Monsoon Dynamics

Out of the five equatorial vortices studied in this investigation, the following significant features are obtained. 1. Disturbances in the trades associated with lateral shear were found to be important for the genesis of these equatorial vortices. 2. Intensification of these disturbances depended very much on the timing of the occurrence of the cold surge and the presence of the disturbance in the trades. 3. Low-Ievel easterly jets at 850 mb were found over the northem part of Peninsular Malaysia during the intensification stage of the four equatorial vortices that interacted with the cold monsoon surge and brought heavy rain to Peninsular Malaysia. Associated with the jet there was significant vertical shear about 20 knots between the lower and middle troposphere. 4. Heavy rain was confined to the cyc10nic shear side of the easterly jet and around the near-equatorial trough axis. 5. For the equatorial vortex that brought along heavy rain only to Sarawak, the low-Ievel easterly jet was absent over Peninsular Malaysia even though there was intense cold surge. 6. For those vortices that affected Peninsular Malaysia, the vertical wind fields were distincdy different from those associated with the vortex that affected only Sarawak. 7. For the maintenance and intensification of the disturbances, a complex combination of CISK mechanism and mixed barotropic and baroc1inic instability is suspected.