Bonn 2010 – scientific programme

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EP: Fachverband Extraterrestrische Physik

EP 2: Near Earth Space II

EP 2.4: Talk

Monday, March 15, 2010, 17:30–17:45, AKM

A Simplified Radiative Transfer Scheme for Use in Mechanistic GCMs — •Rahel Knöpfel and Erich Becker — Leibniz-Institute of Atmospheric Physics, Kühlungsborn, Germany

In the mesosphere and lower thermosphere, radiative damping is an important damping mechanism for gravity waves. The full nonlinearity of this process can only be investigated in high-resolution simulations. This task cannot be achieved with comprehensive general circulation models (GCMs). In the present study, a new radiation scheme which extends continuously from the surface up to the thermosphere is proposed. In the long-wave regime, frequency-averaged Eddington-type transfer equations are derived for six broad absorber bands. The frequency variation inside each band is parameterized by application of the Elsasser band model, yielding additional transfer equations for the perturbation amplitudes. Deviations from local thermodynamic equilibrium are included in terms of isotropic scattering using the two-level model for each band. The absorption of solar radiation is computed for four energetically defined bands from the Beer-Bougert-Lambert relation. Test simulations with a mechanistic GCM run at conventional resolution show quite reasonable results. Since we take the full surface heat budget into account by means of a swamp ocean, and since the internal dynamics and turbulent diffusion of the model is formulated in accordance with the conservation laws, the climatological radiation budget is globally equilibrated. In the future, this model will be applied in gravity-wave resolving simulations.