The vertical component of the geostrophic wind

Abstract

Motion in planetary geostrophic equations (PGEs) is represented by the three-dimensional geostrophic wind (ug, vg, wg) where ug and vg are the standard horizontal components while the vertical component wg can be derived, for example, from the Richardson equation. However, this vertical component appears not to have been evaluated as yet on the Basis of data nor compared to the actual vertical component w. Part of this missing Information is provided here by an evaluation of wg from observations and by analyzing the role of wg in linear versions of PGEs. The time mean fields wg in the Northern Hemisphere as well as the standard deviations σwg are compared to the correponding fields of w. It is found that wg comes reasonably close to w in the troposphere but deviates widely in the stratosphere while σwg is smaller than σw in the troposphere but not in the stratosphere. Linear wave motion is discussed and the linear steady-state response to the forcing by heat sources and mountains is explored to explain these results.