El Niño/SST of Puerto Chicama and indian summer monsoon rainfall: statistical relationships.

Abstract

A detailed statistical investigation of the relationship between All-India (India taken as one unit) summer monsoon (June to September) rainfall and El Niño/SST of Puerto Chicama has been made in the study based on the available data for the period 1871-1985. During the strong/moderate El Niño events, the All-India monsoon rainfall is about 11% below the normal and this is statistically significant at 0.1% level (Student's t-test). The correlation coefficient (CC) between the two series is -0.33 which is highly significant. Superposed epoch analysis has also indicated that monsoon rainfall is very much below normal during El Niño year.  Puerto Chicama (8°S·, 79°W) sea surface temperature (SST) which is a good indicator of El Niño phenomenon. showed significant relationship with All-India rainfall for the period 1925-80 with different seasons as well as months. The CC with the month of May SST is - 0.5 which is highly significant and this relationship is utilized in the development of the regression equation to estimate the All-India rainfall. The regression equation developed for the data years 1925-80 is y = 128.3 - 2.42x where y is the All-India monsoon rainfall and x is the May SST of Puerto Chicama. Estimates from this relationship for the independent years 1981-85 are found to be encouraging. The relationship between sub-divisional monsoon rainfall for different regions of India and May SST of Puerto Chicama is significant at 5% level or above for 11 sub-divisions, mainly these areas lie north of 16°N and west of 80°E.