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Ann. Geophys., 26, 2043-2052, 2008
www.ann-geophys.net/26/2043/2008/
© European Geosciences Union 2008
Analysis of relationships between ultraviolet radiation (295–385 nm) and aerosols as well as shortwave radiation in North China Plain
X. Xia1, Z. Li2, P. Wang1, M. Cribb2, H. Chen1, and Y. Zhao3
1LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
2Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, MD, USA
3Chinese Academy of Meteorological Sciences, Chinese Meteorological Administration, Beijing, China
Abstract. The fraction of ultraviolet (UV) radiation to broadband shortwave (SW)
radiation (FUV=UV/SW) and the influences of aerosol, precipitable water
vapor content (PWV) and snow on FUV were examined using two year's
worth of ground-based measurements of relevant variables in northern China.
The annual mean FUV was 3.85%. Larger monthly values occurred in
summer and minimum appeared in winter. Under cloudless condition, FUV
decreased linearly with τ500 nm and the resulting regression
indicated a reduction of about 26% in daily FUV per unit τ500 nm,
implying that aerosol is an efficient agent in lowering the
ground-level UV radiation, especially when the sun is high. Given that the
annual mean τ500 nm is 0.82, aerosol induced reduction in surface
UV radiation was from 24% to 74% when the solar zenith angle (θ)
changed from 20° to 80°. One cm of PWV led to an increase of about
17% in daily FUV. One case study of snow influence on surface
irradiance showed that UV and SW radiation increased simultaneously when the
ground was covered with snow, but SW radiation increased much less than UV
radiation. Accordingly, FUV increased by 20% for this case. Models
were developed to describe the dependence of instantaneous UV radiation on
aerosol optical depth, the cosine of the solar zenith angle (μ), and
clearness index (Kt) under both clear and all-weather conditions.
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