M. S. Marshunova
The Solar Radiation Regime of the Arctic
(Description of the Marshunova Radiation Climatology)
Overview
Maps of monthly and annual totals of direct solar, total solar and net radiation for the Arctic were compiled using measured and calculated values of these parameters. On annual maps, isolines of 200 MJ/m2 were used for direct radiation, and 500 MJ/m2 for total radiation and net radiation. For monthly maps, isolines of 50 MJ/m2 were used. Maps of direct and total radiation are not presented for the months November through January. Within this period the polar night covers most of the arctic area, and the radiation influx, of course, is zero (Table 1).
Table 1. Duration period of polar day and polar night
Degrees | Polar day | Polar night | |||
North | Beginning | End | Beginning | End | |
66 | 13 June | 30 June | |||
68 | 27 May | 17 July | 9 December | 4 January | |
70 | 17 May | 27 July | 26 November | 17 January | |
72 | 9 May | 5 August | 16 November | 26 January | |
74 | 2 May | 12 August | 9 November | 2 February | |
76 | 25 May | 18 August | November | 9 February | |
78 | 19 April | 24 August | 27 October | 15 February | |
80 | 14 April | 30 August | 22 October | 21 February | |
82 | 8 April | 4 September | 16 October | 26 February | |
84 | 3 April | 9 September | 11 October | 3 March | |
86 | 29 March | 15 September | 6 October | 8 March | |
88 | 24 March | 20 September | 30 September | 13 March | |
90 | 19 March | 25 September | 25 September | 19 March |
Note: Polar day is defined as the period when the sun does not sink lower than 50 minutes below the horizon. Polar night is defined as the period when the sun does not rise higher than 50 minutes above the horizon.
Direct solar radiation
The distribution of direct solar radiation depends on solar elevation, day length, and cloud conditions. Solar radiation generally increases from north to south, but cloud cover can alter this pattern. The isolines of general cloudiness and direct solar radiation tend to coincide with each other. The distributions of direct solar radiation for February through October and the annual total are presented in maps 1-10.
Winter and Spring
In November, December and January direct solar radiation is zero north of 70 degrees north latitude. In February the boundary of polar night is located at about 80 degrees north latitude. North of this area direct solar radiation increases only up to 25 MJ/m2. In March direct solar radiation at the Arctic Circle and northwards increases up to 100 MJ/m2 due to increasing solar elevation, day length, and decreasing cloudiness. In April solar elevation increases. Polar day (24-hour day length) starts at 85 degrees north latitude. The number of clear sky days also increases. Minimum radiation totals are found in the Norwegian and Barents seas region (where cloud cover is maximized). In May the greatest amount of fog and low stratus cloud occurs due to ice melting and advection of ice from the Arctic to the Atlantic Ocean. In April and May, the increase in radiation over the ocean is small.
Summer and Fall
In May, June and July, radiation increases sharply over the continental regions and in the Canadian Arctic Archipelago. While in general direct solar radiation is maximized in June, when the solar elevation is greatest, the radiation maximum for individual years may occur in other months (May-July), depending upon cloud conditions. In August direct radiation decreases, with the largest change from June and July occurring in the central arctic area. In September, solar radiation continues to decrease in conjunction with the decline in solar elevation. Polar day comes to an end north of 80 degrees north. Solar radiation sharply decreases in October. Polar night starts north of 85 degrees north. The 25 MJ/m2 isoline passes along the latitude of the Arctic Circle. In November polar night reaches 70 degrees north. In December solar radiation is absent north of the Arctic Circle.
The annual total for solar radiation in the Arctic ranges from 800 to 1200 MJ/m2. Minimum values are observed to the northeast from Jan Mayen. Direct radiation is less there than at the North Pole. Maximum radiation totals are found over Greenland and in the Canadian Arctic Archipelago.
Total solar radiation
Winter and Spring
In the southern Arctic area polar night comes to an end in February. Total radiation for this month ranges from 0 MJ/m2 at 78 degrees north to 50 MJ/m2 at the Arctic Circle. Monthly radiation in February is less than 2 percent of the annual total, but close to the total possible radiation, due to limited cloud cover. In March total radiation increases very sharply (fluxes are 5 to 10 times greater than in February), reflecting the increase in solar elevation and day length. Totals range from 50 MJ/m2 in the circumpolar region, to 250 MJ/m2 at the Arctic Circle. The highest values are found over Greenland with the lowest values in the vicinity of the Barents and Norwegian seas. Over most of the Arctic, except the Barents and Norwegian seas, cloudiness is at a minimum (4 to 6 tenths) so that monthly total radiation is close to its possible value. The March radiation influx is 4 to 8 percent.
In April radiation continues to increase. In the most northern areas, radiation increases by 7 to 8 times, while in the southern regions it increases only by 2.0 to 2.5 times. The effect of latitude on radiation totals is poorly expressed. Minimum fluxes are found in the cloudiest areas (the Barents and Norwegian seas).
From May through August the total radiation in the Arctic does not have pronounced latitude variability, as the influence of astronomic factors on the flux is small. Regional variability primarily reflects cloud and ice distribution. In May radiation increases by a factor of 1.5 over that received during April. Minimum radiation totals are observed in the Barents and Norwegian seas, where the average monthly cloudiness is 7.5 to 8.5 tenths and ice-free conditions are found. Maximum radiation values are found in the Arctic basin and Canadian Arctic Archipelago. In May total radiation in the Arctic is higher than in more southerly latitudes.
Summer and Fall
Total radiation in May accounts for up to 20 percent of the annual total. Maximum totals occur in June, but spatial patterns are similar to those seen in May. Minimum incoming radiation is still observed in the Barents and Norwegian seas. Maximum incoming radiation occurs in the arctic basin and Canadian Arctic Archipelago. Maximum cloud cover still occurs over the Barents Sea (8 to 9 tenths) in June. In the Arctic basin cloudiness also increases to 8.0 to 8.5 tenths. In the southern areas of the arctic seas, as well as over continents, cloudiness is less (6.5 tenths). The radiation maximum in the Canadian Arctic Archipelago is connected with more cloud-free conditions compared to other regions. In the arctic basin, the increase of the total radiation occurs due to diffuse radiation associated with significant cloudiness and high albedo. The contribution of June into the annual radiation income is the same as that in May.
In July the total radiation income decreases by 1.2 to 1.4 times compared to June, but with similar spatial patterns. The contribution of July to the annual radiation is 17 to 19 percent. In August radiation decreases 1.5 to 1.7 times compared with July. The latitudinal radiation variability is again marked. The contribution of August to the annual radiation is 10 to 12 percent. In September the total radiation is dominated by the effects of latitude. Totals range from 80 MJ/m2 at the pole up to 200 MJ/m2 at the latitude of the Arctic Circle. The contribution of September to the annual radiation income is only 4 to 5 percent. In the middle of October polar night starts north of 82 degrees north. This explains why the zero isoline, which passes approximately along 83 degrees north, appears on the map of total radiation. Radiation is about 100 MJ/m2 along the polar circle.
On the annual map a general pattern of decreasing totals towards the Atlantic Ocean is observed. Totals are lowest in the region of Franz Josef Land, Spitsbergen, and the Barents and Norwegian seas (2200 MJ/m2 to 2500 MJ/m2). This is connected with cloud conditions and properties of underlying surface. This region is the cloudiest in the Arctic and also has a low surface albedo. East of this region cloud decreases and albedo increases, the latter effect associated with the increasing concentration of ice.
Annual sums of total radiation are highest in the central Arctic Ocean despite significant cloud cover in summer (mean cloud is equal to over 8 tenths for April through September). High values of total radiation for the arctic basin are caused by the large surface reflectivity all year round (annual mean surface albedo is equal to about 78percent).
Annual values of total radiation in the Canadian Archipelago reflect the comparatively limited cloud cover in this region of the Arctic (5.0 to 5.5 tenths).
Net radiation
Winter and Spring
During the polar night, net radiation is due to longwave fluxes only. Monthly values of net radiation for November through February range from -59 MJ/m2 to -200 MJ/m2. The most negative values are found in the Barents Sea, Baffin Bay and near the coasts of Spitsbergen. Here, extensive areas of open water observed in winter increase the long-wave loss from the surface. The Norwegian and Greenland seas and adjacent ocean regions are the main areas where the earth's surface loses the radiation heat in winter. The net radiation deficit over the Arctic Ocean and continental regions is less - half (or even less) than that for the open sea.
In March net radiation remains negative for most regions despite the increasing solar flux. Net radiation is positive only in the Norwegian Sea. In April the zero isoline passes along the northern coast of Asia and North America. Maximum positive values of net radiation are observed in the Barents and Norwegian seas.
Summer and Fall
In June the difference in net radiation between the continent and open sea increases further. Values range from 150 to 200 MJ/m2 over the Arctic Basin and 300 MJ/m2 along the Eurasian and North American coasts, compared with maximum values of up to 350 MJ/m2 in the Barents and Norwegian seas and in the Davis Strait. In the southern regions of the Chukchi and Kara Seas the extensive areas of open water between drift ice also increases net radiation.
In July net radiation reaches maximum values, with the highest totals in the Barents and Chukchi seas, and in the southern area of the Baffin Bay. In August net radiation totals decline by 1.5 to 2.0 times compared with July due to the decreasing solar radiation and snow cover formation in the most northern regions. In September the zero isoline passes along 75 degrees north in the region of the Canadian Arctic Archipelago, rounding Spitsbergen and coming to the Taymyr Peninsula. On the coast, net radiation values are slightly positive. In October the net radiation values over the whole Arctic become negative again with totals ranging from -50 MJ/m2 to -100 MJ/m2. Open water areas have totals up to -150 MJ/m2.
Annual net radiation over the continents and sea in the Arctic is positive. Net radiation is negative (-50 MJ/m2 to -80 MJ/m2) on the surface of the Arctic basin and glaciers, ice sheet of Greenland, and the northern islands of the Canadian Arctic Archipelago where albedo exceeds 70 percent throughout the year. The distribution of annual net radiation for the uniform underlying surface exhibits a general latitudinal dependence strongly modified by the albedo effects along the sea ice margin. Annual net radiation values over the Arctic are equal to 200 MJ/m2 to 600 MJ/m2, compared to 700 to 1000 MJ/m2 over the sub-Arctic.
Related work
Related work by M.S. Marshunova is documented in the following publications:
Chernigovskiy, N. T., and M. S. Marshunova, The Climate of the Soviet Arctic (The Radiation Regime), Leningrad: Gidrometeoizdat, 1965, 198 pp. (in Russian).
Marshunova M. S., and N. T. Chernigovskiy, The Radiation Regime of the Foreign Arctic, Leningrad: Gidrometeoizdat, 1971, 180 pp. (in Russian).
The Radiation Regime of the Greenland and Norwegian Seas, Leningrad: Gidrometeoizdat, 1983, 64 pp. (in Russian).
Marshunova M. S., and A. A. Mishin, Handbook of the Radiation Regime of the Arctic Basin (Result from the Drift Stations). Technical Report APL - UW TR 9413, December 1994.
Marshunova M. S., and V. F. Radionov, Dynamics of Arctic Radiation Climate - Problems of the Arctic and Antarctic, 1995, vol. 69, p. 64-73 (in Russian).