A case study of the radiative effects of Arctic aerosols in March 2000

Accurate modelling of the radiative forcing due to Arctic aerosols requires an adequate knowledge about the spectral, spatial and temporal variability of the aerosol. This needs contrasts with the limited measurements of Arctic aerosol characteristics. This paper presents two different approaches to incorporate Arctic aerosols in the regional climate model HIRHAM to overcome this problem. In the first method, Arctic aerosol properties are described via a mixture of different components from the global aerosol data set (GADS). The second method derives the aerosol model input parameter from an Arctic airborne measurement campaign (ASTAR) via a data transformation. Results from a one-dimensional radiative transfer model for a case study are presented for two selected days of March 2000, one with a high and another with a lower aerosol loading, which were considered to be representative for the Arctic spring aerosol loading. The calculated heating rate anomalies are sensitive to the assumed aerosol characteristics (absorption characteristics, particle radius, chemical composition, mass-mixing ratio). The performed study showed the importance of both methods for modelling solar radiative forcing due to Arctic aerosols. For the 2 days selected, calculated local solar heating rate anomalies between 0.05 and 0.3 K day−1 were achieved. An application of a high-resolution regional climate model is presented to determine the regional climatic impact of Arctic aerosols during March 2000. The aerosol effect induced a substantial spatial variability at the regional scale and varies between a cooling of 2 K in the Baffin Bay and Laptev Sea and a warming of 3 K in the Beaufort Sea. Arctic aerosol loading changed the sea level pressure patterns over the Arctic Ocean with implications for additional feedbacks on a coupled atmosphere-ocean-sea ice model of the Arctic.