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1 Problemy Klimatologii Polarnej

1 2011

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Bilans radiacyjny w rejonie Kaffioyry (NW Spitsbergen) w sezonie letnim 2010 roku

Kejna M., Przybylak R., Araźny A.

Problemy Klimatologii Polarnej

2011

nr 21

173-186

W artykule przedstawiono wyniki rejestracji składowych bilansu promieniowania na 3 stanowiskach: Kaffioyra-Heggodden (KH), Lodowiec Waldemara-czoło (LW1) i Lodowiec Waldemara-pole firnowe (NW Spitsbergen) w okresie od 16.07 do 31.08.2010 r. Pomiary prowadzono przy pomocy Radiometru CNR4 firmy Kipp&Zonen. Co minutę rejestrowano natężenie promieniowania słonecznego K?, promieniowania odbitego (K?), promieniowania ziemi (L?) i promieniowania zwrotnego atmosfery (L?). Na tej podstawie obliczono bilans radiacyjny (Q*), składający się z bilansu krótkofalowego (K*) i długofalowego (L*). Stwierdzono niewielkie różnice pomiędzy stanowiskami KH i LW2 założonymi na podłożu morenowym. Najmniej korzystny Q* wystąpił na LW2 nad powierzchnią śnieżno-lodowcową charakteryzującą się wysokim albedo. W artykule zbadano zróżnicowanie przestrzenne składowych bilansu radiacyjnego z dnia na dzień oraz w cyklu dobowym.

Measurements of radiation balance (Q*) were carried out in the Kaffioyra region (NW Spitsbergen) between 16 July and 31 August 2010 at three stations with different surfaces: KH on the glacial moraine of the Aavatsmark (11.5 m a.s.l.), LW1 - on the terminal moraine of the Waldemar Glacier (130 m a.s.l.), and LW2 - on the firn field of the Waldemar Glacier (375 m a.s.l.) - Fig. 1. A Kipp&Zonen CNR 4 Net Radiometer was used to register - minute by minute - the short wave radiation balance (K*), which is the difference between incoming solar radiation K? and reflected solar radiation (K?), and the long wave radiation balance (L*), which is the difference between downward long wave atmospheric radiation (L?) and upward long wave radiation (L?) - Table 1. In the studied period the maximum intensity of incoming solar radiation reached 709.4 W.m-2 at KH, 882.1 W.m-2 at LW1 and 836.2 W.m-2 at LW2. The mean diurnal sums of incoming solar radiation ranged from 11.04 MJ.m-2 at KH to 10.46 MJ.m-2 at LW1 and 10.60 MJ.m-2 at LW2 (Table 2, Fig. 2). The surface albedo varied, reaching between 13% (LW1) and 15% (KH) on the moraines, and up to 61% (LW2) on the firn field (Table 2, Fig. 3). Thus the lowest value of short wave radiation balance, +4.31 MJ.m-2, was registered at LW2, whereas it was doubled on the moraines: KH +9.50 MJ.m-2 and LW1 +9.09 MJ.m-2 (Table 4, Fig. 4). The flux of downward long wave atmospheric radiation coming from the atmosphere does not reveal any significant differences between individual stations: KH: 27.26 MJ.m-2, LW1: 27.47 MJ.m-2 and LW2 - 27.37 MJ.m-2 in 24h (Table 3). The Earth's surface (upward long wave radiation) was losing, on average: 30.31 MJ.m-2, 29.88 MJ.m-2 and 30.10 MJ.m-2, respectively, and the mean daily values of long wave radiation balance were negative: KH -3.05 MJ.m-2, LW1 -2.42 MJ.m-2 and LW2 -2.73 MJ.m-2. The surface radiation balance (Q*) was the most favourable on moraine bases: LW1 +6.67 MJ.m-2, KH +6.45 MJ.m-2, whereas the snow-covered firn field received the smallest amount of energy: LW2 +1.58 MJ.m-2 (Table 4, Fig. 5). In spite of the polar day, the diurnal cycle of the radiation balance components appears symmetrical with regard to the solar noon, related to the elevation of the sun over the horizon and the temperature of the surface and of the atmosphere. The flux of incoming solar radiation reached its peaks during midday hours with the following mean values: KH: 278.7 W.m-2, LW1: 275.9 W.m-2, and LW2: 295.2 W.m-2 (Fig. 6). At the time of lower culmination of the sun the values of K* were falling to zero. The balance of long wave radiation was negative and reached its highest values around midday hours (KH -50.0 MJ.m-2, LW1 -40.1 MJ.m-2 and LW2 -47.5 MJ.m-2). Q* was the highest in midday hours, when it was 2.5 times higher for moraine bases (KH +194.8 MJ.m-2 and LW1 +201.5 MJ.m-2) than for snow and glacial surfaces (LW2 +79.1 MJ.m-2). At low elevation of the sun Q* became negative: KH -6.8 MJ.m-2, LW1 -5.4 MJ.m-2 and LW2 -19.4 MJ.m-2. On individual days the diurnal cycle of the components of Q* was affected not only by the elevation of the sun, but also by the atmospheric state and the presence of clouds, in particular. For example, on 27 and 28 July 2010 a different weather types occurred (Table 5, Fig. 7). On the first day the sky was completely overcast with St and Sc clouds and no sunshine was observed. On the following day it cleared up with partial cloudiness (Cu, Ac, Ci), and the sunshine duration reached 16.2 h. On 27 July a slight influx of incoming solar radiation was registered (mean intensity 68.6 W.m-2, diurnal sum 5.92 MJ.m-2), K* was 5.14 MJ.m-2, and L* -0.84 MJ.m-2 due to the total cloudiness, which supported substantial downward atmospheric radiation (downward long wave atmospheric radiation 339.3 W.m-2). On the other hand, on 28 July, when the amount of cloudi-ness was moderate, the maximum intensity of incoming solar radiation was 668.7 W.m-2. In 24 hours the total radiation that reached the surface amounted to 22.04 MJ.m-2, and K* increased to 18.90 MJ.m-2. L* was negative (-5.26 MJ.m-2) due to substantial radial emittance of the ground (upward long wave radiation 352,0 W.m-2) and some downward atmospheric radiation (downward long wave atmospheric radiation 291.1 W.m-2). However, the overall radiation balance was three times higher than on 27 July and amounted to 13.65 MJ.m-2. In the studied period, the individual components of Q* were decreasing in value, as a result of the lower and lower elevation of the sun over the horizon and the ending of the polar day.