Wind sea and swell characteristics off east coast of india during southwest Monsoon

The waves along the east coast of India during south-west monsoon have great importance due to the prevailing rough conditions. Significant Wave height (Hs) and other wave conditions are measured at a location of 20m water depth off east coast of India during south-west monsoon 2009. Wind-sea (Hsw) and swell (Hss) components are separated from the measured data, to look into the characteristics of the waves at the measured location. It is observed that the sea-state is dominated by swells arriving from south-east (SE) to south (S). The maximum measured Hs is 2.62 m. Good positive correlation of 0.84 is observed between Hss and Hs. The contribution of Hss to Hs is 63.2 and remaining is due to Hsw. Wave age shows the presence of young sea with significant occurrence of swell. The spectral band width parameter (e), calculated from the measured data indicates that the wave components cover wide range of frequencies. The high values of spectral narrowness parameter (v) and peakedness parameter (Qp) are observed during the study period

Modulation of SST, SSS over northern Bay of Bengal on ISO time scale

High resolution observations of atmospheric and oceanic variables are carried out at northern Bay of Bengal from 22nd July to 6th August 2009 on-board ORV Sagar kanya under the Continental Tropical Convergence Zone research/observational programme. Freshening of surface layer by more than 4 psu within 24 hours is observed, which is followed by warming in the surface layer temperature. The heat and salt budget analysis primarily indicates dominant role of advection processes on the evolution of temperature and salinity. The amount of rainfall received at observation site could not explain the observed freshening, thus an extensive analysis using wavelet coherence is done to find out the source of advected fresh water to the observed location. It is found that surface salinity in the northern Bay of Bengal (at 15 N) varies coherently with the rainfall over Ganga-Brahmaputra catchment area on intraseasonal time scale and with lag of about 60 days. Based on above observations, this study hypothesize that the intraseasonal rainfall variation modulates the amount of river discharge, which in turn modulates the salinity over northern Bay of Bengal on intraseasonal time scale. Since surface warming always follows the surface freshening, the time delay between the rainfall over catchment area and freshening at northern Bay of Bengal may explain the post monsoon warming. Importance of atmosphere-ocean coupling in driving the dynamics of the northern bay of Bengal has been clearly brought out in this study