, particularly given January climatology, extreme winter weather may occur from the west coast-central/southern Rockies into the Plains. Heavy rainfall and even severe local storms may be a concern for especially the lower Mississippi and Ohio Valleys. Should phases 5-6 of the GWO occur, say by ~ week 3, Arctic air may spill into the USA. Predicting the latter involves daily monitoring; accept it!!! Finally, on more of a seasonal time scale, “bucking” the La-Nina composite signal, my subseasonal monitoring tells me not to be so pessimistic in regard to dryness across the southwestern states into the Central/Southern Plains for JFM. In fact, precipitation anomalies for portions of California through Desert Southwest and Central/Southern Plains may end up being positive for JFM if on-going feedback processes do not change.

Internationally, heavy-severe rainfall/thunderstorms will be a concern for Eastern Hemisphere areas already discussed above for weeks 1-2. These impacts may spread into the South Pacific Islands and eventually tropical South America ~ weeks 2-4 (could be sooner). Yes, the sprit of “Gabrielle” is currently festering west of Africa.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH(2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will attempt another discussion next weekend.

Ed Berry

Typical El-Viejo??? - Update

There has been no significant change to the distribution of global tropical SSTs since my 15 December post, particularly across the Indo-Pacific region. All Nino regions have well below normal SSTs ~minus 1-3C extending to at least 100-150m deep, flanked by the warm Pacific Ocean horseshoe. An oceanic Kelvin wave with anomalies roughly plus 1-3C continues to propagate east (~2.5 m/s) through the region of 180-160W at around 150m depth per 5-day averaged TAO buoy data. While much of the equatorial and southern Indian Ocean has cooled to less than 28C (anomalies ~minus 1-2C) due to recent moist convection, the very warm waters from north of Australia to the South Pacific Ocean remain. Totals in excess of 30C are common across the latter region.

The Eastern Hemisphere tropical convective forcing has become somewhat better organized during the last few days. Full disk satellite imagery shows this large region of intense anomalous and at times severe tropical rainfall extending from the Arabian Sea to a concentrated area over central Indonesia (~0/120E) into the South Pacific Ocean. Various monitoring tools indicate there have been several components contributing to this tropical forcing. However, as shown by the WH2004 phase space and coherent modes Hovmoller plots, there is a significant MJO contribution (currently MJO phase 3-4). My own back of the envelop phase speed calculation has this convective region shifting east at ~4-5m/s since early this month. I am expecting a roughly 1-2 week period of coupling to the very warm 120E-180 SSTs by early January, before a MJO signal in all likelihood propagates into the Western Hemisphere. Again, I remind the readers there is always LARGE uncertainty about timing.

The global circulation is very much La-Nina like, which can be thought of as an enhanced climatological base state. Global relative AAM is roughly 2 standard deviations below the R1 data climatology (through 18 December) having well above average zonal mean easterly wind flow anomalies across the equatorial and subtropical atmospheres. The GWO is essentially orbiting around phase 3 (old GSDM Stage 1). However, there are always issues of non-linear dynamical feedbacks involving the extratropical eddies. For instance, per animations of daily mean upper tropospheric vector wind anomalies, while twin subtropical anticyclones (cyclones) have become established ~100-120E (~date line), there has been strong Rossby wave energy dispersions (RWDs) into the global extratropics. These RWDs have been very fast (~30m/s) not only leading to the barrage of western USA troughs, but also feeding blocking structures over Scandinavia and very recently northeast Asia. The latter will lead to a build-up of bitterly cold Arctic across Alaska during the next few weeks.

A strong zonal mean poleward AAM transport signal has become evident around 30N during the last few days, with flux divergence from the subtropics and convergence ~35N. In addition to the eddies, this transport signal has also been adding anomalous westerly flow to the northern extratropics (including the North Pacific Ocean). My point is the appearance of an AAM transport signal such as this adds support (through exchange processes involving the surface torques) to the predicted PNA synoptic evolutions I discussed a week ago.

I think there will be ~couple roughly 10-day circuits around GWO phase 3 until early-mid January when a large push to GWO phase 5 (GSDM Stage 2) may occur. That would be most probable after the period of atmosphere-ocean coupling discussed above. An evolution through GWO phases 6-8 (GSDM Stages 3-4) is possible afterwards (~weeks 4-6). Should the latter occur, more significant precipitation for locations such as California and the Desert Southwest may occur.

Hence there is no change to the predictive insights I offered in my 15 December discussion. Several troughs riding a strong North Pacific jet stream (yes, this can happen during a La-Nina) will continue to impact most of the country through early January 2008. I do think it is probable to see large ridge amplification from the east Pacific/off the USA west coast into Alaska by ~mid January 2008. Interestingly, the ESRL/PSD week-2 ensemble mean of 500mb height anomalies suggests this possibility while the NCEP GFS ensemble mean does not. However, even though the week-2 models have been “all over the place” recently, I think there will be upcoming better agreement on this GWO phase 5 scenario. If this happens, severe Arctic air may impact the Plains and eventually the eastern USA by ~mid January, after possibly initially spilling into the Pacific Northwest.

Internationally, severe rainfall and thunderstorms are probable to continue across portions of Australia and Indonesia and even into the Southwest Pacific during the next couple weeks. The north and northeast coast of Australia may become vulnerable to tropical cyclones weeks 2-3. Europe should become active as the Scandinavian blocking breaks down while bitterly cold air even by Siberia standards dominates northeast Asia. Again, some of the latter airmass may plunge into the USA via western Canada by ~mid January 2008.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH2004 “convention”.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will not be able to post another discussion until late next weekend at the soonest.

Ed Berry

AAM Trend Still in Sync with the Financial Markets

I wish the upward trend in the USA financial markets a week ago would have continued this last work week. This makes me wonder if any statistically significant correlations exist between subseasonal-interannual atmospheric variability and the world markets. The former would be in regard to the GWO and MJO while the latter would relate to ENSO.

This posting only updates what I have been writing during the last few weeks. The spatial pattern of tropical SSTs across the Indo-Pacific sector is consistent with a mature La-Nina. Anomalies along the equator from 160E-South America remain negative with magnitudes at least minus 2.5C starting at 140W (per TAO buoy data). At depth these negative anomalies are at least 150-200m deep while comparable positive anomalies (~3C) remain in the region of the equatorial date line. The latter is a response to a deepening of the oceanic thermocline forced by a Kelvin wave initiated by the recent past MJO.

While the equatorial Indian Ocean has cooled during the last week from increased tropical convective rainfall, very warm SSTs are present from about the north coast of Australia to Indonesia into the South Pacific Ocean. SST anomalies are ~plus 1-2C from around 120E-180 south of the equator with totals generally in excess of 30C (86F). These very warm Eastern Hemisphere tropical SSTs will have an important contribution to the evolution of the global circulation during the next several weeks.

Per full disk satellite imagery tropical convective forcing has become very intense across the Indian Ocean centered ~5S/80-90E having OLRA less than minus 70W/m**2 per 3-day averaged BMRC plots. Compensating strong suppression exists downstream from Indonesia-date line. This forcing is tied to the MJO, with latest WH2004 plots projecting onto phase 3 due to RMM2 being strongly negative. For the time being, the MJO signal has stalled. The GWO (which also captures the circulation responses due to the MJO in addition to extratropical non-oscillatory forcing) has remained in-sync with the tropical convective forcing returning to the Indian Ocean. Phase 3 (old GSDM Stage 1) best describes the projection of the current global circulation onto the GWO. Anomalous trades from Indonesia-date line downstream from the convection are reinvigorating La-Nina.

About a week ago global relative AAM tendency crashed to ~minus 50 Hadleys (3-day average/R1 data climatology). As of 13 December this tendency did spike to ~minus 5 Hadleys with a large component coming from a renewed positive global frictional torque. The latter was ~plus 10 Hadleys, seemingly exhibiting a recent periodicity of ~60 days (consistent with the GWO). Strengthening trades throughout the global subtropics have contributed. However, global relative AAM has again become quite low ~minus 2 standard deviations with the redevelopment of intense zonal mean easterly wind flow anomalies (~5m/s at 200mb) throughout the global equatorial and subtropical atmospheres. Also helping to remove westerly flow from the atmosphere are the large north-south mountains, with the global mountain torque ~minus 15 Hadleys having a large component from East Asia.

Animations of upper tropospheric daily mean vector wind anomalies show the expected circulation characteristics per above. Twin subtropical anticyclones are getting better defined ~90-120E with downstream cyclones in the region of the equatorial date line. Westerly wind flow anomalies (~10-20m/s) are developing across the Western Hemisphere particularly across the Pacific Ocean. In fact, some of this upper tropospheric westerly wind flow is being directed toward the southwestern USA.

Zonally oriented rapid Rossby wave energy dispersions (RWDs) directed toward the USA emanating from the Indian Ocean tropical forcing have been a dynamical component to the recent stormy winter weather pattern across the country. Per EMC/NCEP web site visual verification of predicted NCEP/GFS week-2 ensemble means of 500mb height anomalies valid roughly the last 7 days verses observed did not capture the RWDs leading to the recent negative height anomalies across the Desert Southwest. The latter is not only a systematic bias issue, but also the inability of global models to accurately predict tropical convective forcing after about day 5. I speculate that numerical model performance at lead times greater than ~3 days may remain "unusually problematic" for roughly the next 1-3 weeks.

I suspect the GWO may exhibit one or two small roughly 5-10 day circuits around phase 3 (consistent with El-Viejo) before resuming its large orbit toward phase 5 (GSDM Stage 2) and beyond. The WH2004 MJO phase space plot will likely do the same before showing an eastward propagation signal once again. One reason I feel this way is that I think the Indian Ocean tropical convective forcing is likely to shift east-southeast toward the very warm SSTs north of Australia during the next few weeks.

Of course, as always there are large uncertainties about timing and synoptic details. However, I think it is probable for both the GWO and MJO to be in roughly phase 5 by early January 2008, as I discussed a week ago. The seasonal cycle will also have “its say in this matter”, since climatologically SSTs 29C and greater become covered with tropical convection during the first part of January. So, are we going to have a period of ocean-atmosphere coupling ~120E-180 south of the equator in about 3 weeks (with the onset of the Australian monsoon)? Are we going to see another decent GWO/MJO circuit afterwards? The answers to these types of predictability questions are unclear; however, I speculate yes.

A generally active weather regime is probable to continue for most of the country through at least the end of 2007. As I typed a week ago, the period from around Christmas-early January 2008 may be exceptionally stormy focusing on the Rockies and Plains in the presence of an Arctic cold air source. However, both coasts and Alaska are probable to have impacts from our active regime. I also think it is probable to see strong ridge amplification (greater than climatology) from just west of North America-Alaska by mid January per above reasoning. The latter would suggest an anomalous cold regime from east of the Rockies-east coast with the possible exception of the Deep South.

Internationally, the main tropical cyclone hazard should shift from the South Indian Ocean (Bay of Bengal understood) toward the region of Australia and eventually southwest Pacific Ocean weeks 2-3. Surface westerly wind anomalies ~10-15m/s in that region certainly support this notion. By that time the Australian monsoon should be on-going. Indonesia and even the Philippines are also probable to have possibly severe rainfall events by weeks 2-3. I would think the current Scandinavian blocking pattern should break down by week 3, possibly retrograding into the North Atlantic Ocean. In any case, cool/wet conditions seem probable for much of the Mediterranean region through week-2. Arctic air will continue to build up and expand across particularly Siberia as well as Alaska and much of Canada during the next few weeks. Finally, I hope the spirit of Gabrielle will rest for the warm North Atlantic basin until boreal summer 2008.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH2004 “convention”.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I may not be able to post another discussion for at least a couple weeks; stay tuned.

Ed Berry

AAM Crashing (like the recent finacial markets)

Yes, there has been a rebound in the USA stock markets recently especially last week. I hope this trend continues.

There is no change to my reasoning from a week ago; hence some brevity is appropriate for this discussion. The spatial distribution of global tropical SSTs remain essentially the same, with minus 1-3C anomalies along the equator from 160E-west coast of South America. Warmest SSTs across the Indo-Pacific sector are located from the north coast of Australia to Indonesia with totals in excess of 30C in places. Increasing trades from the equatorial date line into the west central Pacific Ocean (anomalies ~5-10m/s) may add some re-invigoration to the on-going El-Viejo.

An oceanic Kelvin wave was generated by the westerly wind burst forced by the recent MJO. Per latest five-day averaged TAO buoy data anomalies in excess of 3C at ~150m depth in the region of the equatorial date line are associated with this Kelvin wave. The impacts of this and additional Kelvin waves onto our basin wide moderate cold event (in terms of SSTs) is a monitoring issue. However, I speculate that the early stages of a transition to El-Nino are in progress, especially given the biennial character of ENSO over the last several years.

The dynamical signal with the MJO is quickly returning to the Eastern Hemisphere. In fact, a back of the envelope calculation from near equatorial velocity potential Hovmoller plots gives me a phase speed of ~30m/s as this signal propagated through the Western Hemisphere. Interactions with the extratropics along with decoupling between the atmosphere and tropical convection allow for these kinds of fast phase speeds as the MJO response moves through the Western Hemisphere.

Full disk satellite imagery shows tropical convective forcing rapidly increasing across the equatorial Indian Ocean during the last several days, with enhanced rainfall still present across portions of tropical South America and South Africa. WH2004 phase space plots support this observation, suggesting that the MJO signal is currently in phase 1. Animations of upper tropospheric daily mean vector wind anomalies not only show twin anticyclones developing in the region of the Indian Ocean, but also easterly wind flow returning to the equatorial atmosphere. In the zonal mean equatorial wind anomalies are already negative, and what is left of the westerly wind flow anomalies has propagated poleward well into the subtropics and midlatitudes of both hemispheres (through eddy feedbacks).

The combination of frictional dissipation, eddy dynamical processes and the tropical forcing returning to the Eastern Hemisphere is rapidly putting the brakes on the global atmosphere (and speeding up the earth shortening the length of day by a few milliseconds) as I type. In other words, easterly wind flow anomalies are quickly being added back to the equatorial and subtropical atmospheres creating a momentum sink. Given our La-Nina base state this circulation response was expected once the MJO returned to the Eastern Hemisphere.

Per ESRL/PSD AAM plots updated through 6 December using the R1 data climatology, 3-day averaged global relative AAM tendency is at least minus 40 Hadleys. The surface torques as well as the Coriolis torque are contributing to this big AAM tendency. Actual global relative AAM will crash very soon, if it is not already doing so. The expected large circuit of the GWO is occurring, currently entering phase 1. During big subseasonal events such as what has been occurring over the last several weeks, both the MJO and GWO are probable to be in similar phases.

My feeling is that another large GWO orbit and respectable MJO are probable during the next ~50 days. Of course, uncertainties about timing, synoptic details, etc., are always an issue. The GWO should circuit to phase 3 (old GSDM Stage 1) by the end of week-2 and perhaps phase 5 (Stage 2) by the end of week-4 (~ 5 January 2008). Thus my USA outlook from a week ago remains the same. I think there will be a bit of a respite from the currently active western/central USA winter regime week-2 as troughs initially deepen along/off the west coast during that period. Most week-2 ensemble means now show this response. While the USA west coast (and Alaska at times) receives several rounds of possibly intense/severe precipitation during week-2, the rest of the country east of the Divide should be milder. More “Kona Lows” may also be probable for Hawaii.

Starting around Christmas and continuing well into January a cold and active regime appears probable especially if the tropical forcing initially couples to the warm SSTs north of Australia. Troughs would again be favored across the western states with an active southwest flow storm track across the Plains. Sparing details, this pattern may shift ~10-20 degrees of longitude farther east during mid-late January bringing possibly intense cold for particularly the northeast states while extending back into the central USA. At that time ridge amplification may occur from just off the USA west coast into Alaska.

Internationally, an increasing tropical cyclone hazard across the South Indian Ocean especially by week-2 is probable. Locations from the Philippines into the west central Pacific should enjoy some quieter weather at least week-1. Cold Arctic air will continue to build up across Siberia as well as Canada during the next several weeks.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH2004 “convention”.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion around next weekend or early week-2.

Ed Berry

Subprime Woes for the AAM Budget?

Other titles for this posting might have been, “The Horrors of Making Weather Predictions”, and “Spinning Wheel”. The latter is a song by Blood, Sweat and Tears a number of years ago, and it had a lyric something to the effect of, “what goes up must come down”. The point is we are in a global circulation state that is extremely difficult to understand (and write about), let alone forecast it. In other words, stochastic forcing rules. Hey, yet another title to use for later discussions. I offer below what some would simply view as an opinion (worth something, anyway).

The spatial distribution of equatorial and tropical SSTs across the Indo-Pacific sector remains consistent with a mature La-Nina (a.k.a. a cold event and El-Viejo). Negative anomalies are present in a wide equatorial band (~ +- 10 deg latitude of zero latitude) from 160E-west coast of South America, with anomalies lower than minus 2C in places extending to depths ~150m. Per 5-day averaged TAO buoy data ending 30 November, anomalies even less than minus -3C were observed ~150m/140W. Also noteworthy is that west of 160W a warm anomaly of ~plus 3C has recently developed at 150m. More said below about the possible importance of this feature.

The large scale character of these below normal El-Viejo SSTs was exasperated by a recent trade wind surge. Positive SST anomalies have become well defined from ~20S/180-north of Australia into the equatorial Indian Ocean, the latter a region of convective suppression during the last few weeks. Contributing to these warm SST anomalies has been the southward shift with the seasonal cycle, having SST totals in excess of 30C in places. Much of the equatorial and northern Atlantic Ocean basin remains above average, as does the North Pacific Ocean basin. In fact, there is still some signal of the warm extratropical horseshoe pattern of SSTs across the Pacific Ocean. Recent East Asian jet extensions and associated cold outbreaks and accompanying baroclinic storm developments across the North Pacific have led to cooling centered around the extratropical date line. The latter is an example of the atmosphere forcing the ocean, typical for the extratropics.

A strong signal of the MJO has emerged during the last several days. This was not expected by me, even though various statistical predictions of the WH2004 phase space diagrams did indicate this possibility. One reason I disagreed (and there were others) is that it is somewhat atypical during a moderate-strong La-Nina to have a coherent eastward propagating MJO globally. I should not be surprised given all the other “craziness” I have had to discuss in these postings during the last couple years. For example, behaviors I have termed as “The New World Atmosphere” and “Nemesis”.

The eastward propagation initiated ~80E along the equator during about mid-October. An intense tropical convective flare-up occurred ~140-160E during roughly 9-26 November, associated with the MJO signal along with extratropical forcing. Currently, the moist convective signal is centered ~15S/160W, but with other convection increasing across tropical South America and Africa. Full disk satellite imagery and coherent modes Hovmollers support this observation. My back of the envelop phase speed computation gives me ~3-4m/s eastward movement for the convective signal during about the last 45 days. Interestingly, there was a weaker but significant tropical convective flare-up ~150E during mid-late September, which is also on the time scale of ~50-60 days. The point is perhaps greater attention should have been paid to those “New World Atmosphere” SSTs across the west central Pacific Ocean.

The strong MJO projection onto the WH2004 RMM phase space plots has been coming from the second EOF, RMM2. Contributions to this ~3 standard deviation signal have been from the convectively suppressed Indian Ocean (positive OLRA) along with the equatorial vertical wind structure. The statistical RMM tools indicate the MJO dynamical signal to return into the equatorial Indian Ocean by the end of week 3. Hey, I have to go with it.

Now comes the portion discussing the AAM budget and GWO. The earth-atmosphere budget is about as complicated as it gets; however, I do think I can make some sense of it. I want to be relative brief about it.

Tied to the ~160E tropical flare-up discussed above along with a largely Southern Hemisphere forced friction-mountain torque (yes, the Northern Hemisphere also helped out) index cycle, a non-trivial amount of westerly wind flow was added to the atmosphere. Since early November ~3 AMUs was added to the global circulation, focusing not only across the equatorial regions, but also the northern and southern midlatitudes, in terms of the zonal mean. The midlatitude contribution was a response to eddy feedback dynamics that much research still needs to be done to understand it. There has been a recent peak of global relative AAM to slightly above the R1 data climatology. Just as the low AAM base state observed much of boreal autumn was an extreme weather event, this sudden increase was also the same.

The GWO presents this signal nicely, very weakly in the phase 7 (legacy GSDM Stage 3) plane through 28 November (5-day averaged). Even though the GWO projection is near zero, the variation is also a 2-3 standard deviation event. So, we have experienced 2-3 sigma events of both the GWO and MJO. The GWO signal can be seen in terms of broad zonal mean westerly wind anomalies from ~30N-30S with magnitudes ~5m/s. A true MJO would be more equatorially confined before propagating poleward. The punch line to all this will be to see if global relative AAM goes down as fast as it came up during the next few weeks. Now you know where analogies to the recent subprime woes of the financial markets come in, etc.

Currently the global surface torques have become weakly negative (through 29 November) as seen by lowering mean sea level pressures along north-south mountain ranges and anomalous surface westerly wind flow across the tropical and extratropical Pacific Ocean. The latter represents frictional dissipation of the westerly flow. In fact, a strong westerly wind burst at ~150E accompanied the MJO convection discussed above, and I think a down welling oceanic Kelvin wave may have been initiated leading to the subsurface warming also mentioned above.

The AAM transport signal is incredibly complicated. However, there is a decent poleward transport signal at centered ~45N and 50S (roughly 10 Hadleys for Northern Hemisphere). There is evidence that these transports (flux divergence of AAM transport) are leading to meriodional propagation of zonal mean zonal wind anomalies. For instance, zonal mean anomalous easterlies (tied to La-Nina) are shifting into the midlatitude atmospheres while the equatorial westerlies also come off. The midlatitude westerly anomalies are also shifting poleward. Again, there is strong inter-hemispheric symmetry of both zonal mean and regional-scale circulation anomalies due to the strong tropical forcing.

Cutting to the chase of this mess, should the tropical convective forcing shift into the Indian Ocean/Maritime Continent during weeks 2-3, while anomalous ridging may be favored at the higher latitudes, anomalous westerly wind flow may be probable from the subtropics-lower midlatitudes. The latter would be a response to anomalous easterly wind flow anomalies returning to the equatorial regions of the atmosphere (more said below).

Animations of fields such as upper tropospheric daily mean vector wind anomalies present one of the best Rossby wave energy dispersions (RWD) across the PNA sector I have seen in a while. Linked to twin subtropical anticyclones along/west of the date line, a low-high-low-high pressure great circle arc including the deep western USA trough can be seen 1 December 2007. A large anticyclone is also bursting into the Arctic, which could help build up more bitterly cold air. Wind anomalies in excess of 50m/s have occurred with this RWD during the last several days. This situation serves as an example of an extreme synoptic weather event linked to the slower processes involving both the GWO and MJO per above. Another point is that we have experienced an extreme event of subseasonal atmospheric variability that already has and will impact multiple time scales until further notice. For instance, are we beginning the slow process of transitioning from El-Viejo to El-Nino?

Let’s move onto insights for weeks 1-4. I can only wish for the day others can observe and appreciate the variations from the GWO (GSDM) perspective that we try to share. As stated above, phase 7 of the GWO best describes the current weather-climate situation. Any predictive information I offer here is likely to going to be “wrong” anyway (low confidence, seriously), so I may as well “go for it”. Again, stochastic forcing rules, and any objective prediction schemes will likely suffer more than usual during the next few weeks.

Most models already suggest some form of amplification weeks 1-2, including the possibility of Plains storm development ~10-14 December. This is a response to the likely collapse of the strong North Pacific jet. In any case, my feeling would be expect a situation of a deep east Asian trough-central/east Pacific ridge (into Alaska and polar latitudes at times) leading to at times an anomalous trough focused across the western/central USA by weeks 3-4. That option would be an opinion to respect should AAM crash and the GWO strongly circuits to ~phase 3 (old GSDM Stage 1) particularly if westerly flow remains strong across the subtropics. Ramifications for the USA may be sporadic episodes of “winter” weeks 1-2 (Pacific Northwest wetness, cold across the northern states, etc), followed by a significant cold and wet regime weeks 3-4. The most intense cold and storm track activity by that time may focus on the Rockies and Plains; however, locations such as the northeast states may be impacted as well. I think other USA concerns are apparent.

Internationally, in addition to an increasing tropical cyclone hazard across the South Indian Ocean weeks 1-2, there should be some concern for this hazard across the South Pacific Ocean paradise islands as well. Much of Europe is likely to remain active while portions of tropical South America get beneficial rainfall. Finally, at least seasonable cold is probable for Siberia (to come into the USA by around Christmas?).

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH2004 "convention”.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion around next weekend or early week-2.

Ed Berry

Postponed again

It is unlikely I will write another complete discussion for this Blog until next weekend at the soonest. Briefly, the change to the USA cold regime I discussed roughly a week ago is generally on track. However, globally westerly wind flow throughout the atmosphere has increased dramatically over the last 7-10 days. Global relative AAM is currently near to slightly above average, up ~3AMUs. The eastward shift of tropical convective forcing to ~0/160E, strong positive surface torques and suspected eddy feedbacks have led to the rapid increase in westerly flow. Largest zonal mean contributions have been from the equatorial and midlatitude atmospheres of both hemispheres.

Phase 5 of the GWO best describes the global weather-climate situation. I think we are in the process of a having a large circuit of the GWO. A wind signal from the MJO is contributing. An important monitoring issue will be to see how far west the tropical convective forcing redevelops across the Eastern Hemisphere during the next few weeks. I speculate that the current extension of the East Asian jet will "break through" the eastern Pacific ridge ~week 2, followed by re-amplification of existing PNA circulation anomalies ~20-30 deg of longitude farther west weeks 3-4.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH2004 “convention”. In addition, the GWO plot does not have the ENSO signal removed.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment composite maps, composite signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post a complete discussion next weekend.

Ed Berry

El-Viejo Update

This posting will be short. One motivation for attempting to “get something out” is my concern for a change to a significant to perhaps severe winter regime focusing on the USA Rockies and Plains by week-3 (roughly the first week in December). Of course, there are always timing issues, and the above statement is made from my conservative perspective when it comes to making any kind of weather predictions.

The same weather-climate issues discussed on my 10 November, 2007, posting remain. The dominate tropical convective forcing has shifted east to ~0/140E during the past week. This was more of an eastward push than I expected a week ago; however, not surprising. Several tropical cyclones have been and still are occurring across the Indo-Pacific region. I am optimistic that the Bay of Bengal tropical cyclone season is “over with”. The low confidence amplification across the Asian-North American sector I also offered a week ago is in progress as I type. Numerical ensemble prediction schemes have been “playing catch-up” to this initial first regional scale response to La-Nina and tropical convective forcing.

Global relative AAM has risen slightly to ~minus 2 standard deviations below the R1 data climatology (14 November last update) with the recent development of equatorial zonal mean upper tropospheric westerly wind flow anomalies. The latter are most robust west of South America, having magnitudes ~20-30m/s. Anomalous twin upper tropospheric subtropical anticyclones have redeveloped ~120-140E, forced by the tropical convection. Rossby wave energy dispersions from these anticyclones will deepen a trough into the Rockies and Plains by the middle of this upcoming week, leading to what may be this cold season’s first winter storm for the Upper Mississippi Valley and Great Lakes regions.

The punch line is that the above mentioned tropical forcing may be the final step for mature coupling to La-Nina. Typically for the ENSO “cycle”, often a MJO or other tropical convective forcing leads to mature coupling during January of the annual cycle. We are concerned this process is starting sooner. Zonal mean subtropical easterly wind flow anomalies remain very intense poleward of the equatorial westerlies already discussed across both hemispheres. At this time, an evolution toward phase 5 of the Global Wind Oscillation (GWO; legacy GSDM Stage 2) appears to be in progress. Updated through 14 November global relative AAM tendency was ~plus 20 Hadleys with the calculated tendency ~plus 30 Hadleys.

Even though statistical tools such as the WH2004 RMMs already indicate and predict a robust MJO during the next couple of weeks, I disagree with that notion. One important point to remember is that these types of techniques do remove the ENSO signal, and that is a problem given the current situation. I do think it is probable for a fast dynamical signal to propagate through the Western Hemisphere over the next couple of weeks. However, as already indicated by satellite imagery, the tropical convective forcing ~140E is starting to “break apart”. One portion should retreat back to the west-northwest while the other enhances a westward shifted South Pacific Converge Zone (SPCZ). Additionally, tropical convection is re-firing across the warm Indian Ocean just south of the equator. Bottom line is tropical forcing should re-intensify back to west ~80-120E during the next few weeks, forcing the GWO back to ~phase 3 (legacy GSDM Stage 1).

For the PNA sector, I think there is a real possibility for a corresponding westward shift of circulation anomalies by early December, perhaps leading to a blocking ridge into Alaska ~140-150W and extratropical cold lows even impacting the USA west coast before coming inland. Cold Arctic air has been recently building up across portions of Siberia into northern Canada. If there is any correctness to these notions, this Arctic air may dump into the USA including locations west of the Continental Divide starting week-2. Weeks 3-4 may see the classic moist southwest flow storm track across the Plains, with intense cold focusing on the Rockies and Northern Plains while the Deep South has above normal temperatures. Areas such as the Desert Southwest and the southwest High Plains may also have decent precipitation in spite of the La-Nina signal. Other weather impacts may include snowfall for Pacific Northwest cities such as Seattle and severe local storms and heavy rainfall from the lower Mississippi Valley into the Ohio Valley.

Finally, any seasonal mean DJF 2007-08 anomalous cold air surface temperature signal which could in reality occur for portions of the USA may be dominated by December. It will be interesting to observe subseasonal activity starting January as tropical convective forcing shifts toward the very warm west central and southwest Pacific Ocean. Will we start to see our "Nemesis"? Is El-Nino in the cards for 2008-09, perhaps even a strong one???

Please see the latest statements from the NOAA/NWS/Tropical Prediction Center and other international centers for tropical cyclone statements. Areas including the Northwest Pacific Ocean around the Philippines, as well as from the South Indian into the Southwest Pacific Oceans including the "paradise islands" may have concerns for tropical cyclones through week-2. Finally, episodes of strong/severe synoptic baroclinic cyclonic systems hammering at least portions of Scandinavia, Europe into the Mediterranean countries/northwest Africa remain probable through week-2.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous the WH2004 “convention”. In addition, the GWO plot does not have the ENSO signal removed.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment composite maps, composite signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion around late next weekend or early week-2.

Ed Berry

El-Viejo Keeps Rocking

There has not been a lot of change to the tropical global SST pattern during the past week. Equatorial Pacific Ocean cold anomalies remain from the west coast of South America to ~160E, with the greatest magnitudes ~minus 3C at about 120W. There is some possibility this cold event may be nearing maturity since the coldest subsurface anomalies have apparently surfaced and magnitudes only around minus 1-2C exist just below the surface east of 150W. Plus 0.5-1C subsurface anomalies (as deep as 150m) remain along the equator from 160W to at least 140E. It is probable for the western tropical Pacific Ocean to remain relatively convectively suppressed thorough at least December (Nemesis is still around), meaning SST anomalies across the warm pool region may increase.

The west central Pacific Ocean still has totals in excess of 30C currently just south of the equator at 140E slowly shifting into the Southern Hemisphere with the annual cycle, linking to a well pronounced positive SST horseshoe into the global midlatitudes. In fact, in the regions of 30-40N and S latitudes, Pacific Ocean SST anomalies are well in excess of plus 3C (totals 22C and colder) as a response to persistent intense subtropical anticyclones. This is a situation of the atmosphere forcing the ocean, unlike the ocean forcing the atmosphere as typically occurs across the deep tropics. Many will argue feedbacks occur from extratropical SSTAs such as these; however, they are only secondary. For instance, should the current intense North Pacific Ocean jet persist, significant SST cooling will occur across that region.

There is once again the warm-cool-warm Indian Ocean to west central Pacific SSTA distribution, with totals in excess of 28C across the equatorial Indian Ocean. I am not going to “go there” in regard to Indian Ocean Dipole (IOD) issues. The Atlantic basin is still warmer than climatology, with a bit of an increase during the past week. Should we start talking about the 2008 North Atlantic tropical cyclone season? Who knows, there may be one or two “Gabrielle-like” systems across the South Atlantic around March 2008.

Repeating from a week ago, the following link is to the WMO news page where a nice discussion about the evolution of this cold event is posted. I recommend reading it, paying attention to the “unusual” characteristics noted.

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

Full disk satellite imagery and other diagnostic monitoring tools present a nice signal of consolidation of tropical convective forcing ~0/90-100E during the last week. The eastward shift into the west central Pacific Ocean discussed last posting has lost coherence. What is left of it is centered ~0/140-150E, while drifting west. I think a combination of these two regions of tropical convective rainfall centered ~0/120E is probable during the next week (or less). Generally diurnal rainfall is present around central/South Africa with some suppression over tropical South America.

I think we are starting to observe the “composite La-Nina” response of tropical convective forcing. However, I do expect this Eastern Hemisphere region of tropical convection to shift east into portions of the west central and even South Pacific (along the SPCZ) especially early 2008, within envelops of other subseasonal variations. There is little, if any, signal of a MJO at this time. Attention needs to be paid if the above convection starts to move east coherently during the next few weeks.

The global circulation has essentially coupled to La-Nina in terns of SST forcing, tropical convective and circulation responses. Animations of daily mean upper tropospheric vector wind anomalies give a decent signal of twin tropical/subtropical anticylones centered ~110E with twin cyclones near the International Date Line. Anomalous zonal mean easterly wind flow anomalies (~5-10m/s at 200mb) persist across the subtropical atmospheres while weak equatorial westerly wind anomalies have become better defined over the Western Hemisphere. In fact, the latter are coming around into portions of Africa (implications are a monitoring issue). Within this coupled base state (GSDM Stage 1), a fairly well pronounced transient evolution partly linked to global topography has contributed to a strong (daily mean anomalies ~50m/s at 250mb) extended North Pacific jet about the slam the USA Pacific Northwest (more said below).

Global relative AAM remains extremely low, ~2.5-3 standard deviations (precisely AMUs) below the R1 data climatology through 7 November. This situation has been observed since about mid August 2007. While the equatorial Pacific SST pattern suggests the current La-Nina is best described as “moderate”, the global circulation is strongly La-Nina like (which could be viewed as seasonal-time scale extreme weather event). In fact, a defensible argument may be made that the tropical SSTs have been catching up to the atmosphere particularly since August. Other terms of the AAM budget also support the notion of a strong La-Nina circulation, including the inter-hemispheric symmetry of poleward AAM transports across the subtropics, and the mass term. The relatively persistent global positive frictional torque of roughly 10 Hadleys is coming from enhanced Northern Hemisphere trades trying to add angular momentum to the atmosphere from the earth. Typical of a cold event, the atmosphere continues to rotate slower than the earth.

The global weather-climate situation is solidly in GSDM Stage 1 as indicated by the Global Wind Oscillation (GWO) updated through 29 October. The GWO continues to orbit around La-Nina. While we can attribute the larger GWO orbits to non-oscillatory slow processes such as friction-mountain torque index cycles, the faster smaller circuits remain a topic of our research. The recent positive AAM tendency of ~20 Hadleys is coming from the tropics and lower midlatitudes. In addition to the current positive global mountain torque of ~15 Hadleys with East Asia leading, I think there has also been a contribution to the positive AAM tendency from the weak eastward shift of tropical forcing discussed a week ago. The strong North Pacific jet is a response from these combined tropical and midlatitude dynamics (bottom line). In any case, when updated, I think there will be another one of those “smaller orbits” of the GWO.

Instead of stating in the Appendix, we are continuing to rework the GSDM and use terminology similar to that of the WH2004 8-section phase space plots of the MJO. In other words, we will be getting way from terms such as “stages” and use phraseology such as “phases” instead. Stages may be used in reference to what will be referred to a the “legacy WB(2007) GSDM”. Hence GSDM Stage 1 will be “GWO phase 3”,GSDM Stage 3 will be referred to as “GWO phase 7”, etc. I know this seems very confusing; however, stay tuned, it will become much easier to understand. We are making these modifications partly in response to users who do not like the word “stages”.

Worth restating, I think the USA seasonal outlooks recently prepared by the Climate Prediction Center (CPC) are the “correct forecast” given La-Nina, keeping in mind to remain diligent for important subseasonal events. The subseasonal evolutions during November-December-January 2006-07 putting an unexpected demise to El-Nino serves as an excellent example. I also want to make clear that blanket statements about the roles of the North Atlantic Oscillation and/or Arctic Oscillation (NAO/AO) for a cold seasonal mean USA outlook are not scientifically defensible. From a subseasonal viewpoint the latter are responses to at times very complex dynamical forcing onto the global circulation and not that predictable especially beyond a few weeks.

Continuing thoughts from the previous posting, the extended North Pacific Ocean jet is likely to collapse during the next 1-2 weeks. Simplistically, it is not unusual to observe jets outrunning Eastern Hemisphere tropical convective forcing, especially boreal autumn. With the exception of episodes of high winds/heavy rainfall across the Pacific Northwest and perhaps portions of Alaska at times, a generally mild and tranquil weather pattern can be expected roughly week-1 for the USA. There will be some trough amplification east of the Mississippi River meaning opportunities for some precipitation and cooler air.

Perhaps most importantly, given the La-Nina coupling and upcoming probable collapse of the North Pacific Ocean jet, I think the possibility of significant amplification across the Pacific North American sector exists roughly days 10-20. Probabilistically, this would lead to blocking around Alaska and a western USA trough. I am making this statement with extremely low confidence, especially since my predictive insights have ____ recently. In fact, I am more confident about the amplification occurring then the synoptic pattern. For example, if the trough ends up across the east Pacific Ocean, while the USA west coast gets possibly hammered with cold systems the rest of the country may stay “boring” (yes, this scenario may also be good for ski resorts west of the Continental Divide). In any event, we need to monitor. If there is actually any truth to this possibility, people planning travel around Thanksgiving may have to deal with possibly intense winter weather should a southwest flow storm track develop across the Plains with an Arctic cold air source. Hopefully, the numerical models will start to support this synoptic evolution (not trying to “monger” winter).

I do think it is highly probable there will be several occurrences of the “classic” legacy GSDM Stage 1 (GWO phase 3) this cold season. Even with that circulation response, cyclonic baroclinic developments across the southwest High Plains may be too progressive for decent precipitation for locations such as the Desert Southwest into western Texas and eastern Colorado/western Kansas unless strong anticyclonic wave breaking of the lows can occur, say, around "4-corners".

Please see the latest statements from the NOAA/NWS/Tropical Prediction Center for tropical cyclone statements. Locations including the Bay of Bengal and the Northwest Pacific Ocean around the Philippines may have concerns for tropical cyclones week-1 and perhaps through week-2. I think flooding rainfall remains a concern for portions of Central America week-1. Finally, episodes of strong/severe synoptic baroclinic cyclonic systems hammering at least portions of Scandinavia, Europe into the Mediterranean countries are probable through week-2.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the GSDM is to extend current thinking beyond the MJO, the purpose of the GWO is to illustrate the non-oscillatory stochastically forced component of the GSDM.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion late next weekend or early the following week after travel.

Ed Berry

The Devil (El-Viejo?) Reigns Supreme

Basin wide (within 5 deg of the equator) moderate La-Nina SST anomalies have intensified slightly during the past week with magnitudes ~minus 1-3C with the coldest along the equator at ~125W per recent 5-day averaged TAO buoy data. These kind of negative SST anomalies along the equatorial Pacific Ocean cold tongue are quite impressive in the presence of the seasonal cooling cycle. The cold anomalies extend down to roughly 200m deep west of South America and as far west at the surface to at least 160E. Strengthening of the near equatorial trades has assisted with the cooling SSTs around and west of the date line.

The west central Pacific Ocean still has totals in excess of 30C along the equator at 140E slowly shifting south with the annual cycle, linking to a well pronounced positive SST horseshoe into the global midlatitudes. Interestingly, weak cool anomalies have recently appeared across the North Indian Ocean, while the Atlantic basin is still warmer than climatology.

The following link is to the WMO news page where a nice discussion about the evolution of this cold event is posted. I recommend reading it, paying attention to the “unusual” characteristics noted.

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

Most dynamical and statistical forecast tools from global weather centers suggest this La-Nina to persist into at least early 2008. That notion is probable based on current subseasonal events (discussed below). However, the weak subsurface warming ~150-160W with anomalies ~plus 1C/150m, discussed last week, remains. Sparing lengthy details, I am unclear how this whole ENSO situation will behave during 2008. I would expect anomalous warmth to “build up” particularly west of the date line as boreal winter and austral summer take their course.

Monitoring satellite imagery and other diagnostic tools during the last few weeks tells me there has been a somewhat unexpected eastward shift of the Eastern Hemisphere tropical convective forcing from the Indian Ocean into Indonesia. Some projection onto a MJO was present, and this may have been, in fact, the truncated event I was expecting per past postings. However, I think the eastward movement has ceased, with consolidation and strengthening of the tropical forcing centered ~0/120-140E currently in progress. Other regions of enhanced tropical rainfall are also present across portions of west central-southeast South America/Brasil and Africa. There is also a weak flare-up across the west central Pacific responding to anticyclonically wave breaking cyclones from both hemispheres.

The gist is the global circulation is again coupling to La-Nina. I can see this even from plots such as Hovmoller representations of 250mb meridional wind anomalies in bands such as 10-40N. Global relative AAM is extremely low ~3 standard deviations below the R1 data climatology through 1 November. Since at least late September there have 2 “pulses” of poleward propagation of anomalous zonal mean easterly winds into the global subtropical atmospheres. Most recently zonal mean AAM anomalies ~minus 2 AMUs have appeared just south of 30N. This translates to zonal mean easterly wind flow anomalies as large as 10m/s at 200mb.

Staying on the topic of the AAM budget, a decent poleward transport signal has oscillated ~35N (weaker Southern Hemisphere signal) during the last week or so. This is why any astute synoptician would have been observing a lot of northeast-southwest (northwest-southeast) tilted eddies across the Northern Hemisphere (Southern Hemisphere) recently. The global frictional torque has increased to ~plus 10 Hadleys with a large source coming from the northern subtropics due to the intensifying trades. The global mountain torque has become slightly negative with a decent signal coming from the Andes Mountains.

In any case, I can very easily see how recent the AAM signals both globally and in the zonal mean are lining up nicely with the La-Nina coupling (SSTAs -> tropical convection-> circulation response, then subsequent interactions). The mass term in the AAM budget shows strong positive zonal mean anomalies (~.5 AMU) across the northern midlatitudes with the opposite over the tropics. This all translates to anomalously intense midlatitude ridges across the Northern Hemisphere. Another way to pitch this is that the atmosphere is currently rotating slower than the earth (increasing the length of the day by ~.005 seconds!).

The global weather-climate situation is solidly in GSDM Stage 1 as indicated by the Global Wind Oscillation (GWO) updated through 29 October. The GWO continues to orbit around La-Nina. While we can attribute the larger GWO orbits to non-oscillatory slow processes such as friction-mountain torque index cycles, the faster smaller circuits remain a topic of our research.

Animations of upper tropospheric daily mean vector wind anomalies give a nice signal of twin tropical/subtropical anticylones centered ~120E with twin cyclones just east of the date line. Anomaly magnitudes at 150mb are roughly 20-30m/s, including the equatorial westerlies across the Pacific west of South America. This is the typical baroclinic response to tropical convective forcing as part of the re-coupling to La-Nina.

The recent eastward shift of the Eastern Hemisphere tropical forcing is leading to an extension of the East Asian Jet as I type. This is an extratropical feedback response to zonally oriented Rossby wave energy dispersions interacting with the convection. Whether or not there will be a positive East Asian and global mountain torque with this event is unclear to me. However, not typical of GSDM Stage 1 and La-Nina is the upcoming development of an anomalous cyclonic circulation gyre across the central North Pacific Ocean per models (which I agree). This reminds a little of what we observed during November-December 2005 having a “Stage 3 circulation with Stage 1 forcing”. The Tropical Northwest Pacific Ocean (TNWP) was quite convectively active then. I speculate that since this La-Nina is stronger (and basin wide) than the 2005-06 event, and the TNWP SSTs do not appear as warm, we will not see our current North Pacific jet extension be as persistent and intense.

I think the USA seasonal outlooks recently prepared by the Climate Prediction Center (CPC) are the “correct forecast” given La-Nina, keeping in mind to remain diligent for important subseasonal events. The subseasonal evolutions during November-December-January 2006-07 putting an unexpected demise to El-Nino serves as an excellent example. I also want to make clear that blanket statements about the roles of the North Atlantic Oscillation and/or Arctic Oscillation (NAO/AO) for a cold seasonal mean USA outlook are not scientifically defensible. From a subseasonal viewpoint the latter are responses to at times very complex dynamical forcing onto the global circulation and not that predictable especially beyond a few weeks. Of course, once established, the decay time scales of the NAO/AO can provide some predictive information. Enough said!

As I stated a week ago, for especially the PNA sector, predictability has been VERY LOW for both myself (frustratingly) and the numerical models during the last couple weeks. In fact, week-two anomaly correlation coefficients (ACC) for both North America and the Northern Hemisphere for the NCEP ensemble mean have at times been near or below zero, per their web site. I think both the recent positive global mountain torque event discussed last week and the eastward shift of the tropical forcing discussed above have contributed to poor model performance. Yes, boreal autumn is also a tough time of the year for the numerical models, in general.

So what useful predictive insights can I offer today? I do think my “classic” GSDM Stage 1 response will occur “sometime”, favoring a western USA trough and southwest flow storm track across the Plains. However, that is not likely through at least well into week-two given the feedback issues discussed above, along with the seasonal cycle. The North Pacific Jet is very likely to blow across the northern part of the country by that time, in the presence of a low amplitude western states ridge and eastern USA trough. As the coupling strengthens, I can see a scenario of a brief GSDM Stage 3-Stage 4 evolution which may lead to a slower moving trough/closed low(s) across the southwest states perhaps later week 2-week 3. Until then, expect generally “boring” weather for the lower 48 states, except for those who enjoy dry weather and high fire dangers in places. As I have stated before, the latter is typical of autumn. Important exceptions are portions of Alaska and the Pacific Northwest where periods of very heavy rainfall and high winds are probable, and possibly the Great Lakes states for lake-effect snowfall and general "clipper systems".

Again, I emphasize the need for daily monitoring. To me, it is highly probable there will be several occurrences of the “classic” GSDM Stage 1 this cold season. Since timing is unclear, only monitoring may catch the evolution, and that may be before the models get it. Even with that circulation evolution, cyclonic baroclinic developments across the southwest High Plains may be too progressive for decent precipitation for that region unless strong anticyclonic wave breaking of the lows can occur over the Desert Southwest. During this upcoming cold season, given an Arctic cold air source, episodes of severe winter weather including substantial snowfall and blizzards may occur from the Northern Plains into the Upper Mississippi Valley while the Ohio Valley region has heavy rainfall and possibly severe thunderstorms.

Please see the latest statements from the NOAA/NWS/Tropical Prediction Center for tropical cyclone statements. Locations including the Bay of Bengal and the Northwest Pacific Ocean around the Philippines may have concerns for tropical cyclones through week 2. Heavy tropical rainfall may be probable for portions of South America and Africa also through week 2. I will let “Gabrielle” rest her soul.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the GSDM is to extend current thinking beyond the MJO, the purpose of the GWO is to illustrate the non-oscillatory stochastically forced component of the GSDM.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion around next weekend after travel, and before another trip the following week. I did fail to keep this discussion short!

Ed Berry

Back to Dealing with the Devil

I want to use this posting as a “precedent” to shortening (still need to work on that!) these discussions given time issues. Interested readers should know where to look on the web to examine details such as, for example, SSTs. There may also be “obvious features” and issues that will be skipped over.

Basin wide (within 5 deg of the equator) moderate La-Nina SST anomalies remain having magnitudes colder than minus 2C near the equator at ~125W per TAO buoy data. The west central Pacific Ocean still has totals in excess of 30C along the equator at 140E slowly shifting south with the annual cycle. Weak warm anomalies remain across the Indian Ocean while the Atlantic basin is still warmer than climatology.

Even though it is probable for this moderate cold event to persist at least through December 2007, I am unclear afterwards. Understanding the seasonal cycle, there is actually weak subsurface warming occurring to at least 150W with anomalies ~plus 1C/150m. This may be a response to equatorial westerly wind events in the region of Indonesia to the date line late September and again about 10 days ago (anybody want to call this an oceanic Kelvin wave?). Trades are again intensifying around the date line in response to tropical convective forcing increasing back to the west. Stay tuned.

Satellite imagery and other diagnostic monitoring tools do give a signal of tropical convective forcing intensifying and organizing in the region the equatorial central Indian Ocean into northern Indonesia. Per animations of upper tropospheric velocity potential fields, the Western Hemisphere dynamical signal is propagating into Africa and the Indian Ocean, enhancing tropical forcing across those regions. The latter was forced by interactions with the extratropics.

Animations of upper tropospheric daily mean vector wind anomalies present an improving signal of twin tropical/subtropical anticyclones ~60-100E with cyclones near 170E. In fact, equatorial westerly wind anomalies having magnitudes ~25m/s have responded over the Western Hemisphere Pacific Ocean. Finally, there are lower level twin cyclonic circulation anomalies ~60-90E which may develop into tropical cyclones. In any case, at least a weak MJO may be in the early stages of formation given the baroclinic structure. The WH (2004) RMM phase space plots present ~1 standard deviation MJO signal across the Eastern Hemisphere with no clear sense of what it will do. My own feeling is we will see at least a truncated weak MJO during the next few weeks, having eastward propagation to ~140-150E where tropical SSTs are the warmest. This may be similar to what happened late September, except that situation not a “true” MJO.

Through 24 October, global relative AAM has dipped to ~minus 2.5-3 standard deviations (approximately AMUs) below the R1 data climatology, after our positive global mountain torque (mostly East Asian; ~25 Hadleys) roughly 10-14 days ago. The Global Wind Oscillation (GWO) which takes into consideration non-oscillatory extratropical dynamics linked to the surface torques and AAM transports, has orbited to ~minus 1.5-2 standard deviations into the phase plane of GSDM Stage 4-1 through 22 October. Zonal mean easterly wind flow anomalies (~5-10m/s at 200mb) have re-intensified throughout the global subtropics. In summary, ocean-atmosphere coupling to La-Nina appears to be once again strengthening, including a poleward AAM transport signal, with perhaps a MJO perturbation.

For the PNA sector, predictability has been VERY LOW for both myself and the numerical models during the last couple weeks. In retrospect, speculation suggests a mountain torque enhanced North Pacific jet (which we had) collapsing in a base state favoring anticyclonic wave breaking (AWB) may not be very predictable even at "short" lead times in regard to synoptic details, particularly during boreal fall. In fact, the above sequence of events greatly contributed to the severity of the wild fires across California. I do think a “classic” GSDM Stage 1 cold season response meaning tilting the odds toward an anomalous western USA trough (with synoptic variations) is in the near future. In the meantime, seasonal strengthening of the westerlies has finally led to a relatively tranquil weather pattern across much of the USA.

Going into week 2, I do have a concern the trough that most models suggest to come into the western USA will be slower and deeper, with even another one of those __________ AWB closed lows. In fact, these kinds of synoptic situations may be probable this cold season, as the southwest flow storm track presumably becomes established across the central states.

Please see the latest statements from the NOAA/NWS/Tropical Prediction Center for tropical cyclone statements. There is evidence at this time a tropical depression may be forming across the southeast Caribbean. Locations including the Arabian Sea, Bay of Bengal and even the South Indian Ocean may need to deal with at least 1 tropical cyclone week 1. The Northwest Pacific Ocean around the Philippines may be a concern for tropical cyclone development through at least week 2. While dryness returns to tropical South America for at least week 1, portions of equatorial Africa may remain quite wet. Will there be another “Gabrielle” across the North Atlantic Ocean sometime soon?

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the GSDM is to extend current thinking beyond the MJO, the purpose of the GWO is to illustrate the non-oscillatory stochastically forced component of the GSDM.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion late next week ~ 2-4 November before travel the following week.

Ed Berry

Major Delay

Travel and other obligations preclude me from comfortably writing a complete posting useful to others. In fact, much of the latter is strongly linked to an effort to implement “operationally” at some time (hopefully reasonably soon) the objective and quantification work discussed in the Appendix. I will try to do a complete discussion during the period of 28 October-3 November.

There is no change from the reasoning about the weather-climate situation discussed 13 October. Full-disk satellite imagery and other diagnostic monitoring tools indicate that the tropical convective forcing is returning to the warm Indian Ocean, while pockets of enhancement still persist across the very warm west Pacific Ocean and around the Americas. There is some possibility for a MJO to evolve from the Indian Ocean forcing during the next few weeks.

Global relative AAM remains very low, ~2.5 AMUs per R1 data through 15 October, and a coupled GSDM Stage 1 base state to La-Nina persists. In the zonal mean anomalous easterly wind flow continues throughout the subtropical atmospheres of both hemispheres, having weekly mean magnitudes of ~3-6m/s. I think it is likely for this GSDM Stage 1 regime to continue (at least on average) through the rest of 2007, possibly longer. Hence our circulation state tilts the odds toward life cycle-1 anticyclonic wave breaking baroclinic development, including the next trough to impact the western USA (addressed below). As discussed in past postings, we need to monitor tropical convective forcing across the west central Pacific Ocean.

Regionally for the PNA sector, the positive East Asian mountain torque (~20 Hadleys) enhanced North Pacific Ocean jet is collapsing as I type. One major synoptic cyclonic baroclinic development event is currently in progress across the Upper Mississippi Valley, and I definitely favor the notion of a second development across the Southern Rockies and Plains by the end of this upcoming weekend. Models have been struggling with this second storm, and the slower and deeper solution is most probable. After a period of respite ~later week 1 into week 2 from active weather across the USA, I think this type of situation is again more likely than climatology by ~ week 3 (1-8 November).

I will be monitoring to see if a more robust western USA trough-southeast states ridge pattern becomes established by later November into December (with synoptic variations). Ramifications for particularly the central USA should be straight forward (to meteorologists) especially if there exists an Arctic cold air source and decent tropical moisture transport from the Gulf of Mexico. Translation is a stormy pattern favoring possibly significant/extreme winter weather from the Rockies into the Northern/Central Plains with heavy rainfall and thunderstorms focusing on the Ohio Valley.

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the GSDM is to extend current thinking beyond the MJO, the purpose of the GWO is to illustrate the non-oscillatory stochastically forced component of the GSDM.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion ~28 October-3 November.

Ed Berry

Sea of Noise

There has not much been much change to the spatial distribution of global tropical SSTs since my 8 October posting. A basin wide cold event appears to be in the process of maturing across the equatorial Pacific Ocean basin (165E -South America) with anomalies ~minus 3C from 120-140W extending to around 200m deep. The warm Indian Ocean -cool Indonesia -warm west central Pacific Ocean pattern of Eastern Hemisphere SSTAs persists with totals in excess of 30C ~0-10N/150-160E (merging with the warm Pacific Ocean horseshoe). Other SST details can be found from the links below in the Appendix and my previous posting.

The gist is that the global circulation remains strongly coupled to La-Nina in terms of circulation response. Given the complex dynamics of forcing-response-feedback global circulation-tropical convection evolutions since around 1 December 2006, perhaps it is the SSTs that have coupled to the atmosphere particularly starting around 1 September 2007. Reiterating, I did not think we would see a basin wide cold event a couple of months ago. In any case, this coupling has been and continues to modulate synoptic variability globally including the USA. From the GSDM (and more generally subseasonal) framework the latter is scientifically defensible; I strongly disagree with statements to the contrary from anywhere. The latter are from a perspective of, for example, 3-month composites of temperature and precipitation anomalies which will average out important subseasonal weather events.

Per ESRL/PSD plots, global relative atmospheric angular momentum (AAM) has decreased during the past week to roughly 3 AMUs below the R1 data climatology. In addition to the well established anomalously strong zonal mean easterly wind flow throughout the subtropical atmospheres (~25N and 25S with magnitudes ~10m/s at 200mb), anomalous easterly wind flow is developing both in the tropics and higher latitudes. The former is tied to the tropical convective forcing and the latter is a response to extremely intense midlatitude anticyclones (anomalies in excess of 40m/s at times) amplifying into the global Polar Regions. In fact, a rare sudden stratospheric warming of the austral (spring) stratosphere may be in progress as a response (also discussed 8 October). Both AAM tendency and the surface torques have become slightly positive; however, the Global Wind Oscillation (GWO) remains solidly in GSDM Stage 1.

There has been a significant subseasonal perturbation onto our GSDM Stage 1 La-Nina basic state during the past week. As seen from animations of daily mean upper tropospheric vector wind anomalies and time-longitude sections of velocity potential (divergent part of the total velocity field), persistent Rossby wave energy dispersions arcing from the twin subtropical anticyclones ~120E through both hemispheres led to an increase of divergence centered around the Americas. Strong convection (OLRA ~ minus 50-90 W/m**2) developed from the East Pacific ITCZ into the Caribbean and the Amazons of South America. Weak anomalous twin subtropical anticyclones have formed as a response ~60-90W leading to Western Hemisphere equatorial easterlies.

Current full disk satellite imagery shows tropical convection enhanced around the Americas. There is also renewed tropical forcing around 0/80E, with strong suppression across Indonesia into the west Pacific. A week ago I thought there was some observational evidence that a MJO may be in the early stages of development. This notion is still not unreasonable. However, I did not think a MJO might develop as the result of an extratropical feedback forcing a Western Hemisphere tropical convective dynamical signal, currently ~60-70W. These dynamical signals typically propagate ~15m/s (roughly 12 deg long/day) when they are in the Western Hemisphere. Simple extrapolation would put this signal solidly across the Indian Ocean in roughly 8-10 days.

Even though we are in a stationary GSDM Stage 1 base state, my confidence for any week 1-3 forecast across the PNA sector is very low. In addition to getting “surprised” (RMM WH2004 phase space plots did suggest this possibility; these kind of chain of events have occurred in the past such as December 2005), seasonal transition into boreal cold season is also adding difficulty. It also seems like any predictive information I have offered lately has been poor. This only confirms once again we are dealing with a dynamical system characterized by a sea of noise that does not like to be predicted. Tools such as the GSDM, GWO quasi-phase space plot and risk assessment plots of subseasonal variability, along with rigorous daily monitoring, help to facilitate “forecasts of opportunity (strong coherent signals above the background noise)” especially when numerical and other statistical tools are also struggling. Like it or not, that is the way it is (the truth)!!

My feeling is to expect a reinvigoration of the tropical convective forcing across the equatorial Eastern Hemisphere from ~60-120E by the end of week 2. The La-Nina enhanced westerlies ~40N have been coming south, regionally recently slamming the USA west coast with several strong troughs. If the Indian Ocean convection becomes quite robust, and that is probable given our base state (which may further strengthen La-Nina), the North Pacific jet would be expected to collapse. In fact, a full-latitude ridge into Alaska may develop initially along the west coast then retrograde to ~140-150W by week 3.

For the USA, this suggests about 1 more week of an unseasonably active weather pattern followed by quieter conditions week 2 (models suggest this). If this were about a month or so later I would be expressing a concern for a cold/stormy regime (with Arctic air) across the western half of the country starting week 3. Should a decent MJO develop across the Indian Ocean along with the GWO, a “classic” GSDM Stage 1 cold season regime for North America may start to evolve by that time (~ 28 October-4 November) in spite of the seasonal cycle. My speculation for this upcoming boreal winter season stated in past discussions remains the same.

Please see the latest statements from the NOAA/NWS/Tropical Prediction Center for tropical cyclone statements. Anticyclonic wave breaking reigns supreme across the North Atlantic. The spirit of “Gabrielle” may still live.

Heavy rainfall may become a concern for portions of equatorial Africa week 1 then into the Indian Ocean weeks 2-3 per above. Tropical cyclone hazards may actually become more probable for the South Indian Ocean (one already did try) than Bay of Bengal weeks 2-3. The west central Pacific will always be the wild card. One would expect general suppression from Indonesia into the west Pacific Ocean weeks 1-2, with activity increasing especially along the equator by week 3. However, who really knows the timing at this point?

Appendix

An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at

http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg

http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg

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

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the GSDM is to extend current thinking beyond the MJO, the purpose of the GWO is to illustrate the non-oscillatory stochastically forced component of the GSDM.

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/

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion ~19-20 October.

Ed Berry