Is solar dimming global or urban? Evidence from measurements in Israel between 1954 and 2007

Daily values of global radiation E-g down arrow measured in a network of six sites within the greater Tel Aviv region indicated a maximum urban dimming effect of 7% with a similar day-to-day range in differences during the week that was significantly negatively related to the number of vehicles using the roads. Interannual variability of E-g down arrow differed between three regions of Israel having very diverse population densities, both in their overall trends and in their rates of change during periods of dimming and brightening. During the 50 years of measurement the overall trends in all regions were negative; the rates of dimming were related to the logarithm of the mean population densities with the greatest net rate of dimming, -3.4% per decade, measured at the downwind edge of the densely populated Tel Aviv conurbation. Rates of change in the dimming and brightening periods were not related to the rates of change in population; maximum rates of both dimming and brightening were measured at the Dead Sea, a desert region with a low and unchanging population. Trends in maximum, minimum, mean, and diurnal range air temperatures were significant and differed between regions, but these differences were not clearly related to those in E-g down arrow or in population density. The results indicate that in Israel the maximum urban effects on E-g down arrow were insufficient to explain the large interannual variability measured during the last 50 years and that population density was not a robust proxy for global radiation change.