Arctic Climate

The arctic climate is characterized by high spatial variability, and includes both polar maritime (influenced by the ocean) and continental (influenced by large land masses) climate subtypes. The main constant is that the climate in all arctic areas is affected by the extreme solar radiation conditions of high latitudes.

For example, the amount of solar radiation received in summer along the Siberian arctic coast compares favorably, by virtue of the long period of daylight, with that in lower middle latitudes. However, the low sun angle (elevation of the sun above the horizon) means that even minor topographic features, such as low hills, can cause major differences in climate at the local level by shading. Even though the Arctic receives a large amount of solar energy in summer, the high reflectivity (albedo) of snow and ice surfaces keeps absorption of solar energy low. Therefore, the heat gained during the long summer days is small and highly dependent on surface properties such as topography and albedo. For instance, wet tundra and bare ground (with low albedo) absorb more solar radiation than do high-albedo ice sheets. Similarly, wet snow absorbs more radiation than dry snow. Solar radiation is small or absent in winter.

Maritime climate conditions prevail over the Arctic Ocean, coastal Alaska, Iceland, northern Norway and adjoining parts of Russia. In these areas, winters are cold and stormy. Summers are cloudy but mild with mean temperatures about 10 degrees Celsius. Annual precipitation is generally between 60 cm and 125 cm, with a cool season maximum (largely snowfall) and about six months of snow cover.

The interior, continental climates have much more severe winters, although precipitation amounts are less. In these regions, permafrost (permanently frozen ground) is wide-spread and often of great depth. In summer, only the top one to two meters of ground thaw. Since the water cannot readily drain away, this "active layer" often remains waterlogged. Although frost may occur in any month, long summer days usually provide three months with mean temperatures above 10 degrees Celsius, and at some stations in the continental interiors temperatures can exceed 30 degrees Celsius.

In winter, arctic weather is dominated by the frequent occurrence of inversions (when warm air lies above a colder air layer near the surface). The inversion layer decouples the surface wind from the stronger upper layer wind. For this reason, surface wind speeds tend to be lower in winter than one might expect. In summer, inversions are less frequent and weaker, and arctic weather patterns are dominated by the movement of low pressure systems (cyclones) across Siberia and into the Arctic Basin.

In many arctic and subarctic regions, the weather is controlled by semipermanent low pressure systems that are weakly developed in summer, but stronger in winter. The most important of these low pressure systems are the Icelandic Low and the Aleutian Low. In winter, eastern Eurasia is dominated by the semipermanent Siberian High. High pressure is also prevalent over the Canadian Arctic Archipelago during the cold season.