Forecasting Indian summer monsoon rainfall by outgoing longwave radiation over the Indian Ocean

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