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Figure 2.21. Mean annual cycle of snow depth (mm) and +/−1 standard deviation over
the central Arctic Ocean based on NP data (from Colony et al., 1998 , by permission of
Cambridge University Press).
The NOAA snow chart climate data record allows for analysis of variability
and trends in terrestrial Northern Hemisphere snow covered area back to 1967. As
assessed for the 1967-2012 period, snow cover extent for winter and autumn has
been variable. By sharp contrast, as introduced in Chapter 1 ( Figure 1.7 ), snow
cover extent for spring (when snow is mainly located in the Arctic) extent exhibits
a pronounced downward trend; the trend is larger over Eurasia than over North
America. Particularly large negative anomalies in spring extent characterize the last
few years of the data record (Derksen and Brown, 2012 ).
Turning to the Arctic Ocean, snow depth data were collected by Russian scien-
tists during airborne landings each spring between 1959 and 1988, under the Sever
(“North”) program (Romanov, 1995 ). These records provide average snow thick-
ness on the predominant sea ice type in the landing area, in sastrugi behind pres-
sure ridges, and an average for the windward and lee side of hummocks (Colony,
Radionov, and Tanis, 1998 ). More consistent spatial information has been derived
from the snow survey lines at the Russian NP drifting stations between 1954 and
1991. These represent measurements from snow lines of 1 km length as well as at
snow stakes installed at the meteorological station sites. Daily measurements were
made at the stakes and once to three times monthly along the snowlines at 10 m
intervals. Snow density along each line was sampled at every 100 m. Snow lines
were chosen to be over flat ice.
The mean seasonal cycles in mean snow height (essentially equivalent to snow
depth and hence treated as such here), snow density, and the +/−1 standard devia-
tions based on grouping all available snow line data are reproduced in Figures 2.21
and 2.22 . The distribution of snow depths in April is given in Figure 2.23 . Snow
depth is greatest in May, with a mean of about 350 mm. The onset of melt is
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