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Roles of Interactions of Typhoon Nesat (2017) and Haitang (2017) in the Formation and Structure of Outer Tropical Cyclone Rainbands
Typhoon,outer tropical cyclone rainbands,formative mechanism,structural feature,multiple-Doppler-derived wind fields,gradient wind balance,
|Publication Year :||2019|
|Abstract:||本研究主要利用氣象都卜勒雷達(七股、墾丁及馬公)觀測資料、National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS)再分析資料、馬公探空及地面測站資料來檢視發生在台灣西南部並造成顯著降水的颱風外圍雨帶個案(2017年7月29日0800~1200 UTC)，此個案期間有尼莎颱風(2017)及海棠颱風(2017)同時影響台灣。藉由多都卜勒雷達反演三維風場探討雨帶之(水平及垂直)降水與氣流結構，並嘗試釐清此雨帶的生成與維持機制及地形可能扮演的角色。
Outside the eyewall, tropical cyclone rainbands (TCRs) are the most striking and threatening region, causing not only heavy precipitation but intense winds. When Typhoon Nesat (2017) and Haitang (2017) were located near Taiwan, outer TCRs oriented approximately normal to the coast were initiated off the southwestern coast of Taiwan and resulted in the severe flood over the coastal and inland regions. Thus, it is crucial to understand the formative mechanism of the studied TCRs. This study used ground-based dual-Doppler and surface observations and NCEP-CFS reanalysis data to document the structural feature of the outer TCRs. The multiple-Doppler-derived wind fields showed that the formation of the TCRs was related to the low-level convergence between the southwesterly flow and the northwesterly flow. According to the budget analysis of radial momentum equations, the southwesterly flow was more subgradient due to the interaction of Typhoon circulations associated with Nesat and Haitang. In contrast, the northwesterly flow that was dominated by the outer circulation of Typhoon Nesat was close to the gradient wind balance. In addition, the structure of the outer TCRs in the nearshore region is different from that seen in the offshore region, which was caused by more pronounced low-level convergence produced as the coastally blocked flow (south-southwesterly flow) that occurred under low Froude number regime encountered the northwesterly flow.
|Appears in Collections:||大氣科學系|
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