Premium
Concerning the effect of surface drag on the circulation of a baroclinic planetary atmosphere
Author(s) -
James I. N.,
Gray L. J.
Publication year - 1986
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711247417
Subject(s) - baroclinity , barotropic fluid , wavenumber , drag , instability , kinetic energy , atmosphere (unit) , mechanics , physics , zonal flow (plasma) , flow (mathematics) , atmospheric sciences , geology , classical mechanics , meteorology , optics , plasma , quantum mechanics , tokamak
Extended runs of a multi‐level spectral numerical model of atmospheric flow on a hemisphere have been used to investigate the effect of surface drag variations on the nature of the time‐averaged flow. It is shown that the most drastic effect of reducing the surface drag is to permit strong horizontal, barotropic shears in the zonal mean flow, which inhibit baroclinic instability. This superficially paradoxical result is implicit in many earlier calculations, most clearly in the lifecycle description of nonlinear baroclinic instability, but appears not to be widely appreciated. The kinetic energy spectra are interpreted in terms of the wavenumber of the most baroclinically unstable normal modes K R , the Rhines blocking wavenumber K β , and a limiting wavenumber based on surface drag K D . The changes in K R and the smaller changes in K β as drag is reduced account satisfactorily for the changes found in the kinetic energy spectra.