Heidelberg 2015 – scientific programme

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UP: Fachverband Umweltphysik

UP 5: Meßtechmik

UP 5.2: Talk

Thursday, March 26, 2015, 09:15–09:30, G/gHS

Diurnal dynamics of land surface-atmosphere exchange inferred from thermodynamic constraints — •Axel Kleidon and Maik Renner — Max-Planck-Institut für Biogeochemie, Jena, Germany

The convective boundary layer strongly shapes the exchange of energy and mass between the land surface and the atmosphere. Here, we approach this tightly coupled system by deriving the thermodynamic limit by which convective motion can be generated from the diurnal radiative forcing. An important part of the derivation is the inclusion of heat storage changes that are caused by the diurnal imbalance of absorbed solar radiation. Using 6-hourly radiosoundings of the Meteorological Observatory Lindenberg - Richard-Assmann-Observatory (MOL-RAO) of the German Meteorological Service (DWD) in Brandenburg we find that most of diurnal heat storage changes take place in the lower atmosphere. Using surface observations of absorbed solar radiation and the ground heat flux, our approach predicts the diurnal course of turbulent heat fluxes at the surface and heat content changes in the lower atmosphere surprisingly well. What this implies is that the diurnal dynamics of the atmospheric boundary layer are strongly constrained by the diurnal imbalance in the local radiative forcing. The resulting dynamics of the atmospheric boundary layer then reflect the tight interaction between turbulent heat fluxes, atmospheric heat storage changes, and thermodynamic limits to generate turbulent exchange.