Extended Abstract (636K)3C.6
Eyewall contraction, breakdown and reformation in landfalling Typhoon (1998)
Kun-Hsuan Chou, National Taiwan Univ., Taipei, Taiwan; and C. C. Wu and Y. Wang
Satellite images showed that during the period when Typhoon Zeb (1998) devastated Luzon, its eyewall shrank before landfall, and then disappeared its inland portion likely due to the terrain effect. Few hours later, a wider eyewall reformed as Zeb left Luzon and re-entered the warm ocean. Besides Zeb, many typhoons that made landfall over Luzon also showed similar eyewall evolution processes. It is worthwhile of studying the dynamical mechanisms that control such eyewall behaviors through a high-resolution numerical model (MM5). The main features of eyewall breakdown and reformation processes during the period when Zeb was near Luzon are well simulated by the numerical model. Further analyses show that the presence of Luzon terrain leads to the eyewall breakdown when typhoon makes landfall at Luzon. The eyewall reforms when Zeb moves back to the warm ocean and reintensifies. During the eyewall breakdown stage, the low-level tangential wind associated with Zeb decreases while the radius of maximum wind (RMW) increases. However, at the eyewall reformation stage, the low-level tangential wind increases while the RMW decreases. In addition, the eyewall of the model typhoon appears in elliptic shape with a cyclonic rotation both during the period when Zeb approachs Luzon and at the reintensifying stage when Zeb re-enters the warm ocean. Detailed analyses also reveal that during these two periods, the core region of typhoon is quite asymmetric with vortex Rossby waves and polygonal eyewall structure that share similar dynamics to those found in Schubert et al. (1999) and Wang (2001). It is also found that the intensity change is related to the interaction between the symmetric vortex and the vortex Rossby waves. Such a wave-mean flow interaction results in this special intensity change of the model typhoon. Detailed analyses are still under going to verify the above model results against theories (e.g., Schubert et al. 1999) and idealized simulations (Wang 2001) and further results will be presented in the conference.
Session 3C, Tropical Cyclone Intensity Change II (Parallel with Sessions 3A, 3B, & 3D)
Monday, 29 April 2002, 4:00 PM-5:30 PM
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