颱風引發海表面溫度冷卻影響大氣邊界層之機制探討

Numerical investigation of the physical mechanism(s) for the modulation of surface winds from the typhoon-induced sea surface temperature cooling

王如馨(Ju-Hsin Wang)

指導教授 ： 吳俊傑

共同指導教授 ： 林依依

國立臺灣大學/理學院/大氣科學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00312

摘要

隨著衛星技術進步，使我們對全球海表面溫度 (Sea Surface Temperature; SST) 與海表面風場有更多的認識，特別是大氣與海表面溫度的交互作用關係。利用微波觀測技術，一些海洋影響大氣邊界層的現象逐漸被發現。Lin et al. (2003) 利用TRMM/TMI的海溫資料以及QuikSCAT風場資料，研究2000年啟德與碧利斯颱風經過海洋時，在其路徑右側所造成的海表面溫度冷卻。當海表面溫度下降時，其上方低層大氣的風速也會隨之減弱，風速與海溫的空間分布有很好的相關性。但由於衛星觀測的限制，無法對此現象有更完整的了解。因此本研究希望透過數值模式，探討由颱風引發海溫冷卻影響大氣邊界層之機制。

模擬結果發現，放入衛星觀測之海溫資料，可使風場的數值模擬與遙測資料較為一致。進一步分析邊界層結構，冷水區 (cold wake) 的低層大氣穩定度較大，而外圍較高海溫區在700公尺以下則呈現均勻混合的狀態。並且從風速的垂直結構可看出，冷水區高層與低層動量交換較少。此外，冷水區的潛熱及可感熱通量與外圍環境場亦有明顯不同。

為了解造成風速減弱之機制，本研究使用動量收支方程進行分析。由低層動量分析結果顯示，氣壓梯度與垂直混合對風場有主要貢獻，氣壓梯度分布為綜觀尺度南北向排列，提供使盛行風加強之分量。而垂直混合項在冷水區有明顯極值分布，提供與盛行風相反的的分量使風速減弱，因而冷水區的低風速值得以維持。經由模式不同邊界層參數化測試，本研究亦顯示一致結果。

關鍵字

海表面溫度 ； 邊界層

並列摘要

Based on the analysis of TRMM/TMI Sea Surface Temperature (SST) and QuikSCAT ocean surface wind vector, significant weakening of surface wind speed over typhoon-induced cold SST patches has been identified (Lin et al. 2003). The purpose of this study is to design numerical experiments to examine the above mechanism on the modulation of the surface wind from the typhoon-induced sea surface temperature cooling.

It is shown that the surface wind simulation is much improved with the use of the TMI-derived SST as the boundary condition. More detailed analysis of the model results indicates that the boundary layer is more stable over cool SST patches, while being well mixed at the surrounding region. The surface heat fluxes are much smaller under the cool SST condition. The momentum budget indicates that the vertical mixing and pressure gradient are the dominating terms in affecting the evolution of the boundary layer wind, while the vertical mixing acts as a frictional drag on the pressure-gradient-driven winds.

並列關鍵字

Sea Surface Temperature ； Boundary Layer

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