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Thompson, David W.J. 
ORCID: https://orcid.org/0000-0002-5413-4376, Lee, Sukyoung and Baldwin, Mark P.
(2003)
Atmospheric processes governing the northern hemisphere annular mode/north atlantic oscillation.
In:
The North Atlantic Oscillation.
Geophysical Monograph Series
.
Blackwell Publishing Ltd, pp. 81-112.
ISBN 9780875909943
Abstract
The North Atlantic Oscillation, referred to herein as the Northern Hemisphere annular mode (NAM), owes its existence entirely to atmospheric processes. In this chapter, we review the structure of the NAM in the atmospheric general circulation, discuss opposing perspectives regarding its physical identity, examine tropospheric processes thought to give-rise to NAM-like variability, and review the role of the stratosphere in driving variability in the NAM. The NAM is characterized by a deep, nearly barotropic structure, with zonal wind perturbations of opposing sign along -55° and -35° latitude. It has a pronounced zonally symmetric component, but exhibits largest variance in the North Atlantic sector. During the Northern Hemisphere (NH) winter, the NAM is strongly coupled to the circulation of the NH stratosphere. The NAM also affects tropical regions, where it perturbs the temperature and wind fields of both the tropical troposphere and stratosphere. The structure of the NAM is remarkably similar to the structure of the leading mode of variability in the Southern Hemisphere circulation. The processes that give rise to annular variability are discussed. In the troposphere, the NAM fluctuates on timescales of -10 days and is associated with anomalous fluxes of zonal momentum of baroclinic waves across ~45°N. It is argued that the tropospheric component of the NAM exhibits largest variance in the Atlantic sector where the relatively weak thermally driven subtropical flow and the relatively warm lower boundary conditions at subpolar latitudes permit marked meridional excursions by baroclinic waves. In the stratosphere, fluctuations in the NAM evolve on timescales of several weeks. Evidence is presented that long-lived anomalies in the stratospheric NAM frequently precede similarly persistent anomalies in the tropospheric NAM. It is argued that variability in the lower stratospheric polar vortex yields a useful level of predictive skill for NH wintertime weather on both intraseasonal and seasonal timescales. The possible dynamics of these linkages are outlined. The recasting of the North Atlantic Oscillation as an expression of an annular mode has generated a debate over the physical identity of the mode in question. This debate attests to the absence of a unique theory for the existence of annular modes in the first place. Our current understanding of the fundamental processes to which the NAM owes its existence is discussed.
| Item Type: | Book Section |
|---|---|
| Additional Information: | Funding Information: Acknowledgments. Thanks to W. J. Randel, W. A. Robinson, J. W. Hurrell, and one anonymous reviewer for their helpful comments and suggestions. Thanks also to T. J. Dunkerton, S. Feldstein, H.-K. Kim, D. J. Lorenz, and J. M. Wallace for their assistance and insight at various stages of this research, and to S.-W. Son for generating Plate 3. DWJT is supported by the National Science Foundation under grant CAREER: ATM-0132190. SL is supported by NSF grant ATM-0001473. MPB is supported by NSF grant ATM-0002485, NASA's SR&T Program for Geospace Science, contract NASW-00018, and NOAA's OGP CLIVAR Atlantic grant NOAA-0572. Funding Information: Thanks to W. J. Randel, W. A. Robinson, J. W. Hurrell, and one anonymous reviewer for their helpful comments and suggestions. Thanks also to T. J. Dunkerton, S. Feldstein, H.-K. Kim, D. J. Lorenz, and J. M. Wallace for their assistance and insight at various stages of this research, and to S.-W. Son for generating Plate 3. DWJT is supported by the National Science Foundation under grant CAREER: ATM-0132190. SL is supported by NSF grant ATM-0001473. MPB is supported by NSF grant ATM-0002485, NASA’s SR&T Program for Geospace Science, contract NASW-00018, and NOAA’s OGP CLIVAR Atlantic grant NOAA-0572. Publisher Copyright: © 2003 by the American Geophysical Union. |
| Uncontrolled Keywords: | geophysics ,/dk/atira/pure/subjectarea/asjc/1900/1908 |
| Faculty \ School: | Faculty of Science > School of Environmental Sciences |
| UEA Research Groups: | Faculty of Science > Research Groups > Climatic Research Unit Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences |
| Related URLs: | |
| Depositing User: | LivePure Connector |
| Date Deposited: | 18 Aug 2022 13:30 |
| Last Modified: | 15 Jun 2023 00:24 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/87452 |
| DOI: | 10.1029/134GM05 |
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