Abstract. We characterize the temperature dependence of the U.S. Environmental Protection Agency/University of Georgia network of Brewer spectrophotometers as used to measure solar ultraviolet (UV) radiation. The instruments used in this study are operated in partnership with the National Park Service at 14 national park sites and in 7 urban areas. The daily and seasonal measurements of UV radiation provided by the instruments can be affected by changes in the internal instrument temperatures at the sites. These effects can lead to errors on the order of _+ 10% in the resulting spectral data and of the same order of magnitude for CIE-weighted UV. Fortunately, the temperature dependence for each instrument can be quantified and the data corrected, improving the accuracy to values closer to the levels attainable with high-quality calibration and operation. The temperature dependence of the Brewers is found to vary significantly among the different instruments. A 0.8% per degree Celsius dependence can result in temperature effects as large as 12% at sites where temperatures can vary by 15øC in 1 day. These effects can result in a _+5% error in the spectral irradiance. The errors to the spectral irradiance vary seasonally in a manner that is not random: in the warmer summertime the temperature dependence of the instruments can cause the irradiances to be underestimated, while during the colder winters the effect will be to overestimate UV amounts. In the part of the spectrum above 325 nm, the temperature dependence is generally independent of wavelength. Below 325 nm the temperature effects vary as a function of wavelength over a range of values and are generally largest at the shortest wavelengths. Because changes in temperature from one calibration to the next can affect an instrument's response, understanding the temperature effects is necessary to ensure that artificial trends are not introduced into the Brewer data records.
A comparison of Umkehr ozone profile data with the reprocessed solar backscatter ultraviolet (SBUV) ozone profile data in the northern middle-latitude region, 30 ø to 50øN, is reported. Although significant biases exist between the two types of observations, the long-term variations and least squares linear regression trends agree remarkably well over the comparison period of 1979 to 1990. The ozone trend in the upper stratosphere is of the order of -0.9% yr -1 . Near 25 km, little if any trend appears, but a larger negative trend is seen in the lower stratosphere near 15 km. Comparisons show that the average annual ozone cycles in the profiles also agree well. The upper stratospheric ozone results are consistent with photochemical model predictions of ozone depletion near 40 km that are due to the release of anthropogenically produced chlorofluorocarbons. The lower stratospheric ozone trend results are in reasonable agreement with published ozonesonde data trends. It is shown that the ozone trends in the lower stratospheric layers impact significantly on the total ozone trend of the order of • -0.47% yr-. The good agreement now seen between the two types of observations suggests that the combined ground-based and satellite approach could provide a valuable database for long-term monitoring of stratospheric ozone for trends and extraordinary variations. Paper number 94JD01518. 0148-0227/94/94JD0-1518505.00 in both. The cause was attributed to a degradation of the diffuser plate that is used to obtain a solar reference observation [Fleig et al., 1981]. The Dobson network has been active up to the present; however, some stations were voluntarily terminated and others were added as time passed. Also, not all stations made U mkehr observations. The network underwent a rapid increase in size about the beginning of 1962 after the World Meteorological Organization (WMO) urged members countries to start ozoneobserving programs. A few stations, including Arosa, Switzerland, and Oxford, England, were operating before the IGY. International data collection and publication by the WMO started with the IGY. Fortunately, a long-term record of total ozone and Umkehr ozone profile data has now been accumulated because of the persistent efforts of the WMO 18,901 18,902 DELUISI ET AL.: OZONE PROFILE FEATURES AND TRENDS, ß [ ß , ß ! ß , ß • ß [ ß , ß T ß [ ß T ß ,
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