Abstract/Summary

The development of the scientific understanding of clear-air turbulence (CAT) as an aviation hazard is described in this article. Topics range from the discovery of CAT during World War II to modern techniques to observe and predict conditions conducive to CAT formation, as well as the role of climate change in increasing CAT occurrence. Important physical processes leading to Kelvin–Helmholtz instability (KHI), a primary producer of CAT, are explained. The frequency of occurrence of KHI is shown to be a maximum near synoptic-scale upper-level frontal zones near jet streams, with mountain waves, and in the vicinity of the tops of severe thunderstorms. Several current physical and statistical approaches to CAT prediction based on this knowledge are described. The impact of climate change on CAT has become an active area of research recently, with evidence that the amount of CAT in the atmosphere has increased over the past few decades, and with projections of further large increases in future.