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sebastiaan1973

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About sebastiaan1973

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  1. HI Tamara, thanks for sharing your thoughts. Did you write somewhere a forecast for the coming weeks ahead? Thanks
  2. So, there is little chance for a substantial period of Northern high pressure in december. And so the seasonal models are right.
  3. On November 18, the World Climate Service issued its seasonal forecast and discussion for winter (December-February) 2019-2020 in the U.S. and Europe. WCS seasonal outlooks include an overview of expected climate anomalies, key drivers, and risk factors for the upcoming three-month season, and our forecast document contains detailed discussion of available predictors, including dynamical model forecasts and statistical and analog guidance.Analog analysis has long been a staple of the WCS methodology for seasonal forecasting, and we invariably rely on diverse sets of analogs derived from numerous aspects of current global climate patterns. Only on rare occasions do we focus on individual analog years, because the climate phase space is rarely a very good match to any previous year in the modern history in more than a few respects; there are nearly always significant differences from any candidate analog year. Moreover, the degrees of freedom in the climate system are too numerous to expect a close correspondence with any past year to continue into the future, and so any search for “the perfect analog” is a fool’s errand (even if the climate were assumed to be unchanging).Nevertheless, the latest WCS seasonal forecast report discusses a very notable confluence of similarities between the present climate and that of winter 2002-2003. In keeping with usual practice, the WCS winter forecast is not unduly influenced by the 2002-03 analog, but the degree of similarity is so striking that it is worth considering the 2002-03 outcome as a plausible outcome and risk scenario for winter 2019-20. The following list of similarities was presented in the forecast document and is reproduced here:2002 is the top QBO analog year, based on the 12-month evolution of the 30mb QBO indexThe Indian Ocean Dipole was strongly positive in September and October 2002, and tropical convective patterns were similar; 2002 is the third best analog year for 200mb equatorial velocity potentialA region of highly anomalous warmth developed in the northeastern Pacific in late summer 2002 and persisted through autumn, similar to 2019Arctic sea ice was low in summer 2002 and set a record at the time for low September ice extentThe October Northern Hemisphere circulation was similar in 2002, with Arctic blocking, a trough over northwestern Europe, and a very similar ridge-trough pattern over western North America. The November MSLP pattern was also similar with respect to high pressure north of Scandinavia, low pressure near the British Isles, and low pressure south of the Aleutians.October 2002 had the highest snow cover on record (1967-present) over North America; October 2019 was the third highestThe 10mb polar vortex was much stronger than usual in the first half of November 2002, but the Arctic Oscillation was negative for November, similar to this year. No other year provides such a close match to this unusual combination, although 2018 is also a good analog.Remarkably, 2002 is nearly a perfect match to 2019 (better than any other year since 1900) for Central England Temperature in August, September, and October. Perhaps coincidentally, October 2002 England & Wales precipitation was also nearly identical to 2019, and November was also extremely wet (October-December 2002 was the third wettest such period on record).2002 and 2019 are the only years on record with a strong Southern Hemisphere SSW (Sudden Stratospheric Warming) event; both of these occurred in late austral winter and led to Southern Hemisphere blocking in both October and November.The most significant difference between 2002 and 2019 is that 2002 had more warmth in the eastern equatorial Pacific and much less in the West Pacific; El Niño was more classical (East Pacific) rather than Modoki-like. There was also much less anomalous warmth in the subtropical and northern North Pacific in 2002.In view of the extensive and remarkable similarities betweeen 2002 and 2019, it is tempting to conclude that winter 2019-2020 will be closely analogous to 2002-2003, with a strongly blocked pattern, unusual cold in the eastern two-thirds of Europe and the eastern United States, and reduced precipitation and wind in central and northern Europe (see below). However, as noted above, the WCS approach is to treat individual analog years with caution, regardless of how impressive the similarities appear to be. The combined consensus of a large array of dynamical and statistical predictors is a more reliable guide to likely seasonal patterns, and the WCS forecast is constructed accordingly, but the winter of 2002-2003 should be regarded as a plausible alternative scenario. From https://wp.worldclimateservice.com/home/2019/11/18/a-remarkable-analog-2002/
  4. http://www.researchgate.net/publication/329300936_Enhanced_StratosphereTroposphere_Coupling_During_Extreme_Warm_Stratospheric_Events_with_Strong_Polar-Night_Jet_Oscillation Latest of Karpechko. Seems to me that this SSW will be a non-PJO. So not enough downwelling. Please see the chart with 1-15 days after CD
  5. I still wonder if this is a dSSW. This is a list of SSWs (with QBO-phawse) and nSSWs dSSWs . The latter is a downwelling. On this list since 1979 there are 13 dSSWs. Of them (and then you use the other list) 11 of them are with an eQBO. Seems to me that a wQBO is a big disadvantage. Just 1979 and 2009 are an exception.
  6. What are there are the consequences of the lower heatflux at 100 hPa? Don't we need enhanced upward planetary wave propagation at 100 hPa - 300 hPa? for downwelling purposes.
  7. Great insights Tamara, I shared them at a Dutch forum and there we discuss it so we can learn from it. For now I'm wondering where I can find the GWO phase 7 chart ? Thanks.
  8. Okay, thanks for sharing your thoughts. Any idea if we can check 100-300hPa -NAM for enhanced wave propagation?
  9. The Downward Influence of Sudden Stratospheric Warmings: Association with Tropospheric Precursors Tropospheric features preceding sudden stratospheric warming events (SSWs) are identified using a large compendium of events obtained from a chemistry–climate model. In agreement with recent observational studies, it is found that approximately one-third of SSWs are preceded by extreme episodes of wave activity in the lower troposphere. The relationship becomes stronger in the lower stratosphere, where ;60% of SSWs are preceded by extreme wave activity at 100 hPa. Additional analysis characterizes events that do or do not appear to subsequently impact the troposphere, referred to as downward and non-downward propagating SSWs, respectively. On average, tropospheric wave activity is larger preceding downward-propagating SSWs compared to non-downward propagating events, and associated in particular with a doubly strengthened Siberian high. Of the SSWs that were preceded by extreme lower-tropospheric wave activity, ;2/3 propagated down to the troposphere, and hence the presence of extreme lower-tropospheric wave activity can only be used probabilistically to predict a slight increase or decrease at the onset, of the likelihood of tropospheric impacts to follow. However, a large number of downward and non-downward propagating SSWs must be considered (.35), before the difference becomes statistically significant. The precursors are also robust upon comparison with composites consisting of randomly selected tropospheric northern annular mode (NAM) events. The downward influence and precursors to split and displacement events are also examined. It is found that anomalous upward wave-1 fluxes precede both cases. Splits exhibit a near instantaneous, barotropic response in the stratosphere and troposphere, while displacements have a stronger long-term influence. https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-18-0053.1
  10. Well according to me there is a good chance for downwelling. We see in the chart of 100 hPa some negative NAM anomalies. Or I'm wrong? Predictability of downward propagation of major sudden stratospheric warmings Alexey Yu. Karpechko,et al
  11. From this studyI selected these charts: Predictability of downward propagation of major sudden stratospheric warmings Alexey Yu. Karpechko,et al Major Sudden Stratospheric warmings (SSW) are striking phenomena of wintertime stratospheric circulation usually defined as a reversal of zonal mean circulation from westerlies to easterlies. SSWs often have significant impacts on tropospheric circulation and cause anomalies in surface climate lasting for up to two months. For this reason, dynamics and predictability of SSW receive considerable attention. It is however well-known that not all SSW cause significant, long-lasting impacts on the troposphere. In order to explain differences in tropospheric impacts following SSWs, several reasons have been previously proposed, including differences in type of SSW (split or displacement), persistence of stratospheric anomalies, preconditioning of the tropospheric circulation, and whether or not SSW was accompanied by a planetary wave reflection in the stratosphere. Here we address the predictability of tropospheric impacts by SSWs by seeking for early precursors of the impacts. We separate mid-winter SSWs into two groups: those which are followed by significant, long-lasting impacts on the tropospheric circulation (defined in terms of anomalous northern annular mode) and those not followed by significant anomalies in the annular mode. We show that SSWs characterised by a more negative Northern Annular Mode index in the lower stratosphere around 150 hPa and enhanced wave activity propagation to the stratosphere during the first few days following the central date have a larger probability to be followed by tropospheric impacts, both in reanalyses and in climate model runs. These anomalies play more important role for the subsequent downward propagation of the signal to the troposphere than the type of SSW: whether it is a split or a displacement, or absorptive or reflective SSW. We propose that using these anomalies as precursors of tropospheric impacts of SSW can enhance climate predictability. Please notice the difference between dSSW and nSSW. With dSSW there is a negative AO around the first day of the SSW. Displacment or split doesn't matter. Important is 100 hPa till 300 hPa! (first i was mistaken and thought it was at 1000 hPa)
  12. What does make you think this way. I see GFS switches from yes to no and back to yes. Seems to me quite normal. And EC seems to more reliable with it's better resolution.
  13. https://pdfs.semanticscholar.org/12d5/f40389c3e38ca4be146450203a275d0ebd31.pdf Abstract Sudden stratospheric warmings (SSWs) contribute to intraseasonal tropospheric forecasting skill due to their surface impacts. Recent studies suggest these impacts depend upon whether the polar vortex splits or is displaced during the SSW. We analyze the annular mode signatures of SSWs in a 1000 year IPSL-CM5A-LR simulation. Although small differences in the mean surface Northern Annular Mode (NAM) index following splits and displacements are found, the sign is not consistent for two independent SSW algorithms, and over 50 events are required to distinguish the responses. We use the wintertime correlation between extratropical lower stratospheric wind anomalies and the surface NAM index as a metric for two-way stratosphere-troposphere coupling and find that the differences between splits and displacements, and between classification methodologies, can be simply understood in terms of their mean stratospheric wind anomalies. Predictability studies should therefore focus on understanding the factors that determine the persistence of these anomalies following SSWs. From the discussion part Recent studies using reanalysis data have suggested that the tropospheric response to SSWs depends upon the type of event, categorized as either a vortex split or displacement [Mitchell et al., 2013; Seviour et al., 2013] (M13 and S13, respectively). These studies found that the surface anomalies following splits project more strongly onto the Northern Annular Mode (NAM) than for displacement events. This is in contrast withCharlton and Polvani [2007] (CP07) and Cohen and Jones [2011] who did not find a consistent difference in the impact of splits and displacements using a different method for identifying SSWs
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