Abstract
A midlevel vortex which occurred during the period of 16-17 June 1987 in the Taiwan Area Mesoscale Experiment (TAMEX) is analyzed in this paper. All of the intensive observational data collected in this period were employed to reveal the structure and evolution of the vortex. These included the conventional surface and upper air observations, conventional and Doppler radar data, and the P-3 aircraft measurements. The cloud top temperatures were also analyzed using enhanced Geostationary Meteorological Satellite (GMS) IR imageries.
Analyses showed that this midlevel vortex had a cold, moist core in the middle and lower troposphere (900-550 hPa; 1-5 km) capped by a warm upper troposphere (300-200hPa) and tilted slightly northwestward towards the mid-tropospheric cold air in the early stage. It developed upward to the 300 hPa (-10 km) warm region and downward to 950 hPa (0.5 km) in the later stage. The horizontal scale of this vortex was about 100-200 km in diameter and the life span was possibly more than 24h. The heavy rainfall (>125 mm/24h) over northeastern Taiwan appeared to be due to the combined effects of the enhanced terrain lifting and the particular structure of the maximum wind over northeastern quadrant of this vortex. Based on the overall results, it is proposed that the vertical vortex stretching process coupled with the local topographical effect and the pre-existing vorticity associated with the westward propogating trough was primarily responsible for the formation of this vortex. The reintensification of the vortex during its northward journey over land in the later stage was perhaps mainly due to the intensification of the mesoscale convective systems over the vortex area.
