Nicholas Brackney Pickett

Models of the Martian thermosphere capture its complex large scale behavior essential to understanding modern dynamics and atmospheric evolution at Mars, but only match observed temperatures through the addition of gravity wave dissipation‐driven cooling. While theory and high resolution simulations suggest this cooling effect to be correct, it has never been confirmed observationally due to the thermosphere's highly complex and variable nature. In this study, we use temperatures derived from the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite's Neutral Gas and Ion Mass Spectrometer (NGIMS) and remove influence of time of day, season, and changes in EUV in order to determine any associations between temperature and gravity wave activity, measured by independent metrics Integrated Wave Power (IWP) and gravity wave potential energy per mass . We find a positive association between gravity wave activity and temperature, counterintuitively providing observational evidence consistent with gravity wave cooling. We interpret our result to mean that, as gravity waves lose IWP and , temperatures decrease. The association between gravity wave activity and temperature is stronger in the northern hemisphere regardless of season, suggesting that gravity wave cooling may be stronger there. The association is inverted in the southern hemisphere during southern summer, suggesting that the influence of gravity waves on temperature may be different than during dusty conditions. The dominance of hemispherical differences over seasonal changes in the variation of association of gravity wave activity and temperature suggests that winter Thermospheric Polar Warming may not be driven by gravity wave activity.

Current Mars thermospheric temperatures databases have course temporal resolution due to either a lack of data or a need to average over several orbits of data, preventing the study of short‐term, rapid changes to the Mars thermosphere. In this study, we present a new Mars thermosphere temperature database derived from individual orbits of Argon density data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer instrument from 01/01/2016 to 12/31/2020 using a Newton gradient descent inverse method. This was enabled by the creation of secondary products like gravity wave potential energy, , the Knudsen number, , and pressure, designed to indicate when the variability in the data is beyond the assumptions of the temperature derivation and provide a better vertical axis to observe changes in the temperature. Here we present validations of the data set against previous models and data alongside some simple analysis of the temperatures in order to demonstrate the sensitivity of the data set to the nuances of the Martian thermosphere. This data set can better enable the study of thermosphere response to solar activity, dust events, and gravity waves.

MAVEN's 10 Deep Dip campaigns, when periapsis altitude was lowered from 150 km to 120 km for short periods in 2015–2019, have made major contributions to current understanding of the thermosphere and ionosphere of Mars, as well as of present escape and implications for past climate. Yet the available literature on the Deep Dip campaigns is fragmentary, naturally tending to emphasize the scientific results of the individual research project being reported. In order to view the Deep Dip campaigns in their totality, to integrate their main findings coherently, and to identify promising opportunities for further exploitation of their data, here we present a comprehensive overview of MAVEN's Deep Dip campaigns. For the thermosphere, MAVEN Deep Dip observations have revealed: the homopause altitude and its notable variability; gravity waves and their dissipation; thermospheric composition, its day‐to‐day variability (exemplified by the O/C ratio), and its response to changing solar irradiance; and the thermal structure of the lower thermosphere between the cold mesopause and the hot, isothermal upper thermosphere. For the ionosphere, MAVEN Deep Dip observations have revealed: ionospheric composition, its day‐to‐day variability (exemplified by the /C ratio), and its response to changing solar irradiance; the dependence of ionization efficiency upon altitude; electron and ion temperatures; and the presence of multiple species of metal ions. Solar conditions and atmospheric dust conditions, relevant observations by MAVEN remote sensing instruments and by other missions, and potential avenues for future analyses of Deep Dip data are also addressed.

Gravity waves in the thermosphere of Mars are complex and variable phenomena capable of causing significant changes to processes in the upper atmosphere of Mars, which can affect atmospheric escape. The objective of this study is to determine how dust storm activity, variation in Local Solar Time (LST), and seasonal changes affect thermospheric gravity wave activity. Analyzing in situ neutral Argon density data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) satellite's Neutral Gas and Ion Mass Spectrometer (NGIMS) using a new metric called Mean Integrated Wave Power (MIWP), we measure the strength of the gravity wave activity across five nightside observation data sets (each of 300 orbits) in a variety of dust conditions: three outside of the Martian Dust season with low dust conditions, one during the 2018 Global Dust Storm (GDS), and one during the regional C storm observed in Mars Year (MY) 34. During nominal, low‐dust conditions, we find the MIWP metric, and thereby gravity wave activity, is twice as high post‐midnight as pre‐midnight. This diurnal behavior is seen here first after L _s = . During the 2018 GDS, MIWP at 18:00–22:00 LST is higher when compared to dust‐free conditions, consistent with past studies. However, MIWP at 22:00–06:00 LST is not statistically different from MIWP during low dust activity, suggesting that dust storm‐driven variation in gravity wave activity is secondary to diurnal effects. MIWP during the MY34 regional C storm point toward 2 novel findings: seasonal variation in gravity wave activity and a strong correlation between dust loading and thermospheric gravity wave activity.

Gravity waves in the thermosphere of Mars are complex and variable phenomena capable of causing significant changes to processes in the upper atmosphere of Mars, which can affect atmospheric escape. The objective of this study is to determine how both dust storm activity and variation in Local Solar Time (LST) affect thermospheric gravity wave activity. Analyzing in-situ neutral Argon density data from the Mars Atmospheric and Volatile EvolutioN (MAVEN) satellite’s Neutral Gas and Ion Mass Spectrometer (NGIMS), we measure the strength of the gravity wave activity across five nightside observation datasets in a variety of dust conditions: three outside of the Martian Dust season with nominal, low dust conditions, one during the 2018 Global Dust Storm (GDS), and one during the regional C storm observed in Mars Year (MY) 34. From nominal conditions, we find thermospheric gravity wave activity increases on the nightside, as seen in previous studies, but is twice as high post-midnight as it is pre-midnight. During the 2018 GDS, the thermospheric gravity wave activity observed between 22:00 and 06:00 LST is generally consistent with gravity wave activity observed during nominal dust conditions. Between 18:00 and 22:00, however, gravity wave activity during the 2018 GDS is ~7 times higher than the weak activity seen during these LSTs in nominal dust conditions. A similar effect is observed during the MY 34 regional C storm, during which gravity wave activity increased in step with the global dust loading.

Characterizing C⁺ ions in the Martian ionosphere is important for understanding the history of the Martian atmosphere and surface due to its place in understanding carbon escape. Measuring minor ions, like C⁺, which are close in mass to major atmospheric ions, in this case O⁺, is difficult, requiring fitting algorithms and accurate background subtraction. Accurate measurement of these species is essential for understanding chemistry and transport in the ionosphere. In this paper, we use data from the Mars Atmospheric and Volatile EvolutioN SupraThermal And Thermal Ion Composition (MAVEN‐STATIC) sensor to report the first C⁺ fluxes measured in the Martian magnetotail. We will describe a multistep method of background subtraction as well as fitting routines that are used to extract C⁺ fluxes from a 40‐orbit subset of STATIC data. Our results show tailward fluxes in both optical shadow and the adjacent sunlit magnetotail at high altitudes (3,000 km) and Mars‐ward at low altitudes (2,000 km) in shadow. These local flux values are similar to estimates of neutral carbon fluxes from photochemical escape. However, total carbon loss comparisons will require a more comprehensive study of integrated C⁺ loss over a larger data set from the Martian magnetotail.