A COMPARATIVE NUMERICAL STUDY OF TWO CUMULUS CONVECTION SCHEMES APPLIED TO HEAVY RAIN EVENTS IN THE WESTERN MEDITERRANEAN

Romero, R. (Departament de Fisica. Universitat de les Illes Balears. Palma de Mallorca. Spain)

Ramis, C. (same affiliation)

Alonso, S. (same affiliation)

A set of mesoscale numerical simulations using two different moist convective adjustments (Emanuel 1991, Kain and Fritsch 1990) has been performed to determine the sensitivity of the forecast fields -specially, the rainfall- to the cumulus convection scheme used. One of the schemes (Emanuel 1991) assumes the existence of a state of quasi-equilibrium between the rate of large scale atmospheric destabilization and the rate of stabilization by the convective processes, whereas the second one (Kain and Fritsch 1990) relies on the local convective available potential energy (CAPE). The study is carried out for the Western Mediterranean region where the coastal topographic forcing is of primary influence, and concentrates on two cases which produced heavy rain in the coastal zone: the first one, representative of most of these episodes, is characterized by a synoptic situation dominated by warm, moist advection at low levels; the second one, of frontal type, presents a much more stronger upper levels dynamic forcing. The results reveal the benefit induced in the forecast by using some type of convective parameterization, preventing from some unrealistic precipitation patterns associated with grid length explicit convection. Although the comparison attempt is conditioned by the limited number of cases considered, the numerical results suggest that the use of the Kain-Fritsch scheme is more appropiate for mesoscale simulations in the region, since the topographic signal on the precipitation field is enhanced in agreement with the observations.


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