| Summary: | 碩士 === 國立臺灣大學 === 大氣科學研究所 === 102 === In this study, microwave satellite products and best track data were used to observe the changes of intensity and structure of the Western North Pacific (WNP) typhoons and the Atlantic (ATL) hurricanes in particular concentric eyewall cases (CEs) from 1997 to 2012. Around the globe, only over the Atlantic and Eastern Pacific basins do routine airborne TC observations be carried out. Previous study had used airborne observations to design K-Vmax diagram, which can simultaneously show maximum sustained wind (Vmax) and circulation size determined from accumulated kinetic energy (K). In this study, similar plots for WNP typhoons were made, which are T-Vmax diagram where T is from cloud-top brightness temperature (TB) to indicate convective activity (CA) and to compensate the lack of airborne observations.
CE was objectively defined by 5 criteria: (1) moat exists, (2) most is clear enough, (3) outer eyewall is strong enough, (4) circulation is axisymmetric enough, and (5) outer eyewall can’t be a spiral-out rainband. CEs were divided into Eyewall Replacement Cycle (ERC), Concentric Eyewall Maintained (CEM), and No Replacement Cycle (NRC). Each month was discerned into warm, cold, and normal episodes based on Ocean El Nino Index (ONI). In this study, climate average linear regression of T was obtained, and the anomaly is symbolized as ΔT. Over the WNP basin, CEM and normal episode CEs have positive ΔT. There is more cloud liquid water content ((CLW) ¯) in CEs than in non-CEs (NCEs), and among CE categories, ((CLW) ¯) is higher in CEM cases than NRC and ERC. 3 upper ocean thermal parameters, SST, T100A, and UOHC, showed that before (after) CE formation, there is more air-sea interaction in NRC (CEM) cases.
In this study, hurricane Wilma (2005) was analyzed by K’-Vmax diagram and T-Vmax diagram to observe intensity and structural change. 5 repeatedly-formed CEs of Hurricane Frances show hurricane size expands after ERC rather than NRC. Followings are comparisons between CEs over WNP and NATL. First, the number of NATL CEs concentrates almost only in September. Second, NATL CE tracks and formation frequencies in different episodes have smaller variation than WNP, which may due to smaller influence by ENSO. Third, WNP CEs have higher intensity than NATL, and among CE categories, CEM (ERC) cases have the highest intensity over the WNP (NATL) basin. Forth, WNP CEs have larger size than NATL. Over both basins, CEM cases have the highest size of all CEs, rapid filamentation zone width of each CE category determines at least 50% of variation of moat width, and obvious characteristic difference of T-Vmax curve between CE and NCE.
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