Temperature and Precipitation

The Arctic climate varies greatly by location and season. Mean annual surface temperatures range from 0°C at Murmansk, Russia (69° N) through -12.2°C at Point Barrow, Alaska (71.3° N), -16.2°C at Resolute, Canada (74.7° N), -18°C over the central Arctic Ocean to -28.1°C at the crest of the Greenland ice sheet (about 71° N). Some of these differences are due to the poleward intrusion of warm ocean currents such as the Gulf Stream that moderate the climate of coastal Alaska, Iceland, northern Norway and adjoining parts of Russia, and the occasional southward extension of cold air masses. Arctic tundra areas in North America have at least a 50% frequency of Arctic air in July. The median location of the Polar Front (separating cold Arctic and polar air masses from warm tropical air masses) in July corresponds approximately with the northern limit of the boreal forest. Lowered temperatures over the Greenland ice sheet are in part due to the increased elevation.

Winter in the Arctic tundra is 6-9 months long and is characterized by a relatively shallow (30-40 cm) snow cover, by darkness, and by January temperatures that average about -30°C in North America, somewhat lower in Asia (Siberia) and much higher (-10°C) in Northern Europe (see Figure 1). Spring and autumn are short transition periods during which the snow either melts or falls again, respectively. Clear skies resulting in receipt of a high percentage of the possible solar radiation generally characterize late winter and spring. Temperatures begin to rise, but lag 4-6 weeks behind the increase in solar radiation. The mean daily temperatures are above freezing during the short summer, but cloudiness and fog over the Arctic Ocean and the coastal areas prevent temperatures there from rising much above 5°C even in July. Temperatures increase from the coast inland until the treeline (forest-tundra ecotone), with July mean temperatures of 10°C and higher, is reached.

-48 -43 -38 -33 -28 -23 -18 -13 -8 -3 2 7 9.5°c

Figure 1: Mean January and July surface air temperatures (°C) in the Arctic. From AMAP Assessment Report: Arctic Pollution Issues, Arctic Monitoring and Assessment Program, 1998. Reproduced with permission

Figure 1: Mean January and July surface air temperatures (°C) in the Arctic. From AMAP Assessment Report: Arctic Pollution Issues, Arctic Monitoring and Assessment Program, 1998. Reproduced with permission

Precipitation in the Arctic is difficult to measure since it is generally light and associated with storms, and also because for the greater part of the year it falls as dry snow, which is redistributed by winds according to exposure and local topography. With an annual

©AMAP2003

precipitation of 200-300 mm and frequently less than 100 mm (104 mm/yr at Barrow (Alaska), 130 mm/yr at Resolute, and 95 mm/yr measured in the central Arctic Ocean on Soviet drifting ice stations), the Arctic is comparable to arid regions elsewhere (see Figure 2). Exceptions include some alpine permafrost areas and polar islands frequented by storms of oceanic origins.

Much of the Arctic consists of cold deserts largely devoid of vegetation. It should be noted, however, that climatically arid regions can have wet surfaces when permafrost prevents drainage of the seasonally thawed layer, even though the precipitation may be low (see Polar Desert).

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