Editorial Type:
Article
Article Type:
Research Article

Dynamics of Zonal-Mean Flow Assimilation and Implications for Winter Circulation Anomalies

Eric DeWeaver Department of Meteorology, University of Maryland, College Park, Maryland

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Sumant Nigam Department of Meteorology, University of Maryland, College Park, Maryland

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Print Publication:
01 Jul 1997
DOI:
https://doi.org/10.1175/1520-0469(1997)054<1758:DOZMFA>2.0.CO;2
Page(s):
1758–1775
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Abstract

Seasonally averaged 200-mb circulations for recent winters (1987/88 and 1988/89) that represent opposite phases of El Niño and a zonal-mean zonal flow index cycle are diagnosed using data assimilated by the Goddard Earth Observing System (GEOS) and operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). The comparison is undertaken to determine whether there are significant differences in the 200-mb vorticity dynamics implied by the mean meridional circulations in the two datasets and whether these differences can be related to the Incremental Analysis Update (IAU) method used in the GEOS assimilation.

The two datasets show a high degree of similarity in their depictions of the large-scale rotational flow, but there are substantial differences in the associated divergent circulations. For the zonal-mean flow, the zonal winds are substantially the same, but the meridional wind in the Tropics and subtropics is considerably weaker in the GEOS assimilation than its counterparts in both the ECMWF data and the GEOS analyses used to produce the assimilation.

The authors examine the assimilation of the Hadley circulation using a zonally symmetric f-plane model. For this model, the IAU method easily assimilates the rotational flow but fails to assimilate the divergent circulation. This deficiency of the IAU method may explain the weakness of the Hadley cell in the GEOS assimilation, at least in relation to the GEOS analysis.

For this simple model, an alternative assimilation method, based on constraints imposed by the analyzed potential vorticity and mean meridional circulation fields, is proposed that simultaneously assimilates both rotational and divergent flow components.

Barotropic modeling suggests that an accurate representation of mean meridional flow anomalies can be important for the diagnosis of both zonal-mean and eddy rotational flow perturbations, particularly during extreme phases of the zonal-mean zonal flow fluctuation.

Corresponding author address: Dr. Eric DeWeaver, Department of Meteorology, University of Maryland, College Park, MD 20742.

Abstract

Seasonally averaged 200-mb circulations for recent winters (1987/88 and 1988/89) that represent opposite phases of El Niño and a zonal-mean zonal flow index cycle are diagnosed using data assimilated by the Goddard Earth Observing System (GEOS) and operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). The comparison is undertaken to determine whether there are significant differences in the 200-mb vorticity dynamics implied by the mean meridional circulations in the two datasets and whether these differences can be related to the Incremental Analysis Update (IAU) method used in the GEOS assimilation.

The two datasets show a high degree of similarity in their depictions of the large-scale rotational flow, but there are substantial differences in the associated divergent circulations. For the zonal-mean flow, the zonal winds are substantially the same, but the meridional wind in the Tropics and subtropics is considerably weaker in the GEOS assimilation than its counterparts in both the ECMWF data and the GEOS analyses used to produce the assimilation.

The authors examine the assimilation of the Hadley circulation using a zonally symmetric f-plane model. For this model, the IAU method easily assimilates the rotational flow but fails to assimilate the divergent circulation. This deficiency of the IAU method may explain the weakness of the Hadley cell in the GEOS assimilation, at least in relation to the GEOS analysis.

For this simple model, an alternative assimilation method, based on constraints imposed by the analyzed potential vorticity and mean meridional circulation fields, is proposed that simultaneously assimilates both rotational and divergent flow components.

Barotropic modeling suggests that an accurate representation of mean meridional flow anomalies can be important for the diagnosis of both zonal-mean and eddy rotational flow perturbations, particularly during extreme phases of the zonal-mean zonal flow fluctuation.

Corresponding author address: Dr. Eric DeWeaver, Department of Meteorology, University of Maryland, College Park, MD 20742.

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  • Bloom, S. C., L. L. Takacs, and E. Brin, 1991: A scheme to incorporate analysis increments gradually in the GLA assimilation system. Preprints, Ninth Conf. on Numerical Weather Prediction, Denver, CO, Amer. Meteor. Soc., 110–112.

  • ——, ——, A. M. DaSilva, and D. Ledvina, 1996: Data assimilation using incremental analysis updates. Mon. Wea. Rev.,124, 1256–1271.

  • Branstator, G., 1984: The relationship between zonal mean flow and quasi-stationary waves in the midtroposphere. J. Atmos. Sci.,41, 2163–2178.

  • Daley, R., 1991: Atmospheric Data Analysis. Cambridge University Press, 457 pp.

  • Davies, H., and R. Turner, 1977: Updating prediction models by dynamic relaxation: An examination of the technique. Quart. J. Roy. Meteor. Soc.,103, 225–245.

  • DeWeaver, E., and S. Nigam, 1995: Influence of mountain ranges on the mid-latitude atmospheric response to El Niño events. Nature,378, 706–708.

  • Eliassen, A., 1952: Slow thermally or frictionally controlled meridional circulation in a circular vortex. Astrophys. Norv.,5, 19–60.

  • Held, I. M., and I.-S. Kang, 1987: Barotropic models of the extratropical response to El Niño. J. Atmos. Sci.,44, 3576–3586.

  • Hoerling, M. P., M. Ting, and A. Kumar, 1995: Zonal flow–stationary wave relationship during El Niño: Implications for seasonal forecasting. J. Climate,8, 1838–1852.

  • Holton, J. R., 1992: An Introduction to Dynamic Meteorology. 3d ed. Academic Press, 507 pp.

  • Hou, A. Y., and R. S. Lindzen, 1992: The influence of concentrated heating on the Hadley circulation. J. Atmos. Sci.,49, 1233–1241.

  • Lorenz, E. N., 1967: The Nature and Theory of the General Circulation of the Atmosphere. World Meteorological Organization, 161 pp.

  • Nigam, S., 1994: On the dynamical basis for the Asian summer monsoon rainfall–El Niño relationship. J. Climate,7, 1750–1771.

  • Pfaendtner, J., S. Bloom, D. Lamich, M. Seablom, M. Sienkiewicz, J. Stobie, and A. da Silva, 1995: Documentation of the Goddard Earth Observing System (GEOS) Data Assimilation System—Version 1. NASA Tech. Memo. No. 104606, Vol. 4, 44 pp. [Available from Goddard Space Flight Center, Greenbelt, MD 20771.].

  • Rossby, C., 1938: On the mutual adjustment of pressure and velocity distribution in certain simple current systems. J. Mar. Res., (Sears Foundation),2, 239–263.

  • Sardeshmukh1, P. D., 1993: The baroclinic chi problem and its applications to the diagnosis of atmospheric heating rates. J Atmos. Sci.,50, 1099–1112.

  • Schneider, E. K., 1988: A formulation for diagnostic anomaly models. Pure Appl. Geophys.,126, 137–140.

  • Schubert, S. D., J. Pfaendtner, and R. Rood, 1993: An assimilated dataset for earth science applications. Bull. Amer. Meteor. Soc.,74, 2331–2342.

  • ——, C.-K. Park, C.-Y. Wu, W. Higgins, Y. Kondratyeva, A. Molod, L. L. Takacs, M. Seablom, and R. Rood, 1995: A multiyear assimilation with the GEOS-1 system: Overview and results. NASA Tech. Memo. 104606, Vol. 6, 183 pp. [Available from Goddard Space Flight Center, Greenbelt, MD 20771.].

  • Takacs, L. L., A. Molod, and T. Wang, 1994: Documentation of the Goddard Earth Observing System (GEOS) General Circulation Model—Version 1. NASA Tech. Memo. No 104606, Vol. 1, 100 pp. [Available from Goddard Space Flight Center, Greenbelt, MD 20771.].

  • Ting, M., M. P. Hoerling, T. Xu, and A. Kumar, 1996: Northern Hemisphere teleconnection patterns during extreme phases of the zonal-mean circulation. J. Climate,9, 2614–2633.

  • Trenberth, K. E., and J. G. Olson, 1988: An evaluation and intercomparison of global analyses from the National Meteorological Center and the European Centre for Medium-Range Weather Forecasts. Bull. Amer. Meteor. Soc.,69, 1047–1057.

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