| 摘要: | 在前人研究中，作業用區域海氣耦合模式Hurricane Weather Research and Forecasting (HWRF)已被證實具有模擬颱風活動的能力。本文即採用HWRF，模擬侵台 颱風尼伯特(2016)，嘗試探討其在不同實驗組中路徑偏折與強度差異的動力因素。實驗首先採用不同物理參數化組合方案驗證模式預報能力，結果顯示模擬結果皆落在各國決定性預報範圍之中。後續實驗採用預報表現最佳的實驗組作為控制實驗組，並從模擬結果中由不同的登陸地點及強度變化選取比較實驗組，比較不同物理參數化實驗組模擬之動力差異。在強度差異上，使用動量與角動量趨勢收支分析發現隨著颱風三維風場強度的不同，可由底層向內傳送的較大角動量值也有所不同，造成底層切向風速增強量值不一。底層的入流亦會進一步影響眼牆附近向上對流的強度，致使可向上傳送的較大角動量有所不同，使隨眼牆上升周圍的切向風速有所不同；在路徑差異上，各物理參數化實驗組模擬路徑差異在開放洋面上主要差異透過位渦趨勢與不對稱量分析，其主要導因於水平平流項的差異，亦即颱風與背景駛流疊加的強風速區所主導，背景駛流差異又與副熱帶太平洋高壓強度不同有關聯。至較接近陸地時，垂直平流及非絕熱加熱項才逐漸有較明顯作用。耦合與未耦合實驗比較中，耦合實驗可反應較真實海洋溫度反饋，從而限制潛熱通量並獲得較為真實的颱風強度模擬。耦合與未耦合實驗在路徑上的差異透過位渦趨勢不對稱量分析可發現亦是由水平平流項所主導。地形移除實驗比較部分，透過位渦趨勢不對稱量分析可發現移除地形將使整體通過臺灣駛流風場增大、風向亦較少偏轉，並反映在水平平流的差異中，使颱風通過臺灣時路徑較少北轉與減速。;In past researches, operational coupled model Hurricane Weather Research and Forecasting (HWRF) have been demonstrated its capability of typhoon simulation. In this research, we applied HWRF to simulated invaded typhoon Nepartak (2016). Investigating the dynamic factors within difference in intensity and track between different experiments. At first, 8 different physics scheme combinations have been selected to demonstrate the
capability of typhoon (tc) simulation. The result shows that the predictions of HWRF are overall captured tc activity. According to the result, the most accurate simulation will be chosen to be CTRL experiment, and as the comparative experiments, different westbound track and intensity simulation will be chosen. For the intensity difference part, we applied the momentum and angular momentum (AM) budget analysis. Through the budget analysis and the 3-dimension wind speed difference in different experiments, the amounts of larger angular
momentum inward transportation will also be different, this effect will influence the wind speed intensification inside the bottom layer. Strong inward motion in the bottom will further enhance vertical convection near RMW, therefore, the upward transportation of angular momentum will be different; For the track difference part, we applied the potential vorticity (PV) budget to analyze it. While tc is moving upon the open ocean, horizontal advection will dominate the translation speed and direction of each experiment, which can be understood as
composition of background steering and typhoon circulation. Once the typhoon approach Taiwan, vertical advection and diabetic heating then become more important for typhoon translation speed and toward direction.
This research has further analyzed the coupled and uncoupled model comparison and the effect of Taiwan topography. As coupled model could provide the sst contains the typhoon induced sst cooling, it will get more accuracy simulation of intensity. Trough the PV budget analysis, The track difference between coupled and uncoupled model have been proved that is also induced by horizontal advection. For the effect of Taiwan topography, once the height of terrain replaced to 0, PV budget analysis demonstrated that the speed of steering flow will grow while the deflection will reduced. This phenomenon will let Typhoon penetrate Taiwan without deflection and deceleration. |
