South American rainfall impacts associated with inter-El Nino variations

The impacts of inter-El Nino events on South American circulation during austral summer are investigated using observations and an atmospheric general circulation model (AGCM). The AGCM was forced with sea surface temperature (SST) anomalies in the tropical Pacific for the two El Nino events of 1997/1998 (EN97) and 2002/2003 (EN02). The strong eastern Pacific SST anomaly of EN97 resulted in a typical displacement of the Walker circulation, causing a decrease in precipitation across the north of South America. A strengthened low-level jet (LLJ) east of the Andes during EN97 enhanced the moisture transport from low latitudes to the subtropics, leading to intensified precipitation over southeastern South America. The simulated circulation in EN02 reveals a weakened LLJ and anomalous convergence of moisture over eastern South America, which can be attributed to a displacement of the Pacific-South American (PSA) mode in response to the different location of the heat sources along the tropical Pacific Ocean. Citation: Hill, K. J., A. S. Taschetto, and M. H. England (2009), South American rainfall impacts associated with inter-El Nino variations, Geophys. Res. Lett., 36, L19702, doi:10.1029/2009GL040164.