Precipitation Of Heavy Ions Research Articles

Influence of the Solar Wind Dynamic Pressure on the Ion Precipitation: MAVEN Observations and Simulation Results

AbstractWe discuss the influence of the solar wind dynamic pressure on the ion precipitation using observations performed by MAVEN from 4 June 2014 to 20 July 2017. The increase of the dynamic pressure from 0.63 to 1.44 nPa is clearly associated with an increase of the same order of magnitude of the precipitating oxygen ion energy flux measured by MAVEN/STATIC from 9.9 to 20.6 × 106 eV · cm−2 · sr−1 · s−1 at low energy (from 30 to 650 eV). In the same way, from 650 to 25,000 eV, MAVEN/SWIA (all species) observed an increase from 22.4 to 42.8 × 107eV · cm−2 · sr−1 · s−1 of the precipitating ion energy flux. Performing two simulations using the average solar wind conditions for both solar dynamic pressure regimes observed by MAVEN as input of the LatHyS model (LATMOS Hybrid Simulation), we reproduce some of the key characteristics of the observed oxygen ion precipitation. We characterize the oxygen ions simulated by LatHyS by their energy and time of impact, their time of injection in the simulation and initial position, and the mechanism by which these ions were created. The model suggests that the main cause of the increase of the heavy ion precipitation during an increase of the solar dynamic pressure is the increase of the ion production by charge exchange, proportional to the increase of the solar wind flux, which becomes the main contribution to the ion precipitation at high energy.

Jovian Auroral Ion Precipitation: X‐Ray Production From Oxygen and Sulfur Precipitation

AbstractMany attempts have been made to model X‐ray emission from both bremsstrahlung and ion precipitation into Jupiter's polar caps. Electron bremsstrahlung modeling has fallen short of producing the total overall power output observed by Earth‐orbit‐based X‐ray observatories. Heavy ion precipitation was able to reproduce strong X‐ray fluxes, but the proposed incident ion energies were very high ( 1 MeV per nucleon). Now with the Juno spacecraft at Jupiter, there have been many measurements of heavy ion populations above the polar cap with energies up to 300–400 keV per nucleon (keV/u), well below the ion energies required by earlier models. Recent work has provided a new outlook on how ion‐neutral collisions in the Jovian atmosphere are occurring, providing us with an entirely new set of impact cross sections. The model presented here simulates oxygen and sulfur precipitation, taking into account the new cross sections, every collision process, the measured ion fluxes above Jupiter's polar aurora, and synthetic X‐ray spectra. We predict X‐ray fluxes, efficiencies, and spectra for various initial ion energies considering opacity effects from two different atmospheres. We demonstrate that an in situ measured heavy ion flux above Jupiter's polar cap is capable of producing over 1 GW of X‐ray emission when some assumptions are made. Comparison of our approximated synthetic X‐ray spectrum produced from in situ particle data with a simultaneous X‐ray spectrum observed by XMM‐Newton shows good agreement for the oxygen part of the spectrum but not for the sulfur part.

Influence of Extreme Ultraviolet Irradiance Variations on the Precipitating Ion Flux From MAVEN Observations

AbstractWe study the influence of the solar extreme ultraviolet (EUV) flux intensity on the precipitating ion fluxes as seen by the Solar Wind Ion Analyzer, an energy and angular ion spectrometer aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We defined three periods with significantly different EUV flux intensity (1.6 and 3.2 times the lowest EUV intensity) and compare the precipitating ion flux measured by MAVEN/Solar Wind Ion Analyzer during each period. At low energy [30–650] eV, we find that the median (average) precipitating ion flux during the medium and low EUV periods are, respectively, 1.7 (2.1) and 3 (3.5) times more intense than the flux during the high EUV period. At high energy [650–25,000] eV, a similar trend in the intensity of the precipitating ion flux is observed but with an increase by 50% (46%) and 70% (79%), respectively. A larger EUV flux does therefore not seem to favor heavy ion precipitation into Mars's atmosphere, contrary to modeling prediction and overall expectations.

Variability of Precipitating Ion Fluxes During the September 2017 Event at Mars

AbstractIn this work, we study the influence of the September 2017 solar event on the precipitating heavy ion fluxes toward Mars' atmosphere as seen by Mars Atmosphere and Volatile EvolutioN/Solar Wind Ion Analyzer, an energy and angular ion spectrometer and by Mars Atmosphere and Volatile EvolutioN/Suprathermal and Thermal Ion Composition instrument, an energy, mass, and angular ion spectrometer. After a careful reconstruction of the background induced by the Solar Energetic Particle event in the Mars Atmosphere and Volatile EvolutioN/Solar Wind Ion Analyzer spectrometer, we investigate the precipitating ion flux responses to the space weather events that took place in September 2017. This period is a unique opportunity to analyze the respective role of various possible drivers of heavy ion precipitation into Mars' atmosphere with a wide range of different space weather events occurring during the same month. This study shows an increase in the precipitation flux by more than 1 order of magnitude during the arrival of the September Interplanetary Coronal Mass Ejection compared to the average flux during quiet solar conditions. We also showed that among the possible solar drivers, the solar wind dynamic pressure is the most significant during September 2017.

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

AbstractA model is described for the transport of magnetospheric oxygen ions with low charge state and energies up to several MeV/nucleon (MeV/u) as they precipitate into Jupiter's polar atmosphere. A revised and updated hybrid Monte Carlo model originally developed by Ozak et al. (2010, https://doi.org/10.1029/2010JA015635) is used to model the Jovian X‐ray aurora. The current model uses a wide range of incident oxygen ion energies (10 keV/u to 5 MeV/u) and the most up‐to‐date collision cross sections. In addition, the effects of the secondary electrons generated from the heavy ion precipitation are included using a two‐stream transport model that computes the secondary electron fluxes and their escape from the atmosphere. The model also determines H2 Lyman‐Werner band emission intensities, including a predicted spectrum and the associated color ratio. Implications of the new model results for interpretation of data from National Aeronautics and Space Administration's Juno mission are discussed. In particular, the model predicts that for a 2 MeV/u oxygen ion energy input of 10 mW/m2: (1) escaping electrons are produced with an energy range from 1 eV to 4 keV, which is a smaller range than previous models by Ozak et al. (2013, https://doi.org/10.1002/2013GL50812) predicted, (2) H2 band emission rates of 75 kR are generated, similar to previous estimates, and (3) a newly calculated Lyman and Werner band color ratio of 10 is expected. The color ratios are put into a context of various methane number density distributions.

Characteristics of north jovian aurora from STIS FUV spectral images

We analyzed two observations obtained in Jan. 2013, consisting of spatial scans of the jovian north ultraviolet aurora with the HST Space Telescope Imaging Spectrograph (STIS) in the spectroscopic mode. The color ratio (CR) method, which relates the wavelength-dependent absorption of the FUV spectra to the mean energy of the precipitating electrons, allowed us to determine important characteristics of the entire auroral region. The results show that the spatial distribution of the precipitating electron energy is far from uniform. The morning main emission arc is associated with mean energies of around 265keV, the afternoon main emission (kink region) has energies near 105keV, while the ‘flare’ emissions poleward of the main oval are characterized by electrons in the 50–85keV range. A small scale structure observed in the discontinuity region is related to electrons of 232keV and the Ganymede footprint shows energies of 157keV. Interestingly, each specific region shows very similar behavior for the two separate observations.The Io footprint shows a weak but undeniable hydrocarbon absorption, which is not consistent with altitudes of the Io emission profiles (∼900km relative to the 1bar level) determined from HST-ACS observations. An upward shift of the hydrocarbon homopause of at least 100km is required to reconcile the high altitude of the emission and hydrocarbon absorption.The relationship between the energy fluxes and the electron energies has been compared to curves obtained from Knight’s theory of field-aligned currents. Assuming a fixed electron temperature of 2.5keV, an electron source population density of ∼800m−3 and ∼2400m−3 is obtained for the morning main emission and kink regions, respectively. Magnetospheric electron densities are lowered for the morning main emission (∼600m−3) if the relativistic version of Knight’s theory is applied.Lyman and Werner H2 emission profiles, resulting from secondary electrons produced by precipitation of heavy ions in the 1–2MeV/u range, have been applied to our model. The low CR obtained from this emission suggests that heavy ions, presumably the main source of the X-ray aurora, do not significantly contribute to typical UV high latitude emission.

Mars heavy ion precipitating flux as measured by Mars Atmosphere and Volatile EvolutioN

AbstractIn the absence of an intrinsic dipole magnetic field, Mars' O+ planetary ions are accelerated by the solar wind. Because of their large gyroradius, a population of these planetary ions can precipitate back into Mars' upper atmosphere with enough energy to eject neutrals into space via collision. This process, referred to as sputtering, may have been a dominant atmospheric loss process during earlier stages of our Sun. Yet until now, a limited number of observations have been possible; Analyzer of Space Plasmas and Energetic Atoms‐3/Mars Express observed such a precipitation only during extreme conditions, suggesting that sputtering might be not as intense as theoretically predicted. Here we describe one example of precipitation of heavy ions during quiet solar conditions. Between November 2014 and April 2015, the average precipitating flux is significant and in agreement with predictions. From these measured precipitating fluxes, we estimate that a maximum of 1.0 × 1024 O/s could have been lost due to sputtering.

Response of Mars O+ pickup ions to the 8 March 2015 ICME: Inferences from MAVEN data‐based models

AbstractWe simulate and compare three phases of the Mars‐solar wind interaction with the 8 March interplanetary coronal mass ejection (ICME) event using Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations in order to derive heavy ion precipitation and escape rates. The MAVEN observations provide the initial conditions for three steady state MHD model cases, which reproduce the observed features in the solar wind density, velocity, and magnetic field seen along the MAVEN orbit. Applying the MHD results to a kinetic test particle model, we simulate global precipitation and escape maps of O+ during the (1) pre‐ICME phase, (2) sheath phase, and (3) ejecta phase. We find that the Case 1 had the lowest precipitation and escape rates of 9.5 × 1025 and 4.1 × 1025 s−1, Case 2 had the highest rates of 9.5 × 1025 and 4.1 × 1025 s−1, and Case 3 had rates of 3.2 × 1025 and 1.3 × 1025 s−1, respectively. Additionally, Case 2 produced a high‐energy escaping plume >10 keV, which mirrored corresponding STATIC observations.

Ultraviolet emissions in the planetary atmospheres

Actual state and perspectives of the observations of the planetary atmospheres in the ultraviolet range of wavelengths are discussed. The main features of the planetary aeronomy for terrestrial planets, giant planets and exoplanets-transits are given. The following hot problems of the planetary astronomy in the UV wavelength range are discussed: (i) UV observations of hot coronas of the terrestrial planets; (ii) formation and morphology of the rarefied H2O-, O2- and O-dominant atmospheres of the icy satellites in the giant planet systems; formation and evolution of the neutral gas clouds in the giant planet systems; (iii) studies of the extended hydrogen coronae of the transit-exoplanets formed due to the stellar UV and plasma wind forcing. The mathematical models such as the Monte Carlo model for the electron, proton, and heavy-ion precipitation into the planetary atmospheres are also discussed. Such models are currently used to calculate the excitation rates of the atmospheric UV emissions and will be used for the interpretation of the expected UV observations of the planetary atmospheres with the space observatory World Space Observatory–Ultraviolet (WSO–UV).

Implications of Jovian X‐ray emission for magnetosphere‐ionosphere coupling

The first observations of Jupiter made by the Chandra X‐Ray Observatory revealed a powerful X‐ray aurora located in the polar caps. The X‐ray emission exhibited a 40‐min periodicity. Such 40‐min periodicities have previously been seen in energetic particle fluxes and in Jovian radio emission. This paper develops scenarios in which the X‐ray emission is produced by energetic heavy ion precipitation, either on open field lines connecting to the solar wind or on closed field lines reaching to the outer magnetosphere. In order to produce enough X‐ray power, both scenarios require the existence of field‐aligned electric fields located somewhere between the ionosphere and the magnetosphere, most likely at a radial distance of a few Jovian radii. The potential needed for solar wind ions to produce the observed X‐rays is about 200 kV and the potential needed for the magnetospheric ions is at least 8 MV. Protons and helium ions are also accelerated by the potential and should produce an intense ultraviolet aurora. Downward electrical current is carried by the precipitating ions and also by upwardly accelerated secondary electrons produced by the primary ion precipitation. The estimated downward Birkeland current is about 1000 MA for the solar wind case and is about 10 MA for the magnetospheric case. For the magnetosphere scenario, this observed current represents part of the “return” current portion of the magnetospheric circuit associated with the departure of the mass‐loaded magnetospheric plasma from corotation. The auroral X‐ray emission maps at least part of this return current in the polar cap, whereas the main oval, produced by electron precipitation, is thought to map the region of upward Birkeland currents. The accelerated secondary electrons could be responsible for the periodic radio emission (i.e., QP‐40 bursts).

Jupiter’s Aurora: Solar Wind and Rotational Influences

AbstractJovian auroral emissions are observed at infrared, visible, ultraviolet, and x-ray wavelengths. As at Earth, pitch-angle scattering of energetic particles into the atmospheric loss cone and the acceleration of current-carrying electrons in field-aligned currents both play a role in exciting the auroral emissions. The x-ray aurora is believed to result principally from heavy ion precipitation, while the ultraviolet aurora is produced predominantly by precipitating energetic electrons. The magnetospheric processes responsible for the aurora are driven primarily by planetary rotation. Acceleration of Iogenic plasma by rotationally-induced electric fields results in both the formation of the energetic ions that are scattered and the formation of strong, field-aligned currents that communicate the torques from the ionosphere. In addition to rotation-driven processes, solar-wind-modulated processes in the outer magnetosphere may lead to highly, time-dependent acceleration and thus also contribute to jovian auroral activity. Observational evidence for both sources will be presented. See Waite et al. (2001, Nat., 410, 787).

Jovian X‐ray emission from solar X‐ray scattering

Soft x‐ray emissions with brightnesses of about 0.01–0.2 Rayleighs have been observed from both the equatorial and auroral regions of Jupiter. It has been proposed that the equatorial emission, like the auroral emission, may be largely due to precipitation of energetic heavy ions into the atmosphere [Waite et al., 1997]. In this paper we model two alternative mechanisms for low‐latitude x‐ray emission: (1) elastic scattering of solar x‐rays by atmospheric neutrals, (2) fluorescent scattering of carbon K‐shell x‐rays from methane molecules located below the jovian homopause. Our modeled brightnesses agree, up to a factor of two, with the bulk of low‐latitude ROSAT measurements. This suggests that solar photon scattering (approximately 90% elastic scattering) may act in conjunction with energetic heavy ion precipitation to generate jovian equatorial x‐ray emission.

Equatorial X-ray Emissions: Implications for Jupiter's High Exospheric Temperatures

Observations with the High Resolution Imager on the Rontgensatellit reveal x-ray emissions from Jupiter's equatorial latitudes. The observed emissions probably result from the precipitation of energetic (>300 kiloelectron volts per atomic mass unit) sulfur and oxygen ions out of Jupiter's inner radiation belt. Model calculations of the energy deposition by such heavy ion precipitation and of the resulting atmospheric heating rates indicate that this energy source can contribute to the high exospheric temperatures(>800 kelvin at 0.01 microbar) measured by the Galileo probe's Atmospheric Structure Instrument. Low-latitude energetic particle precipitation must therefore be considered, in addition to other proposed mechanisms such as gravity waves and soft electron precipitation, as an important source of heat for Jupiter's thermosphere.

The chemical effects of auroral oxygen precipitation at Jupiter

Energetic oxygen precipitation is one possible explanation for the auroral molecular hydrogen emissions observed by the Voyager ultraviolet spectrometer. These ions deposit their energy in the Jovian thermosphere by means of ionization, dissociation, excitation, and heating processes. The photochemistry of both the neutral gas and the ionosphere is altered by the influx of atomic oxygen. The auroral oxygen flux is about 10 7 cm −2 sec −1 if all the observed Lyman and Werner band emissions are due to heavy ion precipitation rather than to energetic electron precipitation. The O atoms react with H + ions forming O + ions, which then react with H 2, starting a chain of chemical reactions involving H 2O + and H 3O + that ultimately leads to the formation of water. The O atoms can also react with CH 3 and will eventually form CO deeper in the atmosphere. A numerical model has been developed to study the effects of odd oxygen (i.e., O, OH, and H 2O) on the auroral ionosphere of Jupiter. In particular, we show that the electron density is reduced by about a factor of 4 due to the removal of H + ions by chemistry associated with odd oxygen species, whereas the electron density reduction required for consistency with observations is more than a factor of 20 suggesting that other H + loss mechanisms must be operating or that sources of oxygen or water other than auroral precipitation are present. The globally averaged flux of oxygen from the aurora is also about a factor of 20 too low to explain the Jovian CO measurements.

Heavy ion dynamics and auroral arc formation in the Jovian magnetosphere

This paper gives a brief review of some of the current controversial issues surrounding the Jovian aurora. In particular, the manner of its excitation be it that of electron or heavy ion precipitation is examined critically in the context of proposed models for magnetospheric dynamics, particle energization, and auroral energy input. A model for the X-ray aurora based on bremsstrahlung by a primary electron beam and its ionization secondaries is highlighted and the connection to the outward magnetospheric transport of heavy ion plasma from the satellite Io is made.

Storm time heavy ion outflow at mid‐latitude

Local ionospheric observations with the Millstone Hill incoherent scatter radar reveal an upward ion bulk velocity in excess of 3 km s−1 at 1000 km altitude during the very large magnetic storm on February 8, 1986. The upward flux of O+ ions exceeded 3×109 cm−2s−1 at 42° geodetic latitude (55°Λ) for a 3‐hour period around 18 MLT during the event. Frictional ion heating with ion temperatures in excess of 4000°K at 500 km altitude was observed by the radar in the vicinity of the ion outflow event. Satellite observations place the ion outflow event within a region of intense ion and electron precipitation on field lines associated with the storm‐perturbed ring current. For a one‐dimensional analysis of the observed plasma profiles, continuity considerations indicate a region of intense O+ production (200 cm−3 s−1) as well as significant upward acceleration (5–10 m s−2) in the region between 600 km and 800 km altitude where the outflow approaches supersonic speed. Ionizing collisions involving fast backsplash neutral O atoms (Torr et al., 1974) produced by ring current heavy ion precipitation can provide sufficient upward momentum to account for the acceleration in the observed outflowing thermal O+ fluxes. Alternatively, the outflow event can be explained in terms of a time‐dependent diffusion process triggered by a sudden change in the frictional heating rate in the collision‐dominated F region (St.‐Maurice, 1989). The concurrence of rapid ion convection and energetic ring current precipitation is unique at mid‐latitudes during intense magnetic storms. Under these conditions, our observations indicate that the mid‐latitude ionosphere constitutes a significant source of upflowing thermal O+ fluxes to the overlying magnetosphere.

The Jovian aurora: Electron or ion precipitation?

High signal‐to‐noise spectra of the Jovian aurora at UV wavelengths obtained using the International Ultraviolet Explorer Observatory (including the brightest Jovian aurora observed to date) are used to study the existence of sulfur and oxygen emissions which would be associated with the precipitation of energetic heavy ions in the upper Jovian atmosphere. Model calculations of heavy ion precipitation and corresponding estimates of the associated sulfur and oxygen UV emissions carried out in the preceding companion paper of Horanyi et al. suggest emission values for 1304‐Å O I emission that are at least 50 times larger than the upper limit values set by the IUE observations reported here. On the other hand a possible emission feature of S II at 1256 Å is comparable to the theoretically predicted emission intensity. Earlier X ray observations and in situ plasma observations have indicated the existence of energetic heavy ion precipitation in the Jovian auroral zone. Based on the IUE observations reported here, we suggest a scenario where heavy ion auroral energy deposition is concentrated at altitudes below the homopause (i.e., >300 keV/nucleon) and electrons with energies of 10 to 30 keV are responsible for the bulk of the observable UV and EUV emissions since they deposit their energy above the methane‐absorbing layer defined by the homopause.

Jovian magnetospheric neutral wind and auroral precipitation flux

We propose a mechanism for the transport of energy from the rotation of Jupiter into the heavy ions whose precipitation into the atmosphere is responsible for the intense ultraviolet aurora. The process involves charge exchange of heavy ions in the Io torus, their flight to the outer magnetosphere as neutrals, and their reionization in a region where the pickup magnetic moment is large. The particles diffuse back inward adiabatically and are precipitated at 9 RJ with an energy exceeding 10 keV/nucleon. A field and flow model based on Voyager observations is used that defines a source region extending from 32 RJ to 80 RJ on the nightside. This region is capable of delivering 4×1013 W of power to the auroral region, well within the realm of the power required by observations. We also demonstrate that this mechanism provides a neutral planetary wind from Jupiter. The predicted wind will consist of two beams: one intense (5×1028 s−1) at 25 eV/nucleon and the other tenuous (1×1025 s−1) at 600 eV/nucleon and above. These neutral particles will appear as a suprathermal heavy ion component in the solar wind.