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Global auroral images and plasma sheet ion distributions and magnetic field data are examined for two intervals when the Ultraviolet Imager (UVI) onboard the Polar spacecraft was imaging the entire northern auroral oval and, at the same time, the Wind spacecraft was passing through the near-Earth plasma sheet. On 26 July 1997, UVI recorded a series of brief, localized auroral brightenings known as pseudobreakups. On 27 March 1996, UVI observed several global expansions of auroral activity. Large variations in the magnetic field were observed by the Wind magnetometer, large velocity moments were derived from Wind ion measurements, and ions were accelerated to mega-electron-volt energies during both types of activity. The plasma sheet dynamics appear very similar during these two different types of auroral activities. Closer inspection of the ion distribution functions and energy spectra indicate that the plasma sheet dynamics need to be characterized kinetically. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Solar activity, in the form of coronal mass ejections and corotating interaction regions, results in changes in the solar wind that propagate out through the solar system and interact with the magnetic field environments of planets. Such phenomena have been observed to affect the magnetic field and plasma around Mars as seen from orbit. However, no surface observations have previously been possible because of the absence of ground‐based instrumentation. Here, for the first time, we observe the effects of increased solar activity with the magnetometer on the InSight mission in December 2020. We find several days of increased activity including magnetic field fluctuations at periods of minutes to hours. Although only the flanks of this relatively weak coronal mass ejection hit Mars, the observed effects provide insight into how solar activity alters magnetic fields at the surface. Plain Language Summary: Space weather can disturb the magnetic field around planets as it travels away from the Sun throughout the Solar System. At Mars, phenomena associated with space weather have previously been observed by orbiting satellites. The InSight mission placed a magnetometer on the martian surface for the first time, allowing surface magnetic field measurements during times of increased solar activity. We observe such a period in December 2020 and find increased amplitudes of the surface magnetic field and increased fluctuations at periods of minutes to hours. These findings provide insight into the effect of magnetic fields on the martian surface. Key Points: We report the first surface magnetometer observations of space weather on MarsWe observe the magnetic field at the InSight landing site before, during and after a coronal mass ejection (CME)We observe increased magnetic field amplitudes and increased variability in the field after the CME [ABSTRACT FROM AUTHOR]

Mars' ultraviolet dayglow has been used to study its upper atmosphere for over four decades. Identifying variations in emission features has provided information on composition, density, and temperature. The Emirates Mars Ultraviolet Spectrometer onboard the Emirates Mars Mission observes Mars' dayglow at Far and Extreme UV wavelengths. Variations in disk emission features are studied, with a focus on O I 130.4, CO Fourth Positive Group and C I 156.1 nm. All show variations with local time (LT) and emission angle as expected. Dawn‐dusk asymmetry observed is attributed to LT differences in advection. Variations in the brightness of several dayglow features, including 130.4 nm, with irregular shapes are noted in around 25% of the disk images. These display some LT and hemispheric asymmetry in their occurrence rates. Examination of their spatial structure, occurrence, and spectra suggests these are associated with variations in composition and photoelectron flux. Plain Language Summary: Measurements of ultraviolet light coming from Mars' upper atmosphere has been used to measure its properties. From the color and brightness of the light, it is possible to identify both what chemical species are present in this region, their temperature and other information. The Emirates Mars Ultraviolet Spectrometer onboard the Emirates Mars Mission makes observations of this ultraviolet light in wavelength regions described as far and extreme ultraviolet. This study looks at emissions of far ultraviolet light that correspond to oxygen atoms, carbon monoxide, and carbon dioxide molecules. The circulation of gases in the upper atmosphere results in a difference in the brightness of these emissions between dawn and dusk. This study also introduces observations of irregularly shaped bright patches in these emissions. The shape, location, and spectra of these suggest they are the result of changes in the chemical composition of the upper atmosphere. Key Points: Variations in the ultraviolet dayglow from the Martian thermosphere with local time (LT) and emission viewing angle are characterizedAsymmetry in the dayglow between dawn and dusk varies by emission from +15.4% to −12.3% in response to transport and temperaturePatches of significant dayglow brightness increase are observed that appear to result from changes in composition and photoelectron flux [ABSTRACT FROM AUTHOR]

Carbon 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. Plain Language Summary: The Emirates Mars Ultraviolet Spectrometer onboard the Emirates Mars Mission observes light in a wavelength region referred to as far ultraviolet. This study focuses on far ultraviolet light that is produced by carbon monoxide (CO). Observations of far ultraviolet light can be used to determine the relative abundance of CO in the upper atmosphere of Mars. Variations in the relative abundance of CO over time and across different locations can provide valuable information regarding the temperatures and winds in the middle atmosphere of Mars, as well as the chemistry that balances the whole atmosphere of Mars. This study presents a method for converting observations of far ultraviolet light into relative abundances of CO in the upper atmosphere of Mars. Key Points: Emirates Ultraviolet Spectrometer (EMUS) observations provide large scale, high cadence, synoptic views of carbon monoxide (CO) relative column abundance in the lower thermosphere of MarsSignificant variability in CO brightness and relative column abundance is regularly observed in EMUS disk imagesObserved variability of CO relative column abundance in local time, latitude, and solar longitude is inconsistent with model predictions [ABSTRACT FROM AUTHOR]

Auroras have been extensively studied using images obtained by space-borne experiments. We use global UVI images obtained from Polar and simultaneous plasma data obtained by the 3D instrument on Wind from the near-earth plasma sheet to study the dynamics of auroras with different size and intensity. Unstable phase space ion distributions are detected in the plasma sheet under diverse geomagnetic and solar wind IMF conditions (positive and negative Bz) and at all phases of a substorm. These results indicate that plasma instability processes with different disturbance levels operate in the plasma sheet and produce a continuum of auroral size and intensity. The criteria for triggering an instability are dependent on the local properties of the plasma distributions. These observations suggest a new framework to integrate previous and current results and a new way to examine the causal relationships of auroral and plasma sheet dynamics. [Copyright &y& Elsevier]

The ion composition experiment on Cluster measures 3-D distributions in one spin of the spacecraft (4 s). These distributions often measure field-aligned ion beams (H+, He+ and O+) accelerated out of the ionosphere. The standard model of these beams relies on a quasi-static Ushaped potential model. The beams contain important information about the structure and distribution of the U-shaped potential structures. For example, a simple beam with a narrow velocity range tells us that the particles are accelerated going through a quasi-static U-shaped potential structure localized in space. A more complex beam with a large range of velocities varying smoothly (a few tens of kilometers per second to >100 km s-1) tells us that the potential structure is extended and distributed along the magnetic field. The Cluster experiment has now revealed new features about the beams. Some beams are broken into many individual structures each with their own velocity. The U-shaped potential model would interpret the new features in terms of particles accelerated by narrow isolated potential structures maintained over an extended region of the magnetic field. Another interpretation is that these features arise as Cluster traverses toward the center of a small-scale U-shaped potential region detecting particles accelerated on different equipotential contours. The estimate of the distance of the adjacent contours is ~590-610m at a Cluster height of ~3.5RE. The observed dimensions map to ~ 295-305m in the ionosphere, suggesting Cluster has measured the potential structure of an auroral arc. [ABSTRACT FROM AUTHOR]

Numerous observations have shown that ions flow out of the ionosphere during substorms with more fluxes leaving as the substorm intensity increases (Wilson et al., 2004). In this article we show observations of low-energy (few tens of electron volts) ionospheric ions flowing out periods without substorms, determined using the Wideband Imaging Camera (WIC) and Auroral Electrojet (AE) indices. We use Cluster ion composition data and show the outflowing ions are field-aligned H+, He+ and O+ beams accelerated to energies of ~ 40-80 eV, after correcting for spacecraft potential. The estimated fluxes of the low-energy O+ ions measured at ~ 20 000 km altitude are > 103-105 cm-2 s. Assuming the auroral oval is the source of the escaping ions, the measured fluxes correspond to a flow rate of ~ 1019-1021 ions s-1 leaving the ionosphere. However, periods without substorms can persist for hours suggesting the lowenergy ions flowing out during these times could be a major source of the heavy ion population in the plasma sheet and lobe. [ABSTRACT FROM AUTHOR]

We combine thermal electron densities in Mars' ionosphere with magnetic topology information to investigate the sources of the nightside ionosphere. Thermal electron density is measured in situ by the Langmuir Probe and Waves experiment onboard Mars Atmospheric and Volatile EvolutioN, while magnetic topology is simultaneously inferred from suprathermal electron energy‐pitch angle distributions measured by the Solar Wind Electron Analyzer and the Magnetometer. Topologically closed regions inhibit electron impact ionization, allowing us to isolate the effects of plasma transport from the dayside, which exhibits a dawn‐dusk asymmetry. Pressure gradient forces on open magnetic field lines connected to the dayside ionosphere source the high‐altitude nightside ionosphere, resulting in higher densities. Regions that are topologically open to the nightside ionosphere allow us to assess in situ production by electron impact ionization, which is responsible for ~50% of the nightside ionosphere below ~160 km and ~25% above ~220 km (on average). Plain Language Summary: Mars' dayside ionosphere is produced by ionization of the neutral atmosphere by solar extreme ultraviolet and X‐ray photons. This photoionization source is absent at night, so the nightside ionosphere must be supplied by plasma transport from day to night or created in situ by impact ionization caused by the precipitation of energetic electrons onto the neutral atmosphere. In this study, we use measurements from the Mars Atmospheric and Volatile EvolutioN spacecraft to identify these sources and estimate their contributions to the nightside ionosphere. At altitudes below ~160 km, electron impact ionization accounts for half of the nightside ionosphere, with the other half supplied by transport from the dayside via collisional coupling with neutral winds. At higher altitudes, the nightside plasma density is found to be higher when it is directly supplied by transport from the dayside ionosphere. Key Points: At low altitudes ion motion collisionally couples to neutral winds, sourcing the nightside ionosphere asymmetrically from dawn and duskOn open field lines connected to the dayside, the nightside ionosphere is sourced by dayside plasma via pressure gradient forcesOn average, electron impact ionization produces ~50% of Mars' nightside ionospheric plasma below ~160 km and ~25% above 220 km [ABSTRACT FROM AUTHOR]