THE OBSERVED MEAN FIELD OF MOTION OF THE ATMOSPHERE.

Abstract

What is observationally known about the atmosphere's mean horizontal motion has here been brought together in an empirical and objective manner. Except for limited use of the geostrophic wind law, there is no dependence on hydrodynamical theory: what actually takes place in the atmosphere is described without reference to preconceived ideas as to what should take place. Following meteorolotical convention, the periods chosen for the computation of the means are the months of July and January, taken over many years. Means taken over these discontinuous periods are not strictly equivalent to steady states, but the differences from the steady state are small and easily computed. The July maps are placed before the January ones in order to show the period of weaker circulation in the northern hemisphere before the period of stronger circulation. Practical considerations have limited the upper-air analysis to a single level: the 500-mb surface, which is in the middle of the troposphere with respect to height and in the middle of the whole atmosphere with respect to its mass. (Author)