Sea-Breeze Circulations over Cape York Peninsula and the Generation of Gulf of Carpentaria Cloud Line Disturbances

Abstract

A numerical study of sea-breeze circulations over Cape York Peninsula in northern Australia is presented. Simulations using a two-dimensional version of the University of Virginia mesoscale model provide insight into the thermally induced circulations over the peninsula during the ?dry? season under typical conditions of a prevailing easterly geostrophic flow. Calculations are performed for a wide southern cross section of the peninsula (400 km of land) and a narrow northern section (200 km of land), with terrain appropriate to these cross sections included. A southern section simulation without topography is discussed for comparison. Particular interest is focused on the collision of the east and west coast sea breezes. The possibility is explored that the double sea-breeze convergence may act as a trigger, not only for morning glory cloud line disturbances in the southern Gulf, but also for the so-called North Australian Cloud Line (NACL). The latter is a line of convective cloud which forms frequently in the early evening on the western side of the peninsula in the north and subsequently moves westwards across the Gulf, and sometimes even across the ?Top-End? of Australia, retaining its identity for up to two days. It is an important feature of the weather in the north Australian tropics. The model calculations show that with a typical easterly geostrophic flow of 5 m s?1, the location and timing of the collision of the sea breezes in the northern section correspond well with those for the onset of the NACL. However, in the absence of moist processes, the disturbance arising out of the collision decays within a few hours. In the southern section, collision occurs in the late evening and leads to the formation of a westward traveling bore wave in the lower atmosphere. The bore continues to propagate throughout the night with little diminution in amplitude and is believed to be the model-analogue of the morning glory disturbance. However, if the easterly geostrophic flow is increased to 8 m s?1, collision of the sea breezes occurs in the early evening and again the resulting disturbance decays within a few hours. The significance of these results in regard to morning glory formation is discussed.