季內震盪與地形之間的交互作用 ─ 利用高解析資料

Abstract

季內震盪(Madden-Julian Oscillation, MJO)為熱帶地區重要的大氣現象。我們的研究分析發現，當在北半球冬季東移經海洋大陸時，它的環流結構、水氣通量輻散場、渦度場、深對流分布、以及相對應的熱力剖面等特性，都會被海洋大陸的高聳複雜地形所影響。 我們以EOF、一元線性迴歸和相位合成分析高解析度的CFSR和低解析度的NCEP R2再分析資料，結果顯示出因解析度的不同，所呈現的地形效應可以總結如下：(1) 隨著高度變化的垂直環流有很明顯地西傾結構產生。(2)在蘇門答臘和新幾內亞迎風面的邊緣，可以看到很強的下沉氣流，且在新幾內亞的背風處出現上升運動。(3)渦度場偶極現象的發生是很接近於海岸線和山脈的邊緣。(4)在新幾內亞的迎風面和背風面分別存在水氣輻散和輻合的現象，且很接近新幾內亞上狹長的山脈。(5)藉由地形的影響，非絕熱量的分布和剖面可以看到在迎風面和背風面的邊緣，存在著加熱和冷卻的作用、(6)非絕熱量緯向剖面中，因為大尺度環流的差異，導致CFSR於東經105-120度的非絕熱量明顯大於NCEP R2。(7)平均南緯10度至北緯5度和南緯15度和南緯5度的非絕熱量、相當位溫和水氣通量輻散場區域，發現前者有明顯的西傾結構、後者為正壓結構。因此從上面的分析結果可知，由於解析度不夠的NCEP R2，是無法完整反映出實際季內震盪的情況。 由此可知，正確解析地形的細部結構，對於季內震盪東移經過海洋大陸的模式模擬，有著重要的影響；而忽略地形影響的模式模擬，可能就不再適用於我們對季內震盪的進一步研究中。

MJO is important atmosphere phenomenon in the tropics. This study demonstrates that during the passage of the MJO through the Maritime Continent in the boreal winter, the corresponding circulation structure, water vapor flux divergence, vorticity, convective systems, as well as consequential heating profiles, are redistributed via complex topographic effects from mountainous islands. We analyzed the CFSR of high-resolution and the NCEP R2 of low-resolution reanalysis data by EOF, linear regression and phase composite Methods. Because the datas of different resolution, the effects could be summarized as follow. 1) Westward tilting of vertical circulation with height is much more evident. 2) Strong downdraft induced in the windward side of Sumatra and New Guinea and upward motion occurred in the lee side of New Guinea. 3) Vorticity dipoles occured near the coastline and mountain slopes. 4) Moisture divergence and convergence at the windward and leeside of New Guinea, respectively, and the div.-conv. pair is most evident near New Guinea, which is a large elongated mountainous island. 5) By topography affected, the Heating distribution and profile demonstrated that the anomalous heating and cooling in the windward and lee side, respectively. 6) Because the large-scale circulation is different, results CFSR apparent heat source is larger than NCEP R2. 7) The apparent heat source, equivalent potential temperature and water vapor flux divergence regional average of the westward tilting structure is evident at 10。S – 5。N, but at 15。S – 5。S, the regional average is not tilt structure. It is suggested that resolving the detailed topographic effects may play a key role in simulating realistic characteristics of the MJO in the Maritime Continent, while ignoring influence from tropical topography with an aqua-planet model may not be a proper approach for our further understanding of MJO.