Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Jeffrey M. Forbes

Second Advisor

Jeffrey P. Thayer

Third Advisor

Scott E. Palo

Abstract

Data from the Mars Global Surveyor (MGS) spacecraft has revealed the presence of gravity waves in Mars' lower atmosphere and thermosphere. From perturbations in radio occultation temperature profiles of the lower atmosphere, global distributions of gravity wave potential energy density were calculated. The potential energy density distributions served as the basis to compute gravity wave source momentum flux used in a Mars dynamical model, marking the first time that a numerical study of Mars' gravity waves was observationally constrained. The gravity wave source spectrum is believed to include a stationary component from topographic forcing and a non-stationary component from atmospheric tides with large zonal wavenumbers. The model used was a Mars-specific version of the Hybrid Lindzen-Matsuno gravity wave parameterization that was created and integrated into the time-dependent, two-dimensional QNLM model for Mars. Due to the non-stationary waves in the gravity wave spectrum, the effect on predicted zonal wind and temperature fields was profound, particularly in the upper atmosphere above 100 km altitude where Mars' atmosphere is poorly observed. At solstice, the middle atmosphere zonal jets were closed near 80 km, and upper atmosphere zonal winds were significantly diminished from 120-140 m s-1 to near zero. Meridional circulation increased to over 50 m s-1 at altitudes where gravity wave breaking occurred, and adiabatic heating above the winter pole was enhanced. The model results were particularly sensitive to the prescribed phase speed distribution, and multiple phase speed spectra were evaluated to assess sensitivity. The effects of the non-stationary tidal components in the gravity wave spectrum indicate that Mars' GCMs may be underestimating their contribution to middle and upper atmosphere forcing, but open questions remain with respect to the phase speed distribution of non-stationary components and the relative contribution to momentum flux of stationary and non-stationary waves. Direct measurements of wind speed are needed to better constrain the gravity wave spectrum and validate predicted results.

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