Cloud-Cover Distributions and Correlations

Abstract

Observations of cloud cover (in oktas or tenths) by ground-based observers have been studied to investigate the distribution of cloud-cover amounts and the correlation of cloud cover in time and space. The correlation between observations at the same station, at different times, was found to vary as an exponential of the time separation. Similarly, the correlation between observations at different stations at the same time was found to vary as an exponential of the distance between the stations. Characteristic scales of cloud variation in space and time were derived from these exponentials and the shape of the distribution (in oktas or tenths) of cloud cover was described by a shape parameter. It was found that the data show only weak correlations between these three derived parameters, although it may be expected from physical arguments that the parameters are related.