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Comparison of Sunshine Records and Synoptic Cloud Observations

Summary: Comparison of Sunshine Records
and Synoptic Cloud Observations:
A case study for Ireland
E. Palle 1;2 & C.J. Butler 1
1 Armagh Observatory, College Hill, BT61 9DG. Armagh, N. Ireland. Fax:+44
02837 527174; e-mail: epb@star.arm.ac.uk, cjb@star.arm.ac.uk
2 Big Bear Solar Observatory, 40386 North Shore Lane, Big Bear City, CA 92314-
9672, U.S.A. Fax:+1 909-866-4240; e-mail: epb@bbso.njit.edu
1 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 signi cant personal
bias which makes it diĘcult, 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 a ected 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.
2 Introduction
Comparisons of synoptic cloud records and sunshine duration have been made in several
areas of the world. Angell (1990) and Angell et al. (1984) compared cloud and sunshine


Source: Armagh Observatory


Collections: Physics