-> +---------+ <- ts - diagnostic surface temperature ( <= 0C )        
        /   |         |                                                         
      hs    |  snow   | <- 0-heat capacity snow layer                           
        \   |         |                                                         
         => +---------+                                                         
        /   |         |                                                         
       /    |         | <- t1 - upper 1/2 ice temperature; this layer has       
      /     |         |         a variable (T/S dependent) heat capacity        
    hi      |...ice...|                                                         
      \     |         |                                                         
       \    |         | <- t2 - lower 1/2 ice temp. (fixed heat capacity)       
        \   |         |                                                         
         -> +---------+ <- base of ice fixed at seawater freezing temp.        

    FIGURE 2:  SEA ICE THERMODYNAMIC STRUCTURE