Impacts of the tropical trans-basin variability on Australian rainfall

Abstract

A large-scale mode of sea level pressure variability between the Pacific and Atlantic basins—referred to as the tropical trans-basin variability (TBV)—has shown multi-year predictability beyond that normally associated with El Nino Southern Oscillation (ENSO). Here we examine the relationship between the TBV and regional rainfall, which, if significant, would imply that the TBV predictability could be used to improve rainfall forecasts. We find TBV to be significantly related to rainfall, a relationship that is strongest over Australia during spring. We find Australia to experience drier conditions during the positive phase of TBV and wetter conditions during the negative phase, a pattern similar to that of ENSO. Furthermore, TBV is associated with rainfall responses that are of similar magnitude to ENSO, but there is some degree of independence between TBV and the Pacific modes defined by sea surface temperature indices. The global teleconnections related to the different TBV phases suggest that though many TBV and ENSO events overlap, pure ENSO events are primarily driven by the Pacific whereas pure TBV events are driven by the Atlantic Ocean. An El Nino coupled with a positive TBV event leads to significant drying over the east coast of Australia while the combined negative phase leads to widespread wetting over most of the country, which can be attributed to an enhancement of the anomalous Walker Circulation and the resulting moisture convergence and wind patterns.