averages of these parameters then were contoured or generalized on an areal 

 basis. Regions where sound velocity perturbations are present more than 80% 

 of the time, 20-80% of the time, and less than 20% of the time also were 

 derived on a two-degree square basis and generalized on an areal basis. 

 Throughout this report, the first type of region above will be referred to as 

 having a PERMANENT upper sound velocity minimum or intermediate sound 

 velocity maximum, the second as TRANSITORY. In the third region, sound 

 velocity perturbations effectively are ABSENT. The treatment of data used 

 in the construction of the sound velocity cross-sections and sound velocity/ 

 T-S comparisons is discussed in Appendices A and B, respectively. 



All available T-S data were analyzed for the depth of salinity maxima 

 and minima in order to determine the causes of various sound velocity features 

 and the circulation of various high and low salinity water masses. Core salinity 

 depths were generalized on an areal basis for the following water masses: 



• high salinity Persian Gulf Intermediate Water (PGIW) 



• low salinity Subtropical Subsurface Water (SSW) 



• high salinity Red Sea Intermediate Water (RSIW) 



• low salinity Antarctic Intermediate Water (AAIW) 



• low salinity Banda Intermediate Water (BIW). 



T-S indices for each of these water masses ore shown on Figure B-1 and generalized 

 flow diagrams are presented in Appendix C. 



The two seasons of winter (November through April) and summer (May 

 through October) are used in this report. These seasons correspond to the maximum 

 duration of the NORTHEAST and SOUTHWEST MONSOONS, respectively. 

 However, April-May and October-November often are representative of inter- 

 monsoonal periods (Duing, 1970). This fact was taken into account during data 

 analysis. Two monsoonal seasons exist throughout the area, but generally are 

 not found south of 10° S. latitude except along major land mass boundaries 

 (Duing, 1970). 



GENERAL OCEANOGRAPHY AS RELATED TO SOUND VELOCITY STRUCTURES 



A general knowledge of the circulation and water mass structure is a 

 prerequisite to the understanding of sound velocity structures. This is particularly 

 true in the North Indian Ocean due to the reversing monsoonal circulation at the 



