Forced Stationary Planetary Waves in Mars's Winter Atmosphere

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  • 1 NASA/Ames Research Center, Moffett Field, California
  • | 2 College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
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Abstract

Mariner 9 and Viking spacecraft observations provided evidence for planetary-scale, wavelike disturbances in the Mars winter atmosphere. Possible sources of the wave activity are dynamical instabilities, for example, barotropic and / or baroclinic instabilities. Other candidate sources are forced. quasi-stationary planetary waves—waves that arise predominantly via zonally asymmetric surface properties. The authors attempt to model aspects of the wave activity, focusing on forced planetary waves in representative wintertime atmospheres for Mars, by applying a spherical linear primitive equations model. Basic states representing relatively “nondusty” and “highly dusty” conditions near winter solstice allow wavenumber 1 and 2 disturbances to propagate meridionally and vertically about the jet. Higher wavenumbers are strongly vertically trapped. Stationary waves during winter in the northern and southern extratropics differ strongly in amplitude, phase, and dominant horizontal wave pattern. Northern extratropical eddies exhibit a definite wavenumber 2 pattern with comparable amplitudes for wavenumbers 1 and 2. Southern eddies, however, are very strongly dominated by wavenumber 1. Because of enhanced refractive properties of the dusty basic state, dusty responses are an order of magnitude larger than nondusty ones. Horizontal and meridional wave propagation is illuminated by diagnostics for the wave activity flux, for example, Eliassen–Palm and Plumb fluxes. As a result of the separation distance between major orographic features on Mars, together with a planetary waveguide that enhances zonal propagation, Rossby wave interferences between western and eastern hemispheric wave trains occur. This analysis is relevant to future global mapping missions to Mars (e.g., polar-orbiting space craft) that will return key atmospheric observations of planetary wave activity.

Abstract

Mariner 9 and Viking spacecraft observations provided evidence for planetary-scale, wavelike disturbances in the Mars winter atmosphere. Possible sources of the wave activity are dynamical instabilities, for example, barotropic and / or baroclinic instabilities. Other candidate sources are forced. quasi-stationary planetary waves—waves that arise predominantly via zonally asymmetric surface properties. The authors attempt to model aspects of the wave activity, focusing on forced planetary waves in representative wintertime atmospheres for Mars, by applying a spherical linear primitive equations model. Basic states representing relatively “nondusty” and “highly dusty” conditions near winter solstice allow wavenumber 1 and 2 disturbances to propagate meridionally and vertically about the jet. Higher wavenumbers are strongly vertically trapped. Stationary waves during winter in the northern and southern extratropics differ strongly in amplitude, phase, and dominant horizontal wave pattern. Northern extratropical eddies exhibit a definite wavenumber 2 pattern with comparable amplitudes for wavenumbers 1 and 2. Southern eddies, however, are very strongly dominated by wavenumber 1. Because of enhanced refractive properties of the dusty basic state, dusty responses are an order of magnitude larger than nondusty ones. Horizontal and meridional wave propagation is illuminated by diagnostics for the wave activity flux, for example, Eliassen–Palm and Plumb fluxes. As a result of the separation distance between major orographic features on Mars, together with a planetary waveguide that enhances zonal propagation, Rossby wave interferences between western and eastern hemispheric wave trains occur. This analysis is relevant to future global mapping missions to Mars (e.g., polar-orbiting space craft) that will return key atmospheric observations of planetary wave activity.

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