The stations examined are Byrd (80°01′ S, 119°31′ W, 1533 m MSL), Wilkes(66°15′ S, 110°35′ E, 12 m MSL) and Sachs, Harbour, N.W.T. (71°57′ N, 124°44′ W, 84.4 m MSL).

Synoptic observations for one year were used to calculate the heat budget terms for surface and atmosphere, using a method modified from one previously described. Monthly mean values are given and five-day values are shown in illustrations.

Little of the available solar radiation is absorbed. It is crucial for the budget, particularly at Wilkes, that snow melt is not delayed in the spring, as the change in albedo allows much more absorbed radiation. Synoptic events, if accompanied by snowfall, reduce absorbed radiation drastically. Without precipitation, the temperature effect on the albedo will tend to smooth and diminish the synoptic fluctuations in absorbed radiation. Generally, absorbed solar radiation in the polar regions is very low compared to the available energy, and the bulk of the heat requirement must be covered by advection. Advection is strongly seasonal in the North, but seasonal changes are less pronounced in the Southern Hemisphere as ice and snow surfaces persist throughout the year.

In polar regions, more of the heat from outside goes to the atmosphere than to the surface, causing a stable vertical temperature distribution. With the advent of spring, the energy supply is shifted from advection to absorbed solar radiation. The surface heat loss is almost exclusively by radiation in winter, but the nonradiative terms become important in summer. The turbulent terms remain small, however, where the surface is snow covered.

It is possible to design a climatic classification for polar climates which specifies such climates to exist when a certain percentage of the surface heat income is contributed by atmospheric (back) radiation from warm air brought in by advection.

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