large areas in minimum time; however, aircraft sensors are limited in 

 subsurface observations. The April series of flights proved to be 

 extremely valuable in pointing out two major characteristics: exist- 

 ence of east-west oriented surface features north of the Gulf Stream 

 boundary and wave-like motion of the boundary. Movement of features 

 north of the stream was not discernible, because the time covered by 

 the survey was too short. However, absolute temperature changes due 

 to atmospheric conditions were observed within features. 



Weather conditions during the ART survey are shown in figure 2. 

 On 10 April the region was dominated by a warm anticyclone with 

 increasing southerly flow as the day progressed. Before the flight 

 on 11 April, a strong cold front swept over the area causing a drop 

 in air temperature of 10°C. Cooling continued through the 12th and 

 13th with decreasing northerly winds. 



Figures 3 and 4 show the aircraft tracks and sea surface tempera- 

 ture (SST) analyses for the 10th and 11th, respectively. The first 

 day had the fewest legs (indicated by the thin black line with arrows), 

 because tracking was required to establish the survey area. Deter- 

 mination of the track before the flight on the following days resulted 

 in more time for surveying the area. The chart for the 10th shows 

 the location of the tight gradient zone which delineates the northern 

 boundary of the Gulf Stream. This chart also contains the highest 

 temperatures and is for the same day that the warm high dominated the 

 area. 



Features worth noting on the 11th include the location of the 

 northern boundary south of 37°N, a cool filament lying just north of 

 the stream, a warm cell north of the cool filament, and overall cooling Y ■ 

 from the 10th. The 10°C area at 72. 5° W reflects this cooling. The ^jjt^ 

 average drop in water temperature was about 1°C in the warm and cold 

 features north of the stream, but the stream temperature showed no 

 significant decrease. The lack of cooling in the stream is due to 

 rapid advection of warm water. 



The pattern for the 12th (figure 5 ) is similar to that of the 11th 

 with minor important changes. The northern boundary in the western por- 

 tion of the area has progressed northward to just south of 37°N, and 

 the cooling of features north of the stream has subsided. The cool 

 water just north of the Gulf Stream is becoming more prominent. The 

 warm cell still exists, and a wave has developed along the wall. 



By the 13th (figure 6), the last day of observations, two days of 

 convective and mechanical mixing have passed and features are well- 

 defined. The northern boundary moved north of 37°N to a point only 

 35 km south of the warm cell. This major wave apparently progressed 

 at a rate of 0.3 m/sec, and its wave length appears to be about 160 to 

 200 km. This wave speed is greater than found in earlier work (The 



