30 



scout such areas as can be done during the day, returning to the 

 berg at night. 



A glance at the weather charts (figs. 8-11) or a United States Hydro- 

 graphic Pilot Chart for the North Atlantic Ocean will readily show 

 the reader that fog enshrouds the ice-patrol area a large percentage of 

 time. During these periods of fog, sometimes lasting for four or five 

 days, or even longer periods, as in June, 1932, no scouting for ice can 

 be done, and the known bergs are lost for these periods. It is readily 

 seen that being able to accurately predict the drift of the ice would be a 

 great help in finding bergs that have been lost in a fog for several 

 days. Also a current chart of the ice regions would indicate areas 

 that are most likely to be berg infested. 



During 1932, as in the past ice-patrol seasons, two methods were 

 used to predict the drift of icebergs near the Grand Banks: (1) 

 Dynamic current charts drawn from data collected by the oceano- 

 graphic vessel (this method is explained elsewhere in this section); 

 (2) surface isotherm charts. 



The ice-patrol vessels have for a number of years plotted their own 

 surface temperature observations, and those sent by radio from other 

 ships crossing the ice-patrol area. The surface isotherms have always 

 been assumed to give a general idea of the prevailing water and ice 

 movements in and about the Labrador current throughout the 

 season. The ice is expected to be found and to remain where the 

 water is coldest. A great percentage of the observed drifts of bergs 

 have been found to parallel rather closely the direction of the surface 

 isotherms. During the season of 1932 the isotherm charts agree with 

 dynamic charts drawn for the same period to a great extent. Five 

 bergs drifted south of the tail of the Grand Banks during the past 

 ice season, and were closely watched until they disappeared. The 

 drifts of four of these bergs agreed fairly closely with the currents 

 computed dynamically, and also the surface isotherm charts. The 

 fifth berg drifted in accordance with the current charts until it 

 reached a point west of the tail of the Banks on May 21. Where both 

 isotherms and dynamic current charts indicated that the currents 

 were southerly, curving to the southeast, this berg drifted north until 

 May 24, when it remained practically stationary until it was lost in a 

 fog on May 26, and not sighted again. Another berg that was just 

 one day's drift behind this berg drifted exactly as the surface iso- 

 therms would indicate. 



