Dynamical forcings in heavy precipitation events over Italy: lessons from the HyMeX SOP1 campaign

[摘要] The first Special Observation Period (SOP1) of HyMeX(Hydrological cycle in the Mediterranean eXperiment) was held in fall 2012 and focused on heavy precipitation events (HPEs) and floods in thenorthwestern Mediterranean. Nine intensive observation periods (IOPs)involved three Italian target areas (northeastern Italy, NEI; Liguria and Tuscany, LT; central Italy, CI), enabling an unprecedented analysis of precipitation systems in these regions. In the present work, we highlightthe major findings emerging from the HyMeX campaign and in the subsequentresearch activity over the three target areas by means of conceptual models and through the identification of the relevant recursive mesoscale features. For NEI, two categories of events (Upstream and Alpine HPEs) wereidentified, which differ mainly in the temporal evolution of the stabilityof the upstream environment and of the intensity of the impinging flow. Thenumerical simulation of convection in the Po Valley was found to be verysensitive to small changes in the environmental conditions, especially whenthey are close to the threshold between “flow-over” and “flow-around” regimes. For LT, HyMeX SOP1 focused on orographically enhanced precipitation over the Apennines and quasi-stationary mesoscale convective systems over the sea orclose to the coast. For the latter category of events, associated with themajority of the recent HPEs, local-scale or large-scale convergence linesappear fundamental to trigger and sustain convection. These lines areaffected not only by the orography of the region, but also by theperturbations induced by Sardinia and Corsica on the environmental flow,and, at later times, by cold pools formed via evaporation of precipitation. For CI, a high low-level moisture content and marked low-level convergenceover the sea were critical to support deep convection in the IOPs affectingthe Tyrrhenian coast. For the HPEs affecting the Adriatic regions, a cut-offlow over the Tyrrhenian Sea induces intense bora over the Adriatic basin. Low-level convergence triggers convection over the sea, while orographicuplift produces stratiform precipitation. The Adriatic Sea plays a criticalrole mainly through air–sea exchanges, which modify the characteristics of the flow and in turn the effect of the orographic forcing.

[学科分类] 妇产科学