A Laboratory Model of the Unstable Planetary Boundary Layer

Abstract

Experimental details of a laboratory model of the unstable planetary boundary layer are given. Measurements of vertical profiles of mean temperature and heat flux, and of velocity and temperature fluctuations are presented and compared with atmospheric observations. Good agreement exists between the model measurements and the atmospheric observations when the variables are appropriately scaled with the depth of the mixed layer zi, and the convective velocity and temperature scales w* and T*. Turbulence kinetic energy budgets for the mixed layer turbulence are presented. The buoyant energy production decreases nearly linearly with height, while the rate of dissipation of kinetic energy is found to be about constant with height. Horizontal temperature spectra at three heights are presented. The temperature spectrum for a height neat the middle of the mixed layer suggests the existence of an inertial subrange as well as a viscous-convective subrange. The temperature spectrum calculated from horizontal traverses in the stable layer displays an extensive range in wavenumber which follows a ?3 power law.