0.056 to 0.318 cycle per minute, which is equivalent to a period of 

 17.9 to 3.1 minutes or a wave length of 1.8 to 0.3 miles. When 

 the peaks are wide they are considered as zones; for example, 

 0.121 to 0.163 cycle per minute (or 0.8- to 0.6-mile wave lengths) 

 is considered a zone. 



The power spectrum curve shows that the greatest power is 

 in the low frequencies which show no peaks. The number of de- 

 grees of freedom is given by ^ = — — . When using 1440 consec- 



n 2 



utive depth sample values and 144 lags, v = 19.5. The correspond- 

 ing ratio of computed to true value """^ falls between 0,54 and 1.60 

 for 90-percent confidence limits. 



The ratio of background to peak height was determined by 

 constructing a base line and vertical height (fig. 8). For example 

 the 4. 6-minute-period peak of this 20°C isotherm depth has a 

 peak-to-background of 52 to 17, or a ratio of 3.06, which is signi- 

 ficant, whereas the 17.9-minute-period peak (fig. 8) has a ratio of 

 1.21, which is not significant. 



To summarize the power spectrum, the peaks and peak zones 

 were read from the individual power spectrum graphs, and the 

 peak-to-background ratio was computed and plotted (fig. 9A) for 

 the data sections in an isotherm in the thermocline and (fig. 9B) 

 for data sections in the isotherm below the thermocline . In both 

 graphs the values were arranged with reference to longitude and 

 frequency. Thus figures 9A and 9B are similarly portrayed as a 

 longitude section from near San Diego to near Honolulu. 



In addition a contour was drawn for ratio values of 1.6 and, 

 when present, 2.0. Values greater than 1.6 are considered signi- 

 ficant in accordance with the 95 -per cent confidence limits. 



The contours show that zones of significant frequencies of 

 vertical changes in isotherm depths vary widely from sample to 

 sample. No value exceeds 3.1. The higher or more significant 

 values appear to be distributed in patches. However, for the shal- 

 low isotherm in the thermocline (fig. 9A) the higher values are a 

 little more frequent near a midway zone and nearly to Hawaii. 



21 



