Covariation in subskin-bulk temperature difference with environmental parameters in the north Indian Ocean
This study aims to explore the dependence of the ocean subskin-bulk temperature difference ΔT (T subskin-T 2.5m) on environmental parameters over the north Indian Ocean. This was possible because of the fortuitous concurrence of two parallel programmes, viz., the Tropical Rainfall Measuring Mission (TRMM) carrying a Microwave Imager (TMI) and the Indian moored buoy programme, over 6 years (1998-2003). The environmental parameters considered in this study are total water vapour (TWV), cloud liquid water content (CLW), sea surface wind speed, bulk temperature (T 2.5m) and T 2.5m-T air temperature difference, consisting of a composite data matrix of more than 3000 sets. The study revealed absence of any perceptible dependence on TWV and CLW. For T 2.5m between 24°C and 28°C, the mean Δ T is a decreasing function of T 2.5m. Data classification indicates that most of the cases of T 2.5m<28°C belong to Bay of Bengal during December to February. For the T 2.5m>28°C, Δ T is very small. Our results on the variation of Δ T with T 2.5m-T air are linear and in opposite phase. The daytime Δ T variation over the north Indian Ocean displays a decreasing trend with increasing wind. The night-time Δ T pattern, especially over the Bay of Bengal, is found to be very unusual: it remains insensitive to the variations in wind speed, and it is predominantly positive. Diurnal variation of Δ T under wind speed below 6 m s-1 is studied for overall data set as well as for the individual season data set. The low wind cases reproduce onset of warming at 9 h local time and a peak around 15 h local time. The average maximum amplitude of Δ T is more than 0.34°C with a standard deviation of greater than 0.7°C. Diurnal warming during pre-monsoon (post-monsoon) is highest (lowest).