On the Dynamic Forcing of the Long-Term Mean Flow by the Large-Scale Reynolds' Stresses in the Atmosphere

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  • 1 Department of Meteorology, University of Helsinki, Finland
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Abstract

Two sets of independent, upper air wind statistical data for the Northern Hemisphere (covering the periods 1950–54 and 1958–62) have been used to make a diagnostic study of some dynamic effects of the transient fluctuations in the horizontal velocity. In this paper the effects of the “frictional” force due to the large-scale Reynolds’ stresses uu′ and uv′ in the mean balance of momentum and vorticity are computed and discussed.

The results obtained indicate that the kinematic forcing effect due to the large-scale Reynolds’ stresses produces ageostrophic components of the long-term mean flow of the magnitude of 1 m s−1. The curl of this forcing, which is related to the anisotropic parts of the large-scale turbulence u2v2, uv′), appears to be very important for the time-mean vorticity balance and thus also for the distribution of the time-mean vertical velocity.

Abstract

Two sets of independent, upper air wind statistical data for the Northern Hemisphere (covering the periods 1950–54 and 1958–62) have been used to make a diagnostic study of some dynamic effects of the transient fluctuations in the horizontal velocity. In this paper the effects of the “frictional” force due to the large-scale Reynolds’ stresses uu′ and uv′ in the mean balance of momentum and vorticity are computed and discussed.

The results obtained indicate that the kinematic forcing effect due to the large-scale Reynolds’ stresses produces ageostrophic components of the long-term mean flow of the magnitude of 1 m s−1. The curl of this forcing, which is related to the anisotropic parts of the large-scale turbulence u2v2, uv′), appears to be very important for the time-mean vorticity balance and thus also for the distribution of the time-mean vertical velocity.

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