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John E. Frederick, Anne E. Koob, Amy D. Alberts, and Elizabeth C. Weatherhead


This work examines the effects of absorption and scattering in the troposphere on solar ultraviolet radiation reaching the ground. A site was established in the city of Chicago for monitoring broadband ultraviolet irradiance, total sunlight, and the ground-level mixing ratios of ozone and nitrogen dioxide. The radiation sensors were a Robertson-Berger meter and an Eppley pyranometer. Interpretation of the measurements leads to the following conclusions. During the time period studied, the attenuation provided by clouds and haze underwent an annual cycle. The monthly mean ultraviolet irradiance measured by the Robertson-Berger meter ranged from 84.0% of the clear-sky value for June 1991 to 49.1% for January 1992. Average ultraviolet irradiances for June and July of 1992 were 10.6% and 21.7% lower than in corresponding months of 1991, owing to differences in local cloudiness. The attenuation of total sunlight provided by local clouds and haze was the same as their attenuation of ultraviolet radiation. Finally, a statistically significant negative correlation existed between the output of the Robertson-Berger meter and ground-level ozone when the atmosphere was relatively free of clouds and haze. This demonstrates that gaseous air pollution had a detectable effect on ultraviolet radiation reaching the ground.

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Elizabeth C. Weatherhead, Greg E. Bodeker, Alessandro Fassò, Kai-Lan Chang, Jeffrey K. Lazo, C. T. M. Clack, Dale F. Hurst, Birgit Hassler, Jason M. English, and Soner Yorgun


Observing systems consisting of a finite number of in situ monitoring stations can provide high-quality measurements with the ability to quality assure both the instruments and the data but offer limited information over larger geographic areas. This paper quantifies the spatial coverage represented by a finite set of monitoring stations by using global data—data that are possibly of lower resolution and quality. For illustration purposes, merged satellite temperature data from Microwave Sounding Units are used to estimate the representativeness of the Global Climate Observing System Reference Upper-Air Network (GRUAN). While many metrics exist for evaluating the representativeness of a site, the ability to have highly accurate monthly averaged data is essential for both trend detection and climatology evaluation. The calculated correlations of the monthly averaged upper-troposphere satellite-derived temperatures over the GRUAN stations with all other pixels around the globe show that the current 9 certified GRUAN stations have moderate correlations (r ≥ 0.7) for approximately 10% of the earth, but an expanded network incorporating another 15 stations would result in moderate correlations for just over 60% of the earth. This analysis indicates that the value of additional stations can be quantified by using historical, satellite, or model data and can be used to reveal critical gaps in current monitoring capabilities. Evaluating the value of potential additional stations and prioritizing their initiation can optimize networks. The expansion of networks can be evaluated in a manner that allows for optimal benefit on the basis of optimization theory and economic analyses.

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CARDS Workshop on Adjusting Radiosonde Temperature Data for Climate Monitoring

Melissa Free, Imke Durre, Enric Aguilar, Dian Seidel, Thomas C. Peterson, Robert E. Eskridge, James K. Luers, David Parker, Margaret Gordon, John Lanzante, Stephen Klein, John Christy, Steven Schroeder, Brian Soden, Larry M. McMillin, and Elizabeth Weatherhead

Homogeneous upper-air temperature time series are necessary for climate change detection and attribution. About 20 participants met at the National Climatic Data Center in Asheville, North Carolina on 11–12 October 2000 to discuss methods of adjusting radiosonde data for inhomogeneities arising from instrument and other changes. Representatives of several research groups described their methods for identifying change points and adjusting temperature time series and compared the results of applying these methods to data from 12 radiosonde stations. The limited agreement among these results and the potential impact of these adjustments on upper-air trends estimates indicate a need for further work in this area and for greater attention to homogeneity issues in planning future changes in radiosonde observations.

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