Interannual variability of arctic radiation balance in July

Measurements of global warming show that in the Arctic region, temperatures have risen twice as fast as the global mean. Furthermore, observations show that the ice cover in the Arctic Ocean has been diminishing over recent years. The reduction of ice will result in a reduction of albedo and increased absorption of solar radiation, thereby enhancing the warming and creating an ice-feedback on the radiation balance. The present paper examines the radiation budget data from the Earth Radiation Budget Experiment (ERBE) for the period 1985 through 1988 and from the Clouds and Earth Radiant Energy System (CERES) for 2000 through 2003. Monthly means of 2.5 degree regions north of 60 degrees North are considered for Julys during these periods. The midpoints of these periods differ by 15 years, permitting study of decadal changes as well as of interannual variations. Throughout this data period, the Arctic Oscillation has been in its positive phase.

Changes in absorbed solar radiation are noted for the 15-year period, but there is little effect on the outgoing longwave radiation. Absorbed solar radiation and net radiation flux vary by +/- 20 W-m-2 over large regions but in geographically complex patterns. Some of these changes are over the Arctic Ocean, where ice has melted, others are over Siberia and the Norwegian Sea. The large interannual variations of absorbed radiation will make it difficult to demonstrate long-term trends with statistical confidence. Nevertheless, over the east coast of Greenland there is an increase in absorbed solar radiation over the period from 1985 to 2003.The solar elevation angle at high latitudes is small, but the long daylight time of summer results in a large change of daily average absorbed solar fluxes with albedo changes. Additional study is needed to discern whether the changes are due to ice cover or cloud cover changes for Ocean regions.

Greenland in the summer is particularly interesting because it is one of the largest radiation sinks on this planet. With its high albedo, its surface reflects most insolation and the outgoing longwave radiation is supported by the transfer of heat through the planetary boundary layer.