AN INTEGRATED VIEW OF THE 1987 AUSTRALIAN MONSOON AND ITS MESOSCALE CONVECTIVE SYSTEMS .2. VERTICAL STRUCTURE

The vertical structure of monsoon thermal forcing by precipitating con vection is diagnosed in terms of horizontal divergence. Airborne Doppl er-radar divergence profiles from nine diverse mesoscale convective sy stems (MCSs) are presented. The MCSs consisted of multicellular convec tive elements which in time gave rise to areas of stratiform precipita tion. Each of the three basic building blocks of the MCSs-convective, intermediary, and stratiform precipitation areas-has a consistent, cha racteristic divergence profile. Convective areas have low-level conver gence, with its peak at 2-4 km altitude, and divergence above 6 km. In termediary areas have convergence aloft, peaked near 10 km, feeding in to mean ascent high in the upper troposphere. Stratiform areas have mi d-level convergence, indicating a mesoscale downdraught below the melt ing level, and a mesoscale updraught aloft. Rawinsonde composite diver gence profiles agree with the Doppler data in at least one important r espect: the lower-tropospheric convergence into the MCSs peaks 2-4 km above the surface. Rawinsonde vorticity profiles show that monsoonal t ropical cyclones spin-up at these elevated levels first, then later de scend to the surface. Rawinsonde observations on a larger, continental scale demonstrate that at large horizontal scales only the 'gravest v ertical mode' of MCS heating is felt, while the effects of shallower c omponents of the heating (or divergence) profiles are trapped near the heating, as predicted by geostrophic adjustment theory.