Reexamination of the Structure of the Ageostrophic Wind in Baroclinic Waves

Abstract

Abstract This paper reexamines the structure of ageostrophic winds in a baroclinic wave presented by Lim, Holton, and Wallace. It is found that the nonzero growth rate is indispensible to the compete explanation of the observed structure of ageostrophic winds. For the unstable mode the isallobaric wind shifts slightly westward by φ = tan−1(σi/σr) from the state of the neutral mode both at the upper and lower level. This makes the convergence and divergence patterns shift eastward at the upper level and westward at the lower level, which comes closer to reality where the vertical motion is nearly upright. The cancellation between the isallobaric wind and the advective part of ageostrophic wind for unstable mode differs from place to place so that zonal asymmetry with respect to the center of each high pressure and low pressure region appears, which results in a dramatic change from the results of the neutral mode. At the upper level the orientation is mainly zonal. But the magnitude of the zonal component ...