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SUMMARYA 10-level primitive equation model suitable for studying the dynamics of fronts and frontal rainfall is described. The atmosphere is assumed to be hydrostatic and inviscid and the effects of friction and topography are ignored. Latent heat due to evaporation and condensation is incorporated in the thermodynamic equation.No distinction is made between the ice and water stage and the atmosphere is assumed to be dry above 300 mb.The horizontal grid length is 40 km. The results of one 24-hr integration are described in detail.

SUMMARYTwo series of 12-hr and Z+hr forecast 500 mb. 1,000 mb and 1,000-500 mb thickness charts have been computed electronically using the Sawyer-Bushby (1053) two-parameter baroclinic model of the atmosphere. The results are compared with the actual charts, and a good degree of correspondence is found between the actual and computed charts.

Subject to various approximations, a system of five simultaneous equations (three partial differential equations and two algebraic equations) is derived to predict the height of three contour surfaces corresponding to the bottom, middle and top of the troposphere and to evaluate the two fields of vertical motion corresponding to the upper and lower halves of the troposphere. The atmospheric model used is an extension of the two‐parameter model proposed by Sawyer and Bushby (1953). Numerical integrations have been carried out for 20 cases and the results are given in statistical form. Two forecasts are illustrated with diagrams. The accuracy is better than that obtained with the two‐parameter model, and the forecasts are of the same standard as those produced by conventional methods.

SuhfhfARYIn an attempt to obtain a better approximation to the horizontal flow of a non-divergent fluid than the geostrophic approximation, a Monge-Ampere type of partial differential equation, similar to that of Charney (1955), is derived to enable a stream function to be found from the contour height field. A method is given for the numerical aolution of this equation.The stream fmction has been used in place of the contour height parameter to represent the flow at the mean level in computing three 24 hr forecasts based on the Sawyer-Bushby two-parameter model of the atmosphere, and the results are compared with similar computations without the stream function.In one situation, the use of the stream function produced a marked improvement in the Computation.