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| Zerefos C.S, D.S. Balis, C. Meleti, A.F. Bais, K. Tourpali, K. Vanicek, F. Cappellani, U. Kaminski, T. Colombo, R. Stubi, L. Manea, P. Formenti and M.O. Andreae | [abstract]
During the solar eclipse of 11 August 1999, intensive measurements of UV solar irradiance and total ozone were performed at a number of observatories located near the path of the moon’s shadow. At the Laboratory of Atmospheric Physics (LAP) of the Aristotle University of Thessaloniki, Greece global and direct spectra of UV solar irradiances (285-365 nm) were recorded with a double monochromator and erythemal irradiances were measured with broadband pyranometers. In addition intensive measurements of global and direct irradiances at six UV wavelengths were performed with a single Brewer spectrophotometer. Total ozone measurements were also performed with Dobson and Brewer spectrophotometers at Hradec Kralove (Czech Republic), Ispra (Italy), Sestola (Italy), Hohenpeissenberg (Germany), Bucharest (Romania), Arosa (Switzerland) and Thessaloniki (Greece). From the spectral UV measurements the limb darkening effect of the solar disk was tentatively quantified from differences of measured solar spectral irradiances at the peak of the eclipse (near to limb conditions) and before the eclipse. Two black body curves were fit to the pre-eclipse and peak eclipse spectra, which have shown a difference in effective temperatures of about 165oK between the limb and the whole of the solar disk. The limb darkening effect is larger at the shorter UV wavelengths. Moreover, the ratio of the diffuse to direct solar irradiances during the eclipse shows that the diffuse component is reduced much less compared to the decline of the direct solar irradiance at the shorter wavelengths. Moreover, a 20 minute oscillation of global UV-B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20 minute fluctuation in total ozone presumably caused by the eclipse induced gravity wave. This work also shows that routine total ozone measurements with a Brewer or a Dobson spectrophotometer should be used with caution during a solar eclipse. This is because the diffuse light increases by more than 30% with respect to the direct solar radiation, increasing more at the shorter wavelength side of the UV spectrum. This plausible mechanism introduces an artificial decrease in total ozone during solar eclipse of more than 30 D.U., which is confirmed by all Brewer and Dobson measurements. Changes in total ozone cited earlier in the refereed literature have not been confirmed in the present study. | [keywords]
irradiance; solar eclipse; total ozone; ultraviolet radiation, Greece | | J. Geophys. Res. 105, D21, 26463-26473, 2000 | | http://www.scopus.com/scopus/inward/record.url?eid=2-s2.0-16644372259&partnerID=40 |  back to publications list |
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