Determination of A Snow Effective Albedo For The Erythemal UV and The UV-a In The French Alps.
Abstract
Multiple reflections between a highly reflecting snow covered ground, and the scattering atmosphere strongly enhance the global irradiance received at the Earth's surface. Measurements of the spectral UV irradiance (280-400nm) have been performed in Briançon (altitude 1300 masl) at the CEMBREU (Centre Européen Médical et Bioclimatique de Recherche et d'Enseignement Universitaire) site, first during a campaign in February 1998. During this campaign, the sky was mostly cloudless, and the variation of the snow cover with meteorological conditions, allowed the study of this enhancement. Comparing measured irradiances and irradiances modellled for a black surface, an effective albedo can be retrieved; as the surface is neither uniform, nor lambertian, the effective albedo is defined as the albedo of a uniform lambertian surface, that has to be introduced in the 1-D radiative transfer model to fit the observed irradiance. In erythemal UV, the effective albedo has been found to be between 0.4 after a snow fall and 0.1 when most of the snow cover has melted. Since September 1999, two ultraviolet spectroradiometers operate regularly at the CEMBREU site, and all the periods with snow cover on the ground have been analysed; a climatology of the effective albedo in Briançon is beeing built.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.5902M