Morning glory wind surges and the Gulf of Carpentaria cloud line of 25-26 October 1984

Observational data on three 'morning glory' wind surges, which occurred in the southern part of the Gulf of Carpentaria region of northern Australia on two consecutive mornings (25 and 26 October 1984), are presented together with a summary of surface synoptic analyses and satellite imagery for the period. On 25 October a wind surge from the south, which passed over Burketown at about 0515 local time, was followed about four hours later by one from the northeast. On 26 October a large amplitude and unusually coherent wave disturbance was associated with a southerly surge in the early morning hours (about 0130 at Burketown). Aircraft temperature soundings ahead of and behind the two surges of 25 October showed significant cooling following the passage of the surge, indicative of its origin as a gravity current, and consistent with a few other documented cases. The northeasterly surge of 25 October was investigated from the air in a region over the Gulf some 100 km northeast of Burketown. There a line of convective cloud appeared to mark Its leading edge, while the evidence is that further to the southeast the leading edge was marked by a series of typical morning glory wave clouds. The latter were imperceptible and the former barely discernable in the Geostatlonary Meteorological Satellite infrared imagery. They were both striking in high resolution visible imagery from the NOAA 6 polar orbiting satellite, but even then the two types could not be distinguished. The synoptic data are suggestive of a possible link between the northward movement of an inland trough during the night and the genesis of the southerly surges. The low-level wind data highlight the role of nocturnal wind surges which, together with sea and land breeze circulations, contribute significantly to the diurnal variability of wind structure below 2 km in the southern Gulf region.