Relationships between daily UV-A, UV-B and hemispherical solar radiation

Previous studies elucidated the relationship between total ultraviolet and total solar radiant exposures at four meteorologically different sites: desert, subtropical, urban smog and high altitude. These studies, which have only been briefly summarized elsewhere, demonstrated that at-latitude daily total ultraviolet plotted against daily at-latitude total solar radiant exposure follows well-defined, site-specific relationships. Namely, data for month-pairs that are symmetrical about the two solstices plot on the same regression line with high correlation coefficients. It was found that the algebraic behavior of the family of regression expressions (DEC, JAN-NOV, FEB-OCT, MAR-SEP, APR-AUG, MAY-JUL, JUN) depend on whether either pollution-related absorption or humidity-related scattering mechanisms predominate one over the other at any given site. More recent studies, which are on-going, have determined the extent to which daily UV-B radiant exposure exhibits the same dependence on latitude, altitude, and local climate atmospheric conditions that was observed for daily UV-A (e.g., total) radiant exposures. It was found that the UV-B histograms for both Arizona and Florida show a much greater degree of scatter than do the UV-A histograms. Solar UV-B radiation is much more sensitive to a combination of atmospheric conditions and ozone than is UV-A, and the differences between the Florida and Arizona UV-B histograms are ascribed to these effects.