SIMPLE TESTS OF A SEMIIMPLICIT SEMI-LAGRANGIAN MODEL ON 2D MOUNTAIN WAVE PROBLEMS

The fully compressible 3D nonhydrostatic semi-implicit semi-Lagrangian MC2 (mesoscale compressible community) model described by Tanguay et al. has been modified in order to incorporate orography through the Ga l-Chen and Somerville transformation of the vertical coordinate by Den is. In this study, a 2D version of the model is tested against classic al solutions covering various mountain-wave regimes for continuously s tratified flows. A close inspection of the propagation of the vertical momentum flux is performed to assess the accuracy and stability of th e numerical method. The study emphasizes also the fact that a correct representation of forced hydrostatic gravity waves is reliable for Cou rant numbers less than 0.5. This limitation may be less severe as the flow becomes more nonhydrostatic. Furthermore, the sensitivity of the isothermal reference state for Rows with realistic static stability an d over steep slope mountain is explored,