| 摘要: | 颱風是地球上破壞力最強的自然災害之一。造成全球每年數百人死亡，經濟損失達數十億以上。因此，準確的颱風預報極為重要，可以減低颱風所帶來的衝擊。在過去幾十年裡，颱風的預報已有明顯的改進，但是強度預報仍然裹足不前。主要原因是由於颱風的增強作用牽涉甚廣，很多背後的物理過程和控制因子還沒有被完全了解。另外，有相當比例的颱風在它的生命週期裡會出現快速增強作用（風速一天內增加15米每秒以上）。這種強度突然快速增強的作用大幅增加了預報的困難度，同時亦提高了颱風的危險性。強度變化一直以來都是颱風研究的重要議題。不過大部分的研究主要都是探討颱風強度在大洋中的變化，討論登陸時的情形相對較少。實際上，颱風在登陸時的強度變化是影響登陸區域和造成災害的關鍵。2017年夏季，颱風天鴿和颶風Harvey幾乎在同一時間分別重創位於中國南部的澳門和美國南部沿海。前者成為過去55年來襲擊澳門最嚴重的颱風，後者則是美國史上造成經濟損失最大的颶風之一(達$1250億美元)。這兩個個案都是在登陸時發生快速增強作用而引起嚴重後果。何種原因造成颱風在登陸時的突然增強是重要的科學議題，並與沿海地區居民息息相關。從海洋能量的角度，我們最新的研究(Pun et al. 2019)指出澳門沿海的大陸棚在天鴿颱風的快速增強作用中扮演非常獨特的角色。我們發現此大陸棚淺水區能夠抑制颱風所造成的海水面冷卻。一般而言，颱風造成海洋垂直混合，較深層的冷水被帶到表面，引致海水面降溫。但在淺水區中，由於缺乏深層冷水，海水面溫度得以維持。因此，能量不斷輸送到登陸中的天鴿颱風，使其快速增強。而Potter et al. (2019)對Harvey颶風的研究中也提出了相同看法。根據以上研究說明沿海的水文狀況對颱風的增強作用有著非常密切的關係，值得繼續深入研究。本計畫提出四年規劃深入探討沿海淺水區對颱風強度變化的影響。第一年將會延伸Pun et al. (2019)的架構，應用到Harvey颶風個案。因為在墨西哥灣沿岸有大量的海洋觀測資料，可以進一步驗正Pun et al. (2019)的結果；第二年會討論大氣因子以及進行模式模擬；第三年對所有歷史個案進行系統性分析和探討對台灣的影響。最後，第四年討論上層海洋熱含量在淺水區之適用性和淺水區內海水溫度之時空變異。預期成果會發表有關這個領域之代表性論文，進而有助台灣在颱風海洋研究上保持領先地位。 ;In August of 2017, Typhoon Hato and Hurricane Harvey struck the casino city of Macau in South Asia and Texas of the US, respectively. Both cases are high impact events that drew international attention. The former became the worst typhoon to hit Macau in 55 years, whereas the latter was the costliest hurricane in US history. Interestingly, what they have in common is the fact that they experienced rapid intensification over the coastal shallow water during the landfall period. Such unexpected fast intensity jump is in part, if not all, responsible for the serious consequences. People started to ask what causes these cyclones to rapidly intensify during the landfall period. Indeed, the intensification of the typhoon is one of the most challenge problems in typhoon research, not to mention the rapid intensity change. Recently, from the ocean prospective, pioneer work from Pun et al. (2019) and Potter et al. (2019) independently suggested that the coastal shallow water may play a unique role to boost typhoon intensity during the landfall. The warm, vertically homogeneous shallow waters found in the northern coasts of the South China Sea and the Gulf of Mexico tend to significantly suppress the critical sea surface temperature (SST) cooling induced by the typhoon or hurricane. Therefore, the negative feedback of SST cooling was minimized, contributing to the rapid intensification during the landfall.This proposal is built on my recent work, i.e., Pun et al. (2019), to continue to investigate this new research topic thoroughly, from case study to systematic work, and then to long-term variation. Furthermore, the possible linkage to Taiwan will be studied too. Typhoon-ocean interaction has been a hot topic in the typhoon community. Taiwan is one of the leading countries in this field. It is believed that this proposal would yield some influencing results and papers, and thus contribute to the leading position of Taiwan. |
