Simple formulation of turbulent mixing in the stable free atmosphere and noctural boundary layer

Abstract

Turbulent mixing lengths and the eddy Prandtl number are estimated by analyzing aircraft data from three different field programs and existing studies in the literature. For small scale turbulence, the estimated mixing lengths appear to decrease rapidly with increasing Richardson number (Ri) and then reach an aproximately constant value of 2.5m for Ri>0.3 with large scatter. A least squares fit of the estimated mixing length for heat using the format of Louis et al. (1981) yields an asymptotic mixing length of 14.2m for neutral stratification. Mixing length values estimated from stronger larger scale disturbances also show a decrease of mixing length with increasing Richardson number although the values of mixing lengths are categorically larger yielding an asymptotic value of 150m. -from Authors