Modeling and Observations of Martian Stationary Waves

A linear σ-coordinate model is used in conjunction with a Mars GCM northern hemisphere winter zonal mean circulation to study the orographically forced stationary disturbances on Mars. The disturbances are compared to their counterparts on Earth and to the bright streak data from the Mariner 9 and Viking images. Diabatic heating on Mars is predominantly radiative, and inversion near the surface causes mountains to cool and depressions to heat the atmosphere. Due to the short radiative timescales and large meridional surface pressure gradient, the atmosphere responds to radiative forcing by changing its temperature and pressure gradient. The strong meridional flow near the equator and short radiative timescales combine to make responses to mechanical and thermal forcing of the same order in the tropics and in parts of the northern midlatitudes. In the subtropics, small zonal and meridional flows allow the response to radiative forcing to dominate. All these factors contribute to making the Martian atmospheric responses to orographic forcing different from the responses found on Earth. The model near-surface winds forced by realistic topography agree well with the Mars GCM stationary wave winds and with the orientation of the bright streaks. The addition of stationary eddies to the zonal mean winds improves all measures of alignment, as does the inclusion of radiative forcing in the linear model. Using the dusty basic-state fields improves wind-streak alignment through a better match between the zonal mean winds and streaks. Even near Olympus Mons, linear stationary waves improve the wind-streak alignment when added to the zonal mean winds.