Wilker son 



strongest horizontal temperature gradients at depths of 100 to 200 

 meters during winter. In late spring and summer, warming of the sur- 

 face layer tends to blur and obscure their relationship. 



Using this accumulation of knowledge, the Naval Oceanographic 

 Office early in 1966 began a series of tracking flights over the Gulf 

 Stream with an oceanographic research aircraft fitted with an airborne 

 radiation thermometer (Pickett and Wilkerson, 1966). Knowledge of the 

 fluctuations of position and shape of the Gulf Stream was required for 

 making more accurate ocean environment forecasts for the Antisubmarine 

 Warfare Environmental Prediction Services (ASWEPS) of the Oceano- 

 graphic Office. 



This paper presents the results of a series of ASWEPS oceano- 

 graphic aircraft (Figure 1) tracking missions made for detecting 

 changes in the shape and position of the Gulf Stream between Septem- 

 ber 1966 and January 1967. 



TECHNIQUE OF MEASUREMENT 



The principal value of the aircraft in Gulf Stream studies is 

 the speed and endurance of the aircraft. An aerial survey of the 

 Gulf Stream boundary from Cape Hatteras to 60''W, requiring about 8 

 hours to complete, results in collection of very nearly synoptic data 

 and virtually eliminates the time changes inherent in ship tracking 

 data. Clouds over the Gulf Stream which would obscure the view from 

 satellite altitudes is generally not a problem in aircraft observa- 

 tion. The cloud base over the Gulf Stream is normally above 300 

 meters. 



Once the boundary has been observed the pilot, guided by radio- 

 metric observation, steers the aircraft left or right along the 

 boundary to cross and recross the zone of abrupt temperature change. 

 A sample surface temperature recording taken as the aircraft crossed 

 the Gulf Stream inshore boundary is shown in Figure 2. 



The characteristically abrupt change in surface temperature (in 

 this case S^C in about 300 meters) is clearly recorded. 



Normally, a boundary crossing can be made every minute so that 

 a position fix of the aircraft is also necessary each minute. With 

 Loran A the location of the boundary can be determined to within 

 about 2 n.m. from Cape Hatteras out to 63''W, and to within about 

 4 n.m. between 59'*W and 63°W. 



RESULTS OF MEASUREMENTS 



On 30 September 1966 the ASWEPS aircraft completed the boundary 

 tracking flight shown in Figure 3. The survey started at Cape 

 Hatteras and continued to 63''W, a distance of about 1,000 km. The 

 data showed two principal meanders in the Stream, one positioned at 



416 



