Long-term variability in surface UV-B radiation across the United States

摘要

The USDA UV-B Monitoring and Research Program maintains a network of Yankee Environmental Systems surface UVB meter instruments at stations throughout the United States. We analyzed the temporal behavior of UV-B at eight stations that were selected because of their early deployment (years beginning in 1995-1997 and ending in 2003). Though calibration methodologies differed before and after 1998, we accounted for variations among instruments and long-term drift in a consistent manner, and estimated a total calibration uncertainty of 7%. We computed mean annual and mean monthly irradiances for each month of the year for each station, and investigated temporal patterns. At Nunn, Colorado, mean annual UV-B irradiance increased by 3.4%, less than the calibration uncertainty. However, UV-B trends in five months exceeded the calibration uncertainty, with the maximum increase occurring in April (28%). Mean annual irradiances increased at all but one of the other seven sites, though only two exceeded the 7% uncertainty.