THE CLOUD EFFECTS ON UV IRRADIANCE MODELED IN ANTARCTICA Rafanelli C. 1, A. Anav 1, L. Ciattaglia 1, I. Di Menno 1, M. Di Menno 1 R. Iturraspe 2, J. Araujo 3, H. Ochoa 3, H. Rodriguez 3 1CNR – Institute of Atmospheric Science and Climate – Rome, Italy, [email protected] 2 CONICET – Centro Austral de Investigaciones Cientificas, Ushuaia, Argentina, [email protected] 3Direcion Nacional del Antartico – Buenos Aires, Argentina, [email protected] Palabras clave: Antártida, UV solar, modelos UV. Keywords: Antarctica, solar UV, UV models. The measurement of solar UV radiation in Antarctica is very important in order to obtain information about Ozone level, and many spectroradiometers are installed in the area to perform this task. Usually, their use is very difficult in harsh environment like Southern polar regions, and several multichannel radiometers have been installed. The evaluation of the irradiance and total ozone levels are done using analytical models. A new semi-analytical method to estimate the solar UV irradiance at ground, named WL4UV, was developed. Using spectral irradiance values at 4 selected wavelengths in the UV-B & UV-A regions (305, 320, 340 & 380 nm), the solar UV irradiance at ground is evaluated with low percent of error. The applicability of the method has been tested for clear sky but such conditions are not common in Antarctic. This work investigate the applicability of the WL4UV model under cloudy sky conditions. The 4 irradiances necessary for the model were selected from spectrophotometer Brewer measurements carried out in the argentinean Belgrano II base (77° 52' S and 34° 38' W). Other tests using spectrophotometers, Brewer and SUV 100, located in Ushuaia, (54° 50’ S and 68° 19’ W), were also too. This proyect was funded by the PNRA, IIA-DNA and CADIC for funding and supporting the activities. They thank also all the Brewer operators that in these years spent their time in the management of the intrsument. Last but not the least they thank all IIA-DNA personnel for the professional help they put in carrying out the activities in all these years..