Localized climatic responses during the 11 July 1991 eclipse: Phoenix AZ

Measurements taken from a variety of land use environments in and around the Phoenix AZ metropolitan area were compared to determine the effects of various land use characteristics on the thermal response to a reduction of 68% in solar radiation during the solar eclipse of 11 July 1991. The results include: (a) The magnitude of the change in ambient air temperature during the eclipse is related to land use. Heavily asphalted military sites and irrigated golf courses recorded small decreases in temperature while natural desert terrain experienced the largest decreases. Variations in thermal response are more closely related to the albedo of the specific land type than to other factors such as thermal admittance but this high correlation is probably an artifact of the combination of other variables such as moisture. (b) Due to the complex mix of land uses and timing of eclipse, marked wind speed changes associated with the eclipse do not appear to be linked directly to land use changes, and, (c) Temperature minima at residential/commercial stations occurred in general, before the minima at stations in agricultural/golf terrains. Because typical albedo differences are not significant between these two land uses, land use characteristics other than albedo are most likely controlling the timing of the temperature minima. Opportunities to empirically examine concepts previously testable only through numerical modeling such as solar reduction experiments should continue to be exploited.