towing direction. The resulting slope curve with reference to 

 direction of tow is shown (fig. 21). The similarity of orientation 

 implies that the vertical wave-like structures, or internal waves, 

 are oriented more to the east and west because the slopes are 

 steeper when they are crossed during towing normal to their 

 crests. Since the steeper values occur towing to the south and 

 southwest, it would seem that the propagation of dominant internal 

 waves was northward and into the Gulf of California. 



45 



90 135 180 225 270 



AVERAGE DIRECTION OF TOW (DEGREES) 



315 



Figure 27. Average 50th percentile slope of deep and shallow isotherms; 45— degree 

 grouping vs direction of tow. 



GEOGRAPHIC DISTRIBUTION 



To be comparable with other sample sections, and to give a 

 geographic distribution of the measure of isotherm slope, the 

 absolute -value 50th and 70th percentiles of vertical change per 

 304 feet for the selected isotherms in the main thermocline were 

 spatially plotted (figs. 22 A and 22B). These median changes in 

 depth are located at a geographic position corresponding to the 

 center of the line of tow (fig. 15). The distribution of slopes is 

 contoured. 



When widely spaced values are contoured, an option may 

 exist of where the contour could be drawn. In such event, the 

 contour can be made to cross itself, indicating both options. The 

 areas of steepest isotherms, however, were clearly defined and 

 the choice was not necessary. The contoured values for the 



44 



