PREDICTIVE MODEL OF HORIZONTAL-TEMPERATURE 

 GRADIENTS 



A predictive horizontal-temperature-gradient model can be 

 constructed in two steps: first, use half the mean wavelength, 

 0.35 mile, as the distance for the periodic sign changes of the 

 horizontal-gradient field;* second, from the results of a single 

 bathythermograph lowering, compute the vertical-gradient 

 strengths in °C/ft for selected depth ranges and assign the 

 horizontal-gradient field with strength two orders of magnitude 

 smaller than that of the vertical field for corresponding depth 

 ranges . 



As an example of the construction of such a model, consider 

 the bathythermograph of figure 13 . The change in the order of 

 magnitude of the vertical-temperature-gradient strength deter- 

 mines the depth range interval as shown in table 2. The 

 horizontal-temperature-gradient strengths for the corresponding 

 depth ranges are also entered in the table. 



The resulting horizontal-temperature-gradient field model 

 is shown in figure 14. The gradient field changes sign each one- 

 half wavelength as shown by the alternating shaded and unshaded 

 areas. The orders of magnitude of the horizontal-gradient 

 strength in °C/ft are contoured at the depths specified by the 

 matching vertical gradients computed from the bathythermograph. 



In the construction of such a model, obviously the larger 

 the number of bathythermographs taken, the more reliable the 

 depth ranges will be for establishing the order-of-magnitude con- 

 tours in the model. The bathythermograph used here was made 

 0815, 7 August 1962, during Cruise 14 with the NEL Thermistor 

 Chain. The simplified model results (fig. 14) may be compared 

 with the more detailed computed horizontal-gradient field for 

 Sample Area 1 in figure 15 . The model is in reasonably good 

 agreement with the more detailed horizontal-gradient field for 

 the same time, place, and depth. There is a slight disagreement 



When a single BT is used, the initial gradient sign of the model has to be arbi- 

 trarily assigned. However, when two closely spaced BT's are used, the actual 

 gradient sign can be determined. 



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