Open AccessUltraviolet spectral irradiance in the French Alps: Results of two campaigns
Author(s) -
Pachart Eric,
Lenoble Jacqueline,
Brogniez Colette,
Masserot Dominique,
Bocquet Jean Louis
Publication year - 1999
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jd900163
Subject(s) - irradiance , spectroradiometer , solar zenith angle , altitude (triangle) , environmental science , atmospheric sciences , zenith , snow , reflectivity , solar irradiance , atmospheric radiative transfer codes , sun photometer , ground level , radiative transfer , aerosol , meteorology , optics , physics , mathematics , architectural engineering , ground floor , geometry , engineering
The ultraviolet spectral irradiance has been measured in the Alps in Briançon (altitude 1300 m asl) in July 1996 and March 1997, with the spectroradiometer of the University of Lille. The erythemal dose rate has been measured simultaneously with a broadband instrument. The aerosol optical depth, necessary as input for modeling, was measured with a Sun photometer. On cloudy days, irradiance is highly variable, with values exceeding those of clear days when the direct solar beam is not obstructed by clouds. For clear days, measured values are compared with the results of a radiative transfer model, and the influence of altitude and ground surface reflectance is analyzed. For the same solar zenith angle, irradiance in UVA is 8–10% higher in Briançon than in Brussels, half of the difference being due to the higher altitude of Briançon. Comparison of winter and summer values shows an amplification of ∼10–15% in winter owing to the snow reflectance; it can be explained by an effective reflectance of 0.3–0.4.