In addition to the horizontal charts, graphs of monthly sea surface 

 temperature variation for selected locations are shown. In this presen- 

 tation the percentage distribution of sea surface temperature in 1°F. 

 class intervals was plotted for each month, and curves of 1, 2.5, 25, 

 50, 75 > 97-5, and 99 percent were constructed. 



The choice of locations for these graphs was governed by the desire 

 to demonstrate the degree of variability which occurs between various 

 regions in this ocean, while attempting to select those locations with 

 a sufficiently high number of observations to allow reasonable analysis. 



In comparing the analyzed charts, several features are noticeable. 

 For example, the upwelling of cold water along the coasts of continents 

 is evident. Of particular interest is the little- studied area off the 

 east coast of the Somali Republic. During the southwest monsoon the 

 persistence of the wind produces general upwelling along this coast. 

 This is most evident off Ras Hafun (10°25'N., 51°l6 , E.), where the July 

 mean temperature in the appropriate 1 square is nearly h°F. less than 

 the July mean temperature in the surrounding 1° squares. In the graphs 

 of monthly variability the double maximum-minimum characteristics of the 

 Indian Ocean's north equatorial waters is strongly accentuated off Ras 

 Hafun. Here, the minimum during July - August may be compared to the 

 warmer minimum temperatures occurring at the same time in nearby regions. 

 In addition to the temperatures shown off Ras Hafun, a low of 55 F. has 

 recently been reported by the Scripps ship ARGO during the International 

 Indian Ocean Expedition. 



The 1° square spacing of these charts, as well as the monthly 

 treatment of data, may hide small local or temporary temperature con- 

 ditions, especially on the mean charts, where the averaging of values 

 may oversimplify the temperature variations of a complex region. These 

 fluctuations may be better determined by referring to the maximum or 

 minimum charts. For example, the Antarctic Convergence Zone, poorly 

 discernible on the mean charts, is well defined on the maximum charts. 

 Major current systems of the Indian Ocean, such as the North Equatorial 

 Current and the Equatorial Countercurrent, are also best defined on the 

 charts of maximum temperatures. In turn, currents of cool water are 

 best defined on the minimum chart, as for example the intrusion of cool 

 water in the South China Sea in February . 



Because of the large quantity of data involved, it is believed that 

 these charts are, in general, more definitive than oceanographic charts 

 of other parameters such as salinity, for which data are sparse. 

 Although these charts may not be considered accurately descriptive where 

 the analysis was based on fewer than 25 observations per 1 square, or in 

 areas where the 1 square averaging disguises more complex thermal 

 structure, they are useful tools for the ocean scientist, especially 

 where other types of data do not exist or are in poor distribution. 



