On the reliability and uncertainties of a regional climate simulation

N. L. PESSACG; S. A. SOLMAN

Buenos Aires

Workshop; Kick-off Meeting, CLARIS-LPB; 2008

CLARIS-LPB PROJECT

The sensitivity of the regional model MM5 was analyzed on a particular period (November/December 1986) associated with extreme climate events. The MRF planetary layer scheme, with different combination of convective scheme, shows a better simulation of precipitation than ETA scheme over our study domain. The experiments using the Kain-Fritsch convective scheme present a systematic error in representing the circulation at lower levels. This fault entails several problems in the representation of moisture advection over La Plata Basin, which leads to an underestimation of precipitation over this region. These anomalies circulations simulated with Kain-Fritsch convective scheme are associated with an overestimation of verticals velocities which produce anomalies convergences in the region. Simulations with Grell convective scheme underestimates precipitation over Brazil, but performs reasonably well over La Plata Basin. We have found a strong sensibility to changes in convective timescale in Grell scheme. Finally, we conclude that the best configuration of the model is found using MRF planetary boundary scheme and Grell convective scheme with a convective timescale dt=900seg and with a closures assumptions: dp=50hPa and pbc=50hPa. This experiment represents well the precipitation and the low level circulation over La Plata basin and improves the simulation of rainfall over South Atlantic Convergence Zone for December.