Influence of Aerosols on the Arctic Climate

Background

Aerosols influence the radiative balance of the atmosphere and surface both directly and indirectly. The direct effect refers to the scattering and absorption of radiation by particles, whereas the indirect effect denotes the effect of aerosols acting as cloud condensation nuclei, possibly modifying cloud albedo and cloud life. In the Arctic troposphere an increased aerosol concentration is found specially during late winter and spring. This phenomenon known as Arctic haze are aerosol particles transported from industrial areas in midlatitudes into the Arctic. The aim of our study is to estimate the climate signal due to the direct effect of Arctic haze.

Global Aerosol Data Set (GADS) and Arctic Haze

To study the Arctic haze phenomenon an aerosol block has been incorporated in the regional atmospheric climate model HIRHAM, taking into account scattering and absorption of aerosol. This aerosol block is based on the Global Aerosol Data Set (GADS; Koepke et al.,1997) and defines the optical aerosol parameters (spectral extinction, absorption, asymmetry factor) of 11 aerosol types. In our study Arctic haze is described by a mixture of water soluble, sea salt and soot components. The calculated optical depth has been tuned with photometer measurements at Ny Ålesund (Spitsbergen).

Sensitivity Studies 

HIRHAM simulations including the direct Arctic haze effect have been carried out for the months March to April 1990-95 and have been compared with simulations without aerosol loading (control runs). Thereby, the Arctic haze was distributed both uniformly and regionally. Figure 1b shows the aerosol forcing when Arctic haze is distributed uniformly over whole model domain and included in all layers below 850 m height.