Mach and Froude Numbers on Mars

Abstract Mars atmospheric global circulation models exhibit transonic jet streaks during northern winter, which motivates this study of the Mach number, Ma (the ratio flow speed to sound), and Froude Fr buoyancy waves), as a function season location. Two reanalyses spanning Years (MY) 24 32 are used input, EMARS OpenMARS. The study’s vertical coordinate is potential temperature, θ , ranging from = 400 1100 K (from z ≈ 66 km); floor set lowest level that avoids intersecting mountains. Area-weighted means standard deviations 5 yr temporal using complete years MY 25, 26, 29, 30, 31 compared. OpenMARS show general agreement below 700 ( 53 km), where observational constraints strongest, but can vary significantly at higher levels. Both contain in every winter sampled. signal roughly twice number signal, expected temperature lapse rate small compared dry adiabatic rate. numbers similar both larger year-to-year variability Maps indicate depression between main peaks Tharsis Mare Boreum than Australe. conclusion atmosphere routinely operates compressible regime (0.3 < 0.8), unlike Earth. Aspects all flow-speed meteorology discussed.