Vertical Variability in the Structure of the Martian Nitric Oxide Nightglow Layer

Understanding the connection between the lower and upper atmospheres is key to determining the atmospheric history of Mars. One such tracer of the connection between Mars’s thermosphere and mesosphere is the nitric oxide (NO) nightglow, an atmospheric airglow phenomenon which is indicative of atmospheric flux between the nightside thermosphere and mesosphere. For my thesis, I analyze a set of altitude profiles of the NO nightglow observed by the Imaging Ultraviolet Spectrograph (IUVS) instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) mission. Using a toy model of the NO recombination, I fit the altitude profiles to determine some char- acteristic atmospheric quantities and how they change over the course of a day during particular seasons and on average between seasons. During winter, I find that the peak altitude does not vary appreciably with local time, while during equinox and summer the peak altitude decreases during evening, reaching a minimum before midnight, then increasing during the early morning hours toward dawn. Between seasons, I find the average peak altitude varies by about 20km between summer/equinox at around 70km and polar winter at around 50km. These results suggest the diurnal variation depends on daily temperature variation, while the seasonal variation exhibits a more complex connection to variables like average nighttime temperature and other factors like the dayside photodissociation rate producing atomic oxygen and nitrogen

Voter Specialization in Local Elections

The established literature on voter behavior suggests that voting typologies can be generally defined as follows: (1) voters participating in all elections, (2) voters participating in state and federal elections only, (3) voters participating only in federal elections, and (4) voters participating only in presidential elections. My thesis investigates whether there are some voters who fall outside of these established voting typologies and focus their civic efforts towards nonpartisan or local issues elections. Utilizing data from the Ohio Secretary of State, I used Q methodology factor analysis to distinguish voter types. While I was unable to establish a local-specialist voter type, I was able to find groups of biennial federal specialists and habitual voters. Using hypotheses for the characteristics local specialists might have in common, I performed multivariate regression analysis to explain the difference between these federal specialists and the habitual voters who participated in local elections. I found that the habitual voters tend to be less partisan and from more rural counties, and turnout more often when elections have tax issues on the ballot and less often when elections have bond issues on the ballot. I found no indications that these habitual voters tend to be older or have specializations in local or miscellaneous issues (as defined by the Ohio Secretary of State)

The Optical Aurorae of Europa, Ganymede and Callisto

The tenuous atmospheres of the Galilean satellites are sourced from their surfaces and produced by a combination of plasma-surface interactions and thermal processes. Though thin, these atmospheres can be studied via their auroral emissions, and most work to date has focused on their aurora at UV wavelengths. Here we present the first detections of Ganymede's and Callisto's optical aurorae, as well detections of new optical auroral lines at Europa, based on observations of the targets over ten Jupiter eclipses from 1998 to 2021 with Keck/HIRES. We present measurements of OI emission at 6300/6364, 5577, 7774, and 8446 A and place upper limits on hydrogen at 6563 A. These constitute the first detections of emissions at 7774 and 8446 A at a planetary body other than Earth. The simultaneous measurement of multiple emission lines provides robust constraints on atmospheric composition. We find that the eclipse atmospheres of Europa and Ganymede are composed predominantly of O2 with average column densities of (4.1 \pm 0.1) x 10^{14} cm^{-2} and (4.7 \pm 0.1) x 10^{14} cm^{-2}, respectively. We find weak evidence for H2O in Europa's bulk atmosphere at an H2O/O2 ratio of $\sim$0.25, and place only an upper limit on H2O in Ganymede's bulk atmosphere, corresponding to H2O/O2 < 0.6. The column density of O2 derived for Callisto is (4.0 \pm 0.9 x 10^{15} cm^{-2} for an assumed electron density of 0.15 cm^{-3}, but electron properties at Callisto's orbit are very poorly constrained.Comment: Published in Planetary Science Journa

MAVEN/IUVS Nitric Oxide Nightglow Apoapse Images

The Laboratoire de M&eacute;t&eacute;orologie Dynamique Mars Global Climate Model (LMD-MGCM) is a whole-atmosphere (ground-to-exosphere) global model. The version used for this study is the same that was used to build the Mars Climate Database version 5.3 (Gonz&aacute;lez-Galindo et al., 2015; Millour et al., 2018). The simulations have been performed using the observed day-to-day variability of the dust load (Montabone et al., 2015) and of the UV solar flux (Gonz&aacute;lez-Galindo et al., 2013) during the period covered by the IUVS observations. The predictions of the model have been interpolated to the location (longitude, latitude) and the time (Ls, local time) of each IUVS observation to make it possible a one-to-one comparison. The simulations dataset "lmd_data.dat" is a text file of point-by-point model simulations to IUVS data. The columns are: latitude, longitude, false altitude (ignore), solar longitude, local time, NO radiance.</p

Diffuse and Discrete Aurora on Mars: Insights into Mars' magnetospheric environment and solar drivers

Planetary auroras reveal the complex interplay between an atmosphere and the surrounding plasma environment. The Imaging Ultraviolet Spectrograph (IUVS) on the MAVEN spacecraft has revealed Mars to be a planet with astonishingly varied auroral activity. Contrary to expectations, the planet's lack of a global magnetic field allows additional types of auroral activity not possible on other worlds. This presentation describes two types of aurora, called diffuse and discrete aurora, while a companion presentation by Hughes et al. will describe proton aurora. The Imaging Ultraviolet Spectrograph (IUVS) on the MAVEN spacecraft has discovered a low-altitude, diffuse auroras spanning much of Mars' northern hemisphere, coincident with a solar energetic particle outburst. During multiple several-day periods, IUVS has detected auroral emission in nightside observations for up to ~5 days, spanning nearly all geographic longitudes. Emission extended down to ~60 kilometer (km) altitude (1 microbar), deeper than confirmed at any other planet. Solar energetic particles were observed up to 200 kilo-electron volts; these particles are capable of penetrating down to the 60 km altitude. Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth. MAVEN/IUVS has also identified 278 occurrences of discrete aurora events on Mars, which are patchy, sporadic ultraviolet emissions emanating from the upper atmosphere. We confirm prior results from Mars Express/SPICAM, finding that emissions are highly correlated with crustal magnetic fields results, with the brightest and most frequent occurrences located around strong crustal fields in the southern hemisphere. A six-year data set shows that events can also occur globally, in regions of weak or absent crustal fields. We find that events occur primarily in evening hours, especially during favorable orientations of the interplanetary magnetic field. Under these conditions, auroral events probably occur nightly and last for hours. Optical counterparts to these UV emissions would probably be detectable with present-day instrumentation, and would be visible to future astronauts. Taken together, the newly discovered and characterized forms of martian aurora are both a remarkable planetary phenomenon and an chance to learn about the martian magnetosphere and its interaction with the solar wind and solar storms. Many further opportunities await future missions instrumented to study aurora, at both ultraviolet and visible wavelengths

Mars Discrete Aurora: A Comprehensive Survey for Detection & Characterization by MAVEN/IUVS

We present the results of a comprehensive search for discrete aurora emissions on Mars from six years of observations by MAVEN's Imaging UltraViolet Spectrograph. Discrete aurora is a localized and transient form of aurora apparently unique to Mars, owing to its lack of a global magnetic field. The auroral emissions originate from precipitating electrons accelerated by the reconfiguration of Mars' crustal magnetic fields as the planet rotates relative to the external magnetic field carried by the solar wind. This process is distinct from other more widespread diffuse and proton aurora also seen at Mars. Discrete aurora was discovered in regions of strong crustal magnetic fields by the SPICAM instrument on Mars Express using limb scanning [Bertaux et al., 2005]. The emission appeared in patches ~tens of km across at altitudes ~130 km. Further analysis revealed a total of 20 instances of auroral patches during 10 years of intermittent SPICAM observations [Gérard et al., 2015]. Auroral excitation was attributed to the precipitation of electrons, typically ~100 eV - 1 keV. MAVEN/IUVS obtained the first images of the phenomenon (Schneider et al. 2018). We have examined MAVEN's mission-long dataset of nightside limb scans spanning more than 10,000 orbits over nearly 6 Earth years. Events were identified by significant emission in the CO Cameron bands (190-270 nm) and were individually confirmed to be free of stray light and cosmic ray interference. More than 500 discrete aurora events were detected, increasing the number of known events by more than an order of magnitude. The figure shows a remarkable string of distinct events seen during a single 20- minute passage of Mars' crustal field region. The observed events show a strong concentration near crustal fields in the south, but also exhibit a substantial distribution spread more uniformly over the entire planet. Some events are seen at the tangent altitude expected for electron precipitation, but many appear at lower projected altitudes. We infer these are small patches of emission in front of (or behind) the limb itself, and in some cases the spacecraft was probably imbedded in the emission

Martian Discrete Aurorae Observed with MAVEN-IUVS: Spectral Composition and Altitude Modeling

Three types of aurorae have been observed in the Martian atmosphere: the discrete, the diffuse (Schneider, 2015) and the proton aurora (Deighan et al., 2018, Ritter et al., 2018). This work concentrates on discrete aurorae, which were first discovered with the ESA Mars Express SPICAM instrument (Bertaux et al., 2005). Discrete aurorae are very localized in space, time and altitude (Leblanc et al., 2008, Gérard et al., 2015, Soret et al., 2016). They are generated by the precipitation of less energetic electrons than for diffuse aurorae (hundreds of eV compared to tens of keV). Bertaux et al. (2005) showed that discrete aurorae are characterized by the presence of the CO (a3Π–X1Σ) Cameron bands between 190 and 270 nm, the CO (A1Π–X1Σ+) Fourth Positive system (CO 4P) between 135 and 170 nm, the (B2Σu+–X2Πg) doublet at 289 nm, the OI at 297.2 nm and the 130.4 nm OI triplet emissions. The discrete aurora can now be studied using observations from the MAVEN-IUVS ultraviolet spectrograph (Schneider et al., 2019). More than 10,000 orbits of the IUVS instrument acquired from 2014 to 2020 have been analyzed for this study. Auroral signatures were automatically selected in 69 different orbits. The spectral emissions intensities have been quantified and the auroral event altitudes of the tangent point have been estimated using limb profiles. We confirm that the CO Cameron bands emission layer is located between 105 and 165 km (Bertaux et al., 2005, Soret et al., 2016). We also show the ratio between the CO Cameron bands and the CO2+ UVD intensities. Finally, we use the MAVEN Solar Wind Electron Analyzer (SWEA) measurements and a Monte-Carlo model to estimate the electron energy needed to produce a discrete auroral event. These results are of a great importance to understand the production mechanisms of discrete aurorae on Mars

All that is known about Mars discrete aurorae so far

peer reviewedThe discrete aurorae on Mars were discovered with the SPICAM spectrograph on board Mars Express. Now, they have been analyzed in detail using the much more sensitive MAVEN/IUVS imaging spectrograph.This presentation gives a summary of the very latest results obtained by Schneider et al. and Soret et al. on this topic.The main conclusions are the following:the number of auroral event detections has considerably increased since the Mars Express observations; many detections have been made outside of the Southern crustal magnetic field structures; the MUV spectrum shows the same emissions as those observed in the dayglow, with similar intensity ratios; the Vegard-Kaplan bands of N2 have been observed for the first time in the Martian aurora; the CO Cameron and the CO2+ UVD emissions occur at the same altitude; the OI emission at 297.2 nm has been analyzed; the CO Cameron/CO2+ UVD ratio is quasi-constant; intensities are higher in B-field regions; auroral emissions are more frequent in the pre-midnight sector; the altitude of the emission layer is independent of local time and presence or absence of a crustal magnetic field; the altitude of the emission layer varies moderately with season (atmospheric effect); the events are spatially correlated with an increase in the flux of energetic electrons simultaneously measured by the MAVEN/SWEA (Solar Wind Electron Analyzer) detectors; the peak altitude of the emission is in good agreement with that expected from the average electron energy

Discrete Aurora on Mars: Spectral Properties, Vertical Profiles, and Electron Energies

We present an analysis of hundreds of middle ultraviolet auroral spectra collected at the limb with the Imaging UltraViolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. While the companion paper by Schneider etal.(2021), https://doi.org/10.1029/2021JA029428 focuses on the detection, location, and occurrence frequency of discrete auroral events, this study addresses the spectral properties and vertical profiles of the auroral emissions. Our independent selection of events is based on a combination of automatic and manual detection methods with adequate signal-to-noise ratio of both the CO Cameron bands and the CO2+ ultraviolet doublet (UVD) at 190–270 and 288–289nm, respectively. We find that the ratio of these two features remains quasi-constant for UVD intensities exceeding 200 rayleighs (R), but the CO Cameron/CO2+ UVD ratio may become increasingly large for low UVD intensities. Three weak N2 Vegard-Kaplan bands are identified in the Martian aurora for the first time. Limb profiles of the [OI] line at 297.2nm indicate that the visible oxygen green line brightness may reach a few kilorayleighs. The distribution of the altitude of the emission peaks in the aurora is identical in and out of the region of crustal magnetic field located in the southern hemisphere. Comparisons of in situ measurements of electron energy spectra and ultraviolet auroral detections have been made for five optical detections. They generally show temporal coincidence but not necessarily quantitative agreement with the altitude and brightness expected from the characteristics of the measured electron energy spectra

Seasonal and Diurnal Variation in the Vertical Structure of the Martian Nitric Oxide Nightglow Layer

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