A STUDY OF SOUTH-WEST MONSOON RAINFALL IN WEST BENGAL & ORISSA AND IT’S CORRELATION WITH SUN SPOT NUMBERS

This paper presents a study of the variation of South West Monsoon Rainfall (SWMR) over two East Coast States(namely West Bengal and Orissa), Western part(Rajasthan and Gujrat), extreme North East(Assam)of India. The main stress has been given to reveal the correlation of this variation with the Sun’s Spot Number (SSN) of More Active Period (MAP) during 124 years (1880-2003).Firstly, it is found that in many cases SSN of MAP has tendency to increase with time having imbedded oscillation of period 22 years (similar to double solar cycle period).

The analysis of SWMR of those states separately or combined reveals that it is moderately influenced by Solar Activities provided SSN lies between 90 and 130. When SSN is less than 90 it becomes too weak to influence - there does not appear any definite pattern of change of SWMR. But when SSN increases from 90 to 130, SWMR tends to decrease. This implies that there may exist a range of critical SSN after which SSN has inverse significant effect on SWMR.

Lastly, when linear trend lines for SWMR are compared it becomes apparent that gradients of SWMR for West Bengal is slightly positive, that for Orissa is slightly negative and almost zero for total SWMR. This implies that overall there is no change in amount of Rainfall due to South West Monsoon in the combined area of West Bengal and Orissa.