Diabatic Processes and the Generation of the Low-Level Potential Vorticity Anomaly of a Rainstorm in Saudi Arabia

Abstract

The diabatic heating is calculated, using the thermodynamic equation in isobaric coordinates, of a heavy rainstorm that developed over Jeddah, Saudi Arabia on 25 November 2009. Throughout the period of study, the horizontal heat advection is the dominant term and the vertical advection term is opposed by the adiabatic one. The contribution of the local temperature term to the change in diabatic heating is relatively very minimal. The presence of the Red Sea and its adjacent mountains suggest that the diabatic heating in the lower atmosphere on that rainy day is primarily due to the latent heat released by convection. The dynamics of the studied case is also investigated in terms of isobaric Potential Vorticity (PV). The results show that the heating region coincides with the location of the low-level PV anomaly. Ertel’s Potential Vorticity (EPV) generation estimates imply that condensation supplies a large enough source of moisture to account for the presence of the low-level EPV anomaly. The low-level diabatic heating-produced PV assisted in amplifying the surface thermal wave early in the rainstorm development and in the upper-level wave during the later stages of the system’s growth.