Simulation und Analyse des globalen atmosphärischen Energiespektrums von der Grenzschicht bis zur Mesopause
Final Report Abstract
We have analyzed the horizontal kinetic energy spectrum and its budget on the basis of a mechanistic general circulation model run at very high spatial resolutions (spectral truncation at total wavenumber 330 and a level spacing of ∼250 m from the lower troposphere to the lower stratosphere). The mechanistic character of the model is due to simplistic parameterizations of radiative and latent heating. On the other hand we employ advanced parameterizations for the subgrid-scale turbulent diffusion which have mainly been developed during the the course of the project. In particular, we use a new Smagorinsky-type horizontal diffusion scheme which is scaled by a Richardson criterion for dynamic instability and combined with a stress-tensor based hyperdiffusion that acts only on the very smallest resolved scales. The overall momentum diffusion includes the frictional heating according to the energy conservation law. This model enabled us to the simulate the transition from the synoptic -3 to the mesoscale -5/3 slope of the upper tropospheric kinetic energy spectrum. For the first time we found strong indications from a GCM that the -5/3 range should be explained as stratified macro-turbulence, as has been proposed in recent works of E. Lindborg and others. In particular, our model shows a forward horizontal energy cascade in the mesoscales around 300-200 hPa that is 1) due to the non-rotational flow and 2) strongly maintained by adiabatic conversion at the mesoscales themselves. The latter effect is analogous to the well-known energy deposition by gravity waves in the middle atmosphere. Within the troposphere, the source of the corresponding vertical pressure flux is located in the mid troposphere, where the enstrophy cascade maintained by baroclinic Rossby waves is strongest. The vertical energy exchange within the troposphere is therefore presumably due to nonlinear inertia gravity waves. A second region of stratified turbulence was identified in the lower troposphere around 850 hPa where mesoscale energy from the mid troposphere is deposited too. The model was extended up to the lower thermosphere. Even though we had to apply a coarser resolution (truncation at wavenumbers 120 or 210, level spacing ∼600 m up to about 105 km), the wave driving of the summer-to-winter-pole residual circulation in the upper mesosphere could be simulated explicitly and in a physically self-consistent fashion for the first time with a GCM. Applying our software package for the spectral kinetic energy budget to the mesosphere, the energetics of nonconservative gravity-wave propagation predicted by recent theoretical accounts could be confirmed.
Publications
- 2006. Enhanced gravity-wave activity and interhemispheric coupling during the MaCWAVE/MIDAS northern summer program 2002. Ann. Geophys., 24, 1175-1188
Becker, E., and D. C. Fritts,
- (2007). Nonlinear horizontal diffusion for GCMs. Mon. Wea. Rev., 135, 1439-1454
Becker, E. and U. Burkhardt
- (2009). Sensitivity of the upper mesosphere to the Lorenz energy cycle of the troposphere. J. Atmos. Sci., 66, 647-666
Becker, E.
