Application of Barotropic Tendency Equation to Medium-Range Forecasting

The simple barotropic vorticity equation has been used to compute height tendencies on a few 5-day mean 500 mb charts. The results are approximately as good as similar computations made on synoptic flow patterns despite the fact that the time interval between observed charts is 5 times as great. The order of magnitude of the computed tendencies may be considerably improved provided some account is taken of the effects of transformation of potential into kinetic energy, surface friction and non-adiabatic heating. A first approximation to these factors may be obtained by setting them equal to their climatological or normal values.

A simple method for integrating the barotropic equation is derived upon assuming that the anomalies of the large-scale flow patterns may be approximated by a relatively small number of Rankine vortices.