COMPARATIVE STUDY OF THE SURFACE RADIATION BUDGET AT NY-ALESUND, SVALBARD AND SYOWA STATION, ANTARCTICA, 1987

摘要

The surface radiation budget in 1987 at Ny-Alesund, Svalbard was measured by the Norwegian Polar Institute, and is discussed as a typical radiative regime for the Arctic, at the edge of the seasonal sea ice area. Following the dramatic change of surface albedo between summer and winter, global solar radiation decreases under clear and overcast conditions at the same solar zenith angle. The apparent transmittance defined as the ratio of the global radiation at the surface to the solar insolation at the top of the atmosphere ranges from 40 to 70% before the decrease of albedo; however, it ranges from 20 to 60% after the decrease of albedo. The downward longwave radiation differs considerably between winter and summer. In summer, the downward longwave radiation has a small range and the difference between clear and overcast is small, while cloud amount is very high. In winter, the range of downward longwave radiation is as great as 150W/m^2,from about 150W/m^2 under clear sky to more than 300W/m^2 under overcast sky in some cases. This great variation in winter is due not only to the variation of cloudiness but also to the variation of air mass surrounding Ny-Alesund. Larger downward longwave radiation with high cloudiness and warmer temperature accompany maritime airmasses; smaller radiation with low cloudiness and colder temerature accompany the Arctic airmass. Normally, polar clouds increase the downward longwave radiation and warm the surface; however, during the summer months when the surface snow cover disappears, clouds reduce the shortwave radiation more effectively than the increase of longwave radiation and the surface is cooled. Compared to the observations on the sea ice at Syowa Station, Antarctica, the net total radiation at Ny-Alesund is much larger in the summer months than at Syowa Station. These are the results of lower albedo in summer months, larger downward radiation due to warmer temperatures and clouds. As a whole, the radiation budget at Ny-Alesund in summer is controlled by the maritime airmass, while in winter it is strongly affected by both maritime air from the south and Arctic air from the north.