Martian Thermosphere Research Articles

Retrieval of Ar, N2, O, and CO in the Martian Thermosphere Using Dayglow Limb Observations by EMM EMUS

AbstractThe 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.

A Comparative Analysis of Gravity Waves in He and Ar Densities in the Martian Thermosphere

AbstractIn this study, we conducted a comparative analysis of gravity waves (GWs) in the Martian upper thermosphere, utilizing He and Ar densities measured by the Neutral Gas and Ion Mass Spectrometer aboard the Mars Atmosphere and Volatile EvolutioN spacecraft. Our investigation revealed that GWs are a persistent phenomenon in Martian thermospheric He densities, akin to their presence in heavier species like Ar and CO2. Intriguingly, we observed that local time and seasonal variations in He GW amplitudes exhibit an almost opposite pattern compared to those in Ar. A significant breakthrough was the identification of a temperature‐dependent transition wavelength distinctly demarcating short and long wavelengths. This transition wavelength, which increases with increasing background temperatures, profoundly influences the dominance of GW amplitudes in He and Ar. In the short‐wavelength limit, GW amplitudes in He prevail, while GW amplitudes in Ar take precedence in the long‐wavelength limit. During periods of lower temperatures during midnight and the dawn terminator, transition wavelengths fall within the observed wavelength range enabling the study of dominance of GWs in He and Ar. Conversely, higher temperatures (>180 K) during daytime and the dusk terminator eliminate transition wavelengths within our observational range. Consequently, the amplitudes of GWs in He dominate over those in Ar. Furthermore, under nominal dust conditions, GWs in both He and Ar exhibit an inverse relationship with their respective background densities. During global dust storm, this inverse relationship is maintained for GWs in He, while GWs in Ar display a slight positive correlation with background Ar densities.

Water Vapor Variability in the Thermosphere of Mars During Mars Years 32–36

AbstractUsing Mars Atmosphere and Volatile Evolution observations, we characterize the variability of water vapor in the Martian thermosphere during Mars Years 32–36. Near a fixed atmospheric pressure level of ∼5 × 10−7 Pa, the typical water density is 1.7 (±1.0) × 103 cm−3 and the typical water mixing ratio is 14.6 (±9.0) ppm. Thermospheric water levels are higher during the southern spring and summer seasons when Mars is near perihelion and there is significant dust loading in the lower atmosphere. However, the seasonal variation is not the same from year‐to‐year, likely due to annual differences in dust loading. Water vapor abundance is highly correlated with the amount of dust in the lower atmosphere, and increases during both regional and global dust storms. Additionally, there is a local time asymmetry with higher mixing ratios observed during morning local times, potentially caused by atmospheric circulation. Our results support previous work that found increased dust levels allow more water to be supplied directly to the thermosphere.

Dynamical Heating in the Martian Thermosphere

AbstractDynamical heating and cooling are prominent features of planetary atmospheres resulting in thermospheric structures on Venus, Earth and Mars. The purpose of this study is to determine the location and amplitude of localized heating regions in the Martian thermosphere, confirm that they occur in regions of wind convergence and compare the observed dynamical heating with that predicted by a global thermospheric model. This investigation uses several years of data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission including observations made by the Neutral Gas and Ion Mass Spectrometer (NGIMS) as well as the Extreme Ultraviolet Monitor (EUVM). Specifically, the analysis focuses on several years of horizontal wind, temperature, and composition data. EUVM measurements provide a solar forcing context for the neutral thermosphere data sets and aid in the statistical analysis. Statistical results are compared with two versions of the Mars Global Ionosphere Thermosphere (M‐GITM) global circulation model: one that includes gravity wave parametrization and a version without gravity wave effects. Data analysis indicates that heating features exist around 2–3 and 17–18 local solar time. These locations coincide with regions of converging winds and are in better agreement with M‐GITM when a gravity wave parametrization is included in the model. An oscillation in the observed wind field also results in convergence and a density enhancement near 15 local time. While a similar oscillation is reproduced by the model, the amplitude is much lower than observed and may be a result of modeled zonal winds that are too low.

Martian Thermosphere Response to Solar Flares: MAVEN NGIMS Observations

The solar flare is a sudden eruptive solar phenomenon with significant enhancements in solar X-ray and Extreme Ultraviolet radiations, resulting in large amounts of energy being injected into the planetary atmosphere. Case studies have been extensively presented to analyze the effect of extremely large flares on the Martian upper atmosphere, but the general features of the Martian thermospheric response to flares are still poorly understood. In this work, we select 12 intense solar flares that occurred between 2015 and 2017 and investigate the densities and compositional variations of the dayside Martian thermosphere to these flares with the aid of the measurements made by the Mars Atmosphere and Volatile EvolutioN. The statistical studies indicate that the responses of the Martian thermosphere to flares are complicated that both the class of the flare and the wavelength of the enhanced radiation may have prominent influences on the thermal expansion of the atmosphere and the atmospheric photochemical reactions.

NGIMS/MAVEN observations of longitudinal structures in the Martian thermosphere

NGIMS/MAVEN observations of longitudinal structures in the Martian thermosphere

Gravity wave driven variability in the Mars ionosphere-thermosphere system

Gravity waves (GWs) have been persistently observed in neutral species in the Martian thermosphere. In this paper, we study characteristics of GWs in O2+ and O+ ions in the Mars ionosphere (∼160–200 km) and examine their relation to GWs in the thermosphere. For this purpose, we use O2+, O+, and Ar densities measured by the Neutral Gas and Ion Mass spectrometer (NGIMS) instrument aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The amplitudes and (horizontal) wavelengths of the GWs are extracted from the density profiles. The results of the present study show that GWs are ubiquitous in the Martian ionosphere-thermosphere system. We found that the amplitudes of GWs in ions are ∼2 times larger than those in neutrals. While the amplitudes in ions reach as high as 70% of the background densities, the most probable amplitude 5%. The amplitudes of the GWs in ions are more on the nightside than on the dayside; more during the 2018 global dust storm period than during nominal dust conditions; and increase with decreasing in solar activity. All these results are qualitatively similar to those observed in neutrals. In addition, amplitudes of the GWs in ions show moderate correlation with those neutrals while the wavelengths show good correlation. The amplitudes of GWs in ions and neutrals show moderate negative correlation with thermospheric temperatures. All these results strongly suggest that the GWs in ions are due to those in neutrals and ion-neutral coupling may be strong in the altitude range of interest. The correlation between the amplitudes of GWs in ions and neutral, however, is local time dependent with weak correlation on the nightside. Other factors such as recombination or particle precipitation may be playing an important role in distorting the wavy nature in ions leading to weaker correlation with neutral waves on the night side. Furthermore, the correlation between GW amplitudes in ions and neutrals is weaker in strong crustal magnetic field regions. This implies that the magnetic fields control the motion of the ions leading to distorting in wavy nature in ions.

Solar Rotation Effects in Earth's and Mars' Thermospheric Densities as Revealed by Concurrent MAVEN, Swarm‐C, and GOES Observations

AbstractThe responses of Earth's and Mars' thermospheric densities to quasi‐periodic (∼27‐day) solar rotation variations in flux were measured contemporaneously by the Mars Atmosphere and Volatile EvolutioN, Geostationary Operational Environmental Satellites, and Swarm‐C satellites. While large solar rotation variability is found in both planetary thermospheres, correlation analyses performed on over 6 years of observations reveal that, independently of extreme ultraviolet flux level, Earth's daytime density response is about 10%–50% larger than Mars' at a similar density level. Important altitude dependencies in the density sensitivity to the solar rotation in solar flux are found in the Martian thermosphere, while the terrestrial thermosphere is shown to exhibit only small (±5%) day/night and latitude variations in the response. Detailed analyses focused on correlative periods in 2015–2016 and 2020 indicate important solar cycle effects in the sensitivities of both planetary thermospheres, with increased slopes under low solar flux conditions. These results provide important new insights into processes relevant to the interpretation of the sources of short‐term density variability in Mars' and Earth's thermospheres associated with solar drivers and point to the need for targeted modeling efforts along with dedicated data analyses to help resolve current unknowns in thermal balance processes.

Impacts of Gravity Waves in the Martian Thermosphere: The Mars Global Ionosphere‐Thermosphere Model Coupled With a Whole Atmosphere Gravity Wave Scheme

AbstractGravity waves are a key mechanism that facilitates coupling between the lower and upper atmosphere of Mars. In order to better understand the mean, large‐scale impacts of gravity waves on the thermosphere, a modern whole atmosphere, nonlinear, non‐orographic gravity wave parameterization scheme has been incorporated into a three‐dimensional ground‐to‐exosphere Mars general circulation model, the Mars Global Ionosphere‐Thermosphere Model (M‐GITM). M‐GITM simulations utilizing the gravity wave parameterization indicate that significant gravity wave momentum is deposited in the thermosphere, especially within the altitude range of 90–170 km. This impacts the winds in the thermosphere; in particular, M‐GITM simulations show a decrease in speed of the wind maximum in the summer hemisphere by over a factor of two. Gravity wave effects also impact the temperatures above 120 km in the model, producing a cooler simulated thermosphere at most latitudes. M‐GITM results were also compared to upper atmospheric temperature and wind data sets from the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft. Some aspects of wind data‐model comparisons improved once the gravity wave scheme was added to M‐GITM; furthermore, a cooler temperature profile produced by these new M‐GITM simulations for the MAVEN Deep Dip 2 observational campaign resulted in a closer data‐model comparison, particularly above 180 km. Overall, these modeling results show that gravity waves play an important role for the energy and momentum budget of the Martian thermosphere.

Spectral Analysis of Gravity Waves in the Martian Thermosphere during Low Solar Activity Based on MAVEN/NGIMS Observations

Gravity waves (GWs) are important for vertical coupling between the lower and upper atmosphere on Mars. Saturated GWs will promote the acceleration of mean flow and turbulence generation, causing diffuse transport of energy and momentum. We analyze the spectral characteristics of GWs in the thermosphere on Mars during the low solar activity of Martian Year (MY) 35, based on CO2 density measured by the Neutral Gas and Ion Mass Spectrometer (NGIMS) on board Mars Atmosphere and Volatile EvolutioN (MAVEN). The results are compared with those of MY33 at the higher solar activity. The vertical wavenumber spectral density obtained in the Martian thermosphere is similar to the semi-empirically predicted saturation spectrum in the Earth’s atmosphere, with a logarithmic spectral slope around −3. The average spectral density of GWs shows saturation between 160 and 200 km and decreases with increasing altitude. Compared to MY33, GW activity is larger and less attenuated in MY35 as it propagates upward, implying that waves experience more favorable propagation conditions during low solar activity. Also, the dependence of GW activity on local time during this period is found to be different from previous studies, with the strongest GWs in the spring of MY35 occurring within 6–12 hr on the dayside, suggesting that the amplitude of the GWs in the Martian thermosphere during low solar activity is less controlled by the background temperature and is subject to dissipative effects of other factors, such as molecular viscosity and thermal conduction.

Retrieval of CO Relative Column Abundance in the Martian Thermosphere From FUV Disk Observations by EMM EMUS

AbstractCarbon monoxide (CO) is a sensitive tracer of the thermal profile and winds in Mars' middle atmosphere and the chemistry that balances CO2 in the whole atmosphere of Mars. The Emirates Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission Hope probe images Mars at ultraviolet wavelengths from approximately 100 to 170 nm. ΣCO/CO2, the column density ratio of CO to carbon dioxide, provides a sensitive measure of CO relative variability within the Martian thermosphere. Derived from the heritage of ΣO/N2 used at Earth, the ΣCO/CO2 algorithm uses emission from the CO Fourth Positive Group band system to derive the relative column abundance of CO above ∼70 km. We describe the EMUS ΣCO/CO2 algorithm, review the Level 3 data product, and discuss preliminary validation of the algorithm. The ΣCO/CO2 algorithm produces column density ratios that characterize the spatial structure and relative variability of CO abundance in the Martian thermosphere.

Emirates Mars Ultraviolet Spectrometer's (EMUS) Observation of Argon in the Martian Thermosphere

AbstractThe Emirates Mars Ultraviolet Spectrometer (EMUS) is a far ultraviolet spectrometer on‐board the Emirates Mars Mission's (EMM) which arrived at Mars on 9 February 2021. EMUS is designed to observe key neutral species in the Martian thermosphere (100–200 km) and exosphere (≥200 km). EMUS has observed two neutral argon (Ar) emission lines, Ar I 104.8 nm and Ar I 106.6 nm, in the thermosphere. Our interest in these emissions stem from argon's non‐reactiveness, making it a tracer for transport between the upper and lower atmosphere. We report average argon disk brightness measured by EMUS and compare them to measurements from Earth orbiting observatories. For the first time, this work investigates the variability of Ar I 106.6 nm brightness due to emission angles, solar zenith angles, solar longitudes, local times and latitudes. To contrast the behavior of inert argon we compare these results with the photochemically reactive oxygen 135.6 nm.

Topographic Gravity Waves Observed in the Martian Thermosphere: A Statistical Perspective From a 1‐D Full‐Wave Model

AbstractGravity waves (GWs) are significant dynamical processes in planetary atmospheres due to their efficient transport of momentum and energy from the lower to the upper atmosphere. Recent observations from in‐situ measurements by spacecraft like Mars Atmosphere and Volatile Evolution (MAVEN) also reveal ubiquitous GW activity in the Martian thermosphere. As a critical parameter for characterizing GWs, the wavelength spectrum has been studied for years. However, most of the current observations for the Martian thermosphere can only determine the apparent GW wavelength because they usually take one‐dimensional measurements within a typical GW period. In this work, we adopt a full‐wave GW model to statistically investigate the upward propagation of the topographic‐generated GWs and how their wavelength spectrum apparently looks in the thermosphere when observed by a spacecraft like MAVEN. We find that the wind significantly modifies the vertical wavelengths of GWs in the Martian atmosphere. Considering the GWs generated from topographic sources, we calculate their wavelength distribution in the thermosphere, with a most probable apparent vertical wavelength of around 14 km, consisting with the MAVEN observation. However, our theoretical wavelength spectrum is mainly concentrated in the low wavelength part (10–20 km), while the observed result contains a long‐tailed component in the long wavelength part. The mismatch between our model and observations indicates that at least 72% of the observed GWs in the thermosphere are not generated from topographic sources.

Disentangling the Dominant Drivers of Gravity Wave Variability in the Martian Thermosphere

In this study, we extracted the amplitudes of the gravity waves (GWs) from the neutral densities measured in situ by the neutral gas and ion mass spectrometer aboard the Mars Atmosphere and Volatile Evolution mission. The spatial and temporal variabilities of the GWs show that solar activity (the F10.7 cm solar flux corrected for a heliocentric distance of 1.66 au), solar insolation, and the lower atmospheric dust are the dominant drivers of the GW variability in the thermosphere. We developed a methodology in which a linear regression analysis has been used to disentangle the complex variabilities of the GWs. The three dominant drivers could account for most of the variability in the GW amplitudes. Variability caused by the sources of GWs and the effects of winds and the global circulation in the mesosphere and lower thermosphere are the other factors that could not be addressed. The results of the present study show that for every 100 sfu increase in the solar activity, the GW amplitudes in the thermosphere decrease by ∼9%. Solar insolation drives the diurnal, seasonal, and latitudinal variations of ∼9%, ∼4%, and ∼6%, respectively. Using the historical data of the dust opacity and solar activity, we estimated the GW amplitudes of the Martian thermosphere from MY 24 to MY 35. The GW amplitudes were significantly reduced during the maximum of solar cycle 23 and were highest in the solar minimum. The global dust storms of MY 25, 28, and 34 lead to significant enhancements in the GW amplitudes.

Topographic gravity waves observed in the Martian thermosphere: a statistical perspective from a 1-D full-wave model

Topographic gravity waves observed in the Martian thermosphere: a statistical perspective from a 1-D full-wave model

The North–South Asymmetry of Martian Ionosphere and Thermosphere

AbstractBased on Mars Atmospheric and Volatile EvolutioN's neutral composition and Langmuir probe electron density and temperature data, we statistically analyzed the climatic variations of the Martian thermosphere and ionosphere and found significant north–south asymmetry. In winter and summer, the asymmetry mainly originates from the north–south asymmetry of the solar zenith angle. However, the observed data still exhibit significant north–south asymmetry in equinox seasons. Under low solar extreme ultraviolet radiation, the thermospheric neutral density in the northern hemisphere is higher than that in the southern hemisphere. As solar radiation increases, the neutral density in the southern hemisphere gradually exceeds that in the northern hemisphere. In addition, the southern hemisphere density increases nonlinearly with the increase of solar radiation, whereas the northern hemisphere density increases linearly. The electron density and electron temperature in the Martian ionosphere also exhibit similar north–south asymmetry. The asymmetries in the ionosphere and thermosphere between the northern and southern hemispheres are likely related to significant differences in Mars' north–south topography or to north–south asymmetries in the residual magnetic field. After preliminary analysis, we found that the north–south asymmetry of Mars' remaining magnetic field would intensify the hemispheric asymmetry of the ionospheric electron density, but have no effect on the thermospheric neutral density. The hemispheric asymmetry may be primarily related to the significant difference in Mars' north–south topography.

Thermospheric density responses to Martian dust storm in autumn based on MAVEN data

The unique seasonal surface dust storms on Mars have a significant impact on the Martian atmosphere. However, due to the lack of observations, semi-empirical models are difficult to simulate the density changes in the thermosphere with the existence of dust storms in detail. Data from multiple Mars probes now offer new opportunities to study the detailed response of Martian dust storms to the upper atmosphere. In this paper, we use MAVEN accelerometer and mass spectrometer to study the variations of the Martian thermosphere density in autumn between MY 32 and MY34 (The corresponding Earth dates: February 11, 2015 to February 28, 2019), and use the seasonal model with dust storm index to fit the annual data of the above three Martian years. The results show that the thermosphere density has a clear response to the surface dust storm activity. Furthermore, the spatial distribution of measured data in autumn (northern hemisphere) is compared with the atmospheric density distribution simulated by the general circulation model (GCM) under specific initial conditions. The model simulation results agree well with the thermospheric density distribution characteristics of each Martian year under the initial strong dust storm conditions. It proves the important role of global dust storm in changing the structure of the Martian thermospheric atmosphere.

MAVEN/NGIMS wind observations in the martian thermosphere during the 2018 planet encircling dust event

During the 2018 planet encircling dust event (PEDE) at Mars, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft’s Neutral Gas and Ion Mass Spectrometer (NGIMS) was able to take a series of neutral wind observations in the thermosphere at around 150–220 km altitude. These MAVEN observations are the first in-situ measurements of thermospheric wind velocities during a Mars global dust storm. From these measurements, it was found that the observed averaged horizontal thermospheric wind speeds peaked to nearly 200 m/s during the onset of the dust storm before decreasing to about 140 m/s near the peak of the storm. The maximum averaged wind speed observed during the dust storm is not significantly greater than averaged wind speeds at other times, but does represent a local maximum that coincides with the timing of the dust storm. Additionally, throughout the mature and early decay stage of the PEDE, NGIMS wind observations show increased short-scale variability that distinguishes this time period from most other observational periods.

Simulation of photoelectron flux, electron density, emission rate and limb intensity of CO(a3π) Cameron bands in the Martian thermosphere: Comparisons with (1) SPICAM and IUVS observations and (2) other model calculations

Simulation of photoelectron flux, electron density, emission rate and limb intensity of CO(a3π) Cameron bands in the Martian thermosphere: Comparisons with (1) SPICAM and IUVS observations and (2) other model calculations

Concurrent effects of Martian topography on the thermosphere and ionosphere at high northern latitudes

Martian topography modulated non-migrating tides play important roles in the upper atmosphere and thus in the ionosphere through their coupling, especially in their longitude variations. In this study, the neutral scale height (Hn) and ionospheric peak electron density (NmM2) and height (hmM2) retrieved from the MGS radio occultation measurements were used to investigate the coupling between the Martian thermosphere and ionosphere under the forcing of topography modulated tides by investigating their concurrent longitude variations. A segment of the measurements with fixed local time was selected to analyze the relationships between the longitude variations of the parameters in detail. Longitude variations of the thermosphere and ionosphere are significant though topographic fluctuations are not very prominent at high northern latitudes. Longitude fluctuations of Hn and NmM2 are nearly in anti-phase and percentage fluctuation amplitudes of Hn are nearly twice as large as those of NmM2, which indicate the non-migrating tide forced coupling between the ionosphere and thermosphere conforms to the Chapman theory, and suggests longitude variation of NmM2 can be used as a quantitative indicator for that of the thermal structure in the lower thermosphere. Longitude variation phases of Hn and hmM2 are also discrepant. That is due to tide vertical propagation since Hn and hmM2 depend on the atmospheric thermal structures at different height levels. The thermosphere and ionosphere show longitude variations due to the topography; however, they are dominated by inconsistent longitude components. This implies discrepant exciting and propagating efficiencies of various topography modulated tides.Graphical