S. V. Singh

Association of the Indian summer monsoon with the northern hemisphere mid-latitude circulation

The association between the mid‐latitude circulation and rainfall over the Indian region on an intraseasonal time‐scale is investigated by considering 11 years (1974‐1984) of Northern Hemisphere 500 hPa geopotential heights and rainfall data for the Indian summer monsoon months June through to September. On the basis of extensive correlation analysis between the geopotential heights and rainfall, it is seen that three regions over the mid‐latitudes, the Manchurian region, the Algerian region and the Caspian sea region show positive correlation with rainfall over India, with higher values north of 20N latitude. Lead 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 West Pacific Oscillation, the North Atlantic Oscillation and the Eurasian) and Indian summer monsoon rainfall (ISMR) are investigated. Only the West Pacific Oscillation pattern shows a significant relationship with the ISMR. Further, the interannual and the decadal variability is examined by using the Northern Hemisphere zonal index data for the period 1900‐1993. Results reveal that the decadal‐scale variability of the ISMR and the circulation features of the Northern Hemisphere are connected. # 1997 by the Royal Meteorological Society. Int. J. Climatol., 17: 1055‐1067 (1997)

EMPIRIACAL STUDY ON NIMBUS-7 SNOW MASS AND INDIAN SUMMER MONSOON RAINFALL

In this study the relationship between Nimbus-7 snow mass and Indian summer monsoon rainfall (ISMR) for the period 1979-1987 is examined. Results reveal that the January snow mass over two regions of the former USSR - one located north-east of Moscow and the other lying between Mongolia and Siberia - shows a high inverse relationship with subsequent ISMR. However, the snow cover over Eurasia for the month of April shows a significant relation with ISMR. Implications of these connections in long-range forecasting of ISMR are also examined.

SEASONAL VARIATIONS OF THE RELATIONSHIP BETWEEN SOME ENSO PARAMETERS AND INDIAN RAINFALL

Canonical correlation analysis is used to examine the seasonal relationship between ENSO and Indian rainfall by analysing their 12 monthly values for an 80-year period. Three ENSO indices are considered. These ENSO indices are the Darwin surface pressure, the sea-surface temperature of the central and eastern equatorial Pacific, and rainfall of central equatorial Pacific islands (hereafter denoted as DSP, SST, and RAIN respectively). The ENSO indices are also analysed for relationships between themselves. The analysis reveals that the seasonal variations of these ENSO indices are highly intercoupled with no lag. These indices show the minimum association during April and the maximum after the monsoon season. Further, the seasonal variation of the Indian rainfall is found to be better associated with the seasonal variations of SST as compared with that of DSP or RAIN. This association is at its strongest during the period August–October. An apparent reversal in the relationship between ENSO and Indian rainfall is also observed from summer to winter. The warm ENSO years are associated with weak summer monsoon rainfall and at the same time high winter monsoon rainfall.