Evidence of local sea surface temperatures overriding the southeast Australian rainfall response to the 1997-1998 El Niño

Abstract

El Niño events typically bring rainfall deficits to southeast Australia (SEA), for example, during the El Niño of 1982-1983. However, SEA experienced near average rainfall during the similar El Niño of 1997-1998. Using an ensemble of atmospheric general circulation models (AGCMs) forced with observed SSTs, we demonstrate that the different September-November rainfall during the 1982 and 1997 events is primarily explained by differences in SST forcing from outside the central and eastern equatorial Pacific. The AGCMs reproduce an observed relationship between SEA rainfall and SSTs to the northeast of Australia. Significantly, cooler northeast Australian SSTs during 1982-1983 shifted the rainfall distribution, making a rainfall deficit more likely (relative to the situation in 1997-1998). However, stochastic atmospheric processes can modulate the El Niño and regional SST influence, and the use of an ensemble of AGCM simulations allows the separation of the effects of stochastic atmospheric processes and SST forcing.