Horizontal Structure and Energetics of Northern Hemisphere Wintertime Teleconnection Patterns

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  • 1 Upper Atmosphere Research Laboratory, Tohoku University, Sendai 980 Japan
  • | 2 Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195
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Abstract

The horizontal structure and dynamical properties of the teleconnection patterns in the interannual variability of the Northern Hemisphere wintertime 500 mb height field are investigated. Regression maps based on indices for the eastern Atlantic (EA), Pacific/North American (PNA), western Atlantic (WA), western Pacific (WP) and Eurasian (EU) patterns defined by Wallace and Gutzler are used to define the geographically fixed patterns. Space-spectrum analysis including a spherical harmonic decomposition is applied to these maps. Anomalous geostrophic wind fields derived from these regression maps are used to estimate the kinetic energy conversion between the climatological mean state and the wave structures associated with the teleconnection patterns.

The teleconnection patterns comprise “seesaw” and/or wavelike structures. In general, the kinetic energy of the teleconnection patterns is concentrated in total wavenumber n = 5 and 6 components with zonal wavenumbers m = 0, 1 and 2, which correspond to zonally elongated “seesaw” structures near the jetstreams. The phase tilt of the wave axes indicates that some wavecomponents of the Atlantic teleconnection patterns (EA, WA and EU) propagate wave energy equatorward, whereas the ultralong wavecomponents of the Pacific patterns (PNA and WP) exhibit poleward energy dispersion, which might possibly be related to the Southern Oscillation.

The zonal component of the extended Eliassen-Palm (E-P) flux associated with the “seesaw” structures accounts for most of the very low frequency barotropic energy conversion from the time-mean flow. The PNA and EA patterns, which have “seesaws” located in the jet exit regions, obtain kinetic energy more efficiently than the other patterns. The time scale for replenishing their kinetic energy is 3–4 days. The EU pattern, which has no “seesaw” structure, exhibits the smallest kinetic energy conversion. The fact that the WA and WP patterns straddle the storm tracks suggests that they may have a special relationship to baroclinic wave activity.

Abstract

The horizontal structure and dynamical properties of the teleconnection patterns in the interannual variability of the Northern Hemisphere wintertime 500 mb height field are investigated. Regression maps based on indices for the eastern Atlantic (EA), Pacific/North American (PNA), western Atlantic (WA), western Pacific (WP) and Eurasian (EU) patterns defined by Wallace and Gutzler are used to define the geographically fixed patterns. Space-spectrum analysis including a spherical harmonic decomposition is applied to these maps. Anomalous geostrophic wind fields derived from these regression maps are used to estimate the kinetic energy conversion between the climatological mean state and the wave structures associated with the teleconnection patterns.

The teleconnection patterns comprise “seesaw” and/or wavelike structures. In general, the kinetic energy of the teleconnection patterns is concentrated in total wavenumber n = 5 and 6 components with zonal wavenumbers m = 0, 1 and 2, which correspond to zonally elongated “seesaw” structures near the jetstreams. The phase tilt of the wave axes indicates that some wavecomponents of the Atlantic teleconnection patterns (EA, WA and EU) propagate wave energy equatorward, whereas the ultralong wavecomponents of the Pacific patterns (PNA and WP) exhibit poleward energy dispersion, which might possibly be related to the Southern Oscillation.

The zonal component of the extended Eliassen-Palm (E-P) flux associated with the “seesaw” structures accounts for most of the very low frequency barotropic energy conversion from the time-mean flow. The PNA and EA patterns, which have “seesaws” located in the jet exit regions, obtain kinetic energy more efficiently than the other patterns. The time scale for replenishing their kinetic energy is 3–4 days. The EU pattern, which has no “seesaw” structure, exhibits the smallest kinetic energy conversion. The fact that the WA and WP patterns straddle the storm tracks suggests that they may have a special relationship to baroclinic wave activity.

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