Turbulence in the Evolving Stable Boundary Layer

Abstract

The turbulence structure observed in seven early evening runs of the 1973 Minnesota experiments is presented and discussed. Wind and temperature sensors mounted on a 32 m tower and on the tethering cable of a large balloon spanned the entire depth of the rapidly evolving nocturnal boundary layer. Spectral shapes and the vertical profiles of turbulence variances and covariances, dissipation rates for turbulent kinetic energy and temperature variance, and energy-containing range length scales show remarkable order when plotted in dimensionless coordinates, even though properties varied widely among the runs. Observed dissipation rates and boundary layer depth agree well with predictions of the Brost-Wyngaard (1978) model. It is shown that the slight (0.0014) terrain slope and possibly baroclinity affected the boundary-layer evolution, and that although the turbulence structure was probably in equilibrium with the wind and temperature fields, these were strongly evolving during the runs.