GENERATION OF LOW-LEVEL MESOSCALE CONVERGENCE LINES OVER NORTHEASTERNAUSTRALIA

Thermally forced atmospheric circulations over the Gulf of Carpentaria region of northeastern Australia are investigated using a mesoscale n umerical model. The region is renown for the common occurrence of long westward-moving convective-and wave-cloud lines, including the celebr ated ''morning glory'' phenomenon. In the model, it is found that for uniform flows over the region ranging from northeasterly to southeaste rly, westward-moving, low-level convergence lines develop over the gul f during the night and early morning. The authors suggest that similar convergence lines in the atmosphere are responsible for the initiatio n and maintenance of the observed cloud lines. For northeasterly and e asterly flow, the convergence lines show little day-to-day variation, despite the relatively long inertial period in the region, which is ne arly two days. The calculations, which extend an earlier study by the same authors, lead to a new hypothesis to account for the observed lon gevity of morning glory bore waves. They provide also an explanation f or the marked diurnal oscillation in the low-level easterly flow obser ved at Weipa during a field experiment to investigate the so-called no rth Australian cloud line.