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2001: Eddy–zonal flow feedback in the Southern Hemisphere
| Venue: | J. Atmos. Sci |
| Citations: | 70 - 5 self |
BibTeX
@ARTICLE{Lorenz_2001:eddy–zonal,
author = {David J. Lorenz and Dennis L. Hartmann},
title = {2001: Eddy–zonal flow feedback in the Southern Hemisphere},
journal = {J. Atmos. Sci},
year = {},
pages = {3312--3327}
}
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Abstract
The variability of the zonal-mean zonal wind in the Southern Hemisphere is studied using EOF analysis and momentum budget diagnostics of NCEP Reanalysis data (1978-1997). The leading EOF of the zonal-mean zonal wind is well separated from the remaining EOF’s and repre-sents the north/south movement of the mid-latitude jet. Analysis of the momentum budget shows that a positive feedback between the zonal-mean wind anomalies and the eddy momentum fluxes accounts for the unusual persistence of EOF1 and plays an important role in the selection of the leading EOF of mid-latitude variability. Further analysis also shows a propagating feedback, com-mon to both EOF1 and EOF2, which is responsible for the poleward drift of wind anomalies with time. The observations support the following feedback mechanism: anomalous baroclinic wave activity is generated at the latitude of anomalous temperature gradient which, by thermal wind, coincides with the latitude of the anomalous zonal jet. The net propagation of baroclinic wave activity away from the jet gives momentum fluxes into the jet. This positive feedback is partially offset by low-frequency, equivalent barotropic eddies which propagate into the jet and remove momentum from it. The bias toward equatorward wave propagation on a sphere contributes to the
Keyphrases
southern hemisphere eddy zonal flow feedback positive feedback zonal-mean zonal wind important role eddy momentum flux account wind anomaly net propagation poleward drift anomalous temperature gradient north south movement anomalous zonal jet eof analysis unusual persistence mid-latitude jet momentum budget diagnostics equivalent barotropic eddy baroclinic wave activity ncep reanalysis data sphere contributes following feedback mechanism momentum budget anomalous baroclinic wave activity zonal-mean wind anomaly mid-latitude variability momentum flux propagating feedback thermal wind
