I fiumi atmosferici e il loro possibile impatto nel Mediterraneo

Atmospheric rivers are defined as long and narrow corridors of strong horizontal water vapour transport, typically associated with a low-level jet ahead of the cold front of an extratropical cyclone. A large fraction of moisture moves from the tropics through the midlatitudes within this filament-shaped structures, where the vapour is focused in the lower troposphere. Atmospheric rivers often lead to heavy or even extreme precipitation where they are forced to rise over mountains or by ascent in a warm conveyor belt. Most of the studies in the last 30 years have focused on the Pacific US Coast, while in the last decade atmospheric rivers over the Atlantic Ocean have been connected to extreme events over western Europe. The science of atmospheric river is pretty new for the Mediterranean basin, and only recently their impact has been revealed. In particular, their important role in intense precipitation events over northern Italy and the Alpine chain is demonstrated in two recent severe events (Vaia storm, 27-29 October 2018; Alex storm 2-3 October 2020) as well as in the infamous historical flood of 1966.