shows that the accumulative per cent of small angles of the deep 

 water isotherms (from the traverses at right angles) is significant- 

 ly greater than for similar isotherms in shallow water. It is 

 therefore reasonable to assume that the shallow water internal 

 waves in the thermocline are considerably steeper than those 180 

 miles farther out to sea. This difference indicates that the inter- 

 nal waves peak as they move into shallow water. 



Autocorrelation of Depth Values 



Another approach to the problem of subsurface temperature 

 variability is by means of autocorrelation coefficients. 16 By 

 using the same half-minute isotherm-depth data, autocorrelations 

 were computed for each leg of the cruise and each selected iso- 

 therm. Elements of successive pairs of points (depth of an iso- 

 therm) at equal but overlapping time intervals were correlated 

 with each other, and the process repeated for each time interval, 

 increasing by half- minute steps from a half -minute to 250 minutes. 

 Autocorrelation, R \ , was computed for increasing intervals, X , 

 of 304 feet (half-minute), using the expression: 



N-X N -X N-X 



(^ Z Vi+r £ x t £ J 7+- 

 i=i l+x i =i l t =i l+i 



R x= 



N-X [N-X ~\ s k\ N-X [N - X T 



(N-X) £ J 3 - EX. \(N-X) D J s - £ I \ 



i=i l L=i *J i-i l+x li =i H 



where X ~ o, 1, 2, .... 500 lag intervals and N is the total num- 

 ber of depth readings in each leg. The computed autocorrelations 

 based on about 1500 depth readings (sample length, 750 minutes) 

 and lag length variable from to 500 steps (0 to 250 minutes) are 

 shown in figures 12 through 16. 



Figure 12 gives the results of the autocorrelation of the half- 

 minute sampling rate for the depth of the 9°C isotherm of offshore 

 traverse, leg 1. The correlation is positive throughout. 



24 



