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  • Author or Editor: Alison F. C. Bridger x
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Alison F. C. Bridger
and
Duane E. Stevens

Abstract

A version of Holton's numerical model of the stratospheric sudden warming is found to be very sensitive to the assumed initial mean zonal wind distribution. In tests with three initial wind profiles, in only one case can we simulate a wavenumber 1 warming involving flow reversal over a deep layer of the polar atmosphere and substantial warming (i.e., a major warming). In the other two cases, flow reversal is noted in restricted areas and warming is less intense. Examination of Eliassen-Palm cross sections and of Matsuno's refractive index squared throughout each integration reveals how the different warnings develop, and why they differ. Examination of refractive index squared in the atmosphere at the time of enhanced wave propagation out of the troposphere may be valuable aid in predicting the likelihood of a warming. Some characteristics of an “ideal” mean zonal wind profile (with which a major warming can develop) are discussed.

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Alison F. C. Bridger
and
Duane E. Stevens

Abstract

The spherical geometry of the earth is replaced by polar cylindrical geometry, with a plane tangential to the earth at the pole. The resulting frequency and structure of free motions in an isothermal, adiabatic atmosphere with a resting basic state is studied in both geometries. The solutions for ν (meridional wind) may be written as a single Bessel function if certain approximations are made. For positive equivalent depths, the geometrical approximation is best when the Lamb parameter ε≳ 10, so that Rossby waves are well modeled, while fast moving gravity waves are not well approximated. The impact of setting f to a constant value when undifferentiated, as in the usual midlatitude beta-plane approximation, is examined. It is found that the value of f is as important in determining how well the model behaves as are the geometrical and other approximations.

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