Diurnal Temperature Ranges and Cloudiness

Based on the results presented in Section 4,2, the general pattern of influence of cloudiness on T and T seems to be quite similar. However, max mm ~ *

the existing differences in magnitudes of this influence (expressed by anomalies) are significant during some seasons and should cause appropriate changes of the DTR in the case of increasing or decreasing trends in cloudiness in the Arctic.

The influence of cloudiness on DTR is presented in Table 4.4 and Figure 4.13. These data clearly show that, on an annual basis, increased cloudiness leads to a decrease in DTR. This influence is at its highest in summer, then in spring and also in autumn, except for the region of Jan Mayen. In winter, the situation is much more complicated because the highest positive anomalies of the DTR occur on partly cloudy days in the whole Arctic. A further increase of cloudiness leads to a decrease in DTR. Slightly positive anomalies of the DTR occur also in some parts of the Arctic, both on clear days (Danmarkshavn and Mys Shmidta) and cloudy days (Ostrov Dikson and t'hokurdakh). It is noteworthy that in the parts of the Arctic where cyclonic activity prevailed (Atlantic, Pacific, and Baffin Bay regions) the anomalies of the DTR on cloudy days were lower than on clear days (see Table 4.4 and Figure 4.13).

Danmarkshavn

Danmarkshavn

Jan-Maysn

jrMAMJJASaND

JFMAVJJABONO

BOND

Ostrov Dikson

Ostrov Dikson

Figure 4.13. Mean annual courses of the DTR on clear (1), partly cloudy (2), and cloudy (3) days al 10 Arctic stations representing the majority of the climatic regions and subregions after Atlas Arktiki (1985). After Przybylak (1999).

Figure 4,13. coiU.

Table 4.4. Mean seasonal anomalies of DTR (in °C) in the Arctic on clear (I), partly cloudy (2) and cloudy (3) days over the period 1951-1990 (after Przybylak 1999)

Season

Element

DAN"

JAN

HOP

NAR*

DIK*

CHO*

SHM*

RRS**

COR**

CI-Y**

1

0.2

0.0

-1.7

-1.2

-1.5

-0.8

0.3

-0.7

-1.4

-0.5

DJF"

2

0.3

0.2

0.4

1.7

0.2

0.6

0.8

0.3

0.6

0.5

3

-0.8

-0.2

-0.1

-1.3

0.2

0.1

-0,8

-0.1

-0.3

-1.3

Mean

8.6

5.2

6.7

8.9

7.1

7.0

7.0

7.2

8J

7.8

1

1.3

1.0

0.0

3.5

0.3

1.2

2.8

0.4

1.5

1.1

MAM

2

0.3

0.5

0.6

1.8

0.5

0.5

1.1

0.3

0.8

0.7

3

-1.9

-0.3

-0.5

-1.9

-0.5

-1.7

-2.1

-1.3

-2.9

-2.6

Mean

8.0

4.5

5.6

8.5

6.9

8.6

7.4

7.1

9.7

9.3

1

1.3

2.3

1.2

4.3

2.8

3,1

3.0

1.9

3.1

2.3

JJA

2

0.8

1.0

0.5

2.3

1.7

2.0

1.6

1.1

1.3

1.4

3

-1.4

-0.4

-0.2

-1.8

-0.4

-1.5

-1.0

-0.9

-2.4

-1.7

Mean

5.6

3.7

3.1

8.8

4.4

8.9

5.8

4.9

8.0

6.7

1

0.5

-0.7

0.6

2.4

-0.2

0.7

2.1

0.6

0.2

1.2

SON

2

0.4

0.2

0.6

18

1.2

1.1

1.9

0.9

1.3

1.5

3

-0.8

0.0

-0.3

-1.2

-0.5

-0.7

-1.2

-1.1

-1.7

-1.5

Mean

6.2

3.8

3.7

6.4

5.0

6.1

5.5

5.8

7.1

5.8

Key: Mean - mean seasonal DTR; other explanations as in Table 4.2

Key: Mean - mean seasonal DTR; other explanations as in Table 4.2

An opposite relation occurs in the Siberian and Canadian regions (with prevailing anticyclones) where radiation plays a significantly greater role than in the previously mentioned regions. On cloudy days (Tables 4.2-4.3), the anomalies of Tnm and 7Vn are nearly the same, but on clear days negative anomalies of T are significantly greater. In the regions where a great number of clouds are transported together with warm and humid air masses from the lower latitudes by a synoptic-scale cyclonic activity, the influence of cloudiness on Tnm and rmjn is different, mainly on cloudy days (opposite to the situation in the Canadian and Siberian regions). This is a consequence of the very similar influence of advcction of warm air masses on T and T . . On

J max mm the other hand, high cloudiness connected with this advection reduces the loss of the long-wave outgoing radiation to space. This radiation flux is relatively more important during the night than during the day, and the resulting positive anomalies of Tmm are higher than Tmn (see Tables 4.2-4.3).

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