surface and the highly complex and interdependent circulation and mixing of 

 high and low salinity water masses at subsurface and intermediate depths. The 

 figures in Appendix C show surface circulation for the northeast and southwest 

 monsoons and the circulation of the two high salinity and three low salinity 

 water masses that markedly effect sound velocity structure at depth, T-S indices 

 for the water masses discussed in the following paragraphs are given on Figure 

 B-1, 



Surface Water Masses 



During the northeast monsoon (Figure C-1), surface circulotion is 

 essentially counterclockwise except in the Arabian Sea, Bay of Bengal, and 

 along the southern boundary of the area (South Equatorial Current). During 

 most of the southwest monsoon (Figure C-2), surface circulation is clockwise 

 throughout the area. The seasonal reversal of surface circulation has noticeable 

 effects on water properties south of about 10° N. latitude. In the Somali Basin, 

 high salinity Arabian Sea Water (ArSW) is carried by the Northeast Monsoon 

 Current, while during the Southwest monsoon lower salinity Indian Equatorial 

 Water (JEW) is brought into this region by the South Equatorial and Somali 

 Currents. Therefore surface and near-surface sound velocities are somewhat 

 higher during the northeast monsoon (Figure B-25). The exact opposite is 

 true in the Mid-Indian Basin, where the Southwest Monsoon Current replaces 

 less saline Bay of Bengal Water (BBW) and lEW with more saline ArSW. This 

 results in somewhat higher velocities during the southwest monsoon (Figure B-23). 

 North of about 10° N. latitude, surface and near-surface sound velocities are 

 more temperature dependent, resulting in higher velocities during the southwest 

 monsoon (Figures B-9 and B-14), except in areas of southwest monsoon upwelling. 

 Figures B-5, B-1 6, and B-35 show sound velocity and T-S profiles typical for 

 ArSW, BBW, and lEW, respectively. 



Substantial regions of upwelling during the southwest monsoon have 

 been documented off Muscat and Oman by Ryther and Menzel, 1965; off the 

 Somali Republic by Warren, et al., 1966; and south of Java by Wyrtki, 1962 

 (Figures B-4, B-ll, and B-38 respectively). In all three cases, surface velocities 

 are less during the southwest monsoon. Off the Somali Republic, velocities are 

 less to depths exceeding 1000 meters (Figure B-1 1). During the northeast mon- 

 soon, regions of upwelling are found at the northern end of the Arabian Sea, 

 off the coast of Kenya, off the east coast of India, and off the coast of Burma. 

 During the northeast monsoon, upwelling is confined to or near the continental 

 shelf. 



