6. Filip VANA : "The dynamical and physical control of kinetic energy spectra in a NWP spectral semi-Lagrangian model"

The work on "semi-Lagrangian horizontal diffusion" (SLHD) restarted, in collaboration with Rok Glavac-Sah (see also the Prague ALATNET report).

Basically from the user's point of view the scheme is ready to be used for current resolutions. The acceptable degree of quasi-independence of SLHD to time-step and horizontal resolution has been confirmed. Thus there are no obstacles to use the scheme within the range of 8-30 km of horizontal mesh-size. On the other side, there are not too many benefits from this scheme on such scales. This can be revisited for mountain regions where it performs better, or once some pure gridpoint prognostic variable will be introduced in the model.

The intention is now to go a bit further, i.e. to test with horizontal mesh-sizes of 2.5 km. Thus the scheme has been implemented as well for NH dynamics and the next step now is to repeat the ALPIA tests with it.

The scheme is not yet available in any ALADIN library, for dynamics is evolving quite rapidly (predictor-corrector approach, new NH variables, etc). Hence phasing will be performed only after the final evaluation of the scheme.

A paper has just been submitted to Ocean-Atmosphere : "Semi-Lagrangian advection scheme with controlled damping - An alternative way to nonlinear horizontal diffusion in a semi-Lagrangian numerical weather prediction model" (by Filip Vana, Pierre Bénard and Jean-François Geleyn), with the following abstract :

<< A nonlinear horizontal diffusion scheme using damping abilities of the semi-Lagrangian advection scheme interpolators is proposed. The behaviour of the scheme is tested in the framework of idealised 3d experiment by a statistical model. Then the scheme is introduced to the spectral LAM model and adapted for the real atmosphere with a typical resolution for current operational regional models. Finally the performance of the proposed scheme is examined by parallel test and for case studies compared with the spectral linear diffusion. >>