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Martian sub-solar electron temperatures obtained below 250 km are examined using data obtained by instruments on the Mars Atmosphere Evolution Mission (MAVEN) during the three sub-solar deep dip ca...

The MAVEN mission has measured an electron temperature spike at altitudes where the Martian atmosphere becomes optically thick and changes occur in the atmospheric chemistry. The temperature spike ...

International audience; Understanding the evolution of the Martian atmosphere requires knowledge of processes transforming solar irradiance into thermal energy well enough to model them accurately. Here we compare Martian photoelectron energy spectra measured at periapsis by Mars Atmosphere and Volatile Evolution MissioN (MAVEN) with calculations made using three photoelectron production codes and three solar irradiance models as well as modeled and measured CO2 densities. We restricted our comparisons to regions where the contribution from solar wind electrons and ions were negligible. The two intervals examined on 19 October 2014 have different observed incident solar irradiance spectra. In spite of the differences in photoionization cross sections and irradiance spectra used, we find the agreement between models to be within the combined uncertainties associated with the observations from the MAVEN neutral density, electron flux, and solar irradiance instruments.

Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an “ambipolar” electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an “electric wind” must be considered when studying the evolution and potential habitability of any planet in any star system.

International audience; We present Mars Atmosphere and Volatile EvolutioN observations of large-amplitude magnetosonic waves propagating through the magnetosheath into the Martian ionosphere near the subsolar point on the dayside of the planet. The observed waves grow in amplitude as predicted for a wave propagating into a denser, charged medium, with wave amplitudes reaching 25 nT, equivalent to ∼40% of the background field strength. These waves drive significant density and temperature variations (∼20% to 100% in amplitude) in the suprathermal electrons and light ion species (H+) that correlate with compressional fronts of the magnetosonic waves. Density and temperature variations are also observed for the ionospheric electrons, and heavy ion species (O+ and O2+); however, these variations are not in phase with the magnetic field variations. Whistler waves are observed at compressional wave fronts and are thought to be produced by unstable, anistropic suprathermal electrons. The magnetosonic waves drive significant ion and electron heating down to just above the exobase region. Ion heating rates are estimated to be between 0.03 and 0.2 eVs-1 per ion, and heavier ions could thus gain escape energy if located in this heating region for ∼10-70 s. The measured ionospheric density profile indicates severe ionospheric erosion above the exobase region, and this is likely caused by substantial ion outflow that is driven by the observed heating. The effectiveness of these magnetosonic waves to energize the plasma close to the exobase could have important implications for the long-term climate evolution for unmagnetized bodies that are exposed to the solar wind.

International audience; Statistical correlations are reported between measured electron temperatures and total electric field wave power (in the 2-100 Hz frequency range), at Mars' subsolar point ionosphere. The observations, made by the Mars Atmosphere and Volatile EvolutioN spacecraft, suggest that electric field wave power from the Mars-solar wind interaction propagates through the Martian ionosphere and is able to heat ionospheric electrons by over 1000 K. Such heating can account for a substantial (but likely not complete) fraction of previously reported discrepancies between modeled and observed electron temperatures in Mars' upper ionosphere. Wave power is typically less than observable thresholds below altitudes of about 200 km, suggesting that energy is deposited into the ionosphere above this. Observed total wave powers range between 10-12 and 10-9 (V/m)2 and decrease with increasing integrated electron density (or decreasing altitude).

International audience; Observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 – 3 Oct 2016). Loss rates for H and O are sufficient to remove ∼2-3 kg/s to space. By itself, this loss would be significant over the history of the planet. In addition, loss rates would have been greater early in history due to the enhanced solar EUV and more-active Sun. Integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar CO2 or 23 m global equivalent layer of H2O; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. Combined with the lack of surface or subsurface reservoirs for CO2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of Mars from an early, warmer environment to the cold, dry one that we see today.

As the solar photon fluxes directly control the production of photoelectrons, it is important to examine the influence of different solar irradiance models on the photoelectron fluxes. In this study, we present the implementation of the two recent solar irradiance models, the Flare Irradiance Spectral Model (FISM) and the Heliospheric Environment Solar Spectral Radiation (HESSR) model, to our SuperThermal Electron Transport (STET) model. In addition, we have proposed a new modification to the Hinteregger-81 model. The resultant photoelectron fluxes from the three solar irradiance models, the Hinteregger-81 model, FISM and the HESSR model, are compared and mostly vary within a factor of 2.

First direct observations of heating of the Mars neutral atmosphere by solar flares are presented in this study. Solar flares were detected using the Extreme Ultraviolet Monitor on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and upper atmospheric temperature enhancements were determined by changes in the density scale height of Argon (Ar) made by the Neutral Gas and Ion Mass Spectrometer also on board MAVEN. We analyzed 14 M-class or greater flares that occurred during the early part of the MAVEN mission in addition to a 30 day period of high flare activity during May 2015. We report that the Mars dayside upper atmosphere shows significant heating near the flare soft X-ray peak; and it responds and recovers rapidly to heating from M-class or larger flares. In addition, we present atmospheric density versus altitude profiles that were taken near the soft X-ray peak of two flares.

Photoelectrons are important for heating, ionization, and airglow production in planetary atmospheres. Measured electron fluxes provide insight into the sources and sinks of energy in the Martian upper atmosphere. The Solar Wind Electron Analyzer instrument on board the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft measured photoelectrons including Auger electrons with 500 eV energies. A two-stream electron transport code was used to interpret the observations, including Auger electrons associated with K shell ionization of carbon, oxygen, and nitrogen. It explains the processes that control the photoelectron spectrum, such as the solar irradiance at different wavelengths, external electron fluxes from the Martian magnetosheath or tail, and the structure of the upper atmosphere (e.g., the thermal electron density). Our understanding of the complex processes related to the conversion of solar irradiances to thermal energy in the Martian ionosphere will be advanced by model comparisons with measurements of suprathermal electrons by MAVEN.

An important mechanism in the generation of polar wind outflow is the ambipolar electric potential which assists ions in overcoming gravity and is a key mechanism for Terrestrial ionospheric escape. At Mars, open field lines are not confined to the poles, and outflow of ionospheric electrons is observed far into the tail. It has thus been hypothesized that a similar electric potential may be present at Mars, contributing to global ionospheric loss. However, no direct measurements of this potential have been made. In this pilot study, we examine photoelectron spectra measured by the Solar Wind Electron Analyzer instrument on the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars Scout to put an initial upper bound on the total potential drop in the ionosphere of Mars of Φ♂≾⊥2V , with the possibility of a further ≾4.5 V potential drop above this in the magnetotail. If the total potential drop was close to the upper limit, then strong outflows of major ionospheric species (H+, O+, and O2+) would be expected. However, if most of the potential drop is confined below the spacecraft, as expected by current theory, then such a potential would not be sufficient on its own to accelerate O2+ to escape velocities, but would be sufficient for lighter ions. However, any potential would contribute to atmospheric loss through the enhancement of Jeans escape.

Electron conic distributions have angular distributions with peak fluxes well separated from the field aligned-direction. They have previously been reported at Earth on auroral field lines and at the Moon and Mars on closed crustal magnetic field lines. Here we report observations of electron conics at Earth on closed magnetic field lines well removed from the aurora. We show how these distributions could be produced without plasma wave interactions when magnetic field lines are illuminated by solar ionizing radiation at relatively high altitudes in the ionosphere. Examination of previous reports of electron conic distributions observed in planetary atmospheres show that there are a variety of physical mechanisms that can lead to their formation, not all of which require wave-particle interactions.

Coastal ocean ecosystems have always served human populations—they provide food security, livelihoods, coastal protection, and defense. Ocean acidification is a global threat to these ecosystem services, particularly when other local and regional stressors combine with it to jeopardize coastal health. Monitoring efforts call for a coordinated global approach toward sustained, integrated coastal ocean health observing networks to address the region-specific mix of factors while also adhering to global ocean acidification observing network principles to facilitate comparison among regions for increased utility and understanding. Here, we generalize guidelines for scoping and designing regional coastal ocean acidification observing networks and provide examples of existing efforts. While challenging in the early stages of coordinating the design and prioritizing the implementation of these observing networks, it is essential to actively engage all of the relevant stakeholder groups from the outset, including private industries, public agencies, regulatory bodies, decision makers, and the general public. The long-term sustainability of these critical observing networks will rely on leveraging of resources and the strength of partnerships across the consortium of stakeholders and those implementing coastal ocean health observing networks

A pioneering leader in unraveling the complex plasma interactions that drive the dynamics of Earth’s magnetosphere and other space plasma environments.

First results from the Juno mission shed new light on Jupiter’s atmosphere, gravity, magnetic field, aurora, history, and more.

International audience; Energetic O+ and O2+ ions with energies of up to a few hundred eV are observed in the Martian ionosphere. Corresponding ion velocity distributions show ion conics, suggesting that the observed ion populations have been heated perpendicular to the local magnetic field before experiencing a magnetic mirror force. Magnetic field observations support these interpretations: wave power at the local O+ and O2+ gyrofrequencies in the spacecraft frame is observed coincident with the energetic ions, within an apparent magnetic field bottle-like topology. Analysis of the observed ion conics leads to estimates of ion temperatures of 10-30 eV. We suggest that the ion populations are initially heated perpendicular to the local magnetic field by wave power propagating inward from the Mars-solar wind interaction. The local magnetic field "balloons out" in response to these enhanced ion temperatures and pressures. The resultant magnetic field topology is bottle like; the transversely heated ions would subsequently experience a magnetic mirror force in the converging field regions, agreeing with the reported observations. Such strong heating events that significantly increase the ion temperature and pressure, thereby decreasing the net magnetic field, are rare and seem to occur under specific interplanetary magnetic field orientations. Events were observed to span the upper exobase region and just above, a region characterized by significant ion densities in an increasingly collisionless domain. Ion heating in this region has the potential to drive significant ion outflows, thus contributing to atmospheric loss from the planet.

Magnetic reconnection changes the topology of magnetic field lines. This process is most readily observable with in situ instrumentation at the Earth's magnetopause as it creates open magnetic field lines to allow energy and momentum flux to flow from the solar wind to the magnetosphere. Most models use the direction of the interplanetary magnetic field (IMF) to determine the location of these magnetopause entry points, known as reconnection lines. Dayside locations of magnetic reconnection equatorward of the cusps are generally found during sustained intervals of southward IMF, while high-latitude region regions poleward of the cusps are observed for northward IMF conditions. In this study we discuss Double Star magnetopause crossings and a conjunction with a Polar cusp crossing during northward IMF conditions with a dominant IMF BY component. During all seven dayside magnetopause crossings, Double Star detected switching ion beams, a known signature for the presence of reconnection lines. In addition, Polar observed a cusp ion-energy dispersion profile typical for a dayside equatorial reconnection line. Using the cutoff velocities for the precipitating and mirrored ion beams in the cusp, the distance to the reconnection site is calculated, and this distance is traced back to the magnetopause, to the vicinity of the Double Star satellite locations. Our analysis shows that, for this case, the predicted line of maximum magnetic shear also coincides with that dayside reconnection location.

Few fisheries oceanography surveys in the United States have sampled hydrography and ichthyoplankton or juvenile fishes for 15 years or more. We describe six long time series surveys, including three from the California Current System, and one each from Alaska (Gulf of Alaska, Bering Sea, and the Arctic), the Northeast US Shelf, and the Gulf of Mexico. We examine the applications of long time series data as well as the output of published analyses, Web-based graphical summaries, and quality controlled data to the broader scientific community (including resource managers and stakeholders). Potential improvements to the surveys using new technologies are evaluated, and possible changes in survey design are discussed. We conclude with a summary of the benefits derived from these long time series fisheries oceanography surveys and make the case for their continuation.

The role of electron precipitation in the auroral zone in driving thermal O+ upwelling is explored by comparison of observations and model results. Previous reports have shown how the ambiguities of such an assessment can be reduced when the problem is addressed in dynamic boundary-related coordinates. Upwelling ion data from the Defense Meteorological Satellite Program (DMSP) satellites are compared using a modeling framework based on the Field Line Interhemispheric Plasma (FLIP) ionospheric model. We focus on geomagnetically quiet intervals, that is, nonstorm times with Dst > −50 nT. We find that low-energy (

Solar extreme ultraviolet (EUV; 10-120 nm) and soft X-ray (XUV; 0-10 nm) radiation are major heat sources for the Mars thermosphere as well as the primary source of ionization that creates the ionosphere. In investigations of Mars thermospheric chemistry and dynamics, solar irradiance models are used to account for variations in this radiation. Because of limited proxies, irradiance models do a poor job of tracking the significant variations in irradiance intensity in the EUV and XUV ranges over solar rotation time scales when the Mars-Sun-Earth angle is large. Recent results from Earth observations show that variations in photoelectron energy spectra are useful monitors of EUV and XUV irradiance variability. Here we investigate photoelectron energy spectra observed by the Mars Global Surveyor (MGS) Electron Reflectometer (ER) and the FAST satellite during the interval in 2005 when Earth, Mars, and the Sun were aligned. The Earth photoelectron data in selected bands correlate well with calculations based on 1 nm resolution observations above 27 nm supplemented by broadband observations and a solar model in the 0-27 nm range. At Mars, we find that instrumental and orbital limitations to the identifications of photoelectron energy spectra in MGS/ER data preclude their use as a monitor of solar EUV and XUV variability. However, observations with higher temporal and energy resolution obtained at lower altitudes on Mars might allow the separation of the solar wind and ionospheric components of electron energy spectra so that they could be used as reliable monitors of variations in solar EUV and XUV irradiance than the time shifted, Earth-based, F(10.7) index currently used.

Changes in submittal, editorial, and review policies support high standards and timely publication in the face of the increasing number of papers submitted.

Ambiguities introduced by the inconsistent definitions of the low and high altitude cusp lead to the inconsistency that at low altitudes the region commonly known as the cusp does not include boundary layer plasmas, but at high altitudes it does. Here we examine plasma data from two high altitude cusp intervals where ∼100 keV ionospheric ions were observed. We show that the data are an average over an interval that includes plasma from both boundary layer and newly injected solar wind plasmas. We find that the ∼100 keV ionospheric ions reported in the high altitude cusp are energized by well-known magnetospheric processes bringing energetic ions to the dayside boundary layers. We conclude that there is no need to postulate new processes associated with waves in diamagnetic cavities commonly found in the high altitude cusp to explain the observation of ∼100 keV ionospheric ions found there.

Energetic O+ ions have important dynamic effects on the ring current. Insights into the effects of O+ on ring current dynamics have come primarily from models, not observations. Here, we discuss observations of O+ populations escaping from the ionosphere and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O+ escapes the ionosphere during geomagnetically quiet intervals. We then estimate the relative magnitude of the O+ population in transit between the ionosphere and ring current during quiet intervals before geomagnetic storms. Our analysis suggests that dynamic reconfigurations of the magnetosphere during geomagnetic storms significantly alter the O+ transport paths from the ionosphere to the ring current. During these reconfigurations some of the pre-existing, quiet time, in-transit O+ populations are captured on magnetic field lines leading to the ring current. The prompt appearance of this O+ population in the ring current could modify the evolution of the ring current in the storm growth phase. Our analysis suggests that the consequences of an activity-dependent O+ transport path to the ring current should be systematically investigated.

This paper examines high resolution (Δ E / E = 0.15) photoelectron energy spectra from 10 eV to 1 keV, created by solar irradiances between 1.2 and 120 nm. The observations were made from the FAST satellite at ∼3000 km, equatorward of the auroral oval for the July–August, 2002 solar rotation. These data are compared with the solar irradiance observed by the Solar EUV Experiment (SEE) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and fluxes calculated using the Field Line Interhemispheric Plasma (FLIP) code. The 41 eV photoelectron flux, which corresponds to solar EUV fluxes near 20 nm, shows a clear solar rotation variation in very good agreement with the EUV flux measurements. This offers the possibility that the 41 eV photoelectron flux could be used as a check on measured solar EUV fluxes near 20 nm. Because of unexpected noise, the solar rotation signal is not evident in the integral photoelectron flux between 156 and 1000 eV corresponding to EUV wavelengths between 0.1 and 7 nm measured by the SEE instrument. Examination of daily averaged photoelectron fluxes at energies between 25 and 500 eV show significant changes in the photoelectron spectra in response X and M class flares. The intensity of photoelectrons produced in this energy region is primarily due to two very narrow EUV wavelength regions at 2.3 and 3 nm driving Auger photoionization in O at 500 eV and N 2 at ∼360 eV. Comparison of calculated and daily averaged electron fluxes shows that the HEUVAC model solar spectrum used in the FLIP code does not reproduce the observed variations in photoelectron intensity. In principle, the 21 discrete photoelectron energy channels could be used to improve the reliability of the solar EUV fluxes at 2.3 and 3 nm inferred from broad band observations. In practice, orbital biases in the way the data were accumulated and/or noise signals arising from natural and anthropogenic longitudinally restricted sources of ionization complicate the application of this technique.