A note on some numerical experiments with model mountain barriers

A two-level, β-plane, quasi-geostrophic model in σ-coordinates has been used to study basic interactions between baroclinic instability waves and standing waves created by planetary scale topographic barriers. Numerical experiments over periods of 100 days were carried out, firstly with a flat topography and secondly with meridionally oriented mountain barriers of heights up to 2300 m. Two interesting results emerged: one was concerned with the computational aspect of modelling, the other with basic large scale dynamics.

The use of a centred differencing formulation of time dependent terms led to no computational difficulties in the case of flat topography, but with even a small barrier computational instability very quickly sets in. An Adams-Bashforth formulation entirely removes this instability.

The insertion of mountain barriers reproduced cyclogenesis in the lee of the barriers with similar primary dynamical characteristics to those found in complex model studies (e.g. Manabe & Terpstra, 1974).