The Mediterranean storm Vaia developed between 27 and 30 October 2018 and was responsible of extreme precipitation and floods over Italy, exceptional windstorms over the Alps and destructive waves and storm surges in both the Ligurian and Adriatic Seas. A pronounced large-scale trough over the western Mediterranean induced intense meridional moisture transport feeding the precipitation and set a favorable environment for Mediterranean cyclogenesis. Several low-pressure areas appeared over the western Mediterranean during these days, but only on 29 October an intense Mediterranean cyclone deepened rapidly and moved across the basin from the Tunisian coast to the western Alps. The cyclone first appeared as a shallow orographic depression on the lee side of the Atlas chain. Then, driven by the large-scale circulation, it moved across Algeria and reached the Mediterranean coast, where it started its explosive intensification, attaining the minimum pressure value of 977 hPa. Simulations performed with the Weather Research and Forecasting (WRF) model and sensitivity numerical experiments with the MOLOCH model allowed to investigate the factors responsible for the cyclone intensification. While the upper-level forcing seems to be critical (in particular the positioning of the left-exit region of the jet stream over the surface pressure minimum), sea surface fluxes played only a marginal role. The application of a diagnostic tool for the potential vorticity (PV) budget, that decomposes the PV into conserved and non-conserved contributions, confirmed the importance of the adiabatic, conserved PV anomaly.
Processes leading to explosive cyclogenesis during the Vaia storm in October 2018
Davolio S
2022
Abstract
The Mediterranean storm Vaia developed between 27 and 30 October 2018 and was responsible of extreme precipitation and floods over Italy, exceptional windstorms over the Alps and destructive waves and storm surges in both the Ligurian and Adriatic Seas. A pronounced large-scale trough over the western Mediterranean induced intense meridional moisture transport feeding the precipitation and set a favorable environment for Mediterranean cyclogenesis. Several low-pressure areas appeared over the western Mediterranean during these days, but only on 29 October an intense Mediterranean cyclone deepened rapidly and moved across the basin from the Tunisian coast to the western Alps. The cyclone first appeared as a shallow orographic depression on the lee side of the Atlas chain. Then, driven by the large-scale circulation, it moved across Algeria and reached the Mediterranean coast, where it started its explosive intensification, attaining the minimum pressure value of 977 hPa. Simulations performed with the Weather Research and Forecasting (WRF) model and sensitivity numerical experiments with the MOLOCH model allowed to investigate the factors responsible for the cyclone intensification. While the upper-level forcing seems to be critical (in particular the positioning of the left-exit region of the jet stream over the surface pressure minimum), sea surface fluxes played only a marginal role. The application of a diagnostic tool for the potential vorticity (PV) budget, that decomposes the PV into conserved and non-conserved contributions, confirmed the importance of the adiabatic, conserved PV anomaly.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
