1 -- SURFACE HEAT BUDGET

The formation and melting of sea ice depends on the net amount of heat the ocean surface gains or loses. Therefore, we'll begin by briefly examining the processes by which the ocean surface gains or loses heat.

The ocean surface will heat up if it receives more heat than it loses and, conversely, will get cooler if it loses more heat than it receives (Figure 1.01). The ocean surface receives heat from

1. incoming shortwave radiation from the Sun
2. incoming longwave radiation from the atmosphere
3. conduction of sensible heat from warmer air toward cooler water (although this is not a common occurrence in the polar regions)
4. gain of latent heat through sea ice formation
5. movement (advection) of warmer water into a region (not shown)

and it loses heat from

1. emitted longwave radiation from the surface to the atmosphere
2. conduction of sensible heat from warmer water toward cooler air
3. loss of latent heat through evaporation
4. movement (advection) of cooler water into a region (not shown).

The relative importance of each process varies greatly with region and time of year. The formation of sea ice further complicates this rather simple picture. Since sea ice is a better reflector of the incoming solar energy than is water, the formation of sea ice has the effect of decreasing the amount of energy the surface receives from the Sun. Stated simply, the ocean will cool and sea ice will form if the net effect of the processes depicted in Fibure 1.01 is such that the ocean surface loses more heat than it receives. Conversely, the ocean surface will heat up and sea ice will melt if the net effect of these processes is such that the ocean surface receives more heat than it loses.