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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L07209, doi:10.1029/2003GL019302, 2004

Trends in the Southern Hemisphere polar vortex in NCEP and ECMWF reanalyses

James A. Renwick

National Institute of Water and Atmospheric Research, Wellington, New Zealand


Abstract

A comparison of tropospheric and stratospheric height fields from ECMWF and NCEP/NCAR reanalyses during 1958–2001 indicates a trend towards a strengthening Antarctic polar vortex. The reanalyses agree well on a daily basis over the Southern Hemisphere, after the advent of satellite observations in 1979. Linear trends in 500 hPa and 50 hPa geopotential height are in close spatial agreement in the period 1980–2001 (correlations >0.8), showing falling heights over Antarctica and strengthening zonal winds above the southern oceans during summer and autumn. Prior to 1980, stratospheric trends agree well (spatial correlations ≥0.7), suggesting a rise in heights over Antarctica and a weakening polar vortex since the late 1950s. Tropospheric trends are not as consistent prior to 1980, but show similar qualitative features. The strong trends observed in the past 20 years dominate the full record, but there are suggestions of cyclical components on the decadal time scale.

Received 16 December 2003; accepted 14 March 2004; published 9 April 2004.

Index Terms: 1610 Global Change: Atmosphere (0315, 0325); 1620 Global Change: Climate dynamics (3309); 3319 Meteorology and Atmospheric Dynamics: General circulation; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology; 3362 Meteorology and Atmospheric Dynamics: Stratosphere/troposphere interactions.

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Citation: Renwick, J. A. (2004), Trends in the Southern Hemisphere polar vortex in NCEP and ECMWF reanalyses, Geophys. Res. Lett., 31, L07209, doi:10.1029/2003GL019302.