Kinematic estimates of horizontal divergence and vertical pressure-velocity were made from routine upper wind measurements over northern Australia for January and July 1979. The mean vertical profiles for each month at the 2300 UTC observation time are consistent with previous climatological studies but a strong and systematic diurnal variation is evident in the January results, with a weaker variation in July. These variations are also evident in operational numerical tropical analyses. Day-to-day Ouctuations in the diagnosed vertical velocity agree with expectations from synoptic patterns. The variance of the daily vertical velocity in July greatly exceeds the subsidence rate required to merely compensate the atmospheric radiative cooling, indicating that the downward branch of the Hadley cell in this region is not in local radiative balance. The mean vertical velocity profiles for January show deep upward motion in the evening (1100 UTC) in contrast to reported profiles over other heat low areas such as Saudi Arabia (Blake et al. 1983). The results for both January and July suggest that the biogeophysical feedback of increases in surface albedo to atmospheric subsidence, as proposed by Otterman (1974) and Charney (1975), could only be a minor effect in the northern Australian region.
T.L. Hart (Fri,) studied this question.
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