Numerical simulation of a heavy rainfall event over Portugal using mesoscale model

Abstract

Strong rainfall events have unquestionably one of the largest economic and social impacts of any atmospheric phenomena. The purpose of this paper is to simulate the weather conditions associated with the heavy precipitation episode during 11-13 March 2002, which generated intense rainfall as well as hail and snow in the central and northern regions of Continental Portugal. The simulation was carried out using the Regional Atmospheric Modeling System (RAMS), through a three nested grids configuration 48 km, 12 km and the highest resolution being 3 km, to capture the synoptic and mesoscale circulation patterns. The initial and lateral boundary conditions necessary to drive RAMS were taken from the Brazilian Center of Weather Prediction and Climate Studies (CPTEC) global model forecasts in the form of spectral coefficients with T62 triangular truncation equivalent to 1.825º resolution in the meridional and zonal directions. The model results show that the RAMS model is a useful framework to describe the rainfall patterns over the region, reproducing the area without rainfall within the domain reasonably well, although the model overestimated or underestimated the observed values at different periods. The spatial distribution of the total accumulated rainfall showed some tendency to predict more precipitation over higher elevations, probably influenced by dynamical forcing and associated microphysical processes.