The development of turbo-jet aircraft has made high-level clear air turbulence a major problem for aviation interests. This paper emphasizes the association of the majority of this turbulence with the pronounced vertical wind shear in and near the maximum wind speed centers that move along the jet stream.

A physical model is proposed as a possible explanation of clear air turbulence, the associated cirrus bands and wind streaks in the jet maxima. This model is supported by an analogy drawn with similar low-level phenomena studied by Woodcock and others. The model can explain distribution of these features in the horizontal by means of helical vortices which are dependent upon proper vertical wind shear and stability conditions. The observed multiple layers in the vertical are also explained by this model.

It is believed that the reason why most of the clear-air turbulence is found near the jet-stream maxima is simply because the necessary shear and stability conditions associated with this turbulence are most frequently fulfilled in that region.

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* Presented at the American Meteorological Society Meetings held in New York, January 1954. Author's present address: Hqs, Air Weather Service (Attn: Scientific Services), Washington 25, D. C.