Parachute Drogue Current Project 



INTRODUCTION 



A project was planned to determine if veloc- 

 ity fluctuations of the Labrador Current as- 

 sociated with the volume transport calculations 

 could be directly observed. In addition to the 

 serial occupations of the western portion of 

 Standard Section 3, parachute drogue measu- 

 rements were conducted. These drogue meas- 

 urements were to determine if velocity varia- 

 tions indicated by the geostrophic equation 

 could be verified. 



MEASUREMENTS 



The drogue studies were made with the 

 time-series study at Standard Section 3. 

 This repeated occupation of the western 

 part of Standard Section 3 was to determine 

 if any short-term variation occurred in the 

 volume transport of the Labrador Current. 

 The weather encountered during this drogue 

 experiment was extremely rough. The average 

 wind force for the cruise was force 6 with the 

 associated high sea states. Figure 70 is a 

 progressive wind vector diagram for the time 

 interval of the drogue study. The visibility 

 was poor in fog and drizzle. 



The experiment was conducted in this man- 

 ner: Seven drogues were set from 1342Z, 17 

 April 1966 to 1256Z, 18 April 1966. Excepting 

 drogue 5, these drogues were set in pairs with 

 a surface drogue and a deep drogue. The pair- 

 ing of drogues is shown in Table V. As each 



Table V. Number, date, time, and depth of each drogue 



set 



drogue was set, a radar range and bearing 

 was taken as close together as possible on the 

 drogue and on the reference buoy. Using this 

 information it is possible to obtain the com- 

 ponents of the position vector extending from 

 the reference buoy to the drogue. Two position 

 vectors may be used to obtain the displacement 

 vector whose magnitude when divided by the 

 time interval produces the magnitude of the 

 velocity vector. The components of the dis- 

 placement vector may also be used to determine 

 the bearing of the velocity vector from north. 

 A program was prepared in FORTRAN for 

 the IBM 1130 computer that would compute 

 the drogue velocity in centimeter/sec and the 

 bearing of the velocity vector from true north. 

 The inputs required for this program were: 



1. Radar range to and true bearing of the 

 reference buoy from the ship. 



2. Radar range to and true bearing of the 

 drogue from the ship. 



3. Time each set of observations was taken. 

 The outputs of this program were: 



1. Magnitude of the velocity vector (speed) 

 for the given interval. 



2. The true bearing of the velocity vector 

 from north. 



The computer program is shown in Figure 71. 

 A flow diagram for this program is presented 

 in Figure 72. 



RESULTS 



The drogue trajectories are shown in Fig- 

 ures 73 through 76. They have been grouped 

 using the time set, the depth at which set and 

 the location where set. It is apparent from these 

 criteria that drogues 1 and 2, 3 and 4, and 

 6 and 7 should be grouped together. Drogue 

 5 should be studied separately. The drogue 

 speed and bearing information is given in 

 Tables VI through X. 



The actual depths of the parachutes are un- 

 known, but Gerard (1965) presented measure- 



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