OBTAINING THE DATA 



Temperature data were selected for analysis from 17 widely 

 separated areas involving several water masses (Sverdrup et al . , 

 1942) , 13 The data were taken during eight cruises with the NEL 

 Thermistor Chain and provide the best available representation 

 of the geographic and water- mass variety of temperature struc- 

 tures (fig. 1). The positions of the sample areas, cruise num- 

 bers, and dates are shown in table I. 



The data were obtained solely from the NEL Thermistor 

 Chain, a massive oceanographic instrument (fig. 2) which has 

 been in operation since 1961. The chain is 900 feet long and 

 capable of measuring and continuously recording the temperature 

 structure to a depth of 830 feet, although the average towing depth 

 is about 750 feet. The chain system consists basically of a hoist, 

 links, storage drum, and electronic temperature recording 



Figure 1. Geographic locations of 17 NEL Thermistor Chain temperature-data 

 sample areas. 



