A Summertime Severe Weather Event Occurring in the Taipei Basin


A case of summertime strong convection occurring on 29 August 1999, producing hail and strong gusts in the Taipei Basin, was studied using conventional and Doppler radar data. Results showed that an upper-level cold vortex to the east of Taiwan provided strong vertical wind shear and increased potential instability favorable for the development of strong convection. Drying of the mid-troposphere was primarily responsible for the strong gusts as mid-level dry air entered the system and caused strong evaporative cooling.

It was found that the convection was triggered by sea breezes, upslope wind, and an accompanying convergent line under a weak synoptic-scale flow. It was suggested that the interaction of the sea breeze/upslope wind with the outflow from the convective system over mountain slopes was responsible for the maintenance and northwestward propagation of the system. Also, an upward dynamic pressure gradient associated with the increase in vertical shear under the influence of an upper-level cold vortex appeared to be a supportive factor for the westward propagation and intensification of this convective system. Finally, a mesovortex formed in the convective system by the tilting process in the area of strong updraft under increased environmental vertical wind shear.

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