Differences of Depth Values (Isotherm Slopes) 



The first method of presenting isotherm variability is by 

 depth differences from point to point along selected isotherms. 

 The isotherm depths were scaled from the original record at half- 

 minute intervals. 



SELECTION OF SLOPE INTERVALS 



From each section shown in table 2 (except J and L), two 

 isotherms were chosen for analysis. One of the selected iso- 

 therms was located in the main thermocline and the other below 

 it. Of two isotherms analyzed in part of section Q (fig. 16), the 

 temperature of the shallower one in the main thermocline was 

 19°C and in the deeper one below the main thermocline, 12°C. 



The depth differences from point to point along the isotherms 

 were determined from the formula 



X t ~ X i+1 Y k 



X t and Xi + 1 are depths (in feet) of a given isotherm at the 

 beginning and end of the i th distance (or time) interval along the 

 track; Y k is the depth difference (in feet). When the isotherm is 

 falling, the difference is negative. 



From ship speed and depth difference, approximate slopes 

 can be calculated. At a speed of 6 knots, the ship traveled 304 

 feet in each half -minute interval; therefore dividing the depth 

 differences by 304 feet gave the slope of the isothermal surface in 

 the direction of the ship's motion. The slope could also be ex- 

 pressed by the angle having this slope for a tangent. 



From 240 to 2040 consecutive observations of isotherm 

 depths were taken from each sample section. The distribution of 

 depth changes and the slopes for each selected isotherm on each 

 2-17 hour section were diagrammed as a cumulative frequency 

 curve of depth changes and slope angle (Appendix B). 



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