AbstractThe dominant features of large‐scale atmospheric motion emerge from a relatively simple treatment of the hydrodynamic equations, thus providing clear, intuitive understanding of the relation between cause and effect in the general circulation. The analysis is made possible by applying the perturbation equations to a sloping stream surface located in the middle troposphere. For reasonable values of the arbitrary parameters, the results show that baroclinic disturbances are unstable poleward of a critical latitude, roughly 35°, and that the preferred number of such unstable disturbances at any one time decreases from about 10 at 45°, to 2 at 80°. Greatest intensity occurs at about 60°. Jet streams must form close to the critical latitude and, in the case of long disturbances, at higher latitudes. Anticyclonic shear has a stabilizing influence, so that the normal velocity distribution in middle latitudes offers considerable resistance to penetration of disturbances to low latitudes. Below the critical latitude unstable disturbances are possible only in relatively small areas where the hydrostatic stability is nearly zero. Growth of these disturbances is favoured by anticyclonic shear, as well as by baroclinicity and by high latitude. Disturbances of maximum rate of growth are practically non‐dispersive so that their growth depends mostly on available potential energy. If sufficient energy is available, the identity of individual disturbances can be maintained over extended time periods. Wave speed relative to the zonal current exhibits a maximum positive value at a high l