Distribution of UV radiation at the Earth's surface from TOMS‐measured UV‐backscattered radiances

Abstract

Abstract. Daily global maps of monthly integrated UV-erythemal irradiance (290-400 nm) at the Earth's surface are estimated using the ozone amount, cloud transmittance, aerosol amounts, and surface reflectivity from the solar UV radiation backscattered from the Earth's atmosphere as measured by the total ozone mapping spectrometer (TOMS) and independently measured values of the extraterrestrial solar irradiance. The daily irradiance values at a given location show that short-term variability (daily to annual) in the amount of UV radiation, 290-400 nm, reaching the Earth's surface is caused by (1) partially reflecting cloud cover, (2) haze and absorbing aerosols (dust and smoke), and (3) ozone. The reductions of UV irradiance estimated from TOMS data can exceed 50 +_ 12% underneath the absorbing aerosol plumes in Africa and South America (desert dust and smoke from biomass burning) and exceeded 70 _ 12% during the Indonesian fires in September 1997 and again during March 1998. Recent biomass burning in Mexico and Guatemala have caused large smoke plumes extending into Canada with UV reductions of 50% in Mexico and 20% in Florida, Louisiana, and Texas. Where available, ground-based Sun photometer data show similar UV irradiance reductions caused by absorbing aerosol plumes of dust and smoke. Even though terrain height is a major factor in increasing the amount of UV exposure compared to sea level, the presence of prolonged clear-sky conditions can lead to UV exposures at sea level rivaling those at cloudier higher altitudes. In the equatorial regions, +_20 ø, the UV exposures during the March equinox are larger than during the September equinox because of increased cloudiness during September. Extended land areas with the largest erythemal exposure are in Australia and South Africa where there is a larger proportion of clear-sky days. The large short-term variations in ozone amount which occur at high latitudes in the range _+65 ø cause changes in UV irradiance comparable to clouds and aerosols for wavelengths between 280 nm and 300 nm that are strongly absorbed by ozone. The absolute accuracy of the TOMS monthly erythemal exposure estimates over a TOMS field of view is within +_6%, except under UV-absorbing aerosol plumes (dust and smoke) where the accuracy is within +_ 12%. The error caused by aerosols can be reduced if the height of the aerosol plume is more accurately known. The TOMS estimated irradiances are compared with ground-based Brewer spectroradiometer data obtained at Toronto, Canada. The Brewer irradiances are systematically 20% smaller than TOMS irradiance estimates during the summer months. An accounting of systematic errors brings the Brewer and TOMS irradiances into approximate agreement within the estimated instrumental uncertainties for both instruments. IntroductionThe global coverage afforded by satellite observations of UV irradiance, or flux density (energy per unit area per unit time), can be used to distinguish regional and global changes in contrast to purely local observations from grou...

Interannual variability of ozone and UV‐B ultraviolet exposure

“…When the effects of cloud cover are included in the zonally averaged annual exposure estimate, based on the TOMS reflectivity measurements [Herman et al, 1996[Herman et al, , 1999Krotkov et al, 1999], the results are substantially the same (Figure 3). There are small percent differences caused by cloud cover variability between successive years that are less than the QBO effect.…”

“…UV-A irradiances (320-400 nm) are not significantly affected by ozone changes because of their small ozone absorption coefficients ax. After the solar zenith angle the second largest cause of daily variability, seasonal variability, and geographic distribution of UV irradiance is from clouds [Herman et al, 1999]. Analysis of the ozoneamount time series Herman et al, 1991] has shown that the major persistent sources of ozone variability are the annual cycle, the 2.3 year quasi-biennial oscillation cycle (QBO) [e.g., Bowman [1989], and the 11.5 year solar cycle [Hood, 1997; Zerefos et al, 1997; Calvo et al, 1995, and references therein].…”

An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet‐B radiation

“…The primary data set used for the current analysis was the DNA-weighted UV-B radiation exposure map obtained by using the Total Ozone Mapping Spectrometer (TOMS). 20,21 TOMS is a spacebased instrument that yields UV data for the entire country with a 1-degree ϫ 1.25-degree grid spacing. The July 1992 TOMS data, posted at the TOMS website, was used.…”

Geographic variation of prostate cancer mortality rates in the United States: Implications for prostate cancer risk related to vitamin D

“…[7][8][9][10] For such cancers, mortality rates are about twice as high in the northeast as in the southwest and strongly inversely correlated with solar UVB radiation. 7,10,11 In addition, 6 types of cancer (breast, colon, endometrial, esophageal, ovarian and non-Hodgkin's lymphoma) are inversely correlated to both solar UVB radiation and rural residence in combination. 11 Urban residence is considered to reduce UVB exposure compared to rural residence in that it does not correlate with any other factor, such as lung cancer.…”

“…7,10,11 In addition, 6 types of cancer (breast, colon, endometrial, esophageal, ovarian and non-Hodgkin's lymphoma) are inversely correlated to both solar UVB radiation and rural residence in combination. 11 Urban residence is considered to reduce UVB exposure compared to rural residence in that it does not correlate with any other factor, such as lung cancer. For prostate cancer, the geographic variation is different.…”