Darwin’s mid-evening surge

Abstract

The passage of a sea-breeze front is a regular occurrence in Darwin, Northern Territory, Australia. On some days, what has been christened a ‘second sea-breeze’ is observed during the evening, an occurrence that has puzzled forecasters. We investigate this phenomenon using high-resolution numerical simulations of selected events. The simulations are compared with available data from automatic weather stations. They show that, on occasions when a ‘second sea-breeze’ is observed, the prevailing easterly to southeasterly winds over the ‘Top End’ advect a band of dry inland air northwestwards towards the Tiwi Islands during the morning. This dry air subsequently moves southwestwards towards Darwin and as it passes in the late evening, it is replaced by moist maritime air. Since this replacement is not a real seabreeze, we refer to the phenomenon as a mid.-evening surge. The results of idealised model calculations support these findings