TOGA COARE期間熱帶西風暴潮與對流的特性分析

Characteristic Analysis of Westerly Wind Burst and Tropical Convection during TOGA COARE

林沛練(Pay-Liam Lin) ； 顏永安(Young-An Yen)

《大氣科學》 24卷3-4期 (1996/12) Pp. 189-210

摘要

熱帶是全球大氣的熱源，熱帶氣象的變化，對全球氣候變遷有巨大的影響，為了進一步了解低頻振盪，ENSO（El Niño/Southern Oscillation）等現象，許多學者致力於探討熱帶海氣之交互作用，一些研究指出太平洋暖水區東移與西風事件有密切的關係。由於洋面上觀測資料稀少，以往研究者只能以有限之資料就西風暴潮的地面特性作分析，無法了解空間上的變化，隨著TOGA COARE（Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment）之展開，獲得豐富的三度空間觀測資料，利用這些資料，本研究進一步研究西風暴潮在空間上之演變、熱帶對流特性及西風與低頻振盪的關聯。由風場的分析顯示，1992年11月至1993年2月間，共有三波段的地面西風暴潮，其位置偏向於南半球，較常出現於赤道與南緯15度之間，中心在南緯5度到10度之間，某些區域之西風有緩慢南移之現象。每次地面西風持續時間皆超過十天，東經140度的西風甚至有85天以上的生命期。除了低層往上發展之西風外，也有由高層往下發展之西風，這些西風是來自中緯的影響。某些時候，北（南）半球西風帶會向南（向北）伸展到另一半球之西風帶，當這些高層西風越過熱帶時，地面西風會停歇，使得高低層緯向風呈現反相位的關係。西風暴潮比超級雲簇約晚十天出現，前者跟隨後者由西往東傳，東移速度3.7 m/s，兩者之週期為40天。由雨量資料發現西風開始後五天內會有較多雨量。停歇期也有一些降雨，西風消失後3天內會有較大之水汽輻合或雨量。

關鍵字

西風暴潮 ； 熱帶對流

並列摘要

The tropical area is a major heat source global atmosphere, and the variation in tropical meteorology has significant effect on global climate change. In order to get through understanding on the Low Frequency Oscillation and ENSO (El Nino/Southern Oscillation), many investigators devote to research the tropical air-sea interactions. Some researches indicated that the eastward moving of the warm pool in the Pacific Ocean is significantly related to easterly wind events. Since the data observed in ocean are sparse, the previous studies can use only limited data to analyze the surface characteristics of Westerly Wind Burst (WWB), yet they can't investigate its spatial variation. During TOGA COARE (Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment), a more generous 3D spatial observation data had been collected. By using these data, we did further research on the spatial variation of WWB, the characteristics of tropical convection and the relations between Weatherly Wind Burst and Low frequency Oscillation.From the wind data analysis, three WWBs had been clearly identified during November 1992 to February 1993. The spatial distribution of WWBs appeared in the tropical ocean between the equator and 15° S, Its center was located at the region between 5° S and 10° S. Some westerly events moved southward slowly. The lasting time of each WWB usually exceeded ten days. The life cycle of some westerly wind event in 140° E could reach up to 85 days. Except the upward propagation, the westerly wind could also propagate downward from the high level. The characteristics were concluded to mid-latitude influence. Sometimes, the westerly wind in northern (southern) hemisphere could develop and migrate to another hemisphere. When these upper level westerly wind burst moved past over tropical ocean, surface westerly wind stopped. Such that, the zonal wind in upper level and low level showed opposite phase relationship.Super-cloud cluster usually occurred 10 days prior to the consent of the WWB. The latter accompanied with the former moving from west to east with 3.7 m/s eastward velocity, and the period was 40 days. By analyzing rainfall data, we found that there was richer rainfall 5 days after the onset of Westerly Wind Burst. During the interruption, there was also some rainfall. We found out there were more moisture convergence or rainfall appeared 3 days after the disappearance of Westerly Wind.

並列關鍵字

Westerly Wind Burst ； Tropical Convection ； TOGA COARE