The Sound Channel Characteristics in the South Central Bay of Bengal

Environmental data collected along 92.5 o E between 2.7 o N and 12.77 o N during late winter show a permanent sound velocity maximum around 75 m and an intermediate minimum between 1350 m and 1750 m. The axis of the deep sound channel is noticed around 1700 m. The shallower axial depth (~1350 m) between 7.5 o N and 10.5 o N coincides with the cyclonic eddy. Within the sonic layer (SLD), Eastern Dilute Water of Indo-Pacific origin and Bay of Bengal Watermass are present whereas its bottom coincides with the Arabian Sea Watermass. Sound speed gradient shows good relationship with temperature gradient (correlation coefficient of 0.87) than with salinity gradient. A critical frequency of 500 Hz is required for the signal to be transmitted through a channel of 50 m thickness and it increases to ~1 kHz for a layer of 20 m. Within SLD, salinity there is 1.54 m/s increase in sound per 1 psu increase in salinity. In the thermocline, the sound speed decreases by 1.95 m/s per degree drop in temperature, whereas at deeper depths pressure effect dominates (@ 1.4 m/s per 100 m depth). Index Terms Bay of Bengal, Sonic Layer Depth, SOFAR Channel, Critical frequency, Watermass.