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Title: Sound speed structure in the Arabian Sea and the Bay of Bengal
Authors: Kumar, S Prasanna
Navelkar, G S
Murty, T V Ramana
Somayajulu, Y K
Murty, C S
Issue Date: Mar-1993
Publisher: NISCAIR-CSIR, India
Abstract: Sound speed computed from annual mean temperature and salinity data of Levitus reveals that spatial variation in the Arabian Sea is greater than that in the Bay of Bengal. Maximum spatial variation of sound speed in the Arabian Sea noticed between the depth levels 200 to 1500 m is due to the combined effect of variation in the salinity (to a larger extent) and temperature. In the Bay of Bengal though the spatial variation of sound speed is marginal, variations observed between 1500 and 2800 m are brought about by warm Andaman Sea waters. The depth limited nature of annual mean sound speed profile for 2 marginal seas suggests that the effective acoustic channel lies much below (approximately 300 m) the surface. This results in acoustic propagation in the form of surface-refracted bottom-reflected (RBR) rays within the SOFAR channel. Acoustic ray arrival pattern, obtained from the ray-tracing software, reveals that in the Arabian Sea middle order rays with launch angles from +/-6.5-degrees to +/-7.5-degrees reach the receiver early. These are followed by rays with flat angle or near-axial rays and the RBR rays. The purely refracted rays with steep as well as flat angles can adequately be resolved in time-a characteristic that make the ray identifications easier at the experimental stages. On the contrary, in the Bay of Bengal, near axial, flat angle rays with launch angles from -4-degrees to +4-degrees reach the receiver faster than the purely refracted, steep angle rays. Further, flat angle rays arrive almost simultaneously making the ray identification complex and difficult. The rays with launch angles between +/-4-degrees and +/-7-degrees undergo total refraction and have a better spread as far as travel time is concerned. The early arrival of the middle order rays in the Arabian Sea has been attributed to the frequent scanning of warm and high saline waters in the depth range of 500-1200 m by these rays. The early arrival of the axial rays in the Bay of Bengal results from weak gradients within the SOFAR channel.
Page(s): 17-20
ISSN: 0975-1033 (Online); 0379-5136 (Print)
Appears in Collections:IJMS Vol.22(1) [March 1993]

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