ESRL/PSD Seminar Series

An eddy kinetic energy perspective on the downstream impact of tropical cyclones undergoing extratropical transition

Julia H. Keller
Deutscher Wetterdienst (DWD), Offenbach am Main, Germay


The extratropical transition (ET) of a tropical cyclone (TC) may strongly impact the midlatitude wave pattern by amplifying or triggering a Rossby wave train. In this way, such an event may facilitate the occurrence of high impact weather even in regions lying far downstream of the transitioning TC. The processes involved in the transition and interaction are often not well represented in numerical weather prediction (NWP) systems. As a result, predictability for downstream regions is frequently reduced during ET. A better understanding of the dominating processes and their representation in NWP systems will help to overcome those issues in predictability. Our study aims to identify the impact of a transitioning TC as an additional source of kinetic energy on the modification of the midlatitude flow and the associated forecast uncertainty. We employ ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) to gain multiple solutions for the interaction of two transitioning TCs with the midlatitude flow. By determining the sensitivity of the amplifying downstream wave train to the eddy kinetic energy (Ke) budget within the ensemble, we are able to identify the role of the ET in modifying the midlatitude flow configuration. Specific features of the Ke budget associated with the transitioning cyclone are found to have a significant impact on the amplification of the downstream wave train, while the Ke budget of the upstream midlatitude flow seems to be of secondary importance in one of the cases. In the seminar, a brief overview on the topic in general will be given, followed by an introduction in the analysis methods and a discussion of the results.

Thursday, August 7
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