ON A MECHANISM FOR THE RELEASE OF POTENTIAL ENERGY IN THE ATMOSPHERE

Abstract

It is shown that solitary atmospheric vortices with vertical axes can not remain in equilibrium in any arbitrary latitude but are subjected to horizontal forces which seek to displace them across the latitude circles, in such a manner as to diminish the kinetic and potential energy of the vortex motion. Hence anticyclonic vortices are driven towards the equator, cyclonic vortices towards the pole. In particular, anticyclonic cold domes tend to move southward and in so doing they sink and spread out along the surface of the earth. If the surrounding air is homogeneous the energy released through the weakening of the vortex motion is converted into translational energy, but if the environment is statically stable a fraction of the energy of the anticyclonic vortex goes into the creation of a cyclonic circulation above the sinking cold dome. Thus the southward movement of anticyclonic cold domes in the lower troposphere gives rise to forced displacements southward of cyclonic vortices in the upper troposphere and at the tropopause level. Ultimately such composite vortices reach an equilibrium latitude and may even slowly return towards higher latitudes. The stability of vortices centered over the pole is investigated. Circumpolar cyclonic vortices are stable but anticyclonic vortices are unstable, unless surrounded by a strong outer belt of cyclonic, i.e. westerly winds. The statistical effect of the behavior of sinking cold domes upon the zonal motion in the upper troposphere is discussed, particularly with reference to the maintenance of the jet stream. It is finally shown that the results of the force calculations in this paper may be obtained also by means of a method developed by C. C. Lin in connection with a study of the stability of laminar flows. A qualitative application of this method to perturbations on barocline zonal currents with easterly winds near the surface of the earth and moderate westerly winds aloft suggests a mechanism for the formation of isolated cold domes, in areas and longitudes prescribed by the long-wave pattern of the upper westerlies.