碩士 / 國立臺灣大學 / 大氣科學研究所 / 106 / Typhoon Soudelor was the most destructive tropical cyclone (TC) in the western North Pacific in 2015, undergoing rapid intensification (RI) with the central minimum sea-level pressure (MSLP) drop of 90 hPa in two days. In this study, a 1.67-km convection-permitting full-physics model simulation is conducted with the track and intensification trend of Soudelor well captured.
To investigate how the surface heat fluxes outside the inner core (IC, the inner core region within the radius of 60 km) affect TC structure and RI process, a series of numerical experiments with the surface wind highly capped at 1 m/s in the calculation of surface latent and sensible heat flux in different radial extent are performed. It is found that the intensification rate is larger than that of the control experiment (CTRL) during RI when the surface heat fluxes are suppressed in the area 150-km (2.5 times of the IC size) away from the TC center, while the TC is significantly weaker and does not undergo RI when the surface fluxes are also suppressed at 60 to 150-km radius (1 - 2.5 times of the IC size). In addition to intensity change, substantial reduction of surface fluxes outside the inner core leads to lower TC strength and smaller radius of maximum wind (RMW), indicating that the most violent winds concentrate in the inner-core region.
As to the inner-core feature in each experiment, the RI cases show stronger mid- to upper-level updrafts, higher axisymmetricity and heating efficiency than that of non-RI cases during convective burst times before RI in CTRL. Furthermore, the upper-level warm core develops significantly during RI, while no evident upper-level warming is found in non-RI cases. Although the surface fluxes outside the inner core in these RI cases are substantially suppressed, stronger intensity and more consolidated inner-core structure than that of CTRL is identified associated with the abundant wind-induced surface heat exchange (WISHE) in the inner core. The stabilization of lower troposphere outside the inner core in RI cases leads to aggregation of deep convection and subsequent generation of potential vorticity near the TC center, concentrating the violent winds in the inner-core region. Special insight is identified that the limitation of surface heat fluxes does not always result in a reduction of TC intensification rate. In other words, if the surface heat fluxes are suppressed in the outer region, against one’s physical intuition, TC can possibly turn even stronger.
| Identifer | oai:union.ndltd.org:TW/106NTU05022021 |
| Date | January 2018 |
| Creators | Chin-Hsuan Peng, 彭欽旋 |
| Contributors | Chun-Chieh Wu, 吳俊傑 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 90 |
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