Radiation in the Arctic Atmosphere and Atmosphere

Arctic surface temperature has been increasing at a rate 2-3 times that of the global average in the last half century. Enhanced warming of the Arctic, or Arctic Amplification, is a climatic response to external forcing. Despite good results obtained by climatic models for the globe, the largest intermodel differences in surface temperature warming are found in the Arctic. The magnitude of this warming drives many different processes and determines the evolution of many climatic parameters such as clouds, sea ice extent, and land ice sheet mass. The Arctic Amplification can be attributed to the peculiar feedback processes that are triggered in the Arctic. Most of these processes include radiation interaction with the atmosphere and with the surface, all of them contributing to the radiation budget. It is then mandatory to correctly evaluate this budget both at the surface and at the top of the atmosphere and in the solar and thermal spectra. This can be done using both direct observations, from ground and from space, and model simulation via radiation transfer codes. This last approach need many observed input parameters anyhow. In this contribution results on the evaluation of the radiation budget in the Arctic are first reviewed. Follows a detailed description of the effects of the most important atmospheric gases (carbon dioxide, methane, ozone etc.) on both shortwave and longwave radiation ranges. The same is illustrated for aerosol loading in the Arctic, based on a large dataset of aerosol radiative properties measured by means of sun-photometers in numerous Arctic stations. Finally, the effect of the surface reflectivity characteristics on the radiation budget is illustrated by means of albedo models specific for the Arctic.