Abstract

Data of Lambertian equivalent reflectivity (LER) in ultraviolet (UV)-A range recorded by Total 17 Ozone Mapping Spectrometer (TOMS) series aboard Nimbus 7 and Earth Probe and by Ozone 18 Monitoring Instrument (OMI) on EOS Aura have been analyzed over eight Chilean locations 19 spanning from about 18° to 62° S (i.e. including Profesor Julio Escudero station, Antarctic 20 peninsula), covering years 1978–2011. Generally the distribution of the reflectivity is similar 21 for both TOMS datasets. A slightly better agreement has been found for the most southern 22 locations while a small discordance appears for northern locations. The latter could be partly 23 due to actual differences in the cloud cover conditions. On the other hand, OMI LER data differ 24 from TOMS ones in almost all locations. Daily cloud modification factor (CMF) values from 25 ground-based global solar irradiance measurements have been compared with OMI LER-based 26 CMF data. The northernmost and southernmost locations characterized by prevalent clear sky 27 and winter snow conditions, respectively, showed the worse agreement with a correlation 28 coefficient r = 0.63 and 0.71, while other stations showed a better correlation (i.e. r = 0.83 29 and r = 85). 30 Clear sky ground UV index values for Santiago de Chile have been estimated for years 1979–2011 by 31 means of an empirical reconstructionmodel based on data recorded by amultichannel radiometer. 32 It allowed computing a ground-based CMF for years 1996–2011 and comparing itwith satellite data. 33 Results show that OMI CMF based on gridded cell LER data introduces significant differences with 34 respect to equivalent TOMS CMF. On the contrary, the use of overpass LER data allows to evaluate 35 changes in cloudiness and, by using the model, reconstructing the actual UV index. Nevertheless, 36 LER CMF overestimates actual cloud cover conditions in winter. The trend in reconstructed satellite 37 (ground) basedUV index during summermonths is+3.3 ± 0.9% (+11.9 ± 2.5%)/decade for years 38 1979–2011 (1997–2011). Further comparisons concerning the Total Cloud Fraction product of 39 Modern-Era Retrospective analysis for Research and Applications (MERRA) suggest that it could be 40 used a further proxy of cloudiness for UV reconstructionmodels; nevertheless additional analysis is 41 necessary.