CLOUD AMOUNT IN THE CENTRAL ARCTIC
Prik (1965) and Voskresenskii and Bryazgin (1988) published comparatively
complete data on the characteristics of cloudiness in the north polar region. On
generalizing data from Russian polar stations and drifting stations through
NP-14, Voskresenskii and Bryazgin found marked spatial nonhomogeneity in the
frequency distribution of clear and overcast skies (Table 1).
Table 1 shows that, in winter, overcast skies occur most frequently in the east-
ern and western regions of the Russian Arctic coast, probably because of the preva-
lence of moist air masses originating over the Atlantic and Pacific Oceans. In the
central region of the Russian Arctic coast and in the eastern part of the Arctic
Basin, where the observations in Table 1 rely heavily on data from the NP drifting
stations, anticyclonic circulation is more common. As a result and also because these
regions are more distant from sources of moist air, periods with clear skies are
roughly twice as likely in winter than along the eastern and western coasts.
In summer, significant uniformity characterizes cloud amount in the Arctic.
Overcast skies occur roughly 80% of the time in all regions and perhaps even more
frequently in the central basin.
Table 1. Percent of the time with overcast (8-10 tenths) and
clear (0-2 tenths) skies in various regions of the Russian
Arctic and in the central Arctic Basin (from Voskresenskii
and Bryazgin 1988).
The opportunity for a more complete analysis of the temporal and spatial vari-
ability of cloudiness in the central Arctic is now, however, available with the cre-
ation of the CD-ROM archiving the standard meteorological observations from all
the Russian North Pole drifting stations (NSIDC 1996). For this purpose, we have
generated, for each drifting station, time series consisting of either 3-hour or
6-hour observations for each month of the station's drift. In other words, for each
month we have about 70 time series, spanning 1938 to 1991, that describe
intermonth and interannual variability of total and low cloud amount in the cen-
tral Arctic. To complement the analysis in Table 1, we averaged these data and
present in Tables 2 and 3 the resulting statistics of total and low cloud amount at
the drifting stations.
As in Table 1, the statistics in Tables 2 and 3 indicate a basic difference between
the modes of total and low cloud amount in winter and summer. In the winter
(November to April), there are two practically equal maxima in the distributions
of total cloud amount, one for 02 tenths and a second for 910 tenths. The
U-shaped form of the frequency distribution is thus quite obvious. Also in winter,
cloud amounts in the 3- to 8-tenths bins have a comparatively consistent distribu-
tion. Lastly, on comparing the winter total and low cloud amounts in Tables 2 and
3, respectively, we see a prevalence of middle and upper level clouds in winter.