Elucidating the characteristics of eyewalls and rainbands associated with a severe typhoon influenced by Taiwan’s high orography using Doppler radar analysis

Radar observations of the strong Typhoon Bilis (2000) are unique for investigating the effect of Taiwan high orography on the mesoscale structures of storm system in the vicinity of southeastern Taiwan. Typhoon Bilis was the first tropical storm, which possessed the double eyewall feature observed by Doppler radar over the Taiwan area. The inner eyewall exhibited an approximately circular shape with a diameter of 20 km. Convections associated with the storm were cyclonically and radially outward propagated, with the linear aspect in the right flank of the system and counterclockwise and spiral migration in the left flank, maintaining the development of the outer eyewall. The low-level maximum Doppler winds in the left and right flanks relative to the typhoon movement were comparable, owing to a prominent confluence in the left flank. The prominent confluent zone was constructed by two wind fields, the northwesterly from the inner circulation of the typhoon and the outer circulation in the streamline analysis. The replacement of maximum wind between the inner and outer eyewalls, extending from low levels to middle levels in the left flank of the storm, was a clear model for the examination of the significance of the orographic effect on a severe typhoon. A conceptual model for a case of super typhoon under the influence of Taiwan high terrain was constructed.