Appendix B 



Oceanographic Conditions on the Grand Banks During the 1983 



International Ice Patrol Season 



By Lieutenant lain Anderson, USCG 



Introduction 



The 1983 Ice Patrol season marked the 

 first time the International Ice Patrol (IIP) 

 was able to operationally track an iceberg 

 by satellite over an extended period of time 

 (up to three months). This was accom- 

 plished in cooperation with the U. S. Coast 

 Guard Research and Development Center 

 by "tagging" three icebergs with TIROS 

 Arctic Drifters (TAD). For the first time, real- 

 time TIROS Oceanographic Drifter (TOD) 

 information was used to permanently 

 modify regions of the IIP historical current 

 file. 



During the 1983 season, seven TIROS 

 Oceanographic Drifters (TOD) were 

 deployed in the IIP operating area. The real- 

 time current information obtained from the 

 TOD drifts was used weekly to temporarily 

 modify the IIP historical current field. The 

 procedure used in this modification is 

 described in detail in Summy (1982). With 

 one exception, all of the TODs and TADs 

 were air-dropped from a Coast Guard 

 HC-130 aircraft during regular ice recon- 

 naissance flights (Table B-1). The excep- 

 tion was TOD #2634 which was deployed 

 from the USCGC NORTHWIND during 

 cruise IIP-1-83. The main purposes of this 

 cruise were to gather environmental data 

 for comparison with that obtained from 

 Fleet Numerical Oceanography Center 

 (FNOC) and to obtain iceberg deterioration 

 data. (For results of this cruise see Appen- 

 dix C.) 



TIROS Arctic Drifters 



During March of 1983, three TADs were 

 deployed on icebergs in the North Atlantic. 

 Positions were determined by Doppler shift of 

 the TAD transmitter's signal received at the 

 satellite and relayed to the International Ice 

 Patrol office via Service ARGOS. Before deploy- 

 ment, the outer cases of all the TADs had been 

 sealed with a waterproofing gasket material, to 

 prohibit spray and moisture from damaging the 



electronics. Unfortunately, the TAD's would 

 float after falling off an iceberg. Without 

 temperature information, it was difficult to 

 determine exactly when a TAD fell off its 

 iceberg. TAD #2611 was deployed on a large 

 tabular iceberg trapped in the sea ice on 27 

 March 1983 at 48°50'N, 50°58'W (Table B-1). 

 TAD #2618 and TAD #2625 were deployed 

 respectively on a large tabular iceberg and a 

 small pinnacle iceberg north of the IIP 

 operating area on 22 March 1983 (Table B-1). 



While trapped in the sea ice, TAD #2611 

 moved in a large counter-clockwise circle 

 (Figure B-1). A rapid increase in velocity in- 

 dicated TAD #2611 broke free from the sea ice 

 on or about 1 May 1983. This large iceberg pro- 

 ceeded in a southward direction along the edge 

 of the Grand Banks. TAD #261 1's velocities 

 (based on 12 hour averages) ranged from 1 

 cm/sec to 89 cm/sec, averaging 33 cm/sec, be- 

 tween 1 May and 27 May. This tagged iceberg 

 was last seen with the TAD aboard on 21 May 

 by Mobil Oil Company, Canada. The size of the 

 iceberg on this date (from a Mobil Oil 

 stereophotograph) was 150m long, 110m wide 

 and 30m above the water. This is a relatively 

 unstable configuration because the center of 

 gravity is extremely close to the center of 

 buoyancy. A major storm system passed 

 through the area on 27 May 1983. There is no 

 assurance after this date that the TAD re- 

 mained on the iceberg. The winds (based on the 

 FNOC analysis) between 27 May and 14 June, 

 which is the last day information was received 

 from TAD #2611, were: 



27 May - 2 June - north to northeast 

 2 June - 13 June - south to southeast 

 13 June - 14 June - northerly. 

 The vast majority of TAD #261 1's movement 

 during this period can be accounted for by the 

 wind driven ourface current (Figure B-1). It is 

 likely that the storm of May 27 caused the TAD 

 to fall off the iceberg and act as a surface 

 drifter until it terminated transmission on 14 

 June. 



51 



