Variations of solar radiation at the Earth's surface during the total solar eclipse of 29 March 2006

Abstract

On 29 March 2006, a total eclipse of the Sun was visible on the Greek island Kastelorizo (36.150°N, 29.596°E). An extended set of instruments was installed in order to measure the variability of different components of the radiation field during the eclipse. Seven spectroradiometers (two scanning double monochromators measuring especially in the UV range, 4 photo diode array instruments and one CCD-spectrograph for the UV and visible wavelength range) performed measurements during 28 and 29 March. A narrow band multi-filter radiometer and two broadband erythemal and UVA radiometers were operated with about 1 sec temporal resolution. Two sun-photometers were used to measure ozone column and aerosol optical depth. The weather conditions on March 28 were almost perfect, whereas on 29 March thin cirrus clouds were occasionally present in front of the sun. Details about the observed changes in the radiation field on the eclipse day are presented and compared with model calculations of the change in extraterrestrial solar irradiance. The results show an underestimation of the model calculations compared with measurements, with respect to the effect of the limb darkening on the spectral behavior of the solar irradiance during the eclipse. The absolute changes in the global and direct irradiance and their wavelength dependencies are discussed. Finally, the decrease in total ozone retrieved during the course of the eclipse from direct irradiance measurements is investigated with respect to the effect of the limb darkening and the influence of the diffuse radiation entering the field of view of the Brewer spectroradiometer.