Date on Master's Thesis/Doctoral Dissertation

5-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Dowling, Timothy

Committee Co-Chair (if applicable)

Bradley, Mary

Committee Member

Holwerda, Benne

Committee Member

Davis, Chris

Author's Keywords

Mars; atmosphere; meteorology; Mach; Froude; compressibility

Abstract

Mars atmospheric global circulation models exhibit transonic jet streaks during
northern winter, which motivates this study of the Mach number, Ma (the ratio of
flow speed to the speed of sound), and the Froude number, Fr (the ratio of flow
speed to the speed of buoyancy waves), as a function of season and location. Two
global reanalyses spanning Mars Years (MY) 24 to 33 are used as input, EMARS
and OpenMARS. The study’s vertical coordinate is the isentropic variable potential
temperature, θ, ranging from θ = 125 to 1100 K, which corresponds to altitudes
ranging on average from z ≈ 5 to 66 km. Area-weighted global means and standard
deviations, and 5-year temporal means using the complete years MY 25, 26, 29, 30,
31, are compared. EMARS and OpenMARS show general agreement below θ =
700 K (z ≈ 53 km), where the observational constraints are strongest, but can vary
significantly at higher levels. Both reanalyses contain transonic jet streaks in every
northern winter sampled. The Fr signal is roughly twice the Ma number signal, as
expected where the temperature lapse rate is small compared to the dry adiabatic
lapse rate. Mach numbers are similar in both reanalyses, but show larger year-to-year
variability in OpenMARS. Maps of standard deviations indicate a depression between
the main peaks in Tharsis, and higher variability in Mare Boreum than Mare Australe.
A key conclusion is that the atmosphere of Mars routinely operates in the compressible regime (0.3 < Ma < 0.8) at altitudes above θ = 400 K, unlike Earth, whereas at lower altitudes it generally operates in the incompressible regime, like Earth. Given the importance of compressibility, aspects of all flow-speed meteorology are discussed.

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