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This article proposes an explanation for High-Energy Atmospheric phenomena through the frames of Hypersphere World-Universe Model (WUM). In WUM, Terrestrial Gamma-Ray Flashes (TGFs) are, in fact, Gamma-Ray Bursts (GRBs). The spectra of TGFs at very high energies are explained by Dark Matter particles annihilation in Geocorona. Lightning initiation problem is solved by GRBs that slam into thunderclouds and carve a conductive path through a thunderstorm. We introduce Multiworld consisting of Macro-World, Large-World, Small-World, and Micro-World, characterized by suggested Gravitational, Extremely-Weak, Super-Weak, and Weak interaction respectively. We propose a new model of Ball Lightning formation based on the Dark Matter Core surrounded by electron-positron plasma in the Small-World.

International audience; The analysis of Lyman α observations in the exosphere of Mars has become limited by the assumption of spherical symmetry in the modeling process, as the models are being used to analyze increasingly detailed measurements. In order to overcome this limitation, a two-dimensional density model is presented, which better emulates the density distribution of deuterium and hydrogen atoms in the exosphere of Mars. A two-dimensional radiative transfer model developed in order to simulate multiple scattering of solar Lyman α photons by an asymmetric, non-isothermal hydrogen exosphere, is also presented here. The models incorporate changes in density and temperature structure of the martian atmosphere with radial distance and solar zenith angle. The 2-D models were applied to the MAVEN-IUVS echelle observations of deuterium and hydrogen Lyman α as well as HST Lyman α observations of hydrogen at Mars. The asymmetric 2-D model provided better fits to the data and smaller thermal escape rates in comparison to the symmetric 1-D model for the exosphere of Mars. However, intensity differences between both models became small above ~2.5 martian radii indicating that the exosphere of Mars approaches spherical symmetry at higher altitudes, in agreement with earlier studies. In addition, a new cross calibration of the absolute sensitivities of two instruments on the Hubble Space Telescope and the MAVEN-IUVS echelle mode is presented based on near-simultaneous observations of the geocorona and Mars.

A systems science examination of the Earth’s fully interconnected dynamic magnetosphere is presented. Here the magnetospheric system (a.k.a. the magnetosphere–ionosphere–thermosphere system) is considered to be comprised of 14 interconnected subsystems, where each subsystem is a characteristic particle population: 12 of those particle populations are plasmas and two (the atmosphere and the hydrogen geocorona) are neutrals. For the magnetospheric system, an assessment is made of the applicability of several system descriptors, such as adaptive, nonlinear, dissipative, interdependent, open, irreversible, and complex. The 14 subsystems of the magnetospheric system are cataloged and described, and the various types of magnetospheric waves that couple the behaviors of the subsystems to each other are explained. This yields a roadmap of the connectivity of the magnetospheric system. Various forms of magnetospheric activity beyond geomagnetic activity are reviewed, and four examples of emergent phenomena in the Earth’s magnetosphere are presented. Prior systems science investigations of the solar-wind-driven magnetospheric system are discussed: up to the present these investigations have not accounted for the full interconnectedness of the system. This overview and assessment of the Earth’s magnetosphere hopes to facilitate (1) future global systems science studies that involve the entire interconnected magnetospheric system with its diverse time and spatial scales and (2) connections of magnetospheric systems science with the broader Earth systems science.

Recent studies suggest that the hydrogen (H) density in the exosphere and geocorona might differ from previously assumed values by factors as large as 2. We use the SAMI3 (Sami3 is Also a Model of the Ionosphere) and Comprehensive Inner Magnetosphere-Ionosphere models to evaluate scenarios where the hydrogen density is reduced or enhanced, by a factor of 2, relative to values given by commonly used empirical models. We show that the rate of plasmasphere refilling following a geomagnetic storm varies nearly linearly with the hydrogen density. We also show that the ring current associated with a geomagnetic storm decays more rapidly when H is increased. With respect to these two space weather effects, increased exosphere hydrogen density is associated with reduced threats to space assets during and following a geomagnetic storm.

The hydrogen exosphere constitutes the uppermost atmospheric layer of the Earth, and its shape may reflect the last stage of the atmospheric escape process. The distribution of hydrogen in the outer exosphere remains unobserved because outer geocoronal emissions are difficult to observe from within the exosphere. In this study, we used the Lyman Alpha Imaging Camera (LAICA) onboard the Proximate Object Close Flyby with Optical Navigation (PROCYON) spacecraft, located outside the exosphere, to obtain the first image of the entire geocorona that extends to more than 38 Earth radii. The observed emission intensity distribution can be reproduced using our analytical model that has three parameters: exobase temperature, exobase density, and solar radiation pressure, which implies that hot hydrogen production in the magnetized plasmasphere is not the dominant process shaping the outer hydrogen exosphere. However, the role of the magnetic effect in determining the total escape flux cannot be ruled out

Circumterrestrial Lyman-α column brightness observations from 3–8 Earth radii (Re) have been used to study temporal density variations in the exospheric neutral hydrogen as response to geomagnetic disturbances of different strength, i.e., Dst peak values between −26 and −147 nT. The data used were measured by the two Lyman-α detectors (LAD1/2) onboard both TWINS satellites between the solar minimum of 2008 and near the solar maximum of 2013. The solar Lyman-α flux at 121.6 nm is resonantly scattered near line center by exospheric H atoms and measured by the TWINS LADs. Along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H column density, assuming optically thin conditions above 3 Re. In the case of the eight analyzed geomagnetic storms we found a significant increase in the exospheric Lyman-α flux between 9 and 23 % (equal to the same increase in H column density ΔnH) compared to the undisturbed case short before the storm event. Even weak geomagnetic storms (e.g., Dst peak values ≥ −41 nT) under solar minimum conditions show increases up to 23 % of the exospheric H densities. The strong H density increase in the observed outer exosphere is also a sign of an enhanced H escape flux during storms. For the majority of the storms we found an average time shift of about 11 h between the time when the first significant dynamic solar wind pressure peak (pSW) hits the Earth and the time when the exospheric Lyman-α flux variation reaches its maximum. The results show that the (relative) exospheric density reaction of ΔnH have a tendency to decrease with increasing peak values of Dst index or the Kp index daily sum. Nevertheless, a simple linear correlation between ΔnH and these two geomagnetic indices does not seem to exist. In contrast, when recovering from the peak back to the undisturbed case, the Kp index daily sum and the ΔnH essentially show the same temporal recovery.

Over the past two decades, instruments designed to image plasmas in energetic neutral atom (ENA) emission have flown in space. In contrast to typical satellite-based in situ instruments, ENA imagers provide a global view of the magnetosphere because they remotely measure ion distributions via neutrals that are not tied to the magnetic field. An intrinsic challenge that arises during analysis of magnetospheric ENA images is that the ENA fluxes are integrated along the line-of-sight of the instrument. We propose a method of enhancing ENA emission from a localized region in space, thereby enabling spatially resolved measurements of ENA emission in a remotely obtained ENA image. Here we show that releases of modest volumes (~ 1.4 m3) of liquid hydrogen in space are sufficient to accomplish the ENA localization.

International audience; The Earth's hydrogen exosphere Lyman‐α radiation was mapped with the SWAN/SOHO instrument in January 1996, 1997 and 1998 (low solar activity). The use of a hydrogen absorption cell allowed to disentangle the interplanetary emission from the geocoronal one and to assign the absorbed signal almost entirely to the geocorona. The geocorona was found to extend at least up to 100 Earth Radii (RE) with an intensity of 5 Rayleigh, an unprecedented distance well exceeding the recent results of LAICA imager (∼50 RE), and encompassing the orbit of the Moon (∼60 RE). We developed a numerical kinetic model of the hydrogen atoms distribution in the exosphere which includes the solar Lyman‐α radiation pressure and the ionization. The radiation pressure compresses the H exosphere on the day side, producing a bulge of H density between 3 and 20 RE which fits observed intensities very well. The SWAN Lyman‐α distribution of intensity was compared both to LAICA (2015) and to OGO‐5 (1968) measurements. Integrated H densities of SWAN at a tangent distance of 7 RE are larger than LAICA/OGO‐5 by factors 1.1‐2.5, while we should expect a stronger effect of the radiation pressure at solar max. We discuss the possible role of H atoms in satellite orbits to explain this apparent contradiction. An onion‐peeling technique is used to retrieve hydrogen number density in the exosphere for the three SWAN observations. They show an excess of density versus models at large distances, which is likely due to non‐thermal atoms (not in the model).

(Abridged) The existence of an extended neutral hydrogen exosphere around small planets can be used as an evidence for the presence of water in their lower atmosphere but, to date, such feature has not been securely detected in rocky exoplanets. Planetary exospheres can be observed using transit spectroscopy of the Lyman-$\alpha$ line, which is limited mainly by interstellar medium absorption in the core of the line, and airglow contamination from the geocorona when using low-orbit space telescopes. Our objective is to assess the detectability of the neutral hydrogen exosphere of an Earth-like planet transiting a nearby M dwarf using Lyman-$\alpha$ spectroscopy and provide the necessary strategies to inform future observations. The spatial distribution in the upper atmosphere is provided by an empirical model of the geocorona, and we assume a velocity distribution based on radiative pressure as the main driver in shaping the exosphere. We compute the excess absorption in the stellar Lyman-$\alpha$ line while in transit, and use realistic estimates of the uncertainties involved in observations to determine the observability of the signal. We found that the signal in Lyman-$\alpha$ of the exosphere of an Earth-like exoplanet transiting M dwarfs with radii between 0.1 and 0.6 R$_\odot$ produces an excess absorption between 50 and 600 ppm. The Lyman-$\alpha$ flux of stars decays exponentially with distance because of interstellar medium absorption, which is the main observability limitation. Other limits are related to the stellar radial velocity and instrumental setup. The excess absorption in Lyman-$\alpha$ is observable using LUVOIR/LUMOS in M dwarfs up to a distance of $\sim$15 pc. The analysis of noise-injected data suggests that it would be possible to detect the exosphere of an Earth-like planet transiting TRAPPIST-1 within 20 transits., Comment: 12 pages, 13 figures, accepted for publication in Astronomy & Astrophysics

Recording the tweeks with a maximum up to eight harmonics using the receiver installed at Tay Nguyen University (12.65° N, 108.02° E) during 2013–2014, we investigated the morphology of the nighttime D-region ionosphere. Tweeks were recorded on 5 quiet nights per month. The results show that the mean reflection height in 2014 ( R z = 79.3 ) is lower by 3.3 km than that in 2013 ( R z = 64.9 ). The reflection height at low latitudes is higher than that at high latitudes. The mean reference height h ′ in 2013 is higher about 0.9 km than that in 2014 and the mean sharpness factor β in 2013 is higher by 0.07 km−1 than that in 2014. The short-term variation of reflection heights for tweeks with harmonics m = 1–3 and sunspot number have the negative correlation coefficients. However, the correlations between them are not clear. On some nights, from 19:00–21:00 LT, the reflection height temporal variability shows a moderate to strong negative correlation with the tweek occurrence. This suggests that the reflection height variation may be caused by QE fields generated by lightning discharges. The variations of tweek reflection heights observed during 2013–2014, at low latitudes could be significantly caused by the ionization effect by Lyman- α and Lyman- β coming from geocorona, variation of neutral density, particle precipitations, and by direct energy coupling between lightning and lower ionosphere.

Terrestrial exospheric atomic hydrogen (H) resonantly scatters solar Lyman-α (121.567 nm) radiation, observed as the glow of the H-geocorona. The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) satellites are equiped with two Lyman-α line-of-sight Detectors (LADs) each. Since during the past solar minimum conditions the relevant solar control parameters practically did not vary, we are using LAD data between June and September 2008 to create a time averaged hydrogen geocorona model representative for these solar minimum conditions. In this averaged model we assume that the H-geocorona is longitudinally symmetric with respect to the earth-sun line. We find a 3-dimensional H-density distribution in the range from 3 to 8 earth radii which with some caution can also be extrapolated to larger distances. For lower geocentric distances than 3 earth radii a best fitting r-dependent Chamberlain (1963)-like model is adapted. Main findings are larger than conventionally expected H-densities at heights above 5 RE and a pronounced day-to-night side H-density asymmetry. The H-geocorona presented here should serve as a reference H-atmosphere for the earth during solar minimum conditions.

The Interstellar Boundary Explorer (IBEX) mission will provide maps of energetic neutral atoms (ENAs) originating from the boundary region of our heliosphere. On IBEX there are two sensors, IBEX-Lo and IBEX-Hi, covering the energy ranges from 10 to 2000 eV and from 300 to 6000 eV, respectively. The expected ENA signals at 1 AU are low, therefore both sensors feature large geometric factors. In addition, special attention has to be paid to the various sources of background that may interfere with our measurement. Because IBEX orbits the Earth, ion, electron, and ENA populations of the Earth’s magnetosphere are prime background sources. Another potential background source is the magnetosheath and the solar wind plasma when the spacecraft is outside the magnetosphere. UV light from the night sky and the geocorona have to be considered as background sources as well. Finally background sources within each of the sensors must be examined.

After geomagnetic storms, Earth’s corona abruptly increases in hydrogen density. For the first time, serendipitous observations have allowed researchers to investigate why.

Space Physics Dissociation of water in Earth's atmosphere produces hydrogen atoms, which escape into space through a combination of thermal and nonthermal processes. These hydrogen atoms resonantly scatter light from the Sun, producing an ultraviolet glow around Earth called the geocorona. Baliukin et al. analyzed ultraviolet observations taken by the Solar and Heliospheric Observatory spacecraft. They found that the geocoronal emission extends to at least 100 Earth radii, almost twice the distance to the Moon. This greater-than-expected extent of the geocorona indicates that nonthermal processes are launching hydrogen atoms from Earth's upper atmosphere at high speeds. J. Geophys. Res. Space Phys. 10.1029/2018JA026136 (2019).

[1] Satellite-based measurements of geocoronal Lyman α (Lyα) emission at 121.6 nm, created through multiple scattering of solar Lyα photons by atomic hydrogen, offer a valuable means of inferring the hydrogen abundance, [H], in the terrestrial thermosphere and exosphere on a global, long-term basis. We present initial results from an analysis of Lyα radiance measurements acquired across the Earth's limb from 2002 to 2007 by the Global UltraViolet Imager (GUVI) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. This data spans nearly half of a solar cycle, and both the absolute Lyα radiance as well as its relative variation across the limb are shown to exhibit a significant dependence on solar activity. We describe sensitivities of a forward radiative transport (RT) model to key parameters governing the [H] distribution in order to assess implications for [H] estimation from the GUVI limb scan data throughout the solar cycle. Based on data-model comparisons, we conclude that the observed solar cycle variability is indicative of a decrease in dayside H density at the exobase with increasing solar activity. These results, along with additional forward RT modeling based on NRLMSISE-00 model specification of [H], are also used to assess contemporary semiempirical model accuracy.

[1] The dominant neutral constituent in Earth's upper exosphere, atomic hydrogen (H), resonantly scatters solar Lyman-alpha (121.567 nm) radiation, observed as the geocorona. We report here observations of an exospheric response to geomagnetic storms obtained using measurements of the geocorona by Lyman-alpha detectors on the Two Wide-angle Imaging Neutral-atom Spectrometers mission. We introduce a new parameter, NH, the number of H atoms in the spherical shell from a geocentric distance of 3 to 8 Earth radii, to quantitatively characterize in a simplified way global exospheric conditions. Five geomagnetic storms observed during three months in the second half of 2011 are accompanied by abrupt temporary increases, spikes, of NH from 6% to 17%, lasting not longer than a day. These increases seem to show some correlation with the minimum Dst index reached during the peak of each storm.

Cascade contributions to geocoronal Balmer α airglow line profiles are directly proportional to the Balmer β/α line ratio and can therefore be determined with near simultaneous Balmer β observations. Due to scattering differences for solar Lyman β and Lyman γ (responsible for the terrestrial Balmer α and Balmer β fluorescence, respectively) there is an expected trend for the cascade emission to become a smaller fraction of the Balmer α intensity at larger shadow altitudes. Near coincident Balmer α and Balmer β data sets, obtained from the Wisconsin Hα Mapper (WHAM) Fabry–Perot, are used to determine the cascade contribution to the Balmer α line profile, and to show, for the first time, the Balmer β/α line ratio, as a function of shadow altitude. We show that this result is in agreement with direct cascade determinations from Balmer α line profile fits obtained independently by high resolution Fabry–Perot at Pine Bluff, WI. We also demonstrate with radiative transport forward modeling that a solar cycle influence on cascade is expected, and that the Balmer β/α line ratio poses a tight constraint on retrieved aeronomical parameters (such as hydrogen's evaporative escape rate and exobase density). Index Terms: Hydrogen Geocorona, Balmer-alpha Line Profile, Fabry–Perot Interferometry

Solar wind interaction with neutral gas has been shown to generate soft X-rays, through the charge-exchange of highly ionized ions with neutral atoms and molecules in the interplanetary space and in the geocorona. The resulting diffuse emission can explain the non-cosmic long term enhancements (LTE) of ROSAT soft X-ray observations, which are produced by strong solar wind flux increases. This paper focuses on the emission pattern resulting from the impact on the interstellar gas of the average, “quiet” solar wind, i.e., the non variable signal “below” the LTEs. A sky map of the heliospheric emission is calculated, based on realistic hydrogen and helium atom distributions under the influence of solar conditions such as those prevailing during the ROSAT survey. It is shown that parallax effects linked to the ROSAT observing strategy have a strong influence on the resultant emission pattern. For a stationary solar wind the modeled emission has an anisotropy factor of $\simeq$1.8, and the emission maxima do not coincide with the interstellar wind axis direction. This emission is compared with the fraction of the ROSAT 0.25 keV emission assigned to hot ($T=10^{6}$ K) gas in the Local Interstellar Bubble and with the dense gas contour maps of the Bubble drawn from NaI absorption. Assuming constancy of the global pattern, but allowing for a variable scaling factor, the maximum heliospheric contribution is derived and this allows the placement of lower limits on the truly interstellar emission in many directions. After subtraction of the heliospheric emission, there is significant interstellar 0.25 keV emission from the Local Bubble “openings” to the lower halo, as expected, but also to neighbouring interstellar “bubbles”, as well as towards a number of regions along the galactic plane. There is evidence that there is hot gas emission attributable to our local cavity and generated throughout its volume, including along the galactic plane, but significantly weaker than initially thought. This would attenuate the discrepancy by a factor of about 4–5 between the hot gas pressure initially derived without heliospheric decontamination and the pressure of the embedded local diffuse clouds.

A secondary proton radiation belt can be observed in the equatorial region between the upper atmosphere and the interior edge of the main radiation belt. It is thought that the protons appear there in a result of ionization of energetic neutral hydrogen atoms coming from the internal area of the traditional radiation belt where they were born in charge exchange collisions of the trapped protons with the cold hydrogen of the gecorona. The process of formation of this secondary belt is numerically simulated in this paper assuming this charge exchangeireionization mechanism. Standard models of the trapped radiation, of the atmosphere and geocorona were used to simulate the source and the exospheric media. Experimental data were used for charge transfer cross sections. Result of simulation agrees very good with the experimental observation.

X-ray emission due to charge transfer collisions between heavy solar wind ions and neutrals has been predicted to exist both in the heliosphere and in the geocorona. The heliospheric X-ray emission can account for roughly half of the observed soft X-ray background intensity. It was also suggested that temporal variations in the heliospheric and geocoronal soft X-ray intensities will result from solar wind variations. In this paper, a simple model of the charge exchange X-ray emission mechanism is combined with measured solar wind parameters as a function of time and used to generate predictions of the temporal variation of the X-ray intensity observed at Earth for the time periods 1990–1993 and 1996–1998. Measured solar wind proton fluxes are also directly compared with the “long-term enhancement” part of the soft X-ray background measured by the Rontgen Satellite (ROSAT). A significant positive correlation exists, which supports the existence of X-ray emission associated with the solar wind interaction with either interstellar neutrals and/or with geocoronal neutral hydrogen.

This review deals with basic results of experimental and theoretical studies (numerical simulations included) of the distributions, composition, and dynamics of particles of a hot plasma in the geomagnetosphere. Attention is drawn mainly to the ring current and the plasma sheet of the magnetotail, which play a key role in physics of the magnetosphere. The integrity (unity) of the system outer radiation belt–ring current–near plasma sheet is substantiated (the concept of a hot plasma geocorona). From the viewpoint of this concept, the physical processes and theories are considered that were suggested in order to explain the structure and dynamics of the hot magnetosphere plasma. An emphasis is made on disputable issues and topical problems so far unsolved.

Thermospheric density and temperature are often derived from ionospheric observables measured by incoherent scatter radar (ISR) via solutions of the F region ion energy balance equation. However, this equation, consisting of an electron heat source balancing a neutral heat sink, can break down near the exobase, where the electron heat source can be too small by as much as 40%. An additional heat source is required, and theoretical and experimental studies point to a hot neutral oxygen (hot O) geocorona near the Earth's exobase to supply it. Hot O must therefore be included in the ion energy balance equation; however, its profile shape and concentration are unknown. We develop a simple method for including hot O profiles in the ion temperature fitting equation by calculating hot O concentration as a function of altitude and including the hot O heat source in the ion energy equation. The technique is tested as a function of solar cycle for March equinox conditions, and a χ2 analysis indicates that the hot O is more likely to form a layer than a concentration profile which decreases as a function of altitude.

The Naval Research Laboratory far ultraviolet experiment on board the OGO 4 satellite accidentally detected hydrogen Lyman α emission following the passage of missiles through the upper atmosphere. The deposition of hydrogenous exhaust products above 100 km results in a local enhancement of hydrogen, which resonantly scatters Lyman α radiation from the Sun and from the geocorona, and produces a far ultraviolet contrail. The observed local enhancement of radiation was as much as 37% above the natural background. All event detections took place at time intervals of 6 min to 10 hours following the passage of a missile or spacecraft. There was no opportunity to observe prompt emissions. We describe the observations of this unusual phenomenon and the implications for hydrogen production mechanisms.

Densities of hot (100 eV{endash}40 keV) ions vary with local time at geosynchronous orbit. Typically, the density is maximum near midnight, falls off toward both terminators, and is minimum near noon. This local time dependence is routinely observed in the Los Alamos geosynchronous plasma data. We use a month of these data (June 1996) and a simple model of particle drifts within the magnetosphere to explore its origins. We first show that the nightside density profile is shaped according to the drift path topology: trapped orbits are depleted, and only particles drifting on open trajectories contribute to this population, particularly for observations taken at times of low K{sub p}. Then, we highlight spectral absorption in dayside fluxes, which occurs when the particles pass through the geocorona. A model of charge exchange accounts for the shape and energy range of the absorption signatures observed at low K{sub p} for varying pitch angles. The density absorption computed versus local time matches the observations. Hence these basic principles of particle motion in the terrestrial magnetosphere readily explain the local time dependence of the hot ion density at geosynchronous orbit. {copyright} 1998 American Geophysical Union

We present results from EUVE measurements obtained during the all-sky survey of interplanetary and geocoronal He I 584-A emission. The data consist of count rates from the long wavelength spectrometer and the long wavelength photometric band (520–750 A) of scanner C obtained over a 1-year period from July 1992 to July 1993. During this period, EUVE was in survey mode so that the scanners made 5° × 360° sweeps of the sky in a plane perpendicular to the Sun-Earth line, while the spectrometers were aligned with the antisolar direction. The interplanetary He I signal is morphologically consistent with previous observations with similar observing geometry, such as Prognoz 6 [Dalaudier et al., 1984]. However, unlike the Prognoz 6 data, the EUVE measurements were made from low Earth orbit (520 km) and so contain geocoronal emission as well. As a result, along sight lines where the relative speed between the interplanetary wind and the Earth is at a minimum, extinction of the interplanetary signal through resonance scattering by the He geocorona occurs. We believe this to be the first detection of line extinction of the local interstellar He wind emissions by the geocorona. We find that the geocoronal extinction signatures provide a new means of determining the interstellar He wind vector and emission line profile and add further constraints on the values of other interplanetary and solar He parameters and the morphology of the He geocorona. On the basis of model fits of the observed interplanetary emission and geocoronal extinction, we determine values for the interplanetary wind ecliptic longitude λ = 76.0 ± 0.4°, latitude ϕ = −5.4 ± 0.6° (downwind direction), speed υ0 = 26.4 ±1.5 km s−1, and temperature T0 = 6900 ± 600 K. In addition, assuming an interplanetary He density of 0.01 cm−3, we determine an average solar He I 584-A line center flux of 1.4 ± 0.3 × 1010 photons cm−2 s−1 A−1 for the data analyzed here.

Energetic neutral atoms are created when energetic magnetospheric ions undergo charge exchange with cold neutral atoms in the Earth's tenuous extended atmosphere (the geocorona). Since they are unaffected by the Earth's magnetic field, these energetic neutrals travel away in straight line trajectories from the points of charge exchange. The remote detection of these particles provides a powerful means through which the global distribution and properties of the geocorona and ring current can be inferred. Due to its 2 × 9 RE polar orbit, the Polar spacecraft provides an excellent platform from which to observe ENAs because it spends much of its time in the polar caps which are usually free from the contaminating energetic charged particles that make observations of ENAs more difficult. In this brief report, we present the first ENA imaging results from Polar. Storm-time ENA images are presented for a northern polar cap apogee pass on August 29, 1996 and for a southern polar cap perigee pass on October 23, 1996. As well, we show with a third event (July 31, 1996) that ENA emissions can also be detected in association with individual substorms.

Energetic neutral atoms (ENAs) were detected by the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail spacecraft during a magnetic storm on October 29–30, 1994. The energetic particles could be identified as neutrals because the direction of the particle flux steadily tracked the direction of the Earth and was uncorrelated with the changing orientation of the ambient magnetic field as the spacecraft viewed the dayside magnetosphere for ∼ 16 hours. These observations provide the first composition measurements of ENAs, yielding the storm-time evolution of ENA fluxes of hydrogen, helium, and oxygen separately as well as their energy spectra. ENA fluxes and the rate of recovery of Dst are both roughly steady, consistent with charge-exchange being a significant energy loss process for the storm-time ring current. For total energies above 200 keV, the intensity of ENA oxygen is the highest, followed by hydrogen, and then by helium. These observations enable us to deduce the line-of-sight (LOS) integrals of the products nH jion, where nH = hydrogen geocorona density, jion = differential ion flux for ion species H+, He+, and O+ at energies between ∼60 and ∼600 keV.

Energetic neutral atoms (ENAs) were detected by the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail spacecraft during a magnetic storm on October 29–30, 1994. The energetic particles could be identified as neutrals because the direction of the particle flux steadily tracked the direction of the Earth and was uncorrelated with the changing orientation of the ambient magnetic field as the spacecraft viewed the dayside magnetosphere for ∼16 hours. These observations provide the first composition measurements of ENAs, yielding the storm-time evolution of ENA fluxes of hydrogen, helium, and oxygen separately as well as their energy spectra. ENA fluxes and the rate of recovery of Dst are both roughly steady, consistent with charge exchange being a significant energy loss process for the storm-time ring current. For total energies above 200 keV, the intensity of ENA oxygen is the highest, followed by hydrogen, and then by helium. These observations enable us to deduce the line-of-sight (LOS) integrals of the products nHjion and nHfion, where nH=hydrogen geocorona density, jion=differential ion flux, and fion=phase space density (PSD), for ion species H+, He+ and O+ at energies between ∼60 and ∼600 keV. A ∼50–60 keV Maxwellian fits the O+ LOS PSD fairly well but fits the He+ and the H+ only poorly.

The Hydrogen Deuterium Absorption Cell (HDAC) is part of the Ultraviolet Imaging Spectrograph (UVIS) experiment aboard the Cassini spacecraft. During Cassini’s Earth swingby on August 18, 1999, HDAC was used as a photometer to measure solar Lyman-α radiation scattered by the neutral hydrogen atoms of the geocorona. These data provide information about the hydrogen column density along HDAC’s line of sight during the Earth swingby. The data cover a large part of the Earth’s exosphere and enable us to determine the distribution of hydrogen atoms in this region. The results are compared to predictions of models providing hydrogen densities of the Earth’s exosphere/geocorona. We found that the models overestimate the decrease of hydrogen density for increasing distance from the Earth.

A model of the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically disturbed nighttime conditions. The precipitation of energetic O+ ions and the subsequent enhancement of the hot O corona at high latitudes is simulated for the September 17, 1971, storm conditions. It is found that in such circumstances, the O+ precipitation is a significant source of superthermal O atoms leading to important perturbations of the velocity distribution of the bulk oxygen population. The effective gas temperature near the exobase is similar to that in the undisturbed atmosphere, but the hot O density rises considerably over the quiet condition values.

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2+ and NO+ dissociative recombination. The Boltzmann equations for thermal and nonthermal populations of O atoms are solved with a Monte Carlo stochastic simulation method. It is shown that the calculated energy distribution functions of O atoms are significantly in nonequilibrium in the transition region between the thermosphere and the exosphere. It is found that the inclusion of additional sources leads to stronger disturbances of the energy distribution function and, as a consequence, increases the nonthermal fraction of hot O atoms. The variation of the vertical distribution of hot O between solar maximum and minimum conditions is also evaluated and shows good agreement with the available experimental evidence.

[1] High spectral resolution line profile observations indicate a reproducible semi-annual variation in the geocoronal hydrogen Balmer α effective temperature. These observations were made between 08 January 2000 and 21 November 2001 from Pine Bluff Observatory (WI) with a second generation double etalon Fabry-Perot annular summing spectrometer operating at a resolving power of 80,000. This data set spans sixty-four nights of observations (1404 spectra in total) over 20 dark-moon periods. A two cluster Gaussian model fitting procedure is used to determine Doppler line widths, accounting for fine structure contributions to the line, including those due to cascade; cascade contributions at Balmer α are found to be 5 ± 3%. An observed decrease in effective temperature with increasing shadow altitude is found to be a persistent feature for every night in which a wide range of shadow altitudes were sampled. A semiannual variation is observed in the column exospheric effective temperature with maxima near day numbers 100 and 300 and minima near day numbers 1 and 200. Temperatures ranged from ∼710 to 975 K. Average MSIS model exobase temperatures for similar conditions are approximately 1.5× higher than those derived from the Balmer α observations, a difference likely due to contributions to the observed Balmer α column emission from higher, cooler regions of the exosphere.

This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and metastable species. Numerical calculations are performed for low altitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of metastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten higher than those due to previously considered O2(+) and NO(+) dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O(+)((sup 2)D), O((sup 1)D), N((sup 2)D), O(+)((sup 2)P) and vibrationally excited N2 by atomic oxygen.

[1] Exospheric atomic hydrogen (H) resonantly scatters solar Lyman-α (121.567 nm) radiation, observed as the geocorona. Measurements of scattered solar photons allow one to probe time-varying three-dimensional distributions of exospheric H atoms. The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission images the magnetosphere in energetic neutral atom (ENA) fluxes and additionally carries Lyman-α detectors (LADs) to investigate exospheric atomic hydrogen. Knowledge of exospheric properties is essential for the interpretation of magnetospheric images in ENA fluxes produced in charge exchange between energetic ions and H atoms. We describe the process of obtaining exospheric distributions and present, as an example, a global H number density distribution for 11 June 2008. The TWINS LAD experimental data are especially sensitive to atomic hydrogen at geocentric distances from 3 to 8 Earth radii. The distribution reveals asymmetries from day to night, dawn to dusk, and north to south. We discuss the available data sets and their coverage, limitations, and promise for a study of exospheric response to seasonal, solar, and geomagnetic variations.

[1] The magnetospheric cusps separate closed dayside magnetospheric field lines from open field lines of the magnetotail mantle and lobes. All magnetospheric field lines that map to the magnetopause also pass through the cusp regions. Thus whenever magnetic reconnection occurs at the magnetopause, magnetosheath plasma can enter one or both of the cusp regions and charge exchange with the geocorona. The resulting energetic neutral atoms (ENAs) resulting from this charge exchange process propagate away from the cusps and are observed remotely by the Interstellar Boundary Explorer (IBEX). The asymmetry of the ENA intensities between the northern and southern cusps are strongly dependent upon the Earth's dipole tilt angle and are consistent with in situ cusp observations. These asymmetric fluxes in the cusp regions are suggested to be explained by the regions at the magnetopause where magnetic reconnection is expected.

The major sources of the Soft X-ray Background (SXRB), besides distinct structures as supernovae and superbubbles (e.g. Loop I), are: (i) an absorbed extragalactic emission following a power law, (ii) an absorbed thermal component ~2x10^6 K) from the galactic disk and halo, (iii) an unabsorbed thermal component, supposedly at 10^6 K, attributed to the Local Bubble and (iv) the very recently identified unabsorbed Solar Wind Charge-eXchange (SWCX) emission from the heliosphere and the geocorona. We study the SWCX heliospheric component and its contribution to observed data. In a first part, we apply a SWCX heliospheric simulation to model the oxygen lines (3/4 keV) local intensities during shadowing observations of the MBM12 molecular cloud and a dense filament in the south galactic hemisphere with Chandra, XMM-Newton, and Suzaku telescopes. In a second part, we present a preliminary comparison of SWCX model results with ROSAT and Wisconsin surveys data in the 1/4 keV band. We conclude that, in the 3/4 keV band, the total local intensity is entirely heliospheric, while in the 1/4 keV band, the heliospheric component seems to contribute significantly to the local SXRB intensity and has potentially a strong influence on the interpretation of the ROSAT and Wisconsin surveys data in terms of Local Bubble hot gas temperature., Comment: 15 pages, 7 figures, 2 tables, 'From the Outer Heliosphere to the Local Bubble' ISSI workshop, Bern October 2007

It was found that the LEP data was sometimes contaminated with unexpectedly larger noise mainly due to the geocorona EUV radiation. Its noise level is so high that we are obliged to substract the background noise in ground processing when we intend to analyze such LEP data. We therefore propose an efficient and useful procedure for eliminating this background noise, which is highly implemented so as to reduce the computing time. This method is based on a Bayesian smoothness prior approach with a state space modeling.

[1] The 11-year solar cycle is a dominant source of natural variability in the upper atmosphere, and its effect on atomic hydrogen distributions and emissions must be understood to investigate possible signs of longer-term climatic trends in this region. We present midlatitude geocoronal hydrogen Balmer a observations from solar cycle 23 (1997-2006) and three solar minimum periods, 1985, 1997, and 2006. The 1997 through 2006 observations were taken with the Wisconsin H-a Mapper Fabry-Perot (WHAM), a ground-based CCD-annular summing instrument that began observations at the Kitt Peak Observatory in Arizona in 1997. The 1985 observations were made with a similarly designed "pre-WHAM" Fabry-Perot Interferometer utilizing photomultiplier detection and located in Wisconsin. WHAM has consistently observed higher column emission intensities during solar maximum periods than during solar minimum conditions, with the ratio dependent upon the viewing geometry. The observations from three solar minimum periods agree to within 18% uncertainties over most of the shadow altitude range. An analysis of recent Fabry-Perot observations of upper atmospheric hydrogen during solar cycle 23 and during three solar minima (1985, 1997, 2006) established a reference data set of highly precise, consistently calibrated, thermospheric plus exospheric hydrogen column emission observations from northern midlatitudes that can be used to compare with future observations.

Observations of the diffuse EUV background towards 138 different directions using the spectrometers aboard the Extreme Ultraviolet Explorer satellite (EUVE) have been combined into a spectrum from 150A to 730A and represent an effective exposure of 18 million seconds. There is no significant evidence for any line flux from any source other than the geocorona. These results are inconsistent with the Wisconsin C and B broad-band surveys assuming the source is a logT = 5.8 − 6.1 hot plasma in ionization equilibrium with solar abundances, confirming the previous result of Jelinsky, Vallerga & Edelstein (1995) (hereafter Paper I) using an observation along the ecliptic with the same instrument. To make these results consistent with the previous broad-band surveys, the plasma responsible for the emission must either be depleted in Fe by a factor of ∼ 6, be behind an absorbing slab of neutral H with a column of 2 × 1019 cm−2, or not be in collisional ionization equilibrium (CIE). One particular non-CIE model (Breitschwerdt & Schmutzler, 1994) that explains the soft x-ray results is also inconsistent with this EUV data.

[1] The role of the auroral sources induced by the electron and proton precipitation in the formation of the hot oxygen corona in the polar upper atmosphere is studied. It is found that both electron precipitation through exothermic chemistry and proton precipitation through atmospheric sputtering significantly contribute to the population of the hot oxygen geocorona. It is also found that only atmospheric sputtering results in the formation of the escape flux of energetic oxygen atoms, providing an important source of heavy atoms for the magnetosphere. The exothermic chemistry induced by the electron precipitation and/or by the absorption of the solar UV radiation is operating continuously in the polar upper atmosphere and results in a steady population of the very near-Earth environment by suprathermal oxygen atoms with energies below a few eV. By contrast, atmospheric sputtering by magnetospheric protons provides a more variable contribution, strongly coupled with the cusp region. It produces the more energetic oxygen atoms that populate the external regions of the hot oxygen geocorona. The results of calculations are in a good agreement with the analysis of the low-latitude perigee Low Energy Neutral Atom (LENA) images showing that the instrument signal consists of low to medium energy (5–30 eV) oxygen atoms produced in and near the cusp region. The more energetic (>30 eV) fraction of energetic oxygen atoms produced by the ioninduced atmospheric sputtering could be responsible for the energetic neutrals observed by the instrument far away from the cusp or oval regions. The total escape flux of oxygen atoms associated with atmospheric sputtering by protons is found about 8 � 10 23 s � 1 ; therefore this mechanism may provide a substantial contribution to the magnetospheric oxygen population.

[1] The high-energy proton-hydrogen (H+/H) beam associated with proton auroral precipitation transfers momentum in elastic and inelastic collisions with ambient thermal atomic oxygen in the high latitude thermosphere. This process provides a localized novel source of hot oxygen atoms in addition to exothermic photochemistry, charge exchange and momentum transfer from O+ ion precipitation and charge exchange with accelerated ionospheric O+ ions. We suggest that this source contributes to the population of the hot oxygen geocorona and to the flux of escaping oxygen atoms. For an incident proton energy flux of 1 mW m−2 and a mean energy Emean ≈ 5 keV, we calculate a density of hot oxygen atoms with energy above 1 eV of 2.0 × 103 cm−3 and a mean kinetic energy of about 3.5 eV at 700 km. The total upward flux of hot oxygen atoms with energies higher 1 eV is estimated as 3.5 × 108 cm−2 s−1.

[1] Analysis of ENA data from the LENA instrument on the IMAGE spacecraft shows that the terrestrial atmosphere is a copious emitter of energetic neutral atoms (