Solar‐Synchronous Tides in Mars Thermosphere CO₂, Ar, and N₂ Densities From MAVEN

Abstract

Measurements of CO2, Ar and N2 densities from the Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution Mission (MAVEN) between 150 and 200 km altitude during 2015–2022 are analyzed to reveal diurnal (DW1), semidiurnal (SW2) and terdiurnal (TW3) solar‐synchronous tides in Mars thermosphere. Multi‐year‐mean tidal perturbations on a diurnal‐ and zonal‐mean background, corrected for solar flux variations, are reported as a function of latitude (48°S–48°N), altitude and solar longitude (Ls). The DW1, SW2 and TW3 amplitudes at for example, 180 km altitude are of order 90%–120%, 15%–20%, and ≲10% for CO2 and Ar, and roughly 2/3 these values for N2, the latter presumably due to the difference in molecular weight from the other species. Through examination of vertical phase progressions, DW1 is concluded to be mainly excited in situ, but SW2 and TW3 contain significant contributions from tides propagating upward from lower altitudes. By analogy with studies for Earth's thermosphere, the DW1 amplitudes and phases are thought to reflect the combined influences of thermal expansion and vertical winds. Points of agreement and disagreement with DW1, SW2, and TW3 amplitudes and phases derived from the Mars Climate Database are noted and interpreted.

Climatology of Martian Ionospheric Disturbances Deduced From MAVEN Data in 2014–2023

“…In Figure 7 we present daily averages of (a) SW electron density, (b) SW electron temperature, (c) [CO 2 ] disturbance strength, and (d) $$\left[{{\mathrm{O}}_{2}}^{+}\right]$$ disturbance strength. The quasi‐5‐month oscillations seen in Figure 7c (magenta curve) and Figure 7d (black curve) seem to reflect the time needed for MAVEN/NGIMS data to cover all the LT sectors (e.g., Forbes et al., 2023, Figure 1b; Yigit et al., 2021, Figure 2d). That is to say, the oscillations represent orbit precession effects that are unrelated to real climatological variations at Mars.…”

“…Also, Forbes et al. (2023) recently used such 120°‐Ls bins for their analyses of Martian thermospheric tides.…”

“…The rationale for using the three-season approach (i.e., combining the spring and fall equinoxes) is to obtain sufficient data coverage for each season as a trade-off, and this convention has been widely used in the terrestrial aeronomy (e.g., Lühr et al, 2019, Figure 2;Jin et al, 2020, Figure 5;Wang et al, 2022, Figure 4). Also, Forbes et al (2023) recently used such 120°-Ls bins for their analyses of Martian thermospheric tides.…”

Ultra‐Fast Kelvin Wave Packets in Mars' Atmosphere and Their Interactions With Tides as Viewed by MAVEN/NGIMS and MRO/MCS

“…As such, any biases in the density data are minimized when cast in percent residuals from the zonal mean. Previous studies (e.g., England et al, 2016England et al, , 2017England et al, , 2019Forbes, Zhang, Fang, et al, 2023;Liu et al, 2017) demonstrated NGIMS densities to be well-suited to characterize the globalscale longitudinal variability of interest which ranges between about 5% and 50%.…”

“…Mars' thermosphere (ca. 100–200 km) is strongly coupled with the lower atmosphere below via gravity waves (GWs), planetary waves (PWs), solar tides, ultra‐fast Kelvin waves (UFKWs), and with the exosphere above via solar radiation and solar wind particles (e.g., Bougher, 1995; Bougher, Brain, et al., 2017; Bougher, Roeten, et al., 2017; Bougher et al., 1999, 2000, 2009, 2015; Forbes & Hagan, 2000; Forbes, Zhang, et al., 2020, 2023; Forbes et al., 2008; Hughes et al., 2022; Gasperini et al., 2023). It is now well established that atmospheric waves propagating from the lower and middle (below ∼100 km) atmospheric regions are a leading source of longitudinal and day‐to‐day variability of Mars' thermosphere (e.g., England et al., 2016, 2017, 2019; Kumar et al., 2022; Yiğit, 2023).…”