Abstract
We compare the trends and inter-annual variability of sunshine duration and synoptic cloud data for three sites in Ireland. Our results suggest that, although observers are usually consistent in their synoptic cloud estimates, they can show a significant personal bias which makes it difficult, if not impossible, to extract meaningful information on long term trends in synoptic cloud cover. A study of the frequency of totally clear skies, however, suggests that this parameter may be less affected by bias and could indicate meaningful trends in total cloud factor. It is concluded that sunshine measurements are likely to provide the most reliable indicators of long term trends in cloudiness.
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