Ground wind convergence as source of deep convection initiation

摘要

The triggering of thunderstorms is a challenging matter in forecasting. Many physical descriptions, observations and simulations have been attempted by the scientific community. This work proposes to try an observational approach to the problem by calculating the 2-dimensional ground wind divergence, computed using 5' time resolution meteorological wind measurements, and the radar reflectivity obtained by the OSMER ARPA FVG C-Band Doppler Polarimetric Radar operating in Friuli Venezia Giulia plain (north eastern Italy).The aim is to search fora correlation between the ground wind convergence (e.g. the negative divergence) and the deep moist convection development The convergence is measured up to 180' in advance with respect to a convective event that occurred in the same area as pointed out by the radar reflectivity. The continuity equation in Boussinesq approximation has been considered and the 2-dimensional divergence has been calculated with a triangles method. X~2 test has been performed over the divergence-reflectivity distribution. Time integration of divergence has been performed to calculate the maximum height which a parcel can be forcefully lifted to, in a purely dynamic sense, to be compared to the Level of Free Convection obtained through radiosounding measurements.