Present status and variations in the Arctic energy balance

The total solar irradiance (TSI, or solar constant) acquired a new value: 1361 W m(-2) instead of 1365 W m(-2). However a long-term variation of TSI was not detected. The solar irradiance at the earth's surface is considerably smaller (170 W m(-2)) than previously believed (e.g. 198 W m(-2) of IPCC AR4). The previous overestimation is due to the underestimation of the absorption of solar radiation in the atmosphere. The absorption of solar radiation in the atmosphere at about 90 W m(-2), or 25-28% of the primary solar radiation from space. The global mean atmospheric downward terrestrial radiation is much larger (345 W m(-2)) than previously assumed (325 W m(-2) of LPCC AR4). The Arctic has regions of negative annual net radiation, a very rare phenomenon on the globe. These regions are the Central Arctic Ocean with its multi-year ice coverage and the accumulation area of the Greenland ice sheet. The energy balance of these regions is presented. Long-wave incoming radiation has been increasing in the Arctic at a rate of 4-5 W m(-2)/Decade. The Greenland ice sheet exhibits a large vertical difference in net radiation from the ablation area to the dry snow zone in summer. It ranges from 80 W m(-2) in the ablation area to 20 W m(-2) at the equilibrium line and to 10 W m(-2) in the dry snow zone. This gradient determines the melt gradient on the ice sheet, and is mainly caused by the altitude variation in atmospheric long-wave radiation, seconded by the albedo variation. The effect of albedo in summer for various surfaces is discussed. Simulation capabilities of radiation for many GCMs are investigated. (C) 2012 Elsevier B.V. and NPR. All rights reserved.