碩士 / 國立中央大學 / 大氣科學學系 / 106 / Topographic effects play an important role in the track and intensity changes of Tropical Cyclones. In this study, the Hurricane Weather Research and Forecast system (HWRF) was used to investigate the mechanism of the track and intensity changes over free ocean and track deflection near landfall. The influences of ocean SST and Taiwan terrain on track changes of Typhoon Megi (2016) and the influences of ocean thermal conditions on intensity and structure of Typhoon Soudelor (2015) are discussed respectively.
Typhoon Megi (2016) headed northwestward toward Taiwan with southward deflection near landfall. HWRF simulations using more realistic Hybrid Coordinate Ocean Model (HYCOM) sea surface temperature (SST) analysis improve the northward-biased track compared with that using Global Forecast System (GFS) SST, due to the initial cooler SST below the storm path. The initial warmer GFS SST leads to a northward track shifting with an over-intensified typhoon. As the Princeton Ocean Model is coupled, the SST over South China Sea (SCS) becomes warmer leading to a northward track shifting compared to a southward shifting induced by the upper ocean cooling due to the typhoon-ocean interactions in the vicinity of the typhoon. Regardless of track shifting, southward deflection near landfall is mainly controlled by orographic effects of the Central Mountain Range (CMR). Cyclonic northerly is enhanced to the west of the typhoon center due to flow channeling that results in southward deflection. Diagnostics of potential vorticity (PV) tendency budget indicates that southward deflection can be explained by the southeastward tendency of latent heating effects near landfall. The combined effects of latent heating and cyclonic rotation of positive wavenumer-1 (WN-1) PV vertical advection dominate the southward deflection when the typhoon is closer to Taiwan. Furthermore, the typhoon movement near landfall is slowed down mainly due to WN-1 negative vertical differential latent heating over the northern CMR.
Typhoon Soudelor (2015) passes serval sizeable preexisting ocean mesoscale eddies which can influences the intensity of typhoon-induced SST cooling. We investigate the typhoon intensity and structure when typhoon translates over different ocean thermal structures. Coupled to HYCOM analysis data can improve intensity simulation due to the more realistic ocean conditions including SST and ocean eddies. The existence of more realistic cold core eddies (CCE) below the typhoon path improves the simulation of rapid weakening of typhoon at the earlier stage. On the other hand, the re-intensification of typhoon at later times prior to landfall can be attributed to the preexisting warm core eddies which restrain the typhoon-induced upper ocean cooling. When typhoon moves over the CCE, the virtual potential temperature near the surface and the depth of thermodynamic typhoon boundary layer at the rear-right quadrant of typhoon translation is largely decreased in the coupled experiment due to the strong cold wake, while the inflow angle is enhanced at this region. Besides, the depth of inflow layer is larger near eyewall at the right-hand side of typhoon moving direction in coupled experiments which may be favorable to the intensification of typhoon. The effects of these structure changes induced by strong SST cooling over ocean eddies are worthy of further study.
| Identifer | oai:union.ndltd.org:TW/106NCU05021006 |
| Date | January 2018 |
| Creators | Dian-Yi Li, 李典宜 |
| Contributors | Ching-Yuang Huang, 黃清勇 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 95 |
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