A physics ensemble performed by changing convective parameterization in a regional climate model

JOSEFINA BLÁZQUEZ AND MARIO N. NUÑEZ

Buenos Aires, Argentina

Otro; Kick off meeting de CLARIS LPB; 2008

A physics ensemble was performed by changing the cumulus parameterization options in WRF regional model. Simulations were carried out in a domain covering southern of South America. The model was run during 60 days (December 1970 - January 1971), in an anomalously rainy period, considering the first 31 days as a spin up period.  We evaluate how much variability is introduced when a particular model is reconfigured and how good the ensemble-mean represent the accumulated and daily precipitation in several regions of southern South America. The ensemble spread of simulated precipitation shows values between 25 and 50 mm in the South of Chile, Paraguay, Uruguay and Northeast of Argentina, but near northern Andes, part of Bolivia and part of South of Brazil the standard deviation reach values between 150 and 300 mm. The ensemble mean had a great agreement with ERA40 reanalysis in both, the daily and the accumulated precipitation in the south of Argentina and over the Andes mountain range, regions where a negative precipitation trend has been observed since 80´s. However, in regions located in the center part of Argentina, where the precipitation is increasing since 70´s, the ensemble mean did not work like we had expected, but we found that the best parameterization in this regions to represent both, the accumulated and daily precipitation was Betts- Miller- Janjic.