探討浮標觀測颱風中心附近海域的風、波浪與海表熱通量變化

Abstract

西北太平洋為颱風產生的熱點地區，每年有超過5個颱風登陸東亞沿岸地區，對其造成嚴重破壞。而在颱風的生命週期中，所經之地的大氣與海表環境皆有大幅度變化，若能連續觀察極端天氣下的海氣象變化，對於日後改善颱風預報將是一大幫助。 本研究利用國立臺灣大學海洋研究所於鵝鑾鼻東南方海域約375與175公里處佈放的海氣象即時傳輸浮標所收集到的氣象、波浪與海表溫資料，探討2018至2021年間共8個颱風中所觀測到的風浪變化，並搭配Coupled Ocean Atmosphere Response Experiment v3.6演算法套件進行海表熱通量估計，並與衛星遙測產品之資料討論颱風期間的潛熱通量與可感熱通量變化。而8個颱風名稱分別為2018年的山竹(Mangkhut)；2019年的丹娜絲(Danas)、利奇馬(Lekima)、白鹿(Bailu)、玲玲(Lingling)、米塔(Mitag)；2020年的閃電(Atsani)；2021年的璨樹(Chanthu)。 經過分析後的結果發現，在颱風影響期間的風浪變化與浮標和颱風中心的相對位置變化有較高的相關性，其中包含浮標位於颱風中心之左右側以及最近相對距離，除了會影響到浪高的成長幅度，風向與浪向開始轉向的時間差異也有所不同，位於颱風中心右側，風向與浪向開始轉向的時間差約為0至3小時，而位於颱風中心左側，風向與浪向開始轉向的時間差約為6至9小時。另外，海表熱通量在颱風影響期間主要受到氣溫與海表溫差所影響，而在一些個案中可看到海表溫降是受到大氣從海洋獲取能量所致，不過降溫的幅度也與颱風本身結構以及大氣比濕有關。除此之外，與衛星資料推估的潛熱通量與可感熱通量進行比對後，可了解到因資料變化的掌握度與時間間隔的不同，觀測資料更能準確觀察短時間尺度內的趨勢變化。

The Western North Pacific Ocean is a hotspot area for generating tropical cyclones, also known as typhoons. Annually, over five typhoons make landfall on the coastal regions of East Asia, which causes serious damage. To better understand the variations of air-sea change under those extreme weather conditions, this study uses the in-situ observation data, including meteorological, wave, and sea surface temperature collected from two air/sea-observing buoys from the southernmost of Taiwan, about 375 km and 175 km, respectively, deployed by the Institute of Oceanography of National Taiwan University (NTU). From 2018 to 2021, NTU buoys recorded eight typhoons: Mangkhut, Danas, Lekima, Bailu, Lingling, Mitag, Atsani, and Chanthu. In addition, the Coupled Ocean Atmosphere Response Experiment algorithm v3.6 is used to estimate the latent and sensible heat flux, and the variation of heat flux is discussed with the satellite product. The meteorological and wave data showed that the wind and wave variations during typhoons could be related to the relative position between buoys and the typhoon center. Suppose the buoy is on the right-hand side of the typhoon center. In that case, the time lag between the wind and wave direction starting to turn is about 0 to 3 hours, while on the left-hand side of the typhoon center, the time lag between the wind and wave direction starting to turn is about 6 to 9 hours. Those effects would also affect the growth rate of the significant wave height. Additionally, the trend of the surface heat fluxes in extreme weather is mainly affected by the air and sea surface temperature difference. In some cases, it can be seen that the heat flux change causes the sea surface temperature to cool, but the magnitude of cooling is also related to the typhoon’s structure and the moisture in the air. Besides, by comparing the heat flux estimated by satellite data, the measured data is more suitable for observing the trend on a short time scale than the satellite data.