A Study of the Relation of Clear Air Turbulence to the Mesoscale Structure of the Jet Stream Region

Abstract

The relationship of clear air turbulence to mesoscale features of the temperature, wind, and ozone concentration fields and to the Richardson number is examined for a case of widespread, persistent CAT observed by a specially instrumented aircraft of the Air Force Cambridge Research Laboratories. The CAT occurred mainly in a sloping layer of about 2 km depth located just above the jet stream core and encompassed a thin inversion layer and a deeper near-adiabatic layer above. The Richardson number was 0.25 or less throughout most of the turbulent region, and the more intense CAT tended to be located near the upper boundary of the inversion, extending into both the inversion layer below and the near-adiabatic layer above.

Isobaric and isentropic trajectories were used to trace the origin of the mesoscale thermal structure. The structure evidently was generated during the period of several hours between the time of the preceding synoptic observations and the time of the research flight. Quantitative arguments are advanced in support of the hypothesis that the observed features were produced by the turbulent heat flux.