Geoscience Reference
In-Depth Information
J
F
MAMJ
J
ASOND
90° N
Continuous
Darkness
Continuous
Darkness
Continuous
Daylight
80°
70°
Arctic Circle
60° N
Summer
Winter
Winter
May
Oct
(Transition)
(Transition)
Figure 2.1.
Duration of daylight and darkness from 60° to 90°N (from Central
Intelligence Agency Polar Regions Atlas,
1978
, by permission of United States
Government).
floating sea ice. Both the sea ice cover and land areas of the Arctic are
snow covered for most of the year. Permanent land ice does not occupy
a large area outside of Greenland. Sub-polar ice caps and glaciers are
found mainly in the mountainous parts of the Siberian and Canadian
archipelagos, and in Svalbard and Iceland. However, most of the lands
are underlain by permafrost (perennially frozen ground), some of which
is rich in ground ice. Based on broad latitudinal, climatic, and biological
characteristics, the Arctic land surface is sometimes broken down into
the High Arctic and the Low Arctic. The land surface in the High Arctic
is often characterized as polar desert, an extreme form of tundra. In the
Low Arctic, the tundra commonly includes shrub vegetation of birch and
willow. Large areas are covered by lakes and wetlands.
Surface air temperatures (SATs, approximately 2 m above the surface)
exhibit remarkable regional and seasonal variability. January mean SATs
of less than −40°C characterize parts of Siberia. Over the central Arctic
Ocean, winter temperatures are somewhat moderated by heat fluxes
through the ice cover. January mean values of −25°C to −32°C are typical.
By sharp contrast, January temperatures around Iceland are near the
freezing mark, manifesting the warm, open ocean waters and atmospheric
heat transports associated with the North Atlantic cyclone track. During
July, mean values over snow-free land surfaces are typically 10°C to
20°C. Over the central Arctic Ocean, the presence of a melting ice surface
keeps summer temperatures close to zero. Mean annual precipitation
ranges widely, from less than 200 mm over parts of the Canadian Arctic
Archipelago to well more than 1,000 mm in parts of the Atlantic sector.
Land areas exhibit a general summer precipitation maximum, whereas
the Atlantic sector exhibits a cold-season maximum. The Arctic is a very
cloudy place. Over the Atlantic sector, there is approximately 80 percent
