average temperature. It is known for example that the rate of iceberg 

 deterioration is closely related to the amount of atmospheric cyclonic 

 activity in the area and also to the average temperature of its environ- 

 ment. We can monitor the weather and we have fairly accurate 

 knowledge of the sea surface temperature based on numerous reports 

 from ships passing through the area. Average temperatures are 

 available only when and where the oceanographic vessel is conducting 

 a survey. 



Forecast accuracy is dependent upon the accuracy of the tools that 

 are available. It is believed that generally the error of the geostrophic 

 current assumed is less than 25 percent of the true values for velocity 

 and within 20° for direction. In areas where marked variations in 

 oceanographic conditions occur, such as the Tail of the Banks, the 

 error may be considerably greater if the normal chart must be used. 

 The average true wind for 12-hour periods is based on the surface 

 weather chart at mid-period biased by any ship reports near the area. 

 Generally, error of wind velocity assumed is believed within 20 percent 

 of true value and the direction within 20° of true direction. When 

 frontal systems or centers of low-pressure areas are located in the 

 area greater error can result in estimating true wind. The relationship 

 between wind and berg drift is imperfectly known. Wind causes a 

 berg to move directly by exerting a physical force on the exposed 

 portion of the berg and indirectly by generating a wind-driven cur- 

 rent. It is known that bergs of various shapes will drift at different 

 rates. Considerable research on the effect of wind on the drift of ice- 

 bergs of various shapes and sizes must be conducted. Consideration 

 of the effect of wind on iceberg drift has been somewhat neglected. 

 In past Ice Patrol bulletins one sees numerous references to wind as 

 a minor or negligible force for moving icebergs in comparison to the 

 Labrador Current or Gulf Stream. When one realizes that the Ice 

 Patrol Vessel operated with poor navigation equipment compared to 

 modern standards, almost entirely at the Tail of the Banks region 

 where current speeds of 2-3 knots are often encountered, it is easy to 

 understand why the effect of wind was not detected except during gale 

 force winds. Another reason why the wind as compared to geostrophic 

 current was considered negligible is the fact that the berg draft/height 

 ratio was believed greater than it rea/lly is. A few measurements 

 made recently by U.S. naval submarines have indicated that an aver- 

 age berg draft height ratio is about 2.5/1 or 3/1. It was assumed in 

 the past that almost all bergs were concentrated in the geostrophic 

 currents or their branches. It should be understood that a great por- 

 tion of the area of responsibility is unsurveyable by dynamic topog- 

 raphy. It was assumed that little or no current existed in these areas 

 believed to be barren of icebergs. The use of aircraft for observing 

 ice conditions has revealed that a great number of icebergs can and 



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