Table 2. Total cloud amounts (n, in percent) observed on the North
Pole drifting stations.
Total cloud amount in tenths
02
34
56
78
910
Mean* Std
Mean
Std
Mean
Std
Mean
Std
Mean Std
Jan
40
15
9
8
5
4
6
5
39
12
Feb
37
15
11
8
5
4
7
4
40
13
March
35
16
12
7
6
4
8
5
40
13
April
34
13
10
7
5
3
7
4
43
13
May
17
8
4
3
3
2
5
2
71
9
June
8
7
3
2
2
2
5
3
82
11
July
6
5
3
2
2
2
5
3
84
9
Aug
4
4
2
2
1
1
4
3
88
8
Sept
6
4
4
2
2
2
4
3
84
7
Oct
13
9
6
4
4
3
7
4
70
10
Nov
33
15
9
6
5
5
7
5
46
16
Dec
38
14
9
8
5
4
6
5
41
12
* "Mean" is the average percentage of the observations in the listed category; "Std"
is the standard deviation of the data in that category.
Table 3. Low cloud amounts (nL, in percent) observed on the North
Pole drifting stations.
Low cloud amount in tenths
02
34
56
78
910
Mean* Std
Mean
Std
Mean
Std
Mean
Std
Mean Std
Jan
77
12
1
2
1
2
1
2
18
11
Feb
78
14
1
2
1
2
1
2
16
11
March
80
12
2
2
2
2
1
1
13
10
April
78
14
2
2
1
2
1
2
16
12
May
38
11
1
1
2
1
2
2
54
11
June
22
11
2
2
2
2
3
2
68
12
July
21
12
2
1
2
2
3
2
69
13
Aug
18
10
2
1
2
2
3
2
73
11
Sept
26
11
2
2
2
2
3
2
65
12
Oct
45
13
2
2
3
2
3
2
45
13
Nov
68
16
2
3
2
2
1
2
24
13
Dec
76
13
1
2
1
1
1
1
19
11
* "Mean" is the average percentage of the observations in the listed category; "Std"
is the standard deviation of the data in that category.
In summer (June to September), overcast skies dominate, there are very few
occurrences of skies with 38 tenths cloud cover, and low clouds constitute most
of the cover. This latter observation is likely a consequence of the cold, wet, and
practically isothermal surface (melting snow on sea ice). May and October are short
transition seasons between the winter and summer cloud distributions.
Next, we use the observations from the drifting stations to consider the
interannual variability of cloud amount in the central Arctic. One feature of the
drifting stations necessary to consider in this analysis, however, is that they con-
stantly changed position. Although this drifting allowed them to sample wide
areas of the Arctic, we worry that their observational time series might not be
homogeneous as a result. Fortunately, we can check for homogeneity. Usually, two
or three drifting stations worked in the Arctic simultaneously. By computing cor-
relation coefficients for 3-hour and daily averaged meteorological data obtained
6
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