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Multiple Comparisons at one Local

As stated earlier there are several locals in the U.S. which have more than one network taking observations. This allows for intercomparisons between the observations and can also be used to exhibit the validity of the UV Index forecast as a unbiased comparison standard.

In Figure 6, the observations from the EPA Brewer at the National Institute for Standards and Technology (NIST) in the northern suburbs of Washington D.C. show a large difference from the UV Index forecasts. These large differences could raise concern for the validity of the UV Index forecast.
However, in the eastern suburbs, in Beltsville, MD is a USDA site.

Figure 7 shows much better agreement. Knowing that similar agreement at the other USDA sites implie that the UV Index forecasts are reliable. As a result, the data from the EPA Brewer is then questionalbe. This same situation occurred at the Table Moutain site outside of Boulder, CO. This time data from a Brewer exhibited a very low bias against the UV Index forecasts. A co-located SURFRAD instrument had a much lower bias. This suggests that this Brewer's data is questionable. This does not mean that data from all the other Brewers is questionable. Other sites compared very well with UV Index forecasts.

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