Importance of aerosol variations for surface UV-B level: Analysis of ground-based data taken at Belsk, Poland, 1992-2004

Abstract

We compare various optical characteristics of atmospheric aerosols derived from ground-based measurements (by Brewer spectrophotometer and Cimel Sun photometer and horizontal visibility from standard observations of the visual range) and satellite measurements (Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument on board the Terra satellite) over Belsk (51°84°N, 20°79°E), Poland. It is shown that aerosol forcing on the erythemally weighted UV at the Earth's surface is as important for the clear-sky radiation level as that due to changes in the columnar ozone amount both on long-term (trend) and short-term (day-to-day) timescales. Real characteristics of aerosols in the UV-B range appear important for estimating of the erythemally weighted irradiance and actinic flux during cloudless conditions. This is demonstrated by a comparison of the results of a radiative transfer model (libRadtran) using input from various measurements carried out at Belsk and the results using restricted input (possible for many other stations). Frequently, the irradiance and actinic flux in the UV-B range cannot be modeled using the aerosols characteristics extrapolated directly from those measured in the visible range. A weak correspondence between the horizontal visibility and aerosol optical depth in the UV range is also found. Thus corrections to the results from the radiative transfer model incorporating restricted input are proposed to account for the specific aerosol properties in the UV range. Copyright 2005 by the American Geophysical Union.