GFDL Formal Seminar

Thu, Nov 21, 2019, 2:00 pm to 3:00 pm

This talk will examine S2S prediction skill associated with tropical-extratropical interaction and the impacts of stratospheric variability on the troposphere. This talk will examine the occurrences of the extratropical-transition (ET) of tropical cyclones in producing early, weak stratospheric polar vortex events that extended the period of influence of an ET's impact on the extratropical waveguide. Using the S2S Prediction Project database, the analysis highlights 1996 and 2016, two seasons where sequential ET events, in the North Atlantic then North Pacific, resulted in large amplitude planetary wavenumber 2 patterns that influenced the stratospheric circulation. Both events produced anomalous upward wave activity flux into the stratosphere and a weak stratospheric vortex. The impacts were enhanced negative Arctic Oscillation (Northern Annular Mode) conditions, associated with cold air outbreaks and high impact weather, for approximately 4 weeks. Analysis of similar events from the 1996-2010 period, available in S2S Prediction Project hindcast data, reveals the implications of resolving the stratospheric variability and the horizon of forecast skill for this sequence of events. The second part of the talk explores these results and considers S2S tropical variability from the MJO, ENSO and the QBO to examine variability of the location, frequency, and duration of October and November ET events. The analysis shows that the sign of the QBO influences not only the frequency of ET events, but also the latitude of intense extratropical cyclones. The mechanisms of the QBO to influence weather systems are discussed in the context of these early season weak vortex events and S2S prediction.

Smagorinsky Seminar Room 209

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