Evidence for increasing ultraviolet irradiance at Point Barrow, Alaska

This paper presents analysis of noontime ultraviolet irradiance measurements made at Point Barrow, Alaska (71.2 degrees N, 159 degrees W) between the years 1991 and 1996. Eighteen wavelengths of the solar irradiance spectrum between 290 nm and 340 nm were examined for multiyear trends. This spectral region is particularly critical as these wavelengths are known to cause biological damage. After reducing the effects of clouds, 305 nanometer wavelength increases ranging between 3 and 10% per year were found in all daylit months except June which exhibited an annual average decline of approximately -3% per year at this wavelength. The correlation between the absorption cross-section of ozone and the spectral character of the UV-B changes suggest that declines in column ozone are responsible for the dramatic 305 nm increases. The unexpected decline in June 305 nm irradiance may be due to an increase in column ozone over this location in June.