Sensitivity of the distribution of thunderstorms to sea surface temperatures in four Australian east coast lows

Abstract

The relationship between the sea surface temperature (SST) distribution and the locations of thunderstorms during four Australian east coast lows is investigated using both lightning observations and numerical simulation results. The focus is placed on investigating changes in convective instability caused by the introduction of complex, high-resolution ocean eddy, and frontal structures present in Bluelink SST datasets. Global Position and Tracking System lightning data are overlaid on maps of SST to investigate whether a thunderstorm–SST relationship is discernible. Weather Research and Forecast model simulations are used to establish what atmospheric changes contribute to the observed distributions of thunderstorms. Maximum convective available potential energy (MCAPE) analysis shows a distinct relationship to the SST distribution. In particular, areas of elevated MCAPE are related to regions of warmer SST with horizontal advection often displacing increased MCAPE downwind of the warmer SST. At short timescales of 3–6 h, the differences in MCAPE become larger and more localised and show a strong correlation with the observed lightning. This suggests that at times the thunderstorms are directly related to the complex structures in the detailed SST dataset. For the damaging Pasha Bulker case, the plume of thunderstorms associated with the coastal damage occurs downwind of the region of enhanced MCAPE on the southern flank of the warm eddy. Based on these results, it is concluded that the particular features of the warm eddy enhanced the thunderstorm potential over the coastal region during this event and helped in localising the area of greatest impact for thunderstorm-related intense rainfall.