The observed variation of updrafts with height in the cumulus topped boundary layer

Buoyant plumes and thermals rising through the convective boundary layer (CBL) modulate the flux of heat, moisture, momentum, and aerosols from the surface to aloft. These fluxes also determine the lower boundary conditions for cumulus development (e.g., shallow vs. deep cumuli) provided that thermals and plumes rise to their condensation level. In coarse resolution climate and weather models these plume fluxes can be represented using "eddy-diffusivity mass-flux" (EDMF) parameterizations, wherein the "mass flux" is accomplished by a spectrum of buoyant plumes. In this presentation we provide observational statistics elucidating the properties of these plumes by analyzing >100,000 updrafts recorded with a network of 5 Doppler lidars in Oklahoma, USA on days with clear and cumulus topped boundary layers. Updraft observations are binned by their height with respect to the boundary layer top (Z_i) and composite properties of these updrafts are examined (Fig. 1). Using these binned data, we then examine how the size, shape, and intensity of the updrafts vary as a function of height. The results indicate the expected quasi-linear broadening of updrafts as they ascend and the increasing skewness of the updraft strength with height. Updrafts near the upper edge of the CBL are found to occasionally contain the strongest updrafts. These data also show that wider updrafts possess stronger updrafts. Finally, we probe how updrafts decay with height as they impinge on the capping inversion layer at Z_i, a process important for cloud initiation. These results will provide a basis for comparing plume transport in large eddy simulations (LES) with observed plume transport and may subsequently contribute to refinements in EDMF parameterizations.