A. IIOTtODUCTICN 



For the past several ye^.TS the Hydi'ographic OIT3.ce has been 

 developing techniques of obsei-ving and forecasting sea ice conditions. 

 Kuch of the effort in this program has been directed toxfard means 

 of predicting the movements of ice on a short-range basis. VJithin 

 the past two years, methods have been developed and used to make 

 forecasts of ice fcd'mation and growth covering periods of several 

 months. Extension of these methods of ice forecasting to large-scale 

 phenomena, such ss the Alaskan shore lead, has proved to be difficulto 

 The recent developn^nt of theories of the ice potential allc'vcs further 

 extension of ice potential calculation^", into the field described in 

 this reporto 



The terminology of the ice potential theory and the method of 

 calculating the ice potential are explained by Lee and Simpson (l95h). 

 The ice potential may be viewed as a measure of the stability of sea 

 water, since it describes the existing vertical distributions of 

 salinity and densityo As a result of the developaonb of analytical 

 methods of calculating tb® ice potential (Brown, 19Sh)i i't ^'-s become 

 possible to obtain machine listings of the ice potential calculations 

 for all oceanographic station data in any desired ai'eao The concept 

 of ice potential climatology has been developed to formalise the pre- 

 sentation of this ice potential datao 



B, TFXIINIQUES OF ICE POlTJvTIAL CLIMATOLOGY 



The ice potential indicates the stability of the -water at a single 

 place and tiirie. In order to examine the relative stability of a number 

 of different water sai'cplings, a method of jireal presentation has been 

 devised. This method is called, by analogy with climatic maps, ice 

 potential climatolcgy« 



There are sevei-al possible traj'S of contouring the ice potential o 

 Souse of these have no physical significance, but others are useful and 

 provide important insights Inbo the physical processes that influence 

 the occurrence, groxrth, and disintegration of sea icco Principal chart 

 forms may be listed as follows: 



(1) Constant Heat Less 



(2) Constant Depth of Convection 



(3) Depth of Convection Asscciated with Constant Heat Less 

 (U) Stability Index 



lo Charts of Constant Heat Loss over an Ocean Area 



The most useful basis for drai-dng climatological charts of the ice 

 potential is to postulate a constant heat loss over an area. By fij>di.ng 

 the potential ice thickness associated with a given heat loss, isoline 

 charts are drawn by conriecting points of equal ice potential. The cal- 

 culation of the ice potential and the associated senciblo hest Ic^n is 

 described by Lee and Simpson (I95lt). The total heat loss consists of 



