Midterm Colloquium by Danny Høgsholt – Niels Bohr Institutet - Københavns Universitet

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Midterm Colloquium by Danny Høgsholt

Accurate simulation of convection is one of the main issues in numerical weather prediction and serves as a standard test when evaluating numerical schemes. The modeling of convection has proven difficult in especially non-hydrostatic high resolution models where convective parametrization has been omitted.

As an attempt to introduce an even more accurate method for the simulation of convective thermals a new non-hydrostatic hybrid Eulerian-Lagrangian (HEL) scheme is tested. Contrary to the Eulerian and semi-Lagrangian schemes the HEL scheme combines Eulerian cells with Lagrangian parcels carried by the flow. With this method the benefits of having stationary grid points are maintained while exploiting the advantages of Lagrangian schemes. Fully Lagrangian schemes produce by definition no artificial numerical mixing which is very desirable in numerical models. Thus, the numerical mixing in the HEL scheme is limited to the mixing produced by transferring information from Lagrangian parcels to Eulerian cells; at each time step the Eulerian cell properties are corrected by the Lagrangian parcels.

During this mid-term colloquium the advantages of each type of scheme will be outlined and the idea of the HEL scheme is introduced. The challenges of implementing hydrostatic features in the model will be discussed and the presentation ends with a simulation of a convective thermal using a non-hydrostatic semi-Lagrangian scheme, which in the thesis eventually will serve as a reference model run to the not yet implemented HEL scheme.