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AS1.20

Dynamical coupling between the stratosphere and the troposphere: sudden stratospheric warmings and tropospheric predictability
Convener: Thomas Reichler  | Co-Conveners: Dann Mitchell , Om Tripathi 
Orals
 / Mon, 13 Apr, 08:30–12:00  / Room B9
Posters
 / Attendance Mon, 13 Apr, 17:30–19:00  / Blue Posters
This session is interested in the dynamical two-way interaction between the stratosphere and the troposphere, the mechanisms for this interaction, and its consequences for explaining both short-term atmospheric weather and longer-term climate variability. In addition to general contributions on the dynamics for stratosphere-troposphere interaction, this year's session will have two additional focus areas:

The first focus is the characterization of Sudden Stratospheric Warmings (SSWs). The most commonly used SSW definition is based largely on zonal wind diagnostics developed in the 1960s-70s, and often referred to as the 'WMO definition,' although there is some ambiguity in its application. Other, more sophisticated diagnostics have also been used to classify SSWs in recent years. What diagnostics are most useful for defining SSWs, and do we need to clarify or update the WMO definition? Given that more tailored diagnostics are useful for studying different aspects of SSWs, what purpose does a standard definition serve?

The second focus is on the SPARC activity SNAP (Stratospheric Network for the Assessment of Predictability). Studies have shown that anomalous conditions in the stratosphere particularly during northern hemispheric winters can influence tropospheric circulation up to 60 days ahead. We invite abstracts that focus on the role of the stratosphere for the predictability of tropospheric forecast in medium-range to sub-seasonal time scale. This includes all aspects of the connections between stratospheric conditions and tropospheric weather: the predictability of weak vortex conditions such as stratospheric major and minor warmings, stratospheric final warmings and stratospheric vortex strengthening events. Advances in operational forecasting that enhance the predictability of SSW events and related skill in tropospheric forecasts are of particular interest.