Appendix B 



Oceanographic Conditions on the Grand Bani(s 

 During the 1982 International Ice Patrol Season 



By LCDR A. D. SUMMY, USCG 



Background 



The 1982 Ice Patrol Season marked the first time that cur- 

 rent information acquired from TIROS Oceanographic 

 Drifters (TODs) was used to successfully modify the 

 historic current data base used by the International Ice 

 Patrol's "IBERG" drift prediction model. The IBERG model 

 which has been in use since the 1979 Ice Patrol season 

 (Ivlurray, 1979) has up to this time used a historic current 

 field with no input of real-time current data. Recognizing 

 this drawback, the Oceanographic Unit (until its closure on 

 1 April 1982) and the Oceanographic Section under the 

 Marine Sciences Branch of Commander, Atlantic Area, pur- 

 sued the problem of how best to make use of the real-time 

 current information that was being obtained via TODs in 

 the Ice Patrol area. 



Procedures 



A series of programs was developed to compute total 

 drift vectors from the TOD data. These vectors were then 

 converted into a "quasi-geostrophic" data base which 

 could be used to modify the existing historical geostrophic 

 currents in the International Ice Patrol area. The conversion 

 from a total drift vector to a geostrophic vector was done by 

 taking "analysis" winds obtained from Fleet Numerical 

 Oceanography Center (FNOC), Monterey, computing a local 

 wind-generated current (Mooney, 1978), and subtracting the 

 wind-generated current from the total current vector. This 

 final current was then used to modify the historic data base 

 with a simple weighted average scheme. The modified cur- 

 rents were then relaxed to return to their original values 

 over a two week period unless modified again by a more re- 

 cent TOD drift. Six TODs were deployed during the 1982 Ice 

 Patrol season (Table B-1). Of the six TODs #2640 and #2598 

 failed within 24 hours of their deployment. The trajectories 

 of the other four are shown in Figure B-1. All of the TODs 

 were air-deployed from a Coast Guard C-130 aircraft on 

 routine ice reconnaissance flights. The TODs were all 

 equipped with window-shade drogues tethered 10 meters 

 below the surface, drogue tension sensors, sea surface 

 temperature (SST) sensors, and battery voltage monitors. 

 Service ARGOS in Toulouse, France collected all sensor in- 

 formation and positions and relayed them to the 

 Oceanographic Section via computer link. The Section 

 recorded all data directly onto disk via an acoustic modem- 

 computer link. The position information, SST, and current 

 vectors were then generated and made available for 

 modification of the Ice Patrol currents. 



1982 Operations 



Two TODs (#2638 and #2640) were deployed on 3 March 

 1982. TOD #2638 was deployed at position 48°58'N, 

 48°38'W which was to the east of the Labrador Current. At 

 deployment, the sea surface temperature it recorded was 

 0.9°C. This drifter initially moved in a southeasterly direc- 

 tion until it approached the 2000-meter contour north of 

 Flemish Cap. From there, it turned counter-clockwise ac- 



celerating to a speed of 35 cm/sec or greater and moved in 

 a northeasterly direction. Near position 51°20'N, 43°50'W, 

 this drifter was caught up in what would appear to be a 

 warm eddy as sea water temperatures increased from ap- 

 proximately 4°C to 7.8 °C and then back to 4.8 °C as the 

 drifter exited this circulation. A similar feature appears on 

 the Canadian Forces METOC Center Sea Surface 

 Temperature (SST) chart published for the period 15-18 

 April 1982. 



TOD #2640 was deployed in position 49°00'N, SO'OO'W, in 

 the center of the Labrador Current. Unfortunately, It 

 malfunctioned and stopped transmitting after 8 hours of 

 operation. During this period, It moved in a southeasterly 

 direction, as expected, at a speed of 53 cm/sec. 



On 1 April 1982, TODs #2637 and #2639 were deployed. 

 Drifter #2637 was deployed in position 49°0rN, 50°30'W 

 which is just to the west of the Labrador Current. The sea 

 surface temperature in this area was -2.1 °C. For the first 

 three days of its deployment, #2637 moved towards the 

 northeast until It entered the Labrador Current near 

 49°20'N, 50°00'W. After entering the Labrador Current, it 

 traveled southeasterly between the 1000m and 2000m con- 

 tours moving at an average speed of 33 cm/sec. From here, 

 the drifter continued to follow the bathymetry and moved to 

 the northeast and then into a clockwise circulation around 

 Flemish Cap. The TOD stopped transmitting on the 25"' of 

 May 1982. 



TOD #2639 was deployed in position 49°00'N, 49°50'W. 

 This would normally have placed it within the Labrador Cur- 

 rent; however, the drifter's movement indicates the current 

 farther west this year. The drifter began an easterly drift 

 that became a northeasterly drift on approximately 21 April 

 1982. The original sea surface temperature at deployment 

 was 1.7°C. This progressively increased as the drifter 

 moved east-northeast to a final temperature of 8.2 °C as the 

 drifter entered the North Atlantic Current. 



TODs #2598 and #2641 were deployed on 4 May 1982. 

 TOD #2598's parachute failed to open and the ensuing im- 

 pact caused this TOD to cease functioning immediately. 

 TOD #2641 however, was deployed successfully in position 

 45°58'N, 47°28'W. This time, we again missed the Labrador 

 Current mainstream indicated by the 4°C sea surface 

 temperatures recorded and the subsequent track of the 

 TOD. As one can see in Figure B-1, this buoy encountered 

 cyclonic circulations and entered an eddy between the 

 Labrador and North Atlantic Currents. The final 

 temperature recorded by this TOD was 7.2°C on 3 June 

 1982. 



Review and Outlook 



Once again, the value of using satellite-tracked TODs 

 was proved. The evaluation of the TOD tracks showed 

 several areas where the historic current file values were not 

 consistent with the values derived from the TOD data. It is 

 within these areas that the modification of the current files 



B-1 



