Edward Michael Benjamin Thiemann

Small‐scale (10 s of km) currents in the Martian atmosphere may result in atmospheric heating, ionization, discrete aurora, and atmospheric escape. We have developed a semi‐automated method to identify current signatures in the Martian upper atmosphere using perturbations in the local magnetic field. We use magnetic field measurements taken by Mars Atmosphere and Volatile EvolutioN to investigate the incidence of ionospheric current signatures on the nightside of the planet in regions of moderate to strong crustal fields ( 25 nT). We find that current signatures are uncommon in horizontal magnetic fields but are detected up to 100% of the time in magnetic cusp regions, where the field is nearly radial. Current signatures are more common post‐dusk than predawn, which is consistent with auroral emission. Current signatures are most common in the ionospheric dynamo region, where ion motion is driven by the neutral atmosphere and electrons are bound to magnetic field lines. The occurrence of current signatures does not appear to be influenced by interplanetary magnetic field direction, solar wind dynamic pressure, or solar extreme ultraviolet photon flux.

Solar extreme ultraviolet (EUV) irradiance predominantly originates from the chromosphere and corona, and variations in EUV irradiance are a significant driver of space weather at Earth, causing increased satellite drag, radio communication disruptions, and reduced GPS accuracy. Since solar EUV irradiance measurements are intermittent and inhomogeneous, models are used to fill spectral and temporal gaps, typically relying on proxy-based methods that utilize linear correlations between emission originating from similar heights or temperatures in the solar atmosphere. Proxy methods can struggle to capture dynamic irradiance variations of the solar corona during flares in part due to the relative infrequency of flares on which to derive correlations and the steep temporal temperature gradients experienced during flares. This paper presents a hybrid method for modeling solar EUV irradiance utilizing forward-modeled physics-informed solar differential emission measures (DEMs) to capture the optically thin coronal emission coupled with traditional proxy-based correlation methods to capture the chromospheric and continuum emission. The model is trained and tested using inputs from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and EUV Variability Experiment (EVE) and compared against a proxy-only method. The results demonstrate that including information from DEMs into a EUV irradiance model improves accuracy for flaring conditions, particularly for high-temperature coronal lines, where the model error is reduced by up to a factor of 3 for M- and X-class flares compared to a proxy-only model trained on the same data.

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.

Disappearing solar wind events (DSWEs), intervals when the solar wind proton density <1 , represent one extreme of the Mars solar wind interaction. Using data from NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission from February 2016 to May 2024, 154 orbits across 90 unique days were identified. During these events, the solar wind kinetic energy flux had a median value of ∼0.08 and never exceeded 0.37 , whereas normal times have a median value twice as large (∼0.16 ) and maximum values exceeding 8 . In contrast, electromagnetic energy fluxes and solar ionizing irradiance remained near normal levels. Observations of and density and fluxes from MAVEN's SupraThermal and Thermal Ion Composition (STATIC) instrument were analyzed. During DSWEs, ion density and ion flux distributions are significantly restructured, consistent with expansion of Mars' ionosphere and induced magnetosphere. Ion escape rates are significantly reduced during DSWEs compared to normal solar wind conditions, with falling to ∼75% and to ∼88% of normal values (9.45 and 1.30 ions/s). DSWE ion fluxes binned by solar wind kinetic and solar ionizing irradiance followed the same empirical relations as under normal conditions, whereas DSWE ion fluxes were depleted relative to the background trend for solar wind electromagnetic energy. Thus, the observed decrease in ion escape is likely attributable to the reduced solar wind kinetic energy flux. These results suggest that even under extreme solar wind density reductions, Mars' ion escape remains mostly governed by the same background drivers as during normal times.

The homopause marks the transition in a planetary atmosphere from turbulent mixing, which maintains a well-mixed composition, to molecular diffusion, which causes the diffusive separation of chemical species, impacting how these are distributed in the upper atmosphere and potentially escape to space. Here, we analyse simulations from the Mars Planetary Climate Model (Mars PCM) to investigate the variability of the Martian homopause in diurnal, seasonal and interannual timescales. The simulations reveal strong seasonal and latitudinal trends, with homopause altitudes peaking in the summer polar regions (∼120–130 km) and showing minimum values during the winter southern polar region (∼60–90 km). The simulations predict diurnal variations in the homopause altitude typically within 5–15 km and suggest that dust events can raise the value of the homopause altitude by 10–20 km, depending on the intensity of the event. When comparing the Mars PCM results with empirical estimates of the homopause altitude and density derived from Martian atmospheric data, we find that the model captures the overall magnitude and seasonal/latitudinal variability of the homopause, but appear to underestimate the strength of the diurnal cycle. Finally, we use the Mars PCM data to constrain the variability of the eddy diffusion coefficient, which can vary by one or two orders of magnitude across latitude and season. The derived parameterisation and variability of the eddy diffusion coefficient is suitable for use in one-dimensional models devoted to understanding seasonal difference in atmospheric photochemistry and escape.

Introduction and GoalThe upper atmosphere of Mars, spanning the mesosphere (60–120 km) and the thermosphere up to the exobase (180–230 km), remains one of the least characterized regions of the planet [1]. Its structure is shaped by solar forcing, upward‑propagating waves, and dust‑driven variability originating in the lower atmosphere; however, the relative importance of these processes and their vertical coupling are not yet fully understood [2]. Two recent missions provide complementary datasets: NASA’s MAVEN mission, operational since 2014, focuses on upper‑atmosphere processes and atmospheric escape, while ESA–Roscosmos’ Trace Gas Orbiter (TGO), in routine operation since 2018, carries the NOMAD and ACS instruments, which retrieve atmospheric profiles from near‑surface layers to the upper thermosphere.In this work, we combine MAVEN and TGO observations with the primary objective of producing a comprehensive climatology of the thermal structure of the Martian upper atmosphere. This study is part of a broader andn recent project funded by the International Space Science Institute (ISSI) entitled “A multi-mission approach to close the gaps in understanding of the structure and variability in the Mars upper atmosphere”. Most TGO datasets concentrate below 100 km, whereas MAVEN primarily samples thermospheric altitudes. Because TGO data extend to lower altitudes, we actually present results spanning from the troposphere to the exosphere. The combined dataset integrates nine types of measurements from both missions, including in situ observations (NGIMS/MAVEN) and remote‑sensing measurements from NOMAD, ACS, EUVM, and IUVS (solar and stellar occultations, as well as dayglow). Together, these datasets cover multiple Martian years and an altitude range of 30–180 km, providing unprecedented vertical and temporal coverage. Exploiting this complementarity, particularly the vertical coupling between the lower and upper atmosphere, is also a major scientific goal of the present research.In this climatological study, we explicitly exclude a set of short‑lived and sporadic phenomena, such as dust storms, solar eruptions, and small‑scale atmospheric waves. Our focus is on the systematic variations associated with the following geophysical variables: altitude, latitude, season, local time, solar cycle, and longitude.Datasets, Synergies, and ChallengesThe datasets exhibit highly diverse characteristics, including field of view, spatial and temporal coverage, sensitivity, and noise levels, posing challenges for the synergetic analysis pursued here. To address coverage differences, we devoted substantial effort to designing appropriate binning strategies and averages across geophysical variables. Regarding sensitivity and retrieval performance, we used nominal uncertainties but filtered out the highest‑uncertainty percentile, and we developed a unified quality‑control framework applied to the nominal errors of each experiment. This framework aims to eliminate spurious values and identify potential biases, as revealed through cross‑comparisons within well‑defined geophysical bins. We also performed a variance‑partitioning analysis as a function of geophysical forcings, enabling us to distinguish intrinsic atmospheric variability from instrumental effects. Two vertical coordinates were used: altitude above the Martian aeroid and a modified‑CO₂ scale‑height coordinate, which is more suitable for upper‑atmosphere comparisons. Special attention was given to solar‑occultation datasets from both MAVEN and TGO (terminator measurements at dawn and dusk) owing to their synergistic local‑time coverage and excellent vertical resolution.Selected ResultsWe will present a representative sample of this extensive analyses across this broad parameter space, including global composite temperature profiles, deviations from mean distributions, multi‑year time series, and an assessment of the dominant sources of thermal variability. Our results reveal substantial atmospheric variability, highly non‑linear with respect to geophysical parameters, and a hierarchy of dominant processes that varies with altitude and which shapes the global thermal structure.In particular we found that thermospheric temperatures respond strongly to solar flux, with variations exceeding 50 K above 150 km and decreasing toward 100 km, being very small below this altitude. In contrast, mesospheric temperatures are dominated by global circulation, producing seasonal and latitudinal gradients of 20–40 K. We will show how the combined datasets also reveal interhemispheric asymmetries, the impact of dust storms at multiple altitudes, and the propagation of atmospheric waves.Comparisons with MarsPCM and MCD simulations demonstrate that the model reproduces very well the mean vertical structure as well the seasonal and latitudinal variations observed, but underestimates the variability by factors of 1.5–2 and exhibit a few biases in the mesopause and upper thermosphere. In particular, tidal amplitudes in the mesosphere are weaker in the models, the lower‑thermosphere thermal gradient occurs at lower altitudes than what is observed, and the coldest thermospheric temperatures predicted by the models are significantly colder than those reported by EUVM.The resulting MAVEN–TGO climatology provides a robust reference for future measurements, model validation, and studies of Martian atmospheric dynamics and evolution. References[1] Bougher et al., JGR-Planets, 2017 [2] López-Valverde et al., Space Sci. Rev., 2018 [3] Giuranna et al., Space Sci. Rev., 2025 [4] Heavens et al., Nature, 2018 [5] Yiğit et al., Nature Geoscience, 2023 [6] Jakosky et al., Science, 2015 [7] Korablev et al., Space Sci. Rev., 2018 [8] Vandaele et al., Space Sci. Rev., 2018

Gravity waves play an important role in the dynamical forcing of the Martian climate. If the horizontal resolution of a Global Climate Model (GCM) is larger than the scale of these waves, their impact should be parameterised to simulate their effects on the mean flow. Typically, the parameterisations derive from Earth models and are not well constrained.The GEM-Mars GCM (Neary and Daerden, 2018; Daerden et al., 2023) has two schemes: one to simulate the impact of gravity waves from orographic sources such as mountains and topography (McFarlane, 1987), and one for non-orographic sources such as convective forcing and baroclinic waves (Hines, 1997a; 1997b; 2004; Charron et al., 2002). Both schemes calculate a deceleration of the grid-scale winds, often termed “gravity wave drag”. This can have an indirect effect on temperature and on the distribution of trace gases.The schemes include some “tuning” parameters that can be adjusted to modify when and where this drag occurs. For example, in the non-orographic scheme, the level at which waves are expected to be launched and the lower bound vertical wavenumber, which limits the maximum vertical wavelength of the spectrum allowed, can be adjusted.Using estimates of wave activity derived from perturbations in observed temperature profiles from the ExoMars Trace Gas Orbiter and MAVEN (Neary et al. submitted), we will explore how these tuning parameters affect the resulting gravity wave drag climatology in GEM-Mars. By comparing model output with observational constraints across latitude, season, and local time, we aim to identify parameter settings that better reproduce the observed distribution and intensity of wave activity. This approach will help assess how well the current parameterisations capture the Martian atmosphere and where further refinement is needed.References:Charron, M. et al., 2002. Intercomparison of gravity wave parameterizations: Hines Doppler-spread and Warner and McIntyre ultra-simple schemes. Journal of the Meteorological Society of Japan 80, 335–345.Daerden, F. et al., 2023. Heterogeneous Processes in the Atmosphere of Mars and Impact on H2O2 and O3 Abundances. Journal of Geophysical Research: Planets 128, e2023JE008014. https://doi.org/10.1029/2023JE008014Hines, C., 1997a. Doppler-spread parameterization of gravity-wave momentum deposition in the middle atmosphere: Part 1 Basic Formulation. Journal of Atmospheric and Solar-Terrestrial Physics 59.Hines, C.O., 1997b. Doppler-spread parameterization of gravity-wave momentum deposition in the middle atmosphere. Part 2: Broad and quasi monochromatic spectra, and implementation. Journal of Atmospheric and Solar-Terrestrial Physics 59, 387–400.Hines, C.O., 2004. The Doppler spread theory and parameterization revisited. Journal of Atmospheric and Solar-Terrestrial Physics 66, 949–956. https://doi.org/10.1016/j.jastp.2004.02.005McFarlane, N.A., 1987. The effect of orographically excited gravity wave drag on the general circulation of the lower stratosphere and troposphere. Journal of the Atmospheric Sciences 44, 1775–1800.Neary, L., Daerden, F., 2018. The GEM-Mars general circulation model for Mars: Description and evaluation. Icarus 300, 458–476. https://doi.org/10.1016/j.icarus.2017.09.028Neary, L., et al., 2026. A multi-mission climatology of gravity waves in the Martian mesosphere and thermosphere. Submitted to Space Science Reviews.

NASA’s Mars Atmosphere and Volatile EvolutioN spacecraft carries an extensive suite of instruments for characterizing the Mars upper atmosphere. Of these, the NGIMS, IUVS, and EUVM instruments produce datasets for CO ₂ density and neutral atmosphere temperature. The different instruments and retrieval methods utilized provide an expansive view of the Mars upper atmosphere. To make full use of the geophysical coverage offered by these datasets, we undertake a systematic comparison of the datasets to understand where they are different and how any biases between datasets can be removed. We conduct pairwise comparisons between datasets, binning the data by geophysical and forcing parameters, to develop adjustment factors that can be used to adjust the measured CO ₂ density and neutral temperature of one dataset to nominal agreement with another. The determined adjustment factors are reported for use by the wider Mars aeronomy community.

We present a comprehensive analysis of Martian thermospheric variability using nearly a decade of solar occultation measurements from the MAVEN Extreme Ultraviolet Monitor (EUVM). These data provide vertical profiles of density and temperature from to 180 km at dawn and dusk, enabling the investigation of long‐term drivers of variability and latitudinal structure. Exospheric temperatures, derived from fits to 130–200 km temperature profiles, are found to be strongly correlated with solar EUV irradiance and track the solar cycle, while densities at 180 km are dominated by seasonal variability driven by total solar irradiance and dust heating of the lower atmosphere. This decoupling of temperature and density highlights the importance of both solar and lower atmospheric processes in regulating thermospheric structure. Latitudinal patterns differ by local time: dawn is influenced primarily by large‐scale meridional circulation, while dusk variability reflects a combination of solar heating and dynamical modulation by dust. Comparisons with the Mars Global Ionosphere‐Thermosphere Model (MGITM) indicate that gravity waves play a key role in shaping the observed latitudinal structure. Regional dust storms enhance dynamical effects at dawn and local heating at dusk, with impacts extending to latitudes decoupled from the storm locations. The exospheric temperature response to solar EUV irradiance is compared to recent measurements at Earth, showing a ∼50% difference from prior comparisons, with Earth being 3–5× more sensitive than Mars to solar EUV irradiance induced temperature changes. These results provide new constraints on the coupled solar, dust, and dynamical forcing of the Martian thermosphere.

Solar extreme ultraviolet (EUV, 10–100 nm) and X‐ray (<10 nm) photons are the primary ionization source for the dayside Mars ionosphere. Their fluxes, especially at short wavelengths, increase significantly during solar flares. Among the series of solar flares and solar storms encountered by Earth and Mars in May 2024, one of the strongest solar flares occurred on 20 May 2024 when the Mars Atmospheric and Volatile EvolutioN (MAVEN) spacecraft was entering the Mars ionosphere. This event provides a unique opportunity to study the Mars ionospheric response to the onset and early phase of an extremely intense flare. This study utilizes two particle measurements onboard MAVEN to infer the flare timeline and a flare class of X12.8. The observed main ionospheric response is the increased density at ∼400 km altitude at the flare onset and at ∼300 km altitude near the flare peak.