過去許多研究指出，印度地區降雨現象主要受到亞洲夏季季風所影響，鮮少討論低頻時間尺度上的變化，如年代際變化(decadal variations)。然而印度地區在年代際上的降水變化有機會造成重大災情，因此在降水變異的研究上不能僅局限於季節(seasonal)或年際(inter-annual)上的變化，了解印度地區降水在年代際變化有助於我們提早應變可能發生的災害。
本文主要研究1979年至2015年觀測資料GPCP在印度地區的降水變化，發現有一明顯年代際尺度的降水變異，並進一步利用多元線性迴歸分析發現，這與南半球氣候主要模態之一的南半球環狀模式(Southern Hemisphere Annular Mode, SAM)的變化有著密切的關係。為了進一步了解SAM影響印度地區降水的過程，我們利用簡單線性迴歸分析探討南半球氣候變異如何改變印度的降雨。研究結果顯示，當SAM為正相位時，南半球海表溫度在副熱帶地區為正異常，在中緯度為負異常，而這樣的海表溫變化會造成大氣經向環流的減弱，導致低雲覆蓋率在印度洋上減少，在亞洲大陸東、南側增加，進而改變地表淨熱通量，使得海陸溫差變大，造成向北跨赤道風增強，因此為印度地區帶來豐沛的雨量。

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