The Effect of Transient Eddies on the Stationary Eddy Isobaric Height Field

Eero Holopainen Department of Meteorology, University of Helsinki, Helsinki, Finland

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Carl Foptelius Department of Meteorology, University of Helsinki, Helsinki, Finland

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Kimmo Ruosteenoja Department of Meteorology, University of Helsinki, Helsinki, Finland

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Abstract

The effect of transient eddies (TE) on stationary eddies (SE) is studied in terms of how the TEs force the SE isobaric height variance in the northern extratropics. The method used correlates the observed SE height field with the TE geopotential tendencies, which describe the net forcing effect that arises from the TE fluxes of beat and momentum and from the associated secondary circulations. Diagnostic estimates are made based on atmospheric circulation statistics for February 1979 and for an ensemble of several winters. The results for the TE forcing of the SE isobaric height variance are compared with those of the SE potential enstrophy.

Although the net forcing effect of all TEs on the SE potential enstrophy is a damping one at all levels, the TEs tend to maintain the SE isobaric height variance in the lower troposphere. This effect is caused by the high-frequency synoptic-scale TEs. The low-frequency TEs, by contrast, tend to damp the SE isobaric height variance at all levels. The sensitivity of the method to uncertainties in the input data is estimated by making calculations from different datasets valid for the same period.

The methods applied in this paper might be used as a diagnostic tool in the validation of general circulation models.

Abstract

The effect of transient eddies (TE) on stationary eddies (SE) is studied in terms of how the TEs force the SE isobaric height variance in the northern extratropics. The method used correlates the observed SE height field with the TE geopotential tendencies, which describe the net forcing effect that arises from the TE fluxes of beat and momentum and from the associated secondary circulations. Diagnostic estimates are made based on atmospheric circulation statistics for February 1979 and for an ensemble of several winters. The results for the TE forcing of the SE isobaric height variance are compared with those of the SE potential enstrophy.

Although the net forcing effect of all TEs on the SE potential enstrophy is a damping one at all levels, the TEs tend to maintain the SE isobaric height variance in the lower troposphere. This effect is caused by the high-frequency synoptic-scale TEs. The low-frequency TEs, by contrast, tend to damp the SE isobaric height variance at all levels. The sensitivity of the method to uncertainties in the input data is estimated by making calculations from different datasets valid for the same period.

The methods applied in this paper might be used as a diagnostic tool in the validation of general circulation models.

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