A sequence of numerical experiments was performed modelling general features of the planetary circulation over a limited region. In the first experiment the results obtained from a primitive equation 2 level model are compared with the results of a geostrophic 2 level model. The equations were integrated over a Beta-plane with two lateral walls in the north and in the south. In the second experiment the results of a 3 level geostrophic model are compared with those of a 2 level geostrophic model. In the third experiment the smoothing effects of a lateral viscosity term are investigated and compared with the smoothing effect of the Matsuno approximation, of the time derivative. In the 4th experiment the spread of radon in a model atmosphere is investigated schematically, the source of the radon being located in the lower boundary.