Synergistic use of polarimetric radar measurements and simulated cloud microphysical profiles for rainfall estimation in mountainous regions

Rainfall estimation in mountainous regions is one of the major problems for radar meteorologists in different parts of the world due to ground clutter contamination and beam blocking at low elevation angles. The approach presented in this paper relies on the particle classification capabilities of a polarimetric radar, allowing a microphysical characterization of the cloud vertical profile. As a matter of fact, using a proper set of elevation angles, the radar can provide estimates of the Water Content by sampling, at least, the upper portion of the cloud in a mountainous area. In such situation, the extrapolation of rainfall rate at ground is completely arbitrary without other information. This paper investigates the use of the upper level radar estimates as a constraint to identify likely WC profiles within the archive generated by detailed numerical simulations of severe Italian storms. The numerical model used is the University of Wisconsin – Nonhydrostatic Modeling System (UW-NMS). The UW-NMS has a unique ability to represent both subtle and severe topography through a new variably stepped topography scheme. The model also features an enstrophy conserving formulation designed to optimally simulate the scale interaction processes, such as that occurring between cumuli and the mesoscale flow regime. The radar data used in this study consist of the polarimetric measurements collected by the weather radar of Fossalon di Grado, in North-Eastern Italy. Results obtained on episodes occurred during the autumn 1999 MAP field campaign will be presented and discussed.