A Formulation of the Continuity Equation of MUSCAT for either Flat or Complex Terrain

Abstract

The Mesoscale Alpine Programme (MAP) involved an ensemble of airborne and ground-based Doppler radars dedicated to the observation of precipitating systems over the Alps. The derivation of the three-dimensional wind fields from the multiple-Doppler synthesis and continuity adjustment technique (MUSCAT) requires that orography-induced air circulation, in particular when solving the mass continuity equation, is taken into account. A formulation of this equation in its flux form is proposed, which has the advantage of applying to either flat or complex terrain and thus eliminating the need to explicitly evaluate the vertical velocity associated with the slope wind at the surface. Pseudo-Doppler observations of a pair of ground-based radars that were operated during MAP, deduced from a modeled pre-MAP case, are used to validate the proposed solution and to investigate the performances of the Doppler wind synthesis above mountainous regions.