National Severe Storms Laboratory

New Concepts for Studying Land-Surface-Atmosphere (LSA) Feedback

Prof. Dr. Volker Wulfmeyer

Director of the Institute of Physics and Meteorology
University of Hohenheim
Stuttgart, Germany

13 June 2013, 11:00 AM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

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 currect 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 (LSM) in the simulation of EBC are 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, surface fluxes must be measured in 2D, particularly in complex and heterogeneous terrain. This is hardly possible with surface in-situ flux measurements, as these are suffering from poor spatial sampling and gaps in the EBC. A new approach is presented using scanning temperature and water-vapor 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. We present new similarity relationships derived by Sorbjan, which have the potential to become part of future ABL parameterization schemes. These relationships permit measurements of entrainment fluxes with a simplified combination of remote sensing systems. First tests of these relationships using lidar systems are presented. Finally, a field campaign employing an optimal sensor synergy for LSA feedback studies is proposed.

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