Some Characteristics of Clear-Air Turbulence in the Middle Stratosphere

Analysis of clear-air turbulence measurements obtained from highly sensitive balloonborne instrumentation is presented. Emphasis is placed on the structure of the turbulent velocity field in the inertial range. Regions of weak turbulence are found to be associated with low Richardson numbers and negative temperature gradients. Measurements of the turbulent energy intensity are presented. The extension of the inertial range is found to be consistent with theoretical values in the case of stably stratified flow. The turbulence intensity varies significantly over a 2-hr time interval. An important result is the observational evidence for a 2/3 law behavior in the structure function at scales where the turbulent velocity field cannot be isotropic: this behavior cannot be explained by a two-dimensional turbulence field.