從觀測與模式資料顯示，全球氣溫增暖的同時，降雨的變化並非普遍性地增加，而是顯現正負錯綜 的分佈。本文採用SSM/I衛星反演之氣柱水汽量（column water vapor，簡稱CWV）及GPCP（Global Precipitation Climatology Project）降水資料，探討1988～2014 年間，氣柱水汽量與降水強度時空關係。分析結果顯示：熱帶地區氣柱水汽量與降水在空間上有高度相關性。平均而言，在ITCZ 附近，每8mm 氣柱水汽量可產生1mm/day 降水強度。不過，氣柱水汽量和降水強度間關係並非線性，而是呈現上拋物線關係，亦即當氣柱水汽量愈大時，降水強度增加幅度反而逐漸趨緩。從時間變化趨勢來看，1988～2014 年間，熱帶地區平均氣柱水汽量大約增加4%左右（由36mm 增加至37.5mm），但同時期降水強度幾無明顯改變，這顯示熱帶地區之降雨效率（定義為降水和氣柱水汽量之比值）在這段期間似乎有下降的趨勢。對於熱帶降雨效率下降的情形，主要是發生在有乾平流逸入 對流區邊緣，和Neelinetal.(2003)所提出之“落井下石機制”(the upped-ante mechanism)相符，亦即大氣暖化雖可增加大氣中的水汽量，但對流增強的同時也將在氣候下沉區以及對流邊緣區抑制對流發生，可解釋整體熱帶地區降水改變並不如氣柱水汽量增加般明顯。另外，我們也發現聖嬰成熟時期熱帶地區降雨變化有長周期南北位移的現象發生，並不對稱於赤道，這與太平洋年代震盪相位有密切關係。

In observed and model simulations, as the global temperature increase, changes in precipitation exhibit positive and negative anomalies. Thus, the relation between column water vapor and extreme rainfall are analyzed using the Special Sensor Microwave Imager( column water vapor, CWV) and Global Precipitation Climatology Project (GPCP, precipitation) during the period 1988-2014. In this study, we have shown a tight relationship between tropical column water vapor and precipitation. Every 8 mm CWV can cause Imm/day of precipitation intensity over the ITCZ. The existence of a non-linear relation between CWV and precipitation is found. The column water vapor of tropical convective zone increases as much as 4% (36 to 37.5mm) from 1988 to 2014, even though on average there is virtually no change of precipitation during this period. In contrast to CWV, the precipitation changes exhibit strong regional discrepancies with the coexistence of positive and negative precipitation trends (e.g., positive trend over ITCZ and negative trend elsewhere), which implies a decrease of the precipitation efficiency under global warming when the tropic is considered as a whole. In the upped-ante mechanism, dry inflow from non-convective regions tends to suppress convection and induce negative precipitation anomalies over margins of convective regions (Neelin et al. 2003), which may plausibly explain why the precipitation change is much less significant as the water vapor under global warming. We also found the hemispherical asymmetry of tropical precipitation changes in El Nifio events. This precipitation asymmetry in the El Nifio cases is associated with the phase change of Pacific Decadal Oscillation (PDO).