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10°C, and at many stations extreme maxima reach
32
2
The sub-Arctic
C or more (see
Figure 10.17
). The Barren
Grounds of Keewatin, however, are much cooler
in summer due to the extensive areas of lake and
muskeg; only July has a mean daily temperature
of 10
°
The longitudinal differences in mid-latitude
climates persist into the northern polar margins,
giving rise to maritime and continental subtypes,
modified by the extreme radiation conditions
in winter and summer. For example, radiation
receipts in summer along the Arctic coast of
Siberia compare favorably, by virtue of the long
daylight, with those in lower mid-latitudes.
The maritime type is found in coastal Alaska,
Iceland, northern Norway and adjoining parts of
Russia. Winters are cold and stormy, with very
short days. Summers are cloudy but mild with
mean temperatures of about 10
°
C. Labrador-Ungava to the east, between
52
N, is rather similar with very high
cloud amounts and maximum precipitation
in June to September (
Figure 10.36
). In winter,
conditions fluctuate between periods of very
cold, dry, high pressure weather and spells of
dull, bleak, snowy weather as depressions move
eastward or occasionally northward over the area.
°
and 62
°
C. For example,
Vardø in northern Norway (70
°
°C
°F
°
N, 31
°
E) has
60
15
monthly mean temperatures of -6
°
C in January
Mean daily
maximum
10
50
and 9
N,
150°W) records -11°C and 14°C, respectively.
Annual precipitation is generally between 600
and 1250mm, with a cool season maximum and
about six months of snow cover.
The weather is mainly controlled by depres-
sions, which are weakly developed in summer. In
winter, the Alaskan area is north of the main
depression tracks and occluded fronts and upper
troughs are prominent, whereas northern Norway
is affected by frontal depressions moving into the
Barents Sea. Iceland is similar to Alaska, although
depressions often move slowly over the area and
occlude, whereas others moving northeastward
along the Denmark Strait bring mild, rainy
weather.
The interior, cold-continental climates have
much more severe winters, although precipita-
tion amounts are smaller. At Yellowknife (62
°
C in July, while Anchorage, Alaska (61
°
5
40
0
30
-5
20
Mean daily
minimum
-10
10
-15
0
-30
-10
-40
-20
J
FM
A
M
J
J
A
S
O
N
D
mm
i
n
4
100
3
50
2
°
N,
114
W), for instance, the mean January tempera-
ture is only -28
°
1
C. In these regions,
permafrost
(permanently frozen ground) is widespread and
often of great depth. In summer, only the top
1-2m of ground thaw and as the water cannot
readily drain away this 'active layer' often remains
waterlogged. Although frost may occur during
any month, the long summer days usually give
three months with mean temperatures above
°
0
0
J
FM
A
M
J
J
A
S
O
N
D
Figure 10.36
Selected climatological data for
McGill Sub-Arctic Research Laboratory, Scheffer-
ville, PQ, 1955-1962. The shaded portions of the
precipitation represent snowfall, expressed as
water equivalent.
Source: Data from J. B. Shaw and D. G. Tout.
