Geoscience Reference
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problem of gauge catch of solid precipitation. The latter issue primarily revolves
around gauge under-catch of solid precipitation. The most important environmental
variable influencing catch efficiency is wind speed (Yang et al.,
2001
). Different
gauge and shield combinations have and continue to be used, which vary in catch
efficiency, especially for high wind speeds. Errors can reach 50-100 percent in cold,
windy environments such as the Arctic. This has created artificial discontinuities in
cold-region precipitation within countries and across national borders.
Efforts have been made to provide data sets with bias adjustments, mostly with
respect to monthly totals. D. Legates and C. Willmott (
1990
) provide a global grid-
ded climatology. P. Groisman and colleagues (
1991
) and E. Mekis and W. Hogg
(
1999
) provide adjusted monthly station data sets for the Former Soviet Union and
Canada, respectively. Adjustments are generally climatological in that they repre-
sent constant multipliers to raw monthly precipitation totals. Corrections require
information on gauge type, mean winds and site conditions. Yang (
1999
) performed
daily corrections to the Russian NP records. Different data sets may also include
adjustments for the neglect of trace amounts, as well as evaporation and wetting
(moisture that sticks to the inside of the gauge after it is emptied). The neglect of
trace precipitation can be important in the Arctic, as total precipitation amounts are
low in many areas.
Figure 2.28
shows the pattern of mean annual precipitation across the Arctic. This
is a best-guess attempt on our part, based on bias adjusted gauge data from several
different data sources, bias-adjusted output from a numerical weather prediction
mode, and satellite retrievals over open-ocean areas. Although annual precipitation
totals for much of the Arctic are rather low, amounts vary widely. Totals of less
than 200 mm are found over the Canadian Arctic Archipelago (polar desert) and the
Beaufort Sea. Over the central Arctic Ocean, mean totals are around 300-400 mm.
The largest amounts in the Arctic, exceeding 1,000 mm and locally much higher, are
found over the Atlantic sector, southeast Greenland, and coastal Scandinavia. This
is essentially a reflection of the northward extension of the primary North Atlantic
cyclone track and Icelandic Low (
Chapter 4
), associated strong horizontal conver-
gence of water vapor and local orographic uplift of moist air.
There is a strong seasonality in Arctic precipitation as well as liquid/solid contri-
butions, which is addressed in
Chapter 6
along with precipitation mechanisms. That
chapter also provides a closer focus on Greenland. For the present, it is sufficient
to state that for the Atlantic sector of the Arctic, precipitation has a cold season
maximum and summer minimum, in accord with seasonality in the strength of the
North Atlantic cyclone track. By contrast, most land areas and the central Arctic
Ocean exhibit a summer maximum and cold season minimum. The summer maxi-
mum over land areas is strongly associated with surface evaporation. The summer
maximum for the central Arctic Ocean, by contrast, is a response to the seasonal
maximum in vapor flux convergence.
Nearly all of the current generation of global climate models project that Arctic
precipitation will increase through the twenty-first century (see
Chapter 11
). Whether
or not Arctic precipitation has exhibited a positive trend over recent decades remains
