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.

Abstract We report the signature of solar forcing in the thermosphere using daytime temperature profiles from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) instrument on NASA's Ionospheric Connection (ICON) Explorer mission. We compare temperatures from 90 to 133 km altitude with solar extreme ultraviolet flux and also with results from a Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM‐ICON) forced with MIGHTI wind and temperature observations at the bottom boundary near 97 km. For moderate solar activity in late 2021 to early 2022, MIGHTI temperature oscillations correlate with the 27‐day solar rotation period (r = 0.84) at 133 km with an average amplitude of 38 K, more than twice the GCM amplitude for the same time period. At 110 km, average amplitudes are 8 K whereas the GCM shows insignificant correlation below 115 km (<0.3). These results reveal that solar forcing in the lower thermosphere is stronger than predicted.

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 CO2 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 CO2 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.

Abstract Using NASA's Global‐scale Observations of the Limb and Disk (GOLD)'s Dark Limb Mode (DLM) observations, we provide a multi‐year characterization of nighttime Equatorial Ionization Anomaly (EIA) morphology and variability. From geostationary orbit, GOLD measures OI 135.6 nm limb radiance at ∼33°E and ∼128°W longitudes, yielding routine, time‐evolving altitude–latitude cross sections of the nighttime ionosphere (∼100–430 km) and enabling investigation of EIA morphology and temporal variability. Forward‐modeled line‐of‐sight integrations using WACCM‐X electron densities and GLOW‐derived volume emission rates indicate that GOLD limb radiance peaks at tangent altitudes ∼40 km lower than the contributing F‐region electron density peak at the limb longitude. Multi‐year (2019–2025) observations reveal limb‐to‐limb differences, pronounced day‐to‐day variability, and strong solar‐flux dependence in the EIA crest. This new DLM data set provides a distinct observational capability for ionosphere–thermosphere coupling studies and space‐weather applications.

AbstractThe 14 October 2023 annular solar eclipse was visible from the US Pacific coast to Brazil's east coast. NASA's Global‐scale Observations of Limb and Disk (GOLD) mission observed the first synoptic thermospheric temperature changes from a geo‐stationary orbit above 47.5°W longitude between 17 and 20 UT during the eclipse. These daytime thermospheric changes were derived using GOLD's disk far ultraviolet (FUV) measurements. A significant decrease in the daytime disk temperatures (∼100 K) was seen near the peak annularity compared to the day before (baseline). The temperature reduction's spatial morphology is also like that of the eclipse shadow. Previous modeling studies of other eclipses typically show a much smaller temperature decrease (∼30–40 K; a factor of 2–3 lower) compared to GOLD observations. These first of kind results provide new insight into the dynamic response of the coupled thermosphere and ionosphere system to transient solar events, including eclipses.

We investigated the effects of storm-time diffuse auroral electron precipitation on ionospheric Pedersen and Hall conductivity and conductance during the CME-driven St. Patrick's Day storms of 2013 (min Dst = -131 nT) and 2015 (min Dst = -233 nT). These storms were simulated using the magnetically and electrically self-consistent RCM-E model with STET modifications, alongside the B3C auroral transport code to compute ionospheric conductivities and height-integrated conductance. The simulation results were validated against conductance inferred from Poker Flat Incoherent Scatter Radar (PFISR) and Millstone Hill Incoherent Scatter Radar (MHISR) measurements. Our simulations show that the magnetic latitude and local time distribution of Pedersen and Hall auroral conductance strongly correlate with diffuse electron precipitation flux, with the plasmapause marking the low-latitude boundary of conductance. Simulated Pedersen/Hall conductance agrees reasonably well with PFISR measurements at 65.9 degrees MLAT during diffuse auroral precipitation. During the intense 2015 storm, diffuse aurora extended down to 52.5 degrees MLAT, with simulated conductance agreeing within a factor of two with MHISR observations. Discrete auroral arcs observed during both storms enhanced PFISR conductance by tens of siemens, though these enhancements were not captured by the model. Additionally, the simulated electric intensity showed development of sub-auroral polarization streams (SAPS) and dawn SAPS features and followed the general trend of Poker Flat electric intensity at 65.9 degrees MLAT during diffuse aurora, despite being updated every 5 min. The overall agreement between simulated ionospheric conductance and electric intensity with observations highlights the model's capability during diffuse auroral precipitation.

The scientific and societal importance of short-term changes in the thermosphere–ionosphere (T–I) system highlights a need to better understand short-term changes in the thermosphere. For collision avoidance, this need becomes increasingly important as the number of low-earth-orbiting satellites increases because geomagnetic activity can cause dramatic, unexpected increases in satellite drag. The thermospheric density changes responsible for changes in drag depend primarily on changes in the thermospheric temperature. However, for collision avoidance, the specification of drag could also be problematic during quiet periods when the number of satellites and the uncertainties in their orbits are large. While temperatures and densities at higher altitudes (≳250 km) have been extensively studied and modeled, there is a knowledge gap for densities at lower-middle-thermosphere altitudes (≲200 km). At these lower altitudes, the primary sources of thermospheric density data, in situ and drag data from satellites, are rarely available. Remote sensing of temperatures and composition by NASA's Global-scale Observations of the Limb and Disk (GOLD) mission can help fill this gap. The GOLD mission produces disk images of neutral temperature, a key parameter for understanding neutral density in the lower-middle thermosphere. However, while disk images of the temperature have been available since the launch of GOLD, recent improvements to its observational capability that are relevant to data interpretation may not be widely known. Also, other temperature retrieval techniques than GOLD's have been published. Comparisons indicate that GOLD's technique gives the most consistent results and yields the lowest uncertainties. This paper discusses both temperature retrieval techniques and issues in interpreting GOLD's images of temperatures.

We present the first observations of the dayside coronal oxygen emission in far ultraviolet (FUV) measured by the Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM). The high sensitivity of EMUS is providing an opportunity to observe the tenuous oxygen corona in FUV, which is otherwise difficult to observe. Oxygen resonance fluorescence emission at 130.4 nm provides a measurement of the upper atmospheric and exospheric oxygen. More than 500 oxygen corona profiles are constructed using the long-exposure time cross-exospheric mode (OS4) of EMUS observations. These profiles range from similar to 200 km altitude up to several Mars radii (>6 R-M) across all seasons and for two Mars years. Our analysis shows that OI 130.4 nm is highly correlated with solar irradiance (solar photoionizing and 130.4 nm illuminating irradiances) as well as changes in the Sun-Mars distance. The prominent short term periodicity in oxygen corona brightness is consistent with the solar rotation period (quasi-27-day). A comparison between the perihelion seasons of Mars Year (MY) 36 and MY 37 shows interannual variability with enhanced emission intensities during MY 37, due to the rise of Solar Cycle 25. These observations show a highly variable oxygen corona, which has significant implications on constraining the photochemical escape of atomic oxygen from Mars.

The Emirates Mars Ultraviolet Spectrometer (EMUS), aboard the Emirates Mars Mission (EMM), has been conducting observations of ultraviolet emissions within the Martian exosphere. Taking advantage of the distinctive orbit of the EMM around Mars, EMUS utilizes a dedicated strafe observation strategy to scan the illuminated Martian exosphere at tangential altitudes ranging from 130 to over 20,000 km. To distinguish between emissions of Martian origin and those from the interplanetary background, EMUS conducts specialized background observations by looking away from the planet. This approach has allowed us to investigate the radial and seasonal variations in Martian coronal emission features at H Lyman-alpha, beta and gamma wavelengths. Our analysis supports the previous studies indicating that Martian exospheric hydrogen Lyman emission brightness attains its highest levels around the southern summer solstice and reaches its lowest levels when Mars is near aphelion. Additionally, a secondary peak emission at all altitudes is observed after perihelion during Martian Year (MY) 36, which can be attributed to a Class C dust storm. Our study establishes a strong correlation between solar flux and coronal brightness for these emissions, highlighting the impact of solar activity on the visibility of Martian corona. In addition, we have examined interannual variability and found that emission intensities in MY 37 surpassed those in MY 36, primarily due to increased solar activity. These observations help to understand potential seasonal patterns of exospheric hydrogen, which is driven by underlying mechanisms in the lower atmosphere and solar activity, eventually suggesting an impact on water loss in the Martian atmosphere. Atomic hydrogen primarily forms as a product when Martian water undergoes various photochemical reactions. These hydrogen atoms encircle Mars and become illuminated by solar radiation, leading to the creation of Martian hydrogen corona. The Emirates Mars Ultraviolet Spectrometer (EMUS), on the Emirates Mars Mission spacecraft, is currently studying the Martian atmosphere using the ultraviolet light emissions of different atoms and molecules on Mars. In this study, we have analyzed EMUS observations and determined that atomic hydrogen emission intensities increase during the Martian southern summer and decrease as Mars moves farther away from the Sun. Furthermore, we have compared the hydrogen brightness between two consecutive Martian years and have found that the hydrogen brightness is higher in the most recent year primarily due to increased solar radiation. These observations help us understand possible patterns that occur during different seasons on Mars and the mechanisms underlying water loss in the Martian atmosphere. We present the variability in Martian atomic hydrogen brightness from early Martian year (MY) 36 to the first quarter of MY 37 Martian exospheric H Ly-beta and gamma emissions reach their peak brightness during the southern summer of MY 36 Martian corona is much brighter at H Ly-beta wavelength in MY 37 compared to the previous year due to increased solar irradiance

Most ionospheric models cannot sufficiently reproduce the observed electron density profiles in the E-region ionosphere, since they usually underestimate electron densities. Mitigation of this issue is often addressed by increasing the solar soft X-ray flux which is ineffective for resolving data-model discrepancies. We show that low-resolution cross sections and solar spectral irradiances fail to preserve structure within the data, which considerably impacts the radiative processes in the E-region, and are largely responsible for the discrepancies between observations and simulations. To resolve data-model inconsistencies, we utilize new high-resolution (0.001 nm) atomic oxygen (O) and molecular nitrogen (N2) cross sections and solar spectral irradiances, which preserve autoionization and narrow rotational lines, allowing solar photons to reach lower altitudes and increase in the photoelectron flux. This work improves upon Meier et al. (2007) by additionally incorporating new high-resolution N2 photoionization and photoabsorption cross sections in model calculations. Model results with the new inputs show increased O+ production rates of over 500%, larger than those of Meier et al. (2007) at 0.1 nm resolution, and total ion production rates of over 125%, while N2+ production rates decrease by ∼15% 30 in the E-region in comparison to the results obtained using the cross section compilation from Conway (1988). Low-resolution molecular oxygen (O2) cross sections from the Conway (1988) compilation are utilized for all input cases and indicate that O2+ is a dominant contributor to the total ion production rate in the E-region. Specifically, the photoionization contributed by longer wavelengths is a main contributor at ∼120 km.

The Emirates Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM) Hope probe images Mars at wavelengths extending from approximately 100 to 170 nm. EMUS observations began in February 2021 and cover over a full Mars year. We report the first limb scan observations at Mars of ultraviolet emissions Ar I 106.6 nm, N I 120 nm, and carbon monoxide (CO) Fourth Positive Group (A - X) band system excited by electron impact on CO. We use EMUS limb scan observations to retrieve number density profiles of argon, molecular nitrogen, atomic oxygen, and CO in the upper atmosphere of Mars from 130 to 160 km. CO is a sensitive tracer of the thermal profile and winds in Mars' middle atmosphere and the chemistry that balances CO2 in the atmosphere of Mars. EMUS insertion orbit special observations demonstrate that far ultraviolet limb measurements of the Martian thermosphere can be spectroscopically analyzed with a robust retrieval algorithm to further quantify variations of CO composition in the Martian upper atmosphere.

We report the highest altitude detection of water vapor on Mars to date. The daytime limb observations by the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are of hydroxyl (OH) prompt emission near 308 nm, which is excited directly from the photodissociation of water vapor by the solar Lyman-alpha flux. Average IUVS daytime water vapor densities near 130 km are 3 x 107 cm-3 around perihelion. The water vapor densities diurnally vary with a peak near midday and no detection at sunrise and sunset. To evaluate the large daytime water vapor densities for self-consistency, we also report the simultaneous observation of OH solar fluorescence emission near 308 nm in the thermosphere, which enables the retrieval of OH densities. Using a one-dimensional photochemical model initialized with the daytime IUVS water vapor densities, modeled peak OH densities are in good agreement with the observed IUVS peak OH densities. Because the observed thermospheric temperatures are controlled by solar insolation and cross the water frost point during the day, we suggest that the IUVS observed water vapor is created by the daily sublimation of water ice particles supplied from below. We discuss the implications of the IUVS observations on the present day loss of water vapor from Mars in the form of atomic hydrogen. The loss of water from Mars is a compelling topic of study that helps trace its transformation from a warm and wet planet to the cold and dry planet that exists today. Water loss is greatly facilitated by water vapor transport to altitudes above 100 km during the dust storm season on Mars. We report the highest altitude detection of water vapor on Mars to date. Daytime observations between 110 and 150 km altitude indicate a strong diurnal variation of water vapor there, with a peak near midday. The observations are made by the Imaging Ultraviolet Spectrograph (IUVS) on NASA's Mars Atmosphere and Volatile Evolution spacecraft currently orbiting Mars. Simultaneous IUVS observations of hydroxyl, a product of water vapor destruction by solar ultraviolet radiation, reveal a self-consistent picture of daytime water vapor variability. We suggest that the water is lofted to these high altitudes from below as ice particles before they reach altitudes where the temperatures are high enough to release the water in the vapor phase. The IUVS daytime water vapor densities in the upper atmosphere indicate that its escape to space is more efficient than previously thought. OH prompt emission observations provide the highest altitude detection of water vapor on Mars to dateThermospheric water vapor concentrations are diurnally dependent, with a peak near midday at perihelionDiurnal temperature variations are consistent with nighttime sequestration of water as ice, followed by its daytime sublimation to vapor

After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth's thermosphere that were observed by NASA's Global-scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of Sigma O/N2 and neutral temperature (at similar to 160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe a heretofore unseen spatial morphology simultaneously in Sigma O/N2, neutral temperature, and total electron content. Equator-to-pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K. On Saturday 10 May 2024, the sun launched a wave of energized plasma toward the Earth. A large disturbance in the Earth's magnetic field associated with the solar wind resulted in an extreme geomagnetic storm. The storm impacted power grids, disrupted navigational systems used by farming equipment, and produced aurora seen around the globe. The storm produced remarkable effects in the Earth's upper atmosphere that were observed by NASA's Global-scale Observations of the Limb and Disk (GOLD) mission. In this letter, we use images measured by GOLD to directly link atmospheric dynamics resulting from the May 10-12 superstorm with dramatic changes in composition, temperature, and global circulation in the Earth's upper atmosphere. We observe previously unseen structure in the upper atmosphere associated with equator-to-pole temperature differences exceeding 400 K. Peak neutral temperatures near 160 km exceed 1400 K at high latitudes. GOLD disk images of Sigma O/N2 and neutral temperature link storm time dynamics with changes in thermospheric composition and temperature We observe a previously unseen spatial morphology in Sigma O/N2, neutral temperature, and total electron content Peak equator-to-pole temperature differences exceed 400 K but relax to pre-storm conditions well before Sigma O/N2

Observations of far‐ultraviolet (FUV) dayglow by the Global‐scale Observations of Limb and Disk (GOLD) mission provide an opportunity for quantifying the global‐scale response of the thermosphere to solar extreme‐ultraviolet variability and geomagnetic activity. Relative temperature changes can be measured by monitoring changes in the rotational structure observed in molecular nitrogen Lyman‐Birge‐Hopfield (LBH) band emissions. We present a new technique for deriving effective neutral temperatures from GOLD FUV observations using optimal estimation fits to spectra containing LBH band emissions. We provide an overview of the theoretical basis for the GOLD Level 2 TDISK algorithm. Effects on derived effective neutral temperatures from instrument artifacts and particle background are reviewed. We also discuss GOLD Level 1C DAY and Level 2 TDISK data products and present representative examples of each. We show that effective neutral temperatures vary with local time, exhibit a strong dependence on season and solar zenith angle, and correlate strongly with geomagnetic and solar activity. Finally, we present results from a preliminary data product validation that show good agreement with coincident GOLD exospheric temperatures and predictions from a global reference atmospheric model.

E-region models have traditionally underestimated the ionospheric electron density. We believe that this deficiency can be remedied by using high-resolution photoabsorption and photoionization cross sections in the models. Deep dips in the cross sections allow solar radiation to penetrate deeper into the E-region producing additional ionization. To validate our concept, we perform a study of model electron density profiles (EDPs) calculated using the Atmospheric Ultraviolet Radiance Integrated Code (AURIC; \citeA{strickland1999atmospheric}) in the E-region of the terrestrial ionosphere. We compare AURIC model outputs using new high-resolution photoionization and photoabsorption cross sections, and solar spectral irradiances during low solar activity with incoherent scatter radar (ISR) measurements from the Arecibo and Millstone Hills observatories, COSMIC-1 observations, and outputs from empirical models (IRI-2016 and FIRI-2018). AURIC results utilizing the new high-resolution cross sections reveal a significant difference to model outputs calculated with the low-resolution cross sections currently used. Analysis of AURIC EDPs using the new high-resolution data indicate fair agreement with ISR measurements obtained at various times at Arecibo but very good agreement with Millstone Hills ISR observations from $\sim96$ km to $140$ km. However, discrepancies in the altitude of the E-region peak persist. High-resolution AURIC calculations are in agreement with COSMIC-1 observations and IRI-2016 model outputs between $\sim105$ km and $140$ km while FIRI-2018 outputs underestimate the EDP in this region. Overall, AURIC modeling shows increased E-region electron densities when utilizing high-resolution cross sections and high-resolution solar irradiances, and are likely to be the key to resolving the long standing data-model discrepancies.

We present temperature maps derived from number density retrievals of carbon dioxide (CO 2 ) for the upper mesosphere and lower thermosphere of Mars using limb observations from the Imaging Ultraviolet Spectrograph (IUVS) aboard NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We retrieve CO 2 densities using O( 1 S) metastable atoms that radiatively relax by emitting photons at 297.2 nm, producing a double‐peaked emission profile detectable by IUVS. Retrieved CO 2 densities are used to derive altitude profiles of temperature as a function of latitude, longitude, local time, season, dust activity, and solar activity. CO 2 density and temperature profiles retrieved using the O I 297.2 nm emission feature presented herein extend previous IUVS retrievals from 130–170 km down to 80 km. We validate retrieved CO 2 densities and derived temperatures using coincident measurements and corresponding data products produced by MAVEN IUVS, as available. Analysis of this comprehensive data set, which spans Mars years 32–36, shows (a) a consistently well‐defined mesopause at approximately 120 km, (b) warming at high pressures (typically below ∼100 km) for a variety of geophysical conditions, (c) asymmetry in temperatures at dawn and dusk with respect to latitude during different seasons (warmer temperatures at dawn during northern hemisphere autumn/winter and cooler temperatures at dusk during spring/summer), and (d) longitudinal waves with a dominant wave‐3 component in both the upper mesosphere and lower thermosphere, with lower (80–90 km) and upper (135–145 km) atmospheric waves about 65° out of phase.

We report six years of observations of dayside temperatures of the middle and upper atmospheres of Mars made by the Imaging Ultraviolet Spectrograph instrument aboard the MAVEN spacecraft. Thermospheric temperatures show strong long-term variability associated with Martian season and solar cycle. Temperatures from both the Martian thermosphere and mesosphere show strong short-term variability indicating coupling from the lower atmosphere. The observed local time effect is strong in both upper and middle atmosphere temperatures. The thermosphere tends to be colder in the morning compared to the evening when temperatures are higher. Middle atmospheric temperatures show cooling during the dawn and dusk hours. Our analysis shows strong tidal activity during aphelion, whereas non-migrating tides are suppressed during perihelion, possibly due to increased dust activity. Observations during the deep minimum of solar cycle 24 reveal that thermospheric temperatures are highly variable with respect to local time if solar forcing, Mars–Sun distance, and spatial effects are removed.

Continuous Global Auroral Imaging observations provide key forecasting information for space weather events and their effect on many technological systems and infrastructure.This includes severe geomagnetically induced currents in power grids, as well as increased risk of spacecraft surface charging and satellite drag.By observing with two spacecraft per hemisphere from a highly elliptical Tundra orbit we can provide continuous high resolution auroral and thermospheric imagery and impactful data products.We recommend a continuous global auroral imaging mission be prioritized over the next decade along with near-term investments in key technologies such as FUV filters and detectors to improve performance and reduce cost.

The Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission spacecraft, which observes ultraviolet emission between approximately 100 and 170 nm, has observed multiple instances of nightside aurora at Mars. Variations in the auroral brightness and morphology have been observed to change on timescales of tens of minutes. The brightest aurorae are typically seen following space weather events, i.e., coronal mass ejection and stream interaction region impacts. The InSight Fluxgate Magnetometer (IFG) on the Interior Explorations using Seismic Investigations, Geodesy and Heat Transport (InSight) lander measured the magnetic field at the surface of Mars. IFG has measured variations in the nightside surface magnetic field, presumably due to variations in ionospheric and magnetospheric currents. Periodic and aperiodic variations in the surface field have been observed, including with timescales of a few minutes to tens of minutes. The magnitude of the fluctuations is often larger following space weather events. We examine the connection between the presence of aurora as observed by EMUS and surface magnetic field fluctuations as measured by IFG. Coincident EMUS and IFG observations show enhanced surface magnetic field fluctuations during times when aurorae were present. Additionally, the timescale of fluctuations in the auroral brightness are similar to the timescale of surface magnetic field fluctuations for non-coincident observations. These results suggest that IFG measured the surface magnetic field effect of time varying ionospheric auroral currents.

&lt;p&gt;The Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM) observes the Martian dayglow at ultraviolet wavelengths (100-170 nm). EMUS disk observations show unexpected variations in atomic hydrogen, atomic oxygen, and carbon monoxide disk emissions. These variations display local time and hemispheric asymmetry and are observed in approximately 25% of the disk images. England et al. (2022; doi:10.1029/2022GL099611) suggested that the spatial structure, occurrence, and spectral characteristics of these variations are associated with changes in composition and photoelectron flux. Using a similar EMUS data set, Chaffin et al. (2022; doi:10.1029/2022GL099881) reported the first observations of neutral atmosphere auroral emission on the Martian dayside, which is not a new type of aurora but another observable form of proton aurora, and suggested that solar wind deposition is responsible for exciting the auroral emission. We further investigate these two potential drivers of the unexpected variations in EMUS disk observations using data from the Imaging Ultraviolet Spectrograph (IUVS), the Solar Wind Ion Analyzer (SWIA), the SupraThermal And Thermal Ion Composition (STATIC) instrument, and a magnetometer (MAG), all onboard NASA&amp;#8217;s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We use vertical profiles of densities and temperatures retrieved from limb scan observations by IUVS to identify signatures of dynamics that correlate with unexpected variations in EMUS disk observations. We use measurements from all of the instruments to categorize and characterize EMUS observations in order to determine how changes in composition and solar wind deposition produce unexpected variations in the Martian ultraviolet dayglow.&lt;/p&gt;