Analyses of atmospheric extinction data obtained by astronomers. II - Seasonal variations in astronomical extinction

Archival astronomical atmospheric extinction records obtained from fifteen observatory sites were analyzed by not strictly rigorous statistical averaging procedures in order to obtain sufficiently reliable pictures of the trends and variations in atmospheric transparency for the period 1956-1972. While the northern hemisphere sites reveal definite seasonal variations with maxima occurring during local summer, the southern hemisphere displays little such effect. The only southern hemisphere sites with any variation were in South Africa, where a late winter maximum was observed.