Study of gravity waves distribution and propagation in the thermosphere of Mars based on MGS, ODY, MRO and MAVEN density measurements

Abstract

By measuring the regular oscillations of the density of CO 2 in the upper atmosphere (between 120 and 190 km), the mass spectrometer MAVEN/NGIMS (Atmosphere and Volatile EvolutioN/Neutral Gas Ion Mass Spectrometer) reveals the local impact of gravity waves. This yields precious information on the activity of gravity waves and the atmospheric conditions in which they propagate and break. The intensity of gravity waves measured by MAVEN in the upper atmosphere has been shown to be dictated by saturation processes in isothermal conditions. As a result, gravity waves activity is correlated to the evolution of the inverse of the background temperature. Previous data gathered at lower altitudes (∼95 to ∼150 km) during aerobraking by the accelerometers on board MGS (Mars Global Surveyor), ODY (Mars Odyssey) and MRO (Mars Reconnaissance Orbiter) are analyzed in the light of those recent findings with MAVEN. The anti-correlation between GW-induced density perturbations and background temperature is plausibly found in the ODY data acquired in the polar regions, but not in the MGS and MRO data. MRO data in polar regions exhibit a correlation between the density perturbations and the Brunt-Väisälä frequency (or, equivalently, static stability), obtained from Global Climate Modeling compiled in the Mars Climate Database. At lower altitude levels (between 100 and 120 km), although wave saturation might still be dominant, isothermal conditions are no longer verified. In this case, theory predicts that the intensity of gravity waves is no more correlated to background temperature, but to static stability. At other latitudes in the three aerobraking datasets, the GW-induced relative density perturbations are correlated with neither inverse temperature nor static stability; in this particular case, this means that the observed activity of gravity waves is not only controlled by saturation, but also by the effects of gravity-wave sources and wind filtering through critical levels. This result highlights the exceptional nature of MAVEN/NGIMS observations which combine both isothermal and saturated conditions contrary to aerobraking measurements.

Density Fluctuations in the Lower Thermosphere of Mars Retrieved From the ExoMars Trace Gas Orbiter (TGO) Aerobraking

“…The plot shows different behaviors over different phases: positive correlation during Phases 1 and 2 (0.689 and 0.729, correspondingly) and anticorrelation (−0.26) during Phase 3. This result is in line with that of Vals et al [48], who analyzed the aerobraking data from MGS, ODY, and MRO. They discussed possible reasons for the difference with the results based on the MAVEN-NGIMS data.…”

“…Overall, there is a clear temperature increase from the mid-, to high latitudes in the southern hemisphere in Phase 2. This thermospheric polar warming is consistent with that found from density measurements by ODY [20] (see also Figure 12 in [48]), which performed aerobraking at similar heights. The Phase 3 observations suggest a much weaker temperature variation between the high-and mid latitudes.…”

“…Next, the latitudinal dependence of density fluctuations is presented in Figure 6. If the subdivision into phases is neglected, the cloud of dots is distributed very similarly to that obtained from MRO aerobraking depicted in the lower left panel of Figure 12 in [48]. This similarity can be appreciated as the coverage in the orbital parameter space is also quite similar.…”

“…So as to analyze the perturbations in this signal, a mean background value has to be estimated. Many previous studies working with similar observations utilized an approximately 40 s-long rolling mean, e.g., [45,48]. However, as many acceleration peaks are narrow in the current data set, applying the 2σ = 40 s filter often introduces a non-negligible bias in the vicinity of the maximum acceleration, as smaller values are inherently included in the filtering window ( Figure 2).…”

GIS analysis of promising landing sites for manned flight to Mars

“…Ground probes: Stationary Automatic Martian Stations (AMS): "Vicking-1", "Viking-2", "Mars Pathfinder", "Phoenix". And mobile Rovers: "Spirit", "Opportunity", "Curiosity" [1,2].…”