Effect of different types of clouds on surface UV-B and total solar irradiance at southern mid-latitudes: CMF determinations at Córdoba, Argentina

MARIA LAURA LÓPEZ; GUSTAVO G. PALANCAR; BEATRIZ M. TOSELLI

ATMOSPHERIC ENVIRONMENT

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2009 vol. 43 p. 3130 - 3136

1352-2310

The effects of clouds on the surface UV and visible radiation have been investigated at Córdoba, Argentina using a period of 10 years data (1998–2008). We have analyzed experimental global measurements obtained with a radiometer YES UVB-1 and a radiometer YES TSP-700, and preliminary measurements obtained with a spectral radiometer Ocean Optics USB-4000. The hourly values of cloudless sky UV-B along with total radiation and consequently the cloud modification factor (CMF) were estimated. An exponential relationship was found for CMF in the UV region as a function of the CMF for the total radiation for cirrus clouds, while linear relationships have been found for stratocumulus and cumulus type of clouds. In all the cases there were very good correlation coefficients. In addition, the attenuation of UV-B radiation could be determined by considering different kind of clouds.  Data reveal several interesting aspects of cloud influences. Enhancements in UV radiation of 20% over clear-sky values are observed for cloudy conditions when the solar disk is unoccluded. We have found spectral differences which might be attributed to the microphysical characteristics of clouds; however, the question of wavelength dependence remains open. Finally we aim to incorporate these properties to estimate the solar actinic flux from irradiance measurements since it is the magnitude necessary to evaluate atmospheric photolysis reactions in real atmospheres using radiative transfer models.