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The satellite derived outgoing longwave radiation (OLR) over the Indian Ocean (30°N–30°S and 40°E–100°E) from 1974 to 1996 has been analysed for the relationship with the Indian summer monsoon total (June–September) rainfall. The OLR of two regions appears to be related to summer monsoon rainfall. One of the regions is located over the Head Bay of Bengal (near 22.5°N and 92.5°E) during May and the other one over the south Indian Ocean (near 30°S and 97.5°E) during April. The average OLR (index) for these two regions shows a strong and stable relationship with the Indian summer monsoon rainfall and they are found to be independent. A multiple linear regression equation is developed to predict the Indian summer monsoon rainfall using these indexes and the empirical relations are verified on independent data. Good results were obtained in forecasting the summer monsoon rainfall for the whole of India. The forecast of summer monsoon rainfall for west‐central India and all‐India rainfall for July also appears to be encouraging. The indexes, thus, seem to be useful in long‐range forecasting of the Indian summer monsoon rainfall. Copyright © 2000 Royal Meteorological Society

The monthly mean outgoing long-wave radiation data from June 1974 to May 1981 were analysed for dominant eigenvector patterns. The first three eigenvector patterns explain nearly 93 per cent of the total variance. The first eigenvector pattern exhibits an annual cycle with a pronounced variation in the outgoing long-wave radiation over the tropical belt between lo" and 2WN. This is largely indicative of strong seasonal shift of the major area of cloudiness associated with the Intertropical Convergence Zone. The second eigenvector pattern shows an out-of-phase relationship between north India and the equatorial region, having a pronounced semi-annual oscillation. The third eigenvector pattern exhibits the characteristic features of the north-east monsoon over south-east peninsular India. The first and second harmonics, corresponding to annual and semi-annual oscillations, exhibit the major characteristic features of the first two eigenvectors, respectively.The interannual variation of the outgoing long-wave radiation for the summer monsoon period shows a close association with the large-scale monsoon rainfall over India.It is concluded that the satellite-derived outgoing long-wave radiation can be used to monitor more comprehensively the large-scale monsoon circulation and its year-to-year variability in view of its spatial coverage over oceanic areas.

The application of a canonical correlation model to the long‐range forecast of the spatial variability of the Indian monsoon (June–September) rainfall has been demonstrated. The predictands used in the model are the summer monsoon rainfall of 29 contiguous meteorological subdivisions of India and the predictors are the 500 hPa ridge axis position over India for April, the Darwin surface pressure tendency (April– January), the sea‐surface temperature of the central and eastern equatorial Pacific for the five successive months preceding the monsoon (January to May) and the rainfall of the southernmost subdivision of India (Kerala) for April. The model is developed on 30 years (1939–1968) of data and tested on 16 independent years thereafter. The model demonstrates positive skill for the large contiguous meteorological subdivisions of India using the first canonical mode (found significant). The root‐mean‐square error and the absolute error between the observed and the predicted rainfall for different meteorological subdivisions are of the order of 1 cm. The high skill score (≥0ċ3) is found particularly for the meteorological subdivisions lying in west‐central India. The performance of the model appears to be better than that of the multiple regression model developed earlier by Prasad and Singh. The combined model (containing the first and the second canonical modes) appears to perform even better than that of the single model. These results, therefore, seem to be important in view of the long‐range forecast of the spatial variability of the Indian monsoon rainfall.