Seminar

Abstract

An accurate representation of land-surface-atmosphere (LSA) feedback is essential for the prediction of the state of the Earth system from nowcasting to decades. Particularly challenging is the correct simulation of the energy balance closure (EBC) and of entrainment fluxes at the top of the atmospheric boundary layer. New concepts for studying surface and entrainment fluxes in complex terrain are presented, which are based on a novel combination of scanning, active remote sensing systems and ensemble-based modeling. At the land surface, severe deficiencies of present land-surface models (LSMs) in the simulation of the EBC have been detected. Soil hydraulic coefficients, root water uptake, and the simulation of plant dynamics need to be improved. For agricultural landscapes, this is possible by the development and application of sophisticated crop growth models.

For closing the gap between models and observations, there are two major roles of new measurements:

1. Initialization of Earth system models by means of data assimilation. This is essential for separating model errors with respect to initialization and physics. An example of an ongoing project on aerosol data assimilation using a network of ground-based backscatter lidar systems is presented and discussed.
2. Advance process understanding and model physics in complex terrain: Surface fluxes must be measured in 2D. This is very challenging using in-situ measurements, as these are limited by coverage of their footprints and gaps in the EBC. An approach is presented using scanning temperature, water-vapor, and wind lidar systems for measuring 2D surface sensible and latent heat fluxes and for testing Monin-Obukhov theory. In order to achieve a good performance of a model system with respect to LSA feedback, entrainment fluxes must be correctly simulated, too. However, only in a few boundary layer parameterizations, entrainment fluxes are explicitely estimated, otherwise these are diagnosed. New similarity relationships derived by Sorbjan have the potential to become part of future ABL parameterization schemes. These relationships permit the simulation of entrainment fluxes and their evaluation with a simplified combination of remote sensing systems. First tests of these relationships using lidar systems are presented.