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D. R. Christie

Abstract

This paper is concerned with the theoretical description of long, finite-amplitude waves in the stably stratified lower atmosphere. The time evolution of these waves is governed to first order by the Benjamin-Davis-Ono (BDO) equation when frictional processes are negligible or by the BDO-Burgers equation when turbulent dissipation is significant. Numerical solutions of both of these model equations are presented for a wide variety of initial conditions ranging from long waves of finite volume to internal deep-fluid bore waves of infinite spatial extent. It is shown that initially smooth long wave disturbances evolve rapidly under ideal homogeneous waveguide conditions into solitary waves of exceptionally large amplitude. The BDO-Burgers equation is found to have highly stable, time-independent, deep-fluid internal bore wave solutions which may be either oscillatory or monotonic depending upon the degree of frictional dissipation. A number of specific models for the time evolution of long nonlinear atmospheric waves are proposed and discussed in detail. Explicit formulae are given for the wave propagation parameters, surface perturbation pressure, and wind components and these are illustrated for a simple, but realistic, boundary-layer waveguide model. A study has also been made of the influence on nonlinear wave propagation of either spatial or temporal variations in the degree of turbulent dissipation. It is shown that an increase or decrease in the frictional damping coefficient, such as might be encountered at a land-sea boundary, can induce a significant variation in the speed of propagation and a substantial change in the morphology of finite-amplitude boundary layer wave disturbances. Finally, it is shown that wave induced turbulence plays an important role in the evolution of long nonlinear atmospheric waves.

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V. R. Krishna Rao
and
A. D. Christie

Abstract

A steady-state mean meridional model of the stratosphere is used to investigate the effects of water vapor and nitrogen oxides on ozone and temperature distributions in the stratosphere. Chapman's classical photochemical scheme for ozone is extended to include the dominant reactions involving hydrogen compounds and nitrogen oxides.

The ozone and temperature changes are studied under radiative-photochemical equilibrium conditions and in a model incorporating both transport and radiative-photochemical processes. It is found that both hydrogen and nitrogen reactions contribute to substantial decreases in ozone and temperature under photochemical equilibrium conditions, but the computed distributions do not resemble those observed. The effect of transport processes is to reduce the deviations in ozone mixing ratio and temperature, with the computed distributions having many features in common with the observations. It is found that ozone and temperature respond more readily to an arbitrary increase of nitrogen oxides than to that of water vapor.

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D. R. Christie
,
K. J. Muirhead
, and
A. L. Hales

Abstract

This paper is concerned with a description and interpretation of two unusual types of isolated atmospheric gravity wave observed near Tennant Creek in central Australia. These waves occur in the form of solitary waves of elevation and solitary waves of depression. Comparison of experimental data with theory leads to the conclusion that the majority of the observed isolated waves of elevation belong to the class of deep-fluid internal solitary waves considered by Benjamin and by Davis and Acrivos. The second fundamentally different type of large-amplitude isolated wave is tentatively identified as a classical solitary wave of depression.A brief discussion is given of a number of possible source mechanisms which may give rise to internal solitary atmospheric waves. It is proposed that the following two dynamical processes play an important role in the creation of solitary atmospheric waves in the arid interior of Australia: 1) the interaction of nocturnal katabatic density currents with an existing radiation inversion; and 2) the interaction of a propagating horizontal sea breeze vortex with the nocturnal inversion.

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