A Predictive Monsoon Signal in the Surface Level Thermal Field over India

Abstract

This is primarily a statistical study based on linear correlation analysis. The mean monthly surface thermal field over India based on a fairly well-distributed network of 119 stations has been examined for March-May during the period 1901?75 for the relationship with rainfall during the following monsoon season. The study brings out three areas (the fist and the third from the central portion of western India, the second from southern peninsular India) for which the relationships between area average of mean monthly minimum temperature for April (for the first and the second area ) or for May (for the third area), and Indian monsoon rainfall are stable and consistently significant for 20 to 30-yr periods after 1940. The best of these relationships is that with the May minimum temperature over the third area, significant at the 0.1% level. The relationships with mean April minimum temperature over the first and the second areas are just significant at the 5% level. The mean May minimum temperature over the third area is significantly related to the 500 mb April ridge, tendency in Southern Oscillation Index (SOI), and the tendency in eastern equatorial Pacific sea surface temperature (SST). In combination with the ridge, the mean minimum May temperature gives forecasts of Indian monsoon rainfall which are as good as those given by tendency in SOI in combination with the ridge. The parameters SOI tendency and the May minimum temperature are found to be equally useful.