A study of the effect of mean surface wind, as indicated by the 

 U.S. Weather Bureau monthly mean seal level atmospheric pressure 

 charts, on the drift of the Grand Banks iceberg supply requires knowl- 

 edge, or at least an educated guess, of the location and distribution of 

 the crop during the months preceding the ice season. Limited evidence 

 from the few preseason northern ice surveys conducted during the past 

 2 years and numerous data on the Grand Banks ice season indicates 

 that as of early November next season's Grand Banks potential iceberg 

 crop is located mostly from Hudson Strait entrance northward in- 

 cluding the western half of Davis Strait and Baffin Bay to Bylot 

 Island. For a more complete discussion of the location of the crop 

 see another section of this Bulletin and also Bulletin 49 of this series. 

 The distance encompassed by the crop is estimated to be about 950 

 miles and corresponds to an estimated average daily travel rate of 8 to 

 9 miles per day and a 31/^ to 4 month ice season. As the effect of 

 pressure distribution might vary considerably over a 950-mile stretch, 

 it will be more discriminating to consider each half of the berg crop 

 separately. The first group includes those bergs located between Hud- 

 son Strait entrance and Cape Dyer in early November. The second 

 group includes those bergs located between Cape Dyer and Bylot 

 Island in early November. The successive monthly locations of the 

 two groups of the berg crop can be assumed or estimated using any 

 available northern ice survey observations and taking into account 

 drift due to the current system and atmospheric pressure patterns. 



Beginning with the U.S. Weather Bureau November sea level pres- 

 sure mean chart, each monthly chart is analyzed for the effect of the 

 mean surface wind on the drift of each group. Each monthly chart 

 is classified qualitatively as favorable, neutral or unfavorable for wind 

 drift of each group toward the Grand Banks. Ice drift is assumed to 

 be 5°-10° to the right of the mean geostrophic wind as portrayed by 

 the isobars. The evaluation of the effect of monthly pressure distri- 

 bution on the drift of the berg groups must, by necessity, be based 

 largely on assumption. Naturally, the drift of individual bergs in a 

 group will be more or less dissimilar for various reasons. The forces 

 acting on bergs will vary with the location. The resulting movement 

 of bergs will vary depending upon their various reactions on account 

 of size, shape, and draft. It is intended that the average effect on most 

 of the bergs in a group will be evaluated. Generally, monthly pressure 

 patterns which effect the alongshore berg drift component are classi- 

 fied as favorable and those causing an opposing berg drift are classi- 

 fied as unfavorable. Pressure patterns causing berg drift alongshore 

 are relatively simple to classify, whereas those patterns causing signif- 

 icant berg drift onshore or offshore, i.e., perpendicular to the current 

 system, are more difficult to classify. Winds causing many of the 

 bergs to ground or remain aground are classified unfavorable. Winds 



47 



