with greatest sound velocity). The duration of both features was somewhat less 

 sporadic. Therefore, identical permanent (greater than 80%) and transitory 

 (20-80%) regions are shown on both figures. 



The three fingerlike regions with deepening permanent perturbations 

 extending from the Gulf of Aden into the Somali Basin correspond well with 

 flows of RSIW (Figure C-5) , as does the region with deepening transitory 

 perturbations that spans the Mid-Indian and North Wharton Basins between about 

 5° N, and 5° S. latitude. The two fingerlike regions with shoaling transitory 

 perturbations extending from about 5° S. latitude into the Somali Basin corres- 

 pond with flows of SSW and AAIW (Figures C-4 and C-6, respectively). The 

 three regions where sound velocity perturbations effectively are absent (Arabian 

 Sea, Bay of Bengal, and Mid- Indian and North Wharton Basins south of about 

 5° S. latitude) all correspond to regions without RSIW (Figures B-5, B-16, and 

 B-36, respectively). 



The complex nature of perturbations in the vertical dimension is best 

 seen on the various sound velocity cross-sections. Figure A-2 shows a permanent 

 upper sound velocity minimum at velocities less than 1510 m/sec and a permanent 

 intermediate sound velocity maximum at velocities between 1510 and 1515 m/sec 

 that extends the length of the Gulf of Aden and terminates near the Owen 

 Fracture Zone. Minima are associated with SSW, maxima with RSIW, East of 

 60° E, longitude, only sporadic perturbations are found (lesser concentrations of 

 RSIW). Figure A-3 shows that perturbations are absent in the Bay of Bengal 

 except along the India and Irrawaddy Delta continental slopes (probably caused 

 by local northeast monsoon upwelling). The effects of upwelling on sound 

 velocity perturbations is demonstrated well on Figure A-4 (northern Somali Basin). 

 During the northeast monsoon, a single minimum and maximum is found on both 

 sides of the Owen Fracture Zone (caused by SSW and RSIW, respectively). 

 However, during the southwest monsoon in the presence of extensive upwelling, 

 two distinct sets of perturbations are found west of 55° E, longitude at velocities 

 up to 5 m/sec less than those during the northeast monsoon (also see Figure B-11). 



Figure A-6 shows a double set of perturbations at velocities greater than 

 1495 m/sec west of the Chain Ridge (southwest monsoon upwelling) that merges 

 into a single minimum/maximum structure at about 56° E. longitude. Only 

 sporadic perturbations are found east of the Carlsberg Ridge at velocities less 

 than 1495 m/sec (lesser RSIW concentrations). Figure A-7 shows a single 

 minimum/maximum structure at velocities less than 1495 m/sec over the southern 

 Somali Basin (interaction of SSW and RSIW). However, on either side of the 

 Seychelles Islands a more complicated pattern of perturbations is associated with 

 intermixing of RSIW, SSW, AAIW, and BIW, East of the Seychelles Islands and 



n 



