Remote impact of North Atlantic hurricanes on the Mediterranean during episodes of intense rainfall in autumn 2012

Abstract

Autumn is the most favourable season for tropical cyclones to undergo extratropical transition and interact with the midlatitude flow over the North Atlantic. Autumn is also the season when intense rainfall over the Mediterranean is often triggered by Rossby wave breaking. The impact of tropical cyclones on downstream wave breaking is investigated here during three episodes of intense rainfall which were the target of HyMeX (Hydrological cycle in Mediterranean eXperiment) in autumn 2012. Five‐day simulations of hurricanes Leslie, Rafael and Sandy were performed with the Meso‐NH model in a domain encompassing the North Atlantic and the Mediterranean. Control simulations were compared to simulations in which the hurricanes were filtered out from the initial conditions. In each case, the hurricane locally impeded the forward progression of an upstream trough, then reintensified as an extratropical cyclone during the wrap‐up of the trough. The local impact of Leslie and Rafael on the midlatitude flow quickly propagated downstream along a polar jet and amplified Rossby wave breaking but decreased the intensity of the forecast precipitation over the Mediterranean. The local impact of Sandy propagated downstream along a subtropical jet in addition to the polar jet and resulted in a weak impact of the forecast precipitation on the Mediterranean. This study suggests that the interaction of tropical cyclones with the midlatitude flow over the western North Atlantic may be considered a perturbation to, rather than a source of, downstream wave breaking.