On equilibrium between orography and atmosphere

A. WIIN NIELSEN

Abstract

The equilibrium conditions between the orography of a planet and its atmosphere are investigated. A first relatively simple example is the solution of the problem in an equivalent barotropic atmosphere, while the two-level quasi-geostrophic model is taken as the second example. The problem can also be solved for multi-level, quasi-geostrophic models. The problem under invesigation is to find the motion which can exist in an atmosphere under steady state conditions in equilibrium with the orography of the planet. A trivial solution is a state of rest, but it is shown that non-trivial solutions can be constructed as well. The investigation is basically different from the classical problem of finding the influence of orography on a preexisting flow which has been solved in numerous cases. On the Earth with its strong meridional temperature gradient created by the differential heating between Pole and Equator and due to diabatic heating processes compensated partly by meridional transport of sensible heat the general circulation is in the first approximation determined by the processes of baroclinic instability deriving its energy from the meridional temperature field and in turn maintaining the zonal currents by heat and momentum transport primarily by the waves. On the global scales the circulation is modified greatly by the existence of continents and oceans and by orography. On other planets, with smaller meridional differential heating than the Earth, the orogrphy may have a major influence on the stationary flow pattern.

 

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