An Investigation on the Climatic Effect of Contrail Cirrus

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Abstract

High cloud cover in the absence of middle and low clouds for Salt Lake City, Utah, during the period 1949–1982 has been analyzed. A significant increase of the mean annual high cloud cover is evident from 1965 to 1982, This increase appears to coincide with the anomalous jet aircraft traffic increase during that period. Analysis of the annual surface temperature for Salt Lake City shows a noticeable increase on the mean annual basis for the period 1965–1982. We have developed a two-dimensional (2-D) cloud-climate model to investigate the perturbation of high cloud cover on the temperature fields. The model consists of a 2-D climate model and a cloud formation model that are interactive through the radiation program. The cloud covers and radiation budgets at the top of the atmosphere computed from the present model compare reasonably well with observations, A 5% uniform increase in high cloud cover at the latitudes between 20° to 70° N would produce an increase in surface temperature by about 1°K with small variations across the latitudes, The positive surface temperature feedback associated with the high cloud cover increase is due to enhanced infrared emission from the additional high cloud cover and specific humidity produced from the 2-D model.