Observations of wind and waves in the central Bay of Bengal during BOBMEX-99 and their effect on mixed layer depth variability due to forced mixing

Abstract

Time-series wind and wave measurements were carried out onboard INS Sagardhwani in the central Bay of Bengal during BOBMEX-99. Various other marine meteorological and oceanographic measurements relevant to monsoon studies were also collected simultaneously. The observed variations of wind and waves and the associated mixed layer depth (MLD) variability based on both temperature and density criteria at 3 hourly intervals are presented in this paper as a case study. At the time-series location (13 • N, 87 • E) wind varied between 6 and 16 m/s and the predominant direction was southwesterly. The significant wave height and period varied from 1.9 to 3.7 m and 8 to 13 s respectively. Some of the available statistical predictive methods for the determination of MLD by forced mixing are utilized to test the extent of mechanical mixing within the top layer of water by the local wind and wave activity. The same is extended to formulate a new empirical relation for gross estimation of effective depth within which the sound energy is generally trapped during its transmission in the surface duct. The present analysis aiming for estimation of observed MLD variability (35 to 75 m) using the suggested simple empirical relation reveals that, the mixed layer variability observed during the experiment depends on both local ocean variability as well as remote forcing as reported earlier.

Effect of the 2004 ‘Boxing Day’ Tsunami on Water Properties and Currents in the Bay of Bengal

“…Two cells of very low density are found off the central east coast of India and northwest of the Andaman Islands, where freshwater discharges from the Krishna and Irrawady Rivers, respectively, enter the Bay [4] . Work has already been done on the entire oceans on geostrophic current using altimetry data and in the Indian Ocean [5][6][7][8] . During the 2004 tsunami, research on a satellite view of internal wave [9] found the effect of tsunami on marine ecosystem [1] .…”