Hydrological and meteorological features associated with onset of southwest monsoon over Tamil Nadu

Abstract

A simple statistical concept has been advanced to determine the  onset dates of southwest monsoon over Tamil Nadu. The normal onset date  has been found to be 4^th June with a standard deviation of 6 days based on 22 years of data. It has been shown that the feeble increase in rainfall  over Tamil Nadu in association with the onset is not sustained  subsequently and the rainfall decreases in the second half of June.  The daily upper air data over Chennai and Karaikal for 10 years have been studied and the change in the temporal profiles of these parameters in response to the monsoon onset over Tamil Nadu has been clearly brought out. Some of the unique features of monthly rainfall distribution of Tamil Nadu vis-à-vis those of other meteorological sub-divisions of India in relation to southwest monsoon onset have been discussed.