No assumptions have been made as to the mechanism of lieat lossi, 

 Actual rate of heat loss may vary in winter from perhaps 100 gmecali/cm^,/ 

 day from an ice surface to perhaps 500 or 600 gm, csl»/cm.»'^/daj from 

 open water. Therefore, figure 1 is not a forecastirig' chart and does 

 not indicate when ice will form in the various areas, 



2o Charts of Potential Ice Thickness Associated tdlh Constant Depth 

 of Convection 



By the nature of the ice potential calculations > every value of 

 ice potential and heat loss has associated with it a depth of mixing 

 by thermohaline convection. Charts showing the potential ice thick- 

 ness associated with a constant convective depth would seem to be 

 useful as indicating the effect of mixing the water to a given level* 

 However, since the vertical gradients of teniperiature and salinity in 

 the surface layers differ from place to place, it is not realistic 

 to compare two water masses by assuming equal thermohaline convective 

 activity. In actuality, water masses differ in the amount of energy 

 necessary to produce convectiono . Hence, charts showing ice thickness 

 associated %cLth a constant mixed layer depth are meaningless physically* 



3. Charts showing Depth of Convection Associated with Constant Heat Loss 



V/hile it is not realistic to draw charts based on a constant depth 

 of mixing, it is useful to consider charts which are based on a constant 

 heat loss over an area and show the depth of mixing associated with the 

 given heat loss. In effect, such a chart shows the stability of" the 

 water. The greater the depth to which convection reaches, the less 

 stable the water mass. 



Figure 3 shovjs depths of convection associated with a standard 

 total heat loss of 20 kg, cal./cme'^ 



[|.. Stability Index 



The data presented in figures 1 and 3, representing potential 

 ice thickness and depth of convection a sociatod with a constant total 

 heat loss., may be combined into a stability index. This index measures 

 the average potential addition of ice in units of potential centimeters 

 of ice per meter of convection when thermohaline convection is extended 

 doiifnward. Thus, the stability indgx shows potential ice thickness as 

 a percentage of the depth of convection. A high percentage indicates 

 high stability and a' low percentage low stability. However, the per- 

 centages are only relative, so that negative |)ercenta.ges may occur with- 

 out implying actual overturn of the water. Figure h is an example of 



-3- 



