Distribution of surface albedo

While albedo is a frequently measured variable, surface observations are insufficient to allow the construction of maps to assess the basic spatio-temporal patterns across the Arctic. However, satellite-derived surface albedo is a standard variable of ISCCP-D and APP-x. Monthly fields from APP-x are displayed for April through September (Figure 5.3).

Over land areas, regional albedos for April typically range from 0.40 to 0.80. Those over the Arctic Ocean are from 0.70 to 0.80. The high albedos over most of the Arctic are of course due to snow cover. The albedo of a fresh snow cover may range from 0.70 to 0.90. Over the ice-covered ocean, Figure 5.3 integrates high-albedo snow surfaces along with lower-albedo features such as open or recently refrozen leads in the ice cover, or areas where winds may have blown the sea ice clear of snow. Similarly, over land, the high albedo of the snow cover will be integrated with effects such as vegetation canopies, or areas where the snow cover is thin enough that darker underlying surfaces (e.g., tundra) "show through". Furthermore, even in cold conditions, snow will age, acting to reduce the albedo. The sharp decline in albedo towards the North Atlantic relates to the decline in ice concentration in the marginal ice zone.

Figure 5.3 Mean monthly surface albedo for April through September based on APP-x satellite data (courtesy of J. Key, NOAA/NESDIS, Madison, WI).

The difference between the April pattern and that for May illustrates the effects of surface melt. Albedos over land areas begin to drop from their April values, most apparent over the southern Arctic lands. Albedos remain high over the Arctic Ocean where it is colder and the snow has not begun to melt. There is a further reduction in albedo between May and June. By July, the snow cover is completely removed from the land surface and some of it has melted from the sea ice cover. However, albedos near the Pole are still around 0.50. Albedos still remain high over central Greenland. Albedos are at a minimum during August and start to increase again in September due to the deposition of fresh snow cover and initial freeze-up of the sea ice surface.

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