HOURS 



1200 1210 1220 1230 1240 1250 1300 1310 1320 1330 



i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i 

 0- / 



100- 



200- ~ 



i- 



LU 



uj 300- 



400- 



500- 



600 



700- 



.20 c 



AREA A , 



Figure 4. Examples of low-pass-filtered NEL Thermistor Chain data; 0.2°C 

 isotherms added by linear interpolation between whole-degree isotherms. 



GRADIENT FIELDS 



The following graphic method of differentiation was used to 

 find the vertical- and horizontal-temperature gradient fields. 

 First, the graph of the smoothed temperature structure was over- 

 laid with an exact copy, but the copy was displaced vertically by 



15 



