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Downward Control from the Lower Stratosphere?

Downward Control from the Lower Stratosphere? The concept of downward control proposes a mechanism for the impact of the stratospheric circulation on the troposphere. Momentum forcing at upper-stratospheric levels induces a meridional circulation that eventually reaches the surface. So far, a lack of sufficiently accurate data hindered an observational test of this downward propagation. The concept is extended in this paper by looking at the effect of angular momentum forcing in prescribed regions in the lower stratosphere on the tropospheric circulation. In that case, the European Centre for Medium-Range Weather Forecasts Reanalysis Project (ERA) data can be used to investigate the atmospheric response to forcing in a prescribed domain. It is found that these forcing events are quite short lived and that angular momentum flux convergence in the prescribed domain is highly correlated with convergence outside this forcing area. Typically, these fields of convergence and also divergence extend to the surface in a quasibarotropic manner outside the Tropics. This structure of the forcing is not compatible with the assumptions of the downward control concept. The observed related meridional circulation therefore differs widely from that predicted. In particular, there is no obvious descent of the circulation to the ground. Even so, such forcing events are accompanied by an intensive exchange of angular momentum between stratosphere and troposphere. The confinement of the forcing to the selected forcing domain is reasonably strict in the Tropics. A relatively narrow tongue of angular momentum is growing at the equator underneath the forcing area. Frictional torques play a role in this development. Altogether, the forcing events as selected involve a strong angular momentum exchange between stratosphere and troposphere but are not suited for a test of the downward control concept. Alternatives are discussed. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Downward Control from the Lower Stratosphere?

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Publisher
American Meteorological Society
Copyright
Copyright © 2005 American Meteorological Society
ISSN
1520-0469
DOI
10.1175/JAS3569.1
Publisher site
See Article on Publisher Site

Abstract

The concept of downward control proposes a mechanism for the impact of the stratospheric circulation on the troposphere. Momentum forcing at upper-stratospheric levels induces a meridional circulation that eventually reaches the surface. So far, a lack of sufficiently accurate data hindered an observational test of this downward propagation. The concept is extended in this paper by looking at the effect of angular momentum forcing in prescribed regions in the lower stratosphere on the tropospheric circulation. In that case, the European Centre for Medium-Range Weather Forecasts Reanalysis Project (ERA) data can be used to investigate the atmospheric response to forcing in a prescribed domain. It is found that these forcing events are quite short lived and that angular momentum flux convergence in the prescribed domain is highly correlated with convergence outside this forcing area. Typically, these fields of convergence and also divergence extend to the surface in a quasibarotropic manner outside the Tropics. This structure of the forcing is not compatible with the assumptions of the downward control concept. The observed related meridional circulation therefore differs widely from that predicted. In particular, there is no obvious descent of the circulation to the ground. Even so, such forcing events are accompanied by an intensive exchange of angular momentum between stratosphere and troposphere. The confinement of the forcing to the selected forcing domain is reasonably strict in the Tropics. A relatively narrow tongue of angular momentum is growing at the equator underneath the forcing area. Frictional torques play a role in this development. Altogether, the forcing events as selected involve a strong angular momentum exchange between stratosphere and troposphere but are not suited for a test of the downward control concept. Alternatives are discussed.

Journal

Journal of the Atmospheric Sciences – American Meteorological Society

Published: Oct 1, 2005

References

  • Middle Atmosphere Dynamics.
    Andrews
  • Comments on “On the ‘downward control’ of extratropical diabatic circulations by eddy-induced mean zonal forces.”.
    Egger
  • Axial angular momentum: Vertical fluxes and response to torques.
    Egger
  • Torques and the related meridional and vertical fluxes of axial angular momentum.
    Egger
  • Is the atmospheric zonal index driven by an eddy feedback?
    Feldstein
  • “Downward control” of mean meridional circulation and temperature distribution of the polar winter stratosphere.
    Garcia