Annual and Interannual Behavior of Solar Ultraviolet Irradiance Revealed by Broadband Measurements¶

Abstract

This research examines the behavior of ground-level solar UV radiation as measured by eight broadband meters in the continental United States during the period from late 1994 to late 1998. The goal is to define the variability that occurs in UV irradiance over time scales ranging from one to several years. The monthly integrated irradiances, from latitude 32؇N to 47؇N, contain large annual cycles and latitudinal gradients which depend on season. Seven of the eight sites show a maximum in July, a behavior related to proximity to the summer solstice, with modifications associated with the annual cycle in column ozone. A large interannual variability in monthly integrated irradiance appears over the 4 year period studied. A comparison of corresponding months during different years shows differences in irradiance of 20% or more in one-third of the cases analyzed. When the solar zenith angle (SZA) is held fixed in the range 60-65؇, a substantial annual cycle in UV irradiance remains where the maximum monthly mean irradiance is 1.4-1.9 times the minimum, depending on location. Furthermore, the annual cycle at fixed SZA is not in phase with the normal seasonal cycle. Maximum irradiances at fixed SZA tend to occur in the October to December period, while minima cluster in April through July. The annual cycle in ozone, with maximum column values in spring and minima in autumn, explains the general character of the fixed-SZA data, although changes in cloudiness are significant contributors to interannual variability.

Evolution of erythemal and total shortwave solar radiation in Valladolid, Spain: Effects of atmospheric factors

“…Maximum monthly average irradiance appears in months ranging from September to November, when ozone values are the lowest. The ratio of maximum SZA-fixed irradiance to minimum in the year is in the range 1.3-1.5, similar to results reported by Frederick et al (2000). Fig.…”

“…In order to observe other atmospheric influences and quantify the ozone effect, measured and calculated values at a fixed SZA were performed (Frederick et al, 2000;Palancar and Toselli, 2003). In this study, SZA was fixed at 651 as this angle is near to the minimum SZA common to all days throughout the year.…”

“…Palancar and Toselli (2003) showed the annual and interannual evolution of UV-B radiation at Có rdoba, Argentina. Other works in this field have been conducted by Casale et al (2000), Frederick et al (2000) and Zerefos (2002).…”

UV‐B climatology in Central Spain

“…The aim of this paper is to analyse UV-B solar irradiance measured in the wavelength interval 280-315 nm, in order to know its characteristics. The paper also examines the magnitude and nature of the inter-annual variability using the irradiation spread and percentage range variables (Frederick et al, 2000), which are related to the optical properties of the atmosphere. UV-B may be absorbed and diffused in its passage through the atmosphere.…”

Antineutrophil cytoplasmic antibody–associated vasculitides: Could geographic patterns be explained by ambient ultraviolet radiation?

“…We estimated both the ambient UV radiation level weighted to erythemally effective wavelengths (UV ery ) (40) and to vitamin D effective wavelengths (UV vitD ) (41) under both clear sky and cloud-inclusive conditions. We used winter UV radiation levels in addition to mean daily ambient UV radiation levels (across the time period of the study) because there is a stronger latitudinal gradient in winter UV radiation compared with summer UV radiation (42). Additionally, it is the lower vitamin D effective UV radiation during the winter that limits vitamin D production from skin irradiation at high latitudes (25).…”