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Li-Huan Hsu

2013-03-06
13:00:00 - 15:00:00

308 , Mathematics Research Center Building (ori. New Math. Bldg.)

This study investigates the influence of topographic induced convection on the landfall typhoon motion in Taiwan. Data for 84 typhoons that reached eastern coast of Taiwan from 1960 to 2010 are analyzed. For 61 continuous track typhoons among all cases, we find that 77% of the slow-moving tropical cyclones (TCs) made landfall on the northern end of Taiwan’s eastern coast, while 60% of the fast storms had southeast coastal landfalls. This geographic asymmetry with respect to typhoon translation speeds widened after landfall, as the slow-movers typically decelerated during the overland period while the faster TCs sped up. In particular, the average overland duration was 16 hours for the slow class, compared to only 3 hours for the fast-moving typhoons. The combination of slower translation with longer duration for the northern class of TCs led to large rainfall on the southwestern slope of the island’s Central Mountain Range. Weather Research and Forecasting Model experiments are used to study the effect of convection on storm motion over Taiwan. Potential vorticity tendency diagnosis method is applied to analyze the contribution of diabatic heating on typhoon motion. Our experiments show that the asymmetric diabatic heating due to the convection will contribute to the typhoon track deflections near Taiwan. After typhoon landfall, the topographically phase-locked convection acts to slow down (speed up) the northern (southern) landfalling typhoons. Our model results also suggest a positive feedback mechanism that exists for the slow storms, in which the convective heating pattern forced by topography acts to reduce the TC motion, leading to even more prolonged precipitation and heating, yielding further speed reductions after landfall for northern landfalling typhoons. Key words: Typhoon track deflection, typhoon translation speed, topographic phase-locked convection, diabatic heating, potential vorticity tendency diagnosis.