Sensitivity of regional climatic simulation over Southeastern South America to SST specification during austral summer

Abstract

AbstractThe impact of the sea‐surface temperature (SST) specification over the South Atlantic Ocean on the interannual variability of the simulated precipitation and air temperature over Southeastern South America (SESA) was studied during ten austral summers, from 1989 to 1998, using the Regional Climate Model version 3 (RegCM3), driven by the National Centers for Environmental Prediction (NCEP) reanalysis. The analyses were performed by comparing simulations forced with: (1) monthly observed SST (OSST); (2) SST composed by the persistence of November SST anomalies superimposed on the climatological observed cycle (persisted SST‐PSST). The results show that, over the continental SESA, the PSST impact is low on the simulated seasonal precipitation and air temperature climatologies. Furthermore, the interannual seasonal anomalies in this area do not change sign as a function of the prescribed SST. This is very important since it shows that, on a seasonal timescale, the use of PSST over the subtropical South Atlantic does not introduce additional error source in the regional model simulations over the continental SESA. Over the Atlantic Ocean, mainly in the region where the South Atlantic Convergence Zone (SACZ) acts, the simulations presented a direct response as a function of the SST, i.e. if the PSST is warmer (colder) than the OSST, the seasonal precipitation increases (decreases).Ensemble simulations of a particular summer showed that the deviation introduced by PSST is of the same intensity of the model internal variability and the use of five members ensemble‐mean eliminates the differences between OSST and PSST experiments over continental SESA. However, this result cannot be applied over the subtropical South Atlantic Ocean, where the differences were not eliminated by calculating the ensemble‐mean, showing a signal generated by the prescribed SST. Copyright © 2006 Royal Meteorological Society