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Joseph A. Pirraglia

Abstract

The atmosphere is assumed to be driven by a polar symmetric temperature field and the equations of motion in pressure ratio coordinates are linearized by considering the zero order in terms of a thermal Rossby number RδT(2aΩ)2 where δT is a measure of the latitudinal temperature gradient. When the eddy viscosity is greater than 106 cm2S−1 boundary layer extends far up into the atmosphere making the geostrophic approximation invalid for the bulk of the atmosphere. The surface pressure gradient exhibits a latitudinal dependence opposite that of the depth-averaged temperature. The magnitude of the gradient is dependent upon the depth of the boundary layer, which depends upon the eddy viscosity, the boundary conditions imposed at the surface, and upon the temperature lapse rate. Using a temperature model for Mars based on Mariner 9 infrared spectral data with a 30% increase in the depth-averaged temperature from the winter pole to the subsolar point, the following results were obtained for the increase in surface pressure from the subsolar point to the winter pole as a function of eddy viscosity and with no-slip conditions imposed at the surface:
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The meridional cellular flow rate is also correlated with the eddy viscosity, causing a complete overturning of the atmosphere in tens of days for an eddy viscosity of 108cm2S−1 and in hundreds of days for 106cm2S−1 The implication of this overturning in the dust storm observed during the early part of the Mariner 9 mission is discussed briefly.

Calculations of the dynamic heating indicate the mechanism for a polar temperature inversion and high-altitude equatorial cooling.

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Joseph A. Pirraglia and Barney J. Conrath

Abstract

Using temperature fields derived from the Mariner 9 infrared spectroscopy experiment, the Martian atmospheric tidal pressure and wind fields are calculated. Temperature as a function of local time, latitude, and atmospheric pressure level is obtained by secular and longitudinal averaging of the data. The resulting temperature field is approximated by a spherical harmonic expansion, retaining one symmetric and one asymmetric term each for wavenumber zero and wavenumber one. Vertical averaging of the linearized momentum and continuity equations results in an inhomogeneous tidal equation for surface pressure fluctuations with the driving function related to the temperature field through the geopotential function and the hydrostatic equation. Solutions of the tidal equation show a diurnal fractional pressure amplitude approximately equal to one-half the vertically averaged diurnal fractional temperature amplitude. These results indicate that a diurnal pressure fluctuation of 6–7% existed during the planet-wide dust storm of 1971–72 as well as during its subsequent decay. The calculated tidal pressure fields, along with the temperature fields, yield tidal wind velocities of the order of 10 m sec−1 near the lower boundary, assumed to be friction-free in the model. Dynamic heating accounts for a 3–4K decrease of the diurnal amplitude of the vertically averaged temperature.

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