Aerosol Forcing due to Arctic Haze
Aerosols influence directly and indirectly the radiative balance of the atmosphere and at the surface. Therefore they play an important role in the climate system. In the Arctic we know the phenomena "Arctic Haze": from winter to spring aerosol particles are transported in the planetary boundary layer from industrial areas in mid-latitudes into the Arctic area. Aerosols decrease the planetare albedo and increase the total energy, which is absorbed in the system surface-atmosphere. The Arctic conditions (high surface albedo, long atmospheric path for radiation) are very complicated and therefore the signal of the aerosols on the energy budget is still not clear, especially for the surface budget. It has to clearify if the climate signal due to "Arctic Haze" would additionally intensify or decrease the carbon dioxide-signal. It seems, that the aerosol signal depends on the chemical composition and vertical distribution of the aerosols, on the emissivity of the atmosphere and on the surface albedo.
The Radiative Transfer Model
The one-dimensional vertical dependent spectral high resolution radiative transport model, LOWTRAN [Kneizys et al., 1989] has been used. This model describes the molecular absorption and scattering and the extinction due to aerosols and cloud/rain droplets. Input parameters are the vertical profils of pressure, temperature, humidity and ozone which are obtained from rawinsonde observations. The aerosol parameters are described in dependence of height and wavelength. The aerosol optical properties were determined on the basis of sun-photometer measurements, i.e. measurements of the aerosol optical depth in Ny-Ålesund/Spitsbergen.
The Calculated Aerosol Forcing
Aerosol forcing in the heating rates (K/d) for a spring case at Ny-Ålesund/Spitsbergen.
The aerosol forcing in the shortwave heating rates were calculated in two case studies for Arctic spring and summer for the station point Ny-Ålesund, assuming cloudless conditions. During spring an aerosol forcing in the heating rates in the planetary boundary layer of +0.3 K/day was calculated, which corresponds to a reduction of the shortwave netto fluxes of 4 W/m2.
References
- Kneizys, F. X., E. P. Shettle, L. W. Abreu, J. H. Chettwynd, G. P. Anderson, W. O. Gallery, J. E. A. Selby, S. A. Clough, User Guide to Lowtran 7, AFGL-TR-88-0177, Environmental research Papers No. 1010, 1989.
- Herber, A., Rinke, A., Schult, I., Gernandt, H., Vogel, G., 1994 : Case study of arctic tropospheric aerosol loading and its spectral influence on the heating rates in the shortwave range. European conference on the global energy and water cycle, London, 18.-22. July.