| 摘要: | 在海洋表面時常有著不同尺度的海氣交互作用，其涵蓋的範圍從區域海域到整個海盆，時間上從短期變動到長時間氣候尺度，特別是西太平洋海域。本研究論文包含三個部分，其主要目的分別為:(i)了解上層海域在不同空間及時間尺度下的變動，及其變動與大氣動力過程之間的交互作用；(ii)分析與模擬熱帶氣旋中浮游生物藻華的現象；(iii)分析與模擬海表面波浪及其與大氣及氣候動力的連結。
本論文共分為三個章節，分別總結如下:
第一章總結了「北南海溫度浮標所量測之Rossby波與渦漩」(Lin, Oey, Wang, and Liu, 2015)，完整全文收錄在附錄一。我們透過研究單一浮標的溫度剖面資料與大範圍的衛星觀測資料，確立了上層海水的溫度波動與大氣驅動力，如風應力旋度、太陽熱能以及西方邊界流等，之間的關係。此研究發現南海北部的渦旋可依形成機制分為兩類，一類是由呂宋島西邊的風應力旋度驅動而形成，另一類則是因黑潮入侵呂宋海峽北部而形成。此兩類渦旋形成後皆向西傳遞至南海北部，同時也隱沒在Rossby波之中，進而在南海北部的溫度浮標內引起不同時間尺度的溫度波動。
第二章總結了「颱風尾流中的降雨藻華」(Lin and Oey, 2016)，完整全文收錄在附錄二。太平洋的颱風(或大西洋的颶風)尾流右側的藻華現象主要是因較強的混合作用、湧升現象、及中小尺度的再循環渦流引起的層化作用。此颱風右側藻華多發生在颱風剛經過(初期)的時候，而颱風左側藻華則發生在颱風經過較久(晚期)的時期。颱風左側的藻華其主要是受到西太平洋的垂直風切將導致颱風下的降雨會偏向颱風軌跡的左側，雨水延長了颱風左側的層化作用而造成颱風左側晚期的藻華。利用海洋數值模式模擬颱風降水以及其他觀測資料同樣都顯示颱風的強降雨會增強海水表層的強化作用，減低紊流產生，進而增強藻華作用。
第三章總結了「熱帶氣旋季中因聖嬰現象引起之波浪的兩個面向」(Lin, Oey, and Orfila, 2019)，完整全文收錄在附錄三。此研究連結海表面顯著波高的變化與受聖嬰現象影響之熱帶氣旋間的關聯。透過經驗證交函數與波浪數值模式的研究，其結果顯示西太平洋海表面顯著波在氣候尺度的變動上主要受到熱帶氣旋風活躍度的影響，而非大尺度環流風場。而此因聖嬰現象影響之熱帶氣旋對海表面波高的作用可延伸至全球各個海盆。其中，西太平洋的海表面波高在熱帶氣旋季內的變動與其之後的聖嬰現象量值有非常好的相關性，可做為一個聖嬰強度預報的參考依據。
;There are multiple air-sea interactions near the ocean surface that covers from regional to basin scale and from short-term to climate variations, especially over the western North Pacific. The thesis consists of 3 parts: (i) to detect and understand annual Rossby waves and mesoscale eddies in South China Sea; (ii) to analyze and model phytoplankton blooming in tropical cyclone wakes, and (iii) to analyze and model surface waves and their connection with atmospheric and climate dynamics. The first part presents an ingenious analysis of detecting Rossby waves and eddies driven by wind stress curl and Kuroshio intrusion based on a single temperature observational mooring coupled with ancillary satellite data in northern South China Sea. The results show the arrivals at subsurface, 300 m depth and deeper, of cool (warm) Rossby waves after their generation near the Luzon Strait in winter (summer). Shorter-period temperature fluctuations, 10~30 days, are caused by southwestward and westward eddies embedded in basin-scale Rossby wave. Two types of eddies were found: eddies propagating southwestward over the continental slope of northern South China Sea, formed southwest of Taiwan triggered by Kuroshio intrusion, and eddies propagating westward from Luzon, forced by annual wind stress curl anomalies and Kuroshio path fluctuation in the Luzon Strait.
The second part of the thesis used 16 years of ocean-color data to identify dominant blooming patterns in the wakes of 141 typhoons in the western North Pacific and the North Atlantic. Right-side asymmetric blooming is observed shortly after the storms, attributed previously to sub-mesoscale re-stratification, but a left-side asymmetry is found thereafter, coinciding with a left-side preference in rainfall due to effect of large-scale wind shear on the storm. Both biophysical model experiments and observations demonstrate that heavier rainfall freshens the near surface water, leading to stronger stratification, decreased turbulence and enhanced blooming. Our results suggest that rainfall plays a previously unrecognized, critical role in TC-induced blooming.
The third part of the thesis examines global ocean wave climate in response to tropical cyclones (TCs), using significant wave height (SWH) observed from satellites and WAVEWATCH III model. Tropical cyclone wind generates local waves (wind seas) under TC and long-period waves (swells) that propagate long distances. The genesis location, intensity, and frequency of TCs over the global ocean are strongly affected by the phases of El Nino and Southern Oscillation (ENSO). Our results show that the interannual variations of global ocean surface waves in the subtropics during the summer are strongly dominated by ENSO-related TC activity. Over the western North Pacific, the wind power is stronger in the TC season before an El Nino and weaker before a La Nina. Using composite, empirical orthogonal function and modeling, we show that ENSO-related TC variations dominate the spatial distribution and temporal variation of SWH. Over the western North Pacific, longer-period waves (swells) are driven into northern South China Sea, toward Japan in mid latitudes and toward the central Pacific along the equator due to ENSO-related TC activities. The wind power and SWH over the subtropical western North Pacific lead and regress well with the ENSO index, suggesting that they may potentially serve as useful ENSO predictors. |
