Effects of the earth's rotation and the balance of zonal kinetic energy

Abstract

According to the symmetric formulation of the zonal kinetic energy equation, positive generations arise through countergradient transports of angular momentum. Five years of northern hemispheric upper air data are used to investigate two of the terms in the equation, which represent the effects of the transport, by the mean general circulation cells, of the angular momentum associated with the earth's rotation. These two Ω-generation terms do not usually appear in the more traditional form of the conservation equation, and results of their evaluation have not appeared previously. It is found that positive generation largely dominates in the Ω-term involving horizontal (meridional) transports of angular momentum, and negative generation in the Ω-term involving vertical transport. In fall and particularly winter, both terms are responsible for very large amounts of generation of opposing sign for the whole atmosphere. The five years of data are also used to evaluate the balance of zonal kinetic energy implied by the symmetric equation in northern hemispheric polar caps of various pressure thicknesses. The vertical processes involved are not directly measured but rather are obtained from observed horizontal motions through use of continuity of mass and angular momentum requirements. Possible reasons for the lack of a perfect balance are offered, but in any case the residuals are generally not large enough to be of too much concern. Vertical eddies are found to play an important role in the balance of zonal kinetic energy. A study of the balance in the upper half of the atmosphere reveals that in spring the vertical eddies (summed for all scales) must tranport angular momentum and zonal kinetic energy upward toward the jet in order to counter the net effect of the mean cells in reducing the zonal kinetic energy in this volume. In the fall however, there is a dramatic change in the direction in which these vertical eddies act, as they now remove zonal kineticenergy from the upper half of the atmosphere in this season.