Observational and Theoretical Study of Shear Instability in the Airflow near the Ground

Abstract Results are presented from a combined observational and theoretical study of apparent shear instability in the airflow near the ground in statically stable (inversion) conditions. Meteorological instruments, including an acoustic echo sounder for time-height visualization, a spaced array of microbarographs and a heavily instrumented tower 150 m tall, provided measurements that were analyzed to determine the phase velocity and amplitude of the wavelike fluctuations and the mean profiles of temperature and wind for the shear flow. A linear, inviscid, dynamic stability analysis performed numerically using spline functions fit through the observed profiles shows that the flow is unstable to perturbations with the observed properties, but with growth rates that are small. A wave critical level is shown to be present at 130 m, as the 8 m s−1 wind velocity there equals the phase velocity determined by cross-correlation analysis of the microbarograph records. Spectral analysis of the wind, temperature an...