Relationship of the Indian monsoon rainfall to the northern hemispheric 700 MB height tendency

Abstract

AbstractIn this study, the fields of northern hemispheric 700 mb height tendency from January to April and from March to April are examined for the period 1950–1984 in relation to Indian monsoon (June to September) rainfall. The height tendency from January to April at three locations (near Pacific high and near Siberian high at sea level, and over southwest U.S.A) and from March to April at one location (about 50° of longitude west of sea level Aleutian low) are found to be significantly related to the Indian monsoon rainfall. These four variables are generally not inter‐related amongst themselves, and are not significantly related to the April 500 mb ridge, the tendency of the Southern Oscillation Index (SOI), and the eastern equatorial Pacific sea surface temperature tendency from DJF to MAM season.The best amongst the height tendency variables is the height tendency from January to April near sea level Pacific high. This variable is not as good as the tendency of SOI; however, when used in conjunction with April 500 mb ridge and the tendency of SOI, it makes a highly significant contribution to the explained variance and improves the forecasts for independent years as judged by different measures of assessment. This height tendency thus makes a useful additional predictor for the Indian monsoon rainfall.The mechanism of the influence of the development of the Pacific high on the Indian monsoon rainfall is not clear. It is, however, possible that the linkage between the development of the Pacific high and the Indian monsoon rainfall is through linkage of the Pacific high with the development of the summer season trough of low pressure over the Indian sub‐continent. This, however, needs to be investigated.