Certain seasonal characteristic features of oceanic heat budget components over the indian seas in relation to the summer monsoon activity over India

Abstract

The present study has been undertaken to examine the oceanic heat budget components and their variability over the Indian seas in relation to the extreme monsoon activity (flood/drought) over the Indian subcontinent. For this purpose, various components of oceanic heat budget have been analysed for pre-monsoon (March-May), monsoon (June-September), post-monsoon (October-December) and winter (January-February) seasons over India. The data base used in this study consists of mean monthly marine meteorological fields for 30 years (1950-1979), which is a part of the Comprehensive Ocean Atmosphere Data Set (COADS) analysed at 1° latitude by 1° longitude resolution. The mean fields of incoming shortwave radiation flux over the Indian seas in different seasons vary in accordance to the sun's position and cloud cover variations. The latent heat flux undergoes considerable seasonal variations, particularly over the Arabian Sea. There is a dominance of latent heat flux (representing the oceanic heat loss) over shortwave solar flux (representing the oceanic heat gain) during the monsoon season, which results in a zone of net oceanic heat loss over the central Arabian Sea. This feature produces a positive feedback for the maintenance of deep cumulus convection over the Arabian Sea in this season. It is also found that oceanic heat budget components over the Indian seas exhibit significant variability in relation to the extreme monsoon activity leading to flood/drought over India. Based on the above analysis, mean monthly variations of the oceanic heat budget components over three smaller sectors of the Indian seas, namely west equatorial Indian Ocean, Arabian Sea and Bay of Bengal, are also examined. The variations are found to be considerably different between the two extreme categories of the monsoon. It becomes evident from this study that the oceanic sectors of west equatorial Indian Ocean and Bay of Bengal experience a large reduction of net heat flux from April to May prior to a flood monsoon season over India. This suggests that a spectacular increase of latent heat flux and decrease of shortwave flux occurs over these oceanic sectors, leading to a sharp reduction of net heat flux.