Martian Tidal Pressure and Wind Fields Obtained from the Mariner 9 Infrared Spectroscopy Experiment

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.