SUMMARY AND 

 CONCLUSIONS 



In 1987 the data return from the 

 buoys was good. The average 

 length of time that a buoy trans- 

 mitted data from the Ice Patrol 

 operations area was 78 days. 

 According to the drogue sensor 

 data, the average drogue life 

 span was somewhat shorter (70 

 days), but its survival is well- 

 matched to the requirement that it 

 remain attached during the period 

 the buoy drift is used for opera- 

 tions. 



Most buoys transmit data far longer 

 than the 78 days they spend in the 

 Ice Patrol operations area. Five 

 continued to transmit for the re- 

 mainder of the calendar year. 

 Three buoys were recovered be- 

 fore leaving the area, one by an Ice 

 Patrol research vessel (for rede- 

 ployment), and two by unknown 

 vessels. Two buoys suffered pre- 

 mature failures, after 65 days and 

 67 days. It is possible that they 

 were recovered by unknown ves- 

 sels, but their fate remains uncer- 

 tain. 



The 1 987 buoy program did an 

 excellent job of monitoring the 

 Labrador Current, particularly 

 from Flemish Pass southward. 

 The trajectories showed strong 

 bathymetric steering of the 

 current, with most buoys following 

 the continental slope (200-1000 

 m) southward through Flemish 

 Pass. 



Substantial temporal variability in 

 the Labrador Current is also 

 evident in the data. Early in the 

 iceberg season (April - May), two 

 buoys (4555 and 4556) left the 

 slope at 44° and moved rapidly to 

 the east, north of a warm-core 

 eddy at the shelf edge. A similar 

 event occurred in 1986 (Ander- 

 son, 1986). Later in the season 

 (July), the track of 4559 suggests 

 that neither the eddy nor any 

 North Atlantic Current meanders 

 were significant factors in the 

 southward movement of the 

 Labrador Current along the slope. 

 After departing Flemish Pass, 

 buoy 4559 moved to the region 

 south of Tail of the Bank ( 41- 

 50N) in 14 days. This is the most 

 dangerous flow pattern in terms 

 of icebergs moving into the North 

 Atlantic shipping lanes. However, 

 it occurred in July when no 

 icebergs were moving southward 

 through Flemish Pass. Had Ice 

 Patrol relied solely on its historical 

 current data base, which is based 

 on many years of hydrographic 

 data and is time-invarient (Mur- 

 ray, 1979), there would have 

 been no recognition of this 

 observed temporal variability of 

 the Labrador Current. 



The 1987 drifting buoy data 

 suggest that the Labrador Current 

 speeds in Ice Patrol historical 

 current data base for the region 

 south of Flemish Pass are too 

 high. [During the iceberg season 

 IIP operations center personnel 

 had to reposition many resighted 

 icebergs upstream from where 

 the drift model had predicted.] 



Six buoys passed southward 

 through Flemish Pass, three of 

 which continued their southward 

 movement along the continental 

 slope well south of the pass. In 

 the data base, typical Labrador 

 Cun-ent speeds in the area along 

 the slope from 44-46°N are 90- 

 1 1 cm/s. None of the 1 987 

 buoys recorded speeds as high 

 as this, even for short periods (3 

 hr). Buoy 4559, which moved 

 from the pass the the Tail of the 

 Bank, recorded the highest 

 speeds, but most were in the 40- 

 60 cm/s range. Ice Patrol has 

 undertaken a program that will 

 make use of all available drifter 

 data to investigate the accuracy 

 of its historical data base. In the 

 regions where sufficient data 

 exist, the data base will be 

 modified to reflect these observa- 

 tions. 



No current data were collected on 

 the Grand Bank or in the inshore 

 branch of the Labrador Current in 

 1987. The distribution of icebergs 

 for this year shows that this is a 

 problem that needs to be ad- 

 dressed. Many icebergs were 

 sighted along the Newfoundland 

 Coast and directly south of the 

 island, a region where the Ice 

 Patrol data base is particulariy 

 poor. Little attention has been 

 given to this region. A new 

 generation of smaller, less 

 expensive satellite-tracked buoys 

 is now available. Ice Patrol has 

 been evaluating these buoys and 

 expects to integrate them into the 

 buoy program within the next few 

 years. They will be particularly 



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