Effects of stratocumulus, cumulus, and cirrus clouds on the UV-B diffuse to global ratio: Experimental and modeling results

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

JOURNAL OF QUANTITATIVE SPECTROSCOPY AND RADIATIVE TRANSFER

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2012 vol. 113 p. 461 - 469

0022-4073

Broadband measurements of global and diffuse UV-B irradiance (280?315 nm) togetherwith modeled and measured diffuse to global ratios (DGR) have been used tocharacterize the influence of different types of clouds on irradiance at the surface.Measurements were carried out during 2000?2001 in Co´ rdoba City, Argentina. TheTropospheric Ultraviolet Visible (TUV) model was used to analyze the behavior of themodeled DGRs for different cloud optical depths and at different altitudes and solarzenith angles (SZA). Different cloud altitudes were also tested, although only theresults for a cloud placed at 1.5?2.5 km of altitude are shown. A total of 16 day withstratocumulus, 12 with cumulus, and 16 with cirrus have been studied and comparedamong them and also against 21 clear sky days. Different behaviors were clearlydetected and also differentiated through the analysis of the averages and the standarddeviations of the DGRs: 1.0270.06 for stratocumulus, 0.7470.18 for cumulus,0.6370.12 for cirrus, and 0.6070.13 for the clear sky days, respectively. Stratocumulusclouds showed a low variability in the DGR values, which were concentrated close toone at all SZAs. DGR values for cumulus clouds presented a large variability at all SZAs,mostly associated with the different optical depths. Finally, the closeness between theDGR values for cirrus clouds and the DGR values for clear days showed that these cloudsgenerally do not strongly affect the UV-B irradiance at the surface at any SZA. In theopposite side, stratocumulus clouds were identified as those with the largest effects, atall SZAs, on the UV-B irradiance at the surface.