Generation of low-level mesoscale convergence lines over northeastern Australia

Thermally forced atmospheric circulations over the Gulf of Carpentaria region of northeastern Australia are investigated using a mesoscale numerical model. The region is renown for the common occurrence of long westward-moving convective-and wave-cloud lines, including the celebrated "morning glory" phenomenon. In the model, it is found that for uniform flows over the region ranging from northeasterly to southeasterly, westward-moving, low-level convergence lines develop over the gulf during the night and early morning. The authors suggest that similar convergence lines in the atmosphere are responsible for the initiation and maintenance of the observed cloud lines. For northeasterly and easterly flow, the convergence lines show little day-to-day variation, despite the relatively long inertial period in the region, which is nearly two days. The calculations, which extend an earlier study by the same authors, lead to a new hypothesis to account for the observed longevity of morning glory bore waves. They provide also an explanation for the marked diurnal oscillation in the low-level easterly flow observed at Weipa during a field experiment to investigate the so-called north Australian cloud line.