Atmospheric convergence diabatically generated in the CBL over a mountainous peninsula

The mesoscale atmospheric flow is investigated that is diabatically forced hy the diurnal warming in the convective boundary layer (CBL) over Calabria , a mountainous peninsula in southern Italy. This study, carried out using a 3D nonlinear numerical model, is concerned with summer time when the larg e-scale flea is weak. Owing to several favourable conditions, strong sea-br eeze and mountain valley hows are developed over this area. The thermal gra dients associated with contrast of either mountain peaks-free atmosphere or land-sea merge together generating wide and intense circulation. The resul ts show strong convergence in the lower and divergence in the mid and upper troposphere. The depth of the CBL is of the order of two thousand metres, while the depth of the mesoscale atmospheric response is of the order of th e troposphere height, and has a horizontal scale of the order of two Rossby radii. The main effect of such circulation is tile reorganisation of the h umid air over the region. Indeed the humid air: that comes from the lower l evels, is advected upward by breeze circulation; determining the onset of c umulus cloud and triggering summer thunderstorm over the region. The model provides successful simulations of the convective development observed by g round stations.