Precipitation changes due to the introduction of eddy-resolved sea surface temperatures into simulations of the “Pasha Bulker” Australian east coast low of June 2007

Abstract

Weather research and forecast (WRF) model simulations are used to investigate how the distribution of precipitation is related to the distribution of sea surface temperatures (SSTs) during the life cycle of the Australian east coast low of 7–9 June 2007. The focus is placed on investigating changes caused by the introduction of complex ocean eddy and filament structures present in the Bluelink ReANalysis (BRAN) SST data set. In the simulations, enhancement of rainfall is found over and downwind of warmer SSTs and suppression of rainfall over and downwind of cooler SSTs. Specifically, a large warm eddy present during this case is associated with an enhancement of rainfall along its downwind (southern) flank where a strong SST gradient exists. Overall, the model demonstrates considerable skill in simulating the event, although the simulated main rainband propagates southward earlier than observed. However, the maximum one hourly rainfall totals at the stations that received the greatest rainfall are greater and closer to the observed maxima when the BRAN SSTs are used. Global position and tracking system lightning data are overlaid on maps of SST and used to investigate whether a thunderstorm–SST relationship is discernable. An ensemble of WRF simulations is used to establish what atmospheric changes contribute to the observed distributions of thunderstorms. It is concluded that the complex upper ocean heat content structure present during this case significantly influenced the storm’s impact. Therefore, an accurate eddy resolving SST data set may be important for accurate forecasts of future storms of similar nature.