Nonlinear Propagation of Zonal Winds in an Atmosphere with Newtonian Cooling and Equatorial Wavedriving

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Abstract
Advection of angular momentum by the mean meridional circulation is important in the quasi-biennial and semiannual oscillations of the tropical middle atmosphere. The advection is nonlinear, implying a finite horizontal or vertical displacement of angular momentum surfaces. Horizontal advection contributes to the easterly phase of the semiannual oscillation, and is sensitive to extratropical body forces. The mean meridional circulation may be thought of as a hybrid Hadley/body-force circulation driven by radiative heating and Eliassen-Palm flux convergence. Realistic steady states are obtained when a mesospheric friction layer, representing gravity wave drag, is included in the problem. This device resolves an ambiguity in the inviscid theory of the middle atmosphere Hadley circulation. Nonlinear advection is also important in the quasi-biennial oscillation; it is responsible, in part, for the strong asymmetry between east and west phases. Diabatic advection of westerly shear displaces angular mo... Abstract Advection of angular momentum by the mean meridional circulation is important in the quasi-biennial and semiannual oscillations of the tropical middle atmosphere. The advection is nonlinear, implying a finite horizontal or vertical displacement of angular momentum surfaces. Horizontal advection contributes to the easterly phase of the semiannual oscillation, and is sensitive to extratropical body forces. The mean meridional circulation may be thought of as a hybrid Hadley/body-force circulation driven by radiative heating and Eliassen-Palm flux convergence. Realistic steady states are obtained when a mesospheric friction layer, representing gravity wave drag, is included in the problem. This device resolves an ambiguity in the inviscid theory of the middle atmosphere Hadley circulation. Nonlinear advection is also important in the quasi-biennial oscillation; it is responsible, in part, for the strong asymmetry between east and west phases. Diabatic advection of westerly shear displaces angular mo...

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