A comparison of mixing depths observed by ground-based wind profilers and an airborne lidar

The authors compare the mixing depths in the daytime convective boundary layers that were observed remotely by wind profilers and an airborne lidar during the 1995 Southern Oxidants Study. The comparison is used to determine whether the mixing depths deduced from radar reflectivity profiles measured by the wind profilers are the appropriate mixing depths to use in air pollution applications. The profiler mixing depth!: are based on evidence that the profile of the refractive index structure function parameter exhibits a peak at the boundary layer capping inversion. The lidar mixing depths are determined from the gradient in aerosol backscatter at the top of an aerosol mixing layer. The results of linear regression analysis show that the mixing depths measured by the wind profiler and lidar are in good agreement, particularly in the absence of scattered clouds forming at the top of the convective boundary layer. When significant cumulus convection occurs, the definition of mixing depth from both experimental and theoretical points of view is ill defined.