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About sebastiaan1973

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  1. 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
  2. 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.
  3. 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.
  4. 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.
  5. Okay, thanks for sharing your thoughts. Any idea if we can check 100-300hPa -NAM for enhanced wave propagation?
  6. 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.
  7. 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
  8. 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)
  9. 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.
  10. 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
  11. Good thinking. My compliments. So, what do you think are the implications in Western Europe?
  12. Wintertime high-latitude blocking is associated with persistent changes in temperature and precipitation over much of the Northern Hemisphere. Studies have shown that the Madden–Julian oscillation (MJO), the primary form of intraseasonal tropical variability, significantly modulates the frequency of high-latitude blocking through large-scale Rossby waves that alter the global circulation. However, the characteristics of MJO teleconnections are altered by El Niño–Southern Oscillation (ENSO), which modifies the global flow on interannual time scales, suggesting that the MJO influence on blocking may depend on the ENSO phase. The characteristics of MJO Rossby waves and blocking during ENSO events are examined using composite analysis and a nonlinear baroclinic model. The ENSO phase-dependent teleconnection patterns are found to significantly impact Pacific and Atlantic high-latitude blocking. During El Niño, a significant persistent increase in Pacific and Atlantic blocking follows the real-time multivariate MJO (RMM) phase 7, characterized by anomalous enhanced tropical convection over the East Indian Ocean and suppressed west Pacific convection. The maximum Atlantic blocking increase is triple the climatological winter mean. Results suggest that the MJO provides the initial dipole anomaly associated with the Atlantic blocking increase, and transient eddy activity aids in its persistence. However, during La Niña significant blocking anomalies are primarily observed during the first half of an MJO event. Significant suppression of Pacific and Atlantic blocking follows RMM phase 3, when east Indian Ocean MJO convection is suppressed and west Pacific convection is enhanced. The physical basis for these results is explained.
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