Dept. of Geosciences Colloquium: Process-based classification of Mediterranean cyclones using potential vorticity

Zoom: https://tau-ac-il.zoom.us/j/87073901428?pwd=Zay3aB8aBEigEH9SC4iEU9pByK9FCN.1

Abstract:

Mediterranean cyclones handle extreme weather events across the Euro-African basin, affecting the lives of hundreds of Millions. Despite many studies addressing Mediterranean cyclones (MCs) in the last decades, their correct simulation and prediction remain a significant challenge to the present day. This may be attributed to the large variability between MCs, which differ greatly from each other in many aspects. Past classifications of MCs are primarily geographical and seasonal, yet, recent advances and the appearance of “Medicanes” – devastating tropical-like Mediterranean cyclones - emphasize the need for a dynamical classification, focusing on cyclone genesis and deepening mechanisms. A variety of processes alternately govern Mediterranean cyclones' genesis and evolution, including diabatic and adiabatic processes, topographic influences, and land-sea contrasts. Fortunately, each process bears a distinct signature on the potential vorticity (PV) field. Therefore, a PV approach is called upon to better understand the driving mechanisms of the different “types” of Mediterranean cyclones. Here, a combined cyclone tracking algorithm is used to detect and track Mediterranean cyclones in ECMWF ERA5 from 1979-2020. Cyclone-centered, upper-level isentropic PV structures in the peak time of each cyclone track are classified using the Self Organizing Map (SOM). The SOM analysis reveals 9 classes of Mediterranean cyclones, with distinct cyclone characteristics, associated hazards, and long-term trends. Though classified by upper-level flow structures, each class shows different flow structures down to the surface. Unique synoptic, thermal, dynamical, seasonal, and geographical features indicate dominant processes in the evolution of each Mediterranean cyclone subset. Furthermore, the tropopause-surface coupling is explored and reveals the importance of topographically induced RWB to the generation of the most extreme Mediterranean cyclones. These results enhance our understanding of Mediterranean cyclones' predictability, by linking predictable Rossby wave formations and life cycles to under-predicted cyclonic variability.

Event Organizer: Dr. Ariel Lellouch