Abstract
Two extensive sets of spectral pyrheliometric data taken at Jerusalem in the years 1930–34 and 1961–68 have been analyzed.
Seasonal and synoptic variations in the optical depth of the atmospheric aerosol and in its wavelength dependence in the visible part of the spectrum are given and compared with those at other locations.
A secular increase in the turbidity of about 10% per decade, since 1930, could be isolated in this study. Similar increases at various other stations throughout the world seem to indicate a global buildup of turbidity, at least in the Northern Hemisphere.
