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Wave‐zonal‐flow interaction and ultra‐low‐frequency variability in a simplified global circulation model
Author(s) -
James P. M.,
Fraedrich K.,
James I. N.
Publication year - 1994
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712051812
Subject(s) - baroclinity , empirical orthogonal functions , diabatic , zonal flow (plasma) , climatology , amplitude , phase space , atmospheric sciences , circulation (fluid dynamics) , mechanics , mode (computer interface) , flow (mathematics) , dissipation , mean flow , phase (matter) , physics , geology , turbulence , thermodynamics , adiabatic process , optics , plasma , quantum mechanics , computer science , tokamak , operating system
The interactions between baroclinic waves and the zonal‐mean mid‐latitude flow are investigated using a multilevel primitive‐equation model of moderate resolution with idealized surface friction and diabatic heating terms. Integrations corresponding to 100 years were performed under perpetual solstice conditions. Empirical Orthogonal Function (EOF) analyses were carried out on the zonal‐mean zonal wind, [ u ]. Adjustments to the winter hemisphere zonal jet due to the growth and decay of baroclinic waves can be described in terms of the first two EOF patterns, which exhibit substantial interannual variability. For a single lifecycle, such adjustments take the form of a circuit of a phase‐space whose axes are defined by the amplitudes of the two EOFs. The cumulative effects of multiple lifecycles lead to a low‐frequency circulation in the phase‐space, with a timescale of about 150 days. We suggest that this effect may be intrinsically related to the internal generation of ultra‐low‐frequency variability in the model. Normal‐mode lifecycle calculations, including dissipation, reveal similar phase‐space properties. The growth rates of normal‐mode disturbances are shown to be highly sensitive to the phase of the first EOF.