Orography Effects on the Structure of Typhoons:Analyses of Two Typhoons Crossing Taiwan


Taiwan is a unique place to study typhoon-orography interactions. On the average, four typhoons encounter the high Central Mountain Range (CMR) per year. This study analyzes the hourly surface wind and pressure structure over the Taiwan area during typhoon Nadine (1971) and typhoon Betty (1961). The results show the center of Nadine passed over the CMR continuously. On the other hand, secondary circulation and a secondary low formed over western Taiwan when typhoon Betty moved close but still to the east of the CMR. The original center and the secondary circulation/low moved in different directions. When the original center of Betty weakened over the east side of the CMR, the secondary circulation/low became the dominating system. This situation is very different from a typhoon track over an open ocean. The formation of the secondary circulation/low started from a pronounced wind shift from northerly to southwesterly over southwestern Taiwan. The southwesterly wind blew against the CMR and induced a ridge in the low pressure zone over the west side of the CMR was separated from the original center over the east side. The southwesterly near the CMR was further deflected to northward by the mountain to form a cyclonic circulation over the west side of the CMR.

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