Three-Dimensional Buoyancy- and Shear-Induced Local Structure of the Atmospheric Boundary Layer

Abstract
Three-dimensional visualization together with statistical measures are used to describe the instantaneous local structure of the atmospheric boundary layer (ABL) under various stability states using large-eddy simulation (LES) data. To explore the relative roles of buoyancy and shear in ABL structure, a wide range of −zi/L ABL states, from 0.44 to 730, is analyzed. It is known that buoyancy-induced updrafts and downdrafts are primarily responsible for the upward flux of momentum, heat, and passive scalar, and strongly influence near-ground horizontal motions. These buoyancy-induced features of the convective boundary layer (CBL) are presented here in clearly observable 3D visual images of vertical velocity and temperature, showing large turbulent cell-like structure several zi in horizontal extent. The horizontal length scales of the temperature field near the ground are found to be of the order of the horizontal velocity length scales. It is noted by comparing visual structure with spectra that ... Abstract Three-dimensional visualization together with statistical measures are used to describe the instantaneous local structure of the atmospheric boundary layer (ABL) under various stability states using large-eddy simulation (LES) data. To explore the relative roles of buoyancy and shear in ABL structure, a wide range of −zi/L ABL states, from 0.44 to 730, is analyzed. It is known that buoyancy-induced updrafts and downdrafts are primarily responsible for the upward flux of momentum, heat, and passive scalar, and strongly influence near-ground horizontal motions. These buoyancy-induced features of the convective boundary layer (CBL) are presented here in clearly observable 3D visual images of vertical velocity and temperature, showing large turbulent cell-like structure several zi in horizontal extent. The horizontal length scales of the temperature field near the ground are found to be of the order of the horizontal velocity length scales. It is noted by comparing visual structure with spectra that ...