ASSOCIATION OF THE INDIAN-SUMMER MONSOON WITH THE NORTHERN-HEMISPHEREMIDLATITUDE CIRCULATION

The association between the mid-latitude circulation and rainfall over the Indian region on an intraseasonal time-scale is investigated by c onsidering 11 years (1974-1984) of Northern Hemisphere 500 hPa geopote ntial heights and rainfall data for the Indian summer monsoon months J une through to September. On the basis of extensive correlation analys is between the geopotential heights and rainfall, it is seen that thre e regions over the mid-latitudes, the Manchurian region, the Algerian region and the Caspian sea region show positive correlation with rainf all over India, with higher values north of 20 degrees N latitude. Lea d and lag correlations between the heights at the locations identified above and rainfall over India reveals that some common element of low -frequency variability is influencing the mid-latitude circulation and Indian rainfall. On the interannual scale the connections between the winter-time low-frequency patterns (the Pacific/North Atlantic, the W est Pacific Oscillation, the North Atlantic Oscillation and the Eurasi an) and Indian summer monsoon rainfall (ISMR) are investigated. Only t he West Pacific Oscillation pattern shows a significant relationship w ith the ISMR. Further, the interannual and the decadal variability is examined by using the Northern Hemisphere zonal index data for the per iod 1900-1993. Results reveal that the decadal-scale variability of th e ISMR and the circulation features of the Northern Hemisphere are con nected. (C) 1997 by the Royal Meteorological Society.