An experiment with RAMS on the SACZ dependence on SST

One of the main features of the South American summer climate is the South Atlantic Convergence Zone (SACZ). In the present work, the dependence of the SACZ on the sea surface temperature (SST) is analysed with an experiment performed with the Regional Atmospheric Modelling System (RAMS). Two one-month integrations are done: a control run with fixed monthly mean January 1997 Reynold's SST; and an anomaly SST run. In the latter, a steady positive SST anomaly ranging between 0 and 2C is added to the SST field northward of the monthly mean position of the control run SACZ. The regional model is initialized at 00Z January 1, 1997 with NCEP analysis. Its lateral boundary conditions are updated each 6 hours also by NCEP analysis. The regional model domain covers southeast Brasil and the southeastern South Atlantic. The resolution is 30 km in the horizontal and 28 levels in the vertical.

The control integration is compared with observational data and analysis. The comparison shows that RAMS produced realistic patterns of precipitation, surface temperature, and circulation, and it simulated well the SACZ. The anomaly SST experiment shows that the SACZ does not substantially depend on the SST for its formation, but a signal is observed on its location and intensity.