Investigations of Humidity Skewness and Variance Profiles in the Convective Boundary Layer and Comparison of the Latter with Large Eddy Simulation Results

Abstract

Differential absorption lidar (DIAL) measurements of humidity variance and skewness profiles are presented. A detailed error analysis demonstrates that measurements throughout the convective boundary layer can be performed with an accuracy that is mainly limited by sampling errors due to turbulent statistics. The water vapor variance profiles are compared with results from a large eddy simulation (LES) model to estimate surface and entrainment latent heat fluxes. A promising agreement with surface latent heat fluxes derived by the bulk formula is achieved, but a strong deviation of the variance profiles from the LES results is found in the entrainment zone. Reasons for these discrepancies are discussed. A new approach for the investigation of top?down variance functions using the measured variance profiles is introduced. It is investigated whether the skewness profiles give further information on the turbulent transport of water vapor. This is accomplished by the analysis of the skewness budget equation and a comparison of the skewness profiles with latent heat flux profiles. The results demonstrate that DIAL measurements provide unique datasets for studies of turbulent transport processes in the lower troposphere, finally allowing for comprehensive intercomparisons with models.