91. How accurately can oceanographers predict ice formation, 

 size, and movement? 



The accuracy of ice forecasting depends on the locale, details re- 

 quired, time range of the prediction, and accuracy of the input weather 

 information. Ice formation predictions are based on heat content and 

 salinity of the water mass, currents, and expected heat exchange from 

 water to atmosphere (weather prediction and climatology). The required 

 heat, salinity, and current information is obtained by oceanographers 

 aboard icebreaker survey ships when the ice coverage of the sea is at its 

 annual minimum. From ocean data so obtained, the "ice potential" of 

 the water can be determined. 



With a known ice potential and expected air temperature data applied 

 to the basic laws of thermodynamics one can derive the ice formation 

 "forecast". 



In the far north, long-range predictions of ice formation are accurate 

 within 2 to 4 days. Farther south, however, where the environmental 

 conditions tend to be more variable, the formation predictions are accu- 

 rate within 8 to 12 days. 



Size of the ice pack varies relatively little from year to year in the 

 general area. Variations occur mostly on the southernmost fringes where 

 shipping must travel; here variations are of critical importance. Predic- 

 tions of the size of the pack are therefore generally quite accurate, but 

 the predictions of ice in the shipping lanes need to be improved. 



The movement of ice in and out of shipping lanes, or leads, depends 

 substantially on the wind; therefore the accuracy of an ice forecast is de- 

 pendent on a good wind forecast. An accurate 48-hour to 5-day ice fore- 

 cast is possible because meteorologists can produce reasonably good wind 

 forecasts. For long-range (seasonal) ice prediction, which must be based 

 in part on the area climatology, the dates for opening or closing of leads 

 on the Labrador coast may be in error by as much as 6 weeks. 



Recently the problem of predicting "heavy ice" and "open" areas in 

 the polar ice pack for submarine operations has been tackled by 

 oceanographers using aerial and submarine surveys and wind climatology. 



Oak, W. W. and H. V. Myers 



"Ice Reporting on the Great Lakes," Weatherwise, Vol. 6, No. 1, 



Feb. 1953. 

 Perchal, R. J. and S. O. Marcus 



"The U. S. Navy Hydrographic Office Ice Observing and Forecasting 



Program," Mariners Weather Log, Vol. 5, No. 6, Nov. 1961. 

 Wittmann, W. I. 



"Polar Oceanography," Ocean Sciences, edited by Capt. E. John 



Long, U. S. Naval Institute, Annapolis, 1964. 



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