Saturation fraction and gross moist stability in severely precipitating systems in the midlatitude Mediterranean environment

Deep moist convection is a severe phenomenon that recurrently hits both the Mediterranean basin and the tropical seas. Many attempts have been made to try to characterize and predict it, thus several physical indices have been proposed in literature during the last decade. Among these and for tropical environments, this study focuses on saturation fraction and gross moist stability, which are a measure of water vapor atmospheric columnar saturation, and an estimation of the convective behavior through the relation of its forcing and response, respectively. For the midlatitude, Mediterranean convection, the convective adjustment timescale τc has been introduced, which is an estimation of the convective equilibrium of the environment with the large scale.This paper tests the idea of a potential suitability of the tropical indices in a continuously-warming Mediterranean atmosphere, by testing them for the set of severe rainfall events that hit Italy from January 2007 to February 2009. In another study, those events have already been successfully classified into two categories showing equilibrium (type 1) or non-equilibrium (type 2) conditions, by using the convective adjustment timescale τc. Our results indicate that the classification based on such convective equilibrium criterion shows interesting differences in the saturation fraction against rain rates between the two event types, while their mean normalized gross moist stability turns out to be near zero for both and thus shows no tendency for the different flow regimes. Saturation fraction appears to vary somewhat with time, revealing a seasonality with an apparent maximum during summer–autumn.