The structure and variability of the temperature in the upper layers (0–200 m) of the northeast Arabian Sea have been studied in relation to the southwest monsoon over the Indian peninsula. Data from repeated bathythermograph (BT) lowerings at three-hourly intervals at a station around 18° N, 67° E during the periods 28 to 31 May 1973 and 29 June to 2 July 1973 (representing conditions before and after the onset of the monsoon) have been used for these studies. Mean temperature differences and autocorrelation coefficients have been computed and analysed for assessment of short-period variations.

The mixed layer was well developed with an average thickness of about 70 m during the monsoon period, while its thickness was about 40 m during the premonsoon period. The thermal structure reveals the presence of internal waves in the thermocline.

Studies of short-period variations indicate that changes of temperature occur in the upper part of the thermocline during the premonsoon and monsoon periods; however, the maximum temperature changes for the monsoon period are generally larger (ranging from 0.8 °C for a 3-hour interval to 1.2 °C for 9-hour and 12-hour intervals) than those for the premonsoon period, which are of the order of 0.8 °C for time intervals up to 12 hrs. Autocorrelation values reveal significant correlation (at the 1%; level) in the upper part of the mixed layer for intervals greater than 3 hours, the feature being more prominent during the monsoon period. […]