Geosciences Dept. Seminar: The importance of warm conveyor belts for Mediterranean cyclones

Abstract: 

Extreme precipitation events are associated with the passage of cyclones and their attendant fronts in the Mediterranean region. Particularly, large scale extreme precipitation is of societal importance for its association with a high risk for extended flooding and severe damage. Using ERA-Interim reanalysis data from ECMWF and mesoscale model (COSMO) simulations, we study the dynamics that govern large-scale extreme precipitation, where the central role of cyclones and warm conveyor belts (WCBs) is highlighted. Within WCBs, moist air rises slantwise from the surface to the upper troposphere, while releasing latent heat and producing precipitation. However, the organized release of latent heat within the WCB, has implications beyond the local precipitation impact. In the second part of the talk, the dynamical role that WCBs play as precursors of intense Mediterranean cyclones will be quantified climatologically. Rossby-wave breaking is shown to be a precursor to intense Mediterranean cyclones, which may be enhanced by WCBs developing over the Atlantic Ocean. More precisely, WCBs supply the upper troposphere with air masses of low potential vorticity that, in turn, amplify ridges and thus favor Rossby wave breaking. We identify and validate the relevance of the mechanism that connects Atlantic cyclones and intense mature Mediterranean cyclones through ridge amplification by WCBs. Using a feature-based approach, we analyze the 200 most intense Mediterranean cyclones for the years 1989-2008 and show that their majority (181 cases) is indeed associated with this mechanism upstream. 

Seminar Organizer: Prof. Eyal Haifetz