How important is the entrainment flux for characterizing land-atmosphere feedback in the convective boundary layer?

A high quality of the representation of land-atmosphere (L-A) feedbacks is fundamental for advancing the performance of weather forecasts, seasonal simulations, and climate projections. These feedbacks are due to a highly complex interaction of variables related to the exchange and conservation of momentum, energy, and mass. The Land-Atmosphere Feedback Initiative (LAFI, see https://www.lafi-dfg.de) is the Collaborative Research Unit 5639 funded by the German Research Foundation (DFG). The overarching goal of LAFI is to understand and quantify L-A feedbacks via unique synergistic observations and model simulations from the micro-gamma (» 2 m) to the meso-gamma (» 2 km) scales from diurnal to seasonal time scales.The fundament to reach this goal is provided by the observation of L-A system processes and feedbacks at the Land-Atmosphere Feedback Observatory (LAFO) of the University of Hohenheim in Stuttgart, Germany. Here, a worldwide-unparalleled synergy of measurements is realized including water stable isotopes, temperature by fiber-optic distributed sensors, and a suite of atmospheric variables with turbulence resolution using scanning lidar systems.A key research objective of LAFI is to quantify entrainment in the convective boundary layer (CBL), to separate and quantify related processes such as engulfment, and to derive similarity relationships for parameterizing entrainment fluxes. We will present first measurements of entrainment fluxes at LAFO with lidar synergy, which are typically on the order of 100-200 W/m2 around noon with respect to the latent heat. These new measurements allow for quantifying the flux divergences in the CBL that are an essential part of the heat and water-vapor budget equations. Furthermore, we will relate the entrainment flux to surface variables for characterizing feedback metrics such as the relative humidity tendency and the mixing diagram. Finally, we will present an outlook of future work and its collaboration and coordination with the Global Land-Atmosphere System Studies (GLASS) Panel of the Global Energy and Water Exchanges (GEWEX) project.