ENSO-regional rainfall relationships have been used to develop statistical prediction techniques of seasonal regional precipitation based on the ENSO state in subregion of SESA (see Pisciottano et al. 1997, 1999, 2000, 2001) which have been evaluated a-posteriori.

Also, regional scale upper troposphere (200 hPa) circulation above the SESA + Atlantic sector statistical patterns have been described (and will be shortly revised here) and also its relationships to rainfall in SESA, at interannual and seasonal time scales. Particularly for spring, an anticyclonic vortex is identified as the most relevant mode of variation of the upper troposphere circulation, and it appears to be associated to increased seasonal rainfall in the UYRS subregion. (Cassarin and Kousky 1986, Mo and Nogues-Peagle 2001, Barros et. al. 2000, Robertson et. al. 2001). This allow us to built a statistical downscaling technique from atmospheric circulation to regional rainfall.

As NCEP CMP 14 Tropical Pacific (TP) SST forecast (Ji et. al. 1998) are available, we use that SST forecast to simulate an ensemble mean of the global atmospheric circulation. Then the downscaling technique allow us to ?project? the regional part of this circulation on the statistical patterns and estimate the regional rainfall in UYRS based on statistical relationships between these projections and rainfall. In these way we by-pass the use of model-calculated seasonal rainfall which we know have deficiencies derived from the low resolution of the version of the model used, and from other causes as deficiencies in the tropical South America processes, etc. Then, we expect that, as, for spring, the most relevant part of the ENSO influence on rainfall in SESA is caused via subtropical and extratropical changes of the atmospheric circulation (as PSA type patterns), we can simulate the large scale regional aspects of the atmospheric circulation affecting SESA and then estimate the regional rainfall at regions in SESA (UYRS).

First, we show results for the simulation of the atmospheric circulation of five warm TP cases (1982, 1986, 1991, 1994, 1997) and its projection in the most relevant statistical pattern, in order to approach to have a qualitative idea of the skill of the NCEP-forecasted TP-SST based UCLA-AGCM ensemble simulation during warm Pacific events. Second, we use August/2002 calculated NCEP TP-SST forecast for Oct-Dec/2002, to simulate the Oct-Dec/02 atmospheric circulation, and then we project this (regional) circulation on the principal mode in order to infere the regional rainfall for this season by using the downscaling technique, in four regions in UYRS.