Nature and observation of high-level turbulence especially in clear air

Abstract

Abstract : This is a ''state-of-the-art'' report on clear air turbulence (CAT) research. Knowledge of micro-structural details of flow patterns in the free atmosphere is of importance to aircraft and missile designers. It also is of interest in considering passenger comfort. There may be at least three different causes for bumpiness experienced by an aircraft flying horizontally: convective currents, gravity waves on interfaces, and temperature discontinuities intercepted by a supersonic aircraft. For vertical take-off vehicles excessive shears of alternating sign in the vertical wind or momentum profiles should be considered as possible sources of vibration. So far, observations of high-level turbulence have been made by aircraft and by balloon-borne gust sondes. Especially aircraft measurements present a problem inasmuch as the response characteristics of the vehicle usually make it difficult to evaluate the actual atmospheric gust input. With our present theoretical modelling capabilities we may be able to study wave perturbations in the free atmosphere from detailed measurements of wind and temperature profiles. Such measurements will have to be orders of magnitude more accurate however, than the ones provided by the synoptic rawinsonde and radiosonde network.