臺灣東南海域颱風所引起的近慣性運動

Near-inertial motion caused by typhoon in Taiwan southeast sea area

李致廷(Chih-Ting Lee)

指導教授 ： 楊穎堅

國立臺灣大學/理學院/海洋研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102742

摘要

西北太平洋為颱風路徑的熱區，颱風除了對大氣環境有影響外，對海洋的影響也非常重要。颱風經過後會對當地引發慣性運動，除了會對海流造成影響外亦會對溫度的變化帶來影響。
本研究使用臺灣大學海洋研究所佈放於鵝鑾鼻東南方海域約175及375公里處的海氣象即時傳輸浮標所蒐集的資料，探究2016年至2019年12個颱風經過時所觀測到的海氣象變化。12個颱風的名稱分別為尼伯特(Nepartak)、莫蘭蒂(Meranti)、馬勒卡(Malakas)、梅姬(Megi)、尼莎(Nesat)、天鴿(Hato)、山竹(Mangkhut)、丹娜絲(Danas)、利奇馬(Lekima)、白鹿(Bailu)、玲玲(Lingling)及米塔(Mitag)。將浮標觀測到的上層海洋500公尺之溫度剖面資料進行分析後探究颱風所引發的慣性運動。
結果發現，各個颱風經過後，從溫度變化來看慣性運動，其結構與性質不盡相同，影響的要素可能有：颱風與浮標之間的相對位置和距離及颱風的強度。在我們挑選的12個颱風中有幾個案例呈現的慣性運動結構是類似的：當強烈颱風的颱風眼中心直穿浮標時，會對上層海洋300公尺之溫度造成劇烈變化，並持續2至3天後，再從較淺的深度開始減弱，而垂直傳遞的趨勢較不顯著；當浮標位在輕度颱風中心及強烈颱風中心左側附近時，會先於水深100公尺附近開始有溫度變化，並隨時間遞增往深海延伸；當浮標位在颱風中心路徑左側一段距離時，其影響的深度為水深200公尺以淺，持續約3到4天後逐漸減弱，垂直傳遞的趨勢較不明顯；當浮標位在颱風中心路徑右側且靠近八級風暴風圈半徑邊緣時，上層100公尺的溫度變化會在3至4天後才開始變得顯著。除此之外，發現環境背景場的中尺度渦旋也會對慣性運動的結構及性質造成影響。

關鍵字

海氣象浮標 ； 颱風 ； 近慣性運動

並列摘要

When a typhoon passes by, it not only affects the atmosphere but also has an impact on the ocean. It triggers the inertial motion that not only induces the current changes but also the temperature variations. Western North Pacific Ocean is a hot spot area where typhoons generate. The Institute of Oceanography of National Taiwan University (NTU) had deployed two air/sea-observing buoys from the southernmost of Taiwan about 175 km and 375 km, respectively in order to provide in-situ data. In this research, the in-situ data were used to study the upper ocean’s current and temperature fluctuations. NTU buoys had record twelve typhoons from 2016 to 2019, which were Nepartak, Meranti, Malakas, Megi, Nesat, Hato, Mangkhut, Danas, Lekima, Bailu, Lingling, and Mitag.
The upper ocean 500 m temperature profile data showed that the structure and characteristics of near inertial motion varied along with different typhoons. It indicated that the inertial motion induced by typhoons affected the seawater temperature. However, the variations varied by several factors such as the distance and the position between buoys and typhoons, the typhoon intensity, and the background vorticity. Different near inertial motion structures were observed within these twelve typhoons. In these cases, there were some similar effects, which could be classify into four patterns. First, when severe typhoon’s typhoon eye run into buoy, the upper ocean 300 meters’ temperature had extreme fluctuation and last for two to three days without downward propagate. Second, when buoy was located on the course of mild typhoon’s eye or on the left-hand side around the severe typhoon, seawater temperature started fluctuate at the depth around 100 meter and then extended to deeper ocean gradually. Third, when buoy was located at a distance on the left-hand side of the typhoon, seawater temperature in upper layer 200 m varied and last for three to four days without downward propagate. Fourth, when buoy was located at the edge of wind speed 34-knot radius of typhoon, seawater temperature started varied about three to four days later without downward propagate. Besides, mesoscale eddy might cause near inertial motion’s structure to change.

並列關鍵字

Air/sea-observing buoy ； Typhoon ； Near inertial motion

參考文獻

Archiving, Validation and Interpretation of Satellite Oceanographic data (2021) 上網日期：2021年4月1日，檢自 (https://www.aviso.altimetry.fr/)

Benoit cushman-roisin (1994). Introduction to Geophysical Fluid Dynamics, 139-142.

Black, W. J., and T. D. Dickey, 2008. Observations and analyses of upper responses to tropical storms and hurricanes in the vicinity of Bermuda, J. Geophys. Res., 113, C08009

Chen, G., H. Xue, D. Wang, and Q. Xie (2013), Observed near-inertial kinetic energy in the northwestern South China Sea, J. Geophys. Res. Oceans, 118, 4965–4977

D’Asaro, E. A., C. C. Eriksen, M. D. Levine, P. Niiler, C. A. Paulson, and P. van Meurs , 1995: Upper-ocean inertial currents forced by a strong storm. Part I: Data and comparisons with linear theory. J. Phys. Oceanogr., 25, 2909–2936.