Temperature Gradients and Clear-Air Turbulence Probabilities

Abstract

From the end of October 1973 to the beginning of January 1974, Continental Airlines operated one of its Boeing 747 aircraft with special instrumentation for the study of clear-air turbulence (CAT). The observations were compared with satellite-derived radiance gradients, conventional temperature gradients from analyzed maps, and temperature gradients obtained from a Rosemount total air temperature sensor on the plane. The results led to the following conclusions: 1) In regions of weak gradients of temperature or of CO2 band radiance, the probability of CAT is extremely small. 2) CAT probabilities are significantly higher over mountains than flat terrain. 3) Even over mountains the probability of CAT is greatly increased by large gradients of temperature or radiance. 4) Satellite radiance gradients appear to discriminate between CAT and no CAT better than conventional temperature gradients over flat lands, whereas the reverse is true over mountains?although the differences between the two techniques are not large over mountains. Since most of the flights over flat terrain were flown over the Pacific Ocean, the result, if significant, may suggest that conventional temperature gradients over regions of sparse data are not as accurate as temperature gradients which can be inferred from satellites. 5) Temperature gradients obtainable from aircraft temperature sensors are not correlated with CAT statistics.