ALADIN/HR: TESTING THE NEW SEMI-LAGRANGIAN HORIZONTAL DIFFUSION SCHEME

Main role of the horizontal diffusion schemes in numerical models nowadays is to remove the information without forecast value and the energy accumulated due to finite truncation of a model spectrum acting as a numerical filter. However, during intensive cyclogenesis, especially over steep surfaces, the physical horizontal diffusion should not be neglected. A stable and efficient non-linear horizontal diffusion, based on the control of the degree of interpolation needed for the Semi-Lagrangian advection scheme, has been implemented in ALADIN. The results of several numerical experiments show better simulation of a mesoscale Adriatic cyclones, upper troposphere cyclones and beneficial impact on forecast of low cloudiness in anticyclones