Solar Wind Protons Research Articles

Ion escape from the upper ionosphere of Titan triggered by the solar wind

The observed escape of ions from the ionosphere of Titan suggests a potential role of the solar wind in the interaction with the upper atmospheric layers. We investigate such a plausible scenario using a hydrodynamic fluid approach for the plasma expansion in the upper ionosphere of Titan, combining (Maxwellian) electrons and three different species of positive ions which interact with the solar wind electrons and protons. Using a self-similar transformation, a numerical analysis is performed to solve the basic equations and characterize the plasma density, velocity, and electric potential during the expansion. It is found that increasing the solar wind proton number density leads to a reduction of the ion escape, while the effect of electrons is opposite stimulating the ion escape. Moreover, the expansion domain does not change for more energetic protons. The heavier ions play the leading role in controlling the ion escape, i.e. by comparison with CH $_{5}^{+}$ ions, C2H $_{5}^{+}$ ions appear to have more influence in the loss from Titan ionosphere. For a higher temperature contrast between ions and electrons, the depletion rate of the density increases and the ions move faster, leading to a higher ionic loss.

Solar Wind Proton Deceleration in Front of the Terrestrial Bow Shock

AbstractThe terrestrial foreshock as a region permeated by different types of plasma waves, various particle populations, and strong wave activity is a subject of intensive investigations. Our statistical study of the solar wind proton velocity deceleration in the foreshock uses multipoint observations of the THEMIS mission and compare them with the Wind solar wind monitor with a motivation to estimate the factors influencing evolution/modification of the solar wind speed. In order to follow changes of the solar wind proton speed, our moment calculations do not include the reflected particles as well as heavier ions. We have found a systematic deceleration of the solar wind protons with a decreasing distance to the bow shock that is correlated with the flux of reflected and accelerated particles, with the level of magnetic field fluctuations in the ultralow frequency range, and with their compressibility. We can conclude that the reflected particles excite waves of large amplitudes and, as a consequence, modify median values of the velocity measured in an unperturbed solar wind. The deceleration is as high as 3% in front of the quasi‐parallel bow shock and decreases with the distance being observable up to 50 RE. We found similar effects in front of the Moon and attributed them to an influence of the solar wind ions reflected from the lunar surface.

The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena

AbstractThe neutral exosphere of Mars extends far upstream beyond the bow shock, and as a result, solar wind protons can charge exchange with this neutral exosphere to produce energetic neutral atoms. Energetic neutral atoms produced directly upstream of Mars will precipitate into the Martian dayside atmosphere, where some fraction can undergo a charge stripping reaction and can be observed as “penetrating protons.” Clear, quasiperiodic modulations in penetrating proton densities are observed during certain Mars Atmosphere and Volatile EvolutioN (MAVEN) periapsis passes, and we show that these modulations occur during radial interplanetary magnetic field conditions. During such times, the region sunward of Mars is defined by quasi‐parallel shock conditions, generating foreshock structures characterized by enhancements in magnetic field strength, enhancements in proton density, and deceleration and deflection of the solar wind flow. These structures are observed at time cadences equal to the modulation of penetrating proton densities at periapsis. Particle tracing simulations show that the convection of these structures with the solar wind leads to localized enhancements in the rate of charge exchange upstream of the shock, producing the observed temporal variations in penetrating proton densities at periapsis. The observation of modulated penetrating proton densities at periapsis can thus be used to infer the existence of radial interplanetary magnetic field conditions upstream of the bow shock at Mars at times when MAVEN does not sample the upstream solar wind.

Reply to: Comment on “The Dominant Role of Energetic Ions in Solar Wind Interaction With the Moon” by Poppe

AbstractIn all kinetic simulations of the solar wind interaction with the moon, dayside absorption of the core solar wind protons results in the formation of a numerically unstable vacuum in the tail requiring a fix. In Omidi et al. (2019, https://doi.org/10.1029/2018JA026243) it was shown that replacing the vacuum with a cold plasma results in unacceptable magnetic fields when compared to observations. It was also demonstrated that when the presence of energetic ions in the solar wind is accounted for, the tail is no longer a vacuum but contains a low‐density plasma. In addition, the resulting magnetic fields are in excellent agreement with the observations including the presence of the compressional wake. Poppe (2019) shows results from the Amitis, which employs a different vacuum model and produces a magnetic field profile in the central tail that agrees with observations. However, the results do not account for the presence of low‐density plasma in the tail and the formation of the compressional wake. To explain these shortcomings, Poppe (2019) questions the existence of plasma in the tail and attributes the compressional wake to lunar crustal fields. Here we address the criticism of plasma observations and provide additional data from ARTEMIS spacecraft that demonstrates the compressional wake is an inherent part of the lunar tail structure. As such, the Amitis vacuum simulations do not capture the full physics of the interaction. In contrast, when the energetic protons are included in the model, all aspects of the lunar tail structure are accounted for.

Decrease of the interplanetary magnetic field strength on the lunar dayside and over the polar region

The Moon interacts with the incident solar wind plasma in various ways, and most of these interactions are accompanied by variations of the interplanetary magnetic field (IMF) around the Moon. Here we first report decreases of the IMF strength observed at 100 km altitude on the lunar dayside and over the polar region, comparing upstream solar wind data from ACE with Kaguya (SELENE) data. We note that the magnetic field decreases are observed above non-magnetized regions or very weakly magnetized regions. In one event the IMF is weakened in the dayside northern hemisphere when the IMF is roughly anti-parallel to the solar wind flow. We estimate that the decrease in the magnetic pressure can be partly compensated by the thermal pressure of the back-scattered solar wind protons, which suggests that the magnetic field decrease is interpreted as diamagnetic effect by the back-scattered protons. In another event an IMF decrease is continuously detected from the northern polar region to the dayside mid-latitude region, which is not fully explained by the thermal pressure of the back-scattered protons. We also discuss the diamagnetic current system in the upstream (fore-moon) solar wind region formed by the back-scattered protons.

Ultra-dense hydrogen H(0) as dark matter in the universe: new possibilities for the cosmological red-shift and the cosmic microwave background radiation

50 experimental publications exist on ultra-dense hydrogen H(0) from our laboratory. A review of these results was published recently (L. Holmlid and S. Zeiner-Gundersen in Phys. Scr. 74(7), 2019, https://doi.org/10.1088/1402-4896/ab1276). The importance of this quantum material in space is accentuated by a few recent publications: The so called extended red emission (ERE) spectra in space agree well (L. Holmlid in Astrophys. J. 866:107, 2018a) with rotational spectra measured from H(0) in the laboratory, supporting the notion that H(0) is a major part of the dark matter in the Universe. The proton solar wind was shown to agree well with the protons ejected by Coulomb explosions in p(0), thus finally providing a convincing detailed energy mechanism for the solar wind protons (L. Holmlid in J. Geophys. Res. 122:7956–7962, 2017c). The very high corona temperature in the Sun is also directly explained (L. Holmlid in J. Geophys. Res. 122:7956–7962, 2017c) as caused by well-studied nuclear reactions in H(0). H(0) is the lowest energy form of hydrogen and H(0) is thus expected to exist everywhere where hydrogen exists in the Universe. The so called cosmological red-shifts have earlier been shown to agree quantitatively with stimulated Raman processes in ordinary Rydberg matter. H(0) easily transforms to ordinary Rydberg matter and can also form the largest length scale of matter, with highly excited electrons just a few K from the ionization limit. Such electronic states provide the small excitations needed in the condensed matter H(0) for a thermal emission at a few K temperature corresponding to the CMB, the so called cosmic microwave background radiation. These excitations can be observed directly by ordinary Raman spectroscopy (L. Holmlid in J. Raman Spectrosc. 39:1364–1374, 2008b). A purely thermal distribution from H(0) and also from ordinary Rydberg Matter at 2.7 K is the simplest explanation of the CMB. The coupling of electronic and vibrational degrees of freedom observed as in experiments with H(0) gives almost continuous energy excitations which can create a smooth thermal CMB emission spectrum as observed. Thus, both cosmological red-shifts and CMB are now proposed to partially be due to easily studied microscopic processes in ultradense hydrogen H(0) and the other related types of hydrogen matter at the two other length scales. These processes can be repeated at will in any laboratory. These microscopic formation processes are much simpler than the earlier proposed large-scale non-repeatable processes related to Big Bang.

Observations of short large amplitude magnetic structures at the Kronian bow shock

We present observations of Short Large Amplitude Magnetic Structures (SLAMS) upstream of the quasi-parallel bow shock of Saturn. Cassini surveyed the quasi-parallel bow shock regime during 2004 and 2005, and from this time period we chose four events for a detailed study. For our analysis we used the measurements of the Cassini Plasma Spectrometer (CAPS) and the Magnetometer (MAG).Locally the SLAMS act as a fast mode shock wave, and we observed possible ion beam reflection, multiple beams, deceleration and plasma heating of the solar wind protons. These features are in agreement with the near Earth observations. We also detected whistler precursor waves multiple times, which was also documented in studies of the Earth's foreshock region. Since the frequency of the upstream ULF waves detected at Saturn is lower than it is at Earth, it also has an effect on the spatial extension of the SLAM structures, which arise from these waves. With only one spacecraft's measurements it is not possible to study the SLAMS with the same efficiency as with the four-point measurements of the CLUSTER probes, but the basic observational features and the description of their evolutional characteristics are summarized.

Acceleration of Solar Wind Particles by Traveling Interplanetary Shocks

Abstract The acceleration of thermal solar wind (SW) protons at spherical interplanetary shocks driven by coronal mass ejections is investigated. The SW velocity distribution is represented using κ-functions, which are transformed in response to simulated shock transitions in the fixed-frame flow speed, plasma number density, and temperature. These heated SW distributions are specified as source spectra at the shock from which particles with sufficient energy can be injected into the diffusive shock acceleration process. It is shown that for shock-accelerated spectra to display the classically expected power-law indices associated with the compression ratio, diffusion length scales must exceed the width of the compression region. The maximum attainable energies of shock-accelerated spectra are found to be limited by the transit times of interplanetary shocks, while spectra may be accelerated to higher energies in the presence of higher levels of magnetic turbulence or at faster-moving shocks. Indeed, simulations suggest that fast-moving shocks are more likely to produce very high energy particles, while strong shocks, associated with harder shock-accelerated spectra, are linked to higher intensities of energetic particles. The prior heating of the SW distribution is found to complement shock acceleration in reproducing the intensities of typical energetic storm particle (ESP) events, especially where injection energies are high. Moreover, simulations of ∼0.2–1 MeV proton intensities are presented that naturally reproduce the observed flat energy spectra prior to shock passages. Energetic particles accelerated from the SW, aided by its prior heating, are shown to contribute substantially to intensities during ESP events.

Untangling the formation and liberation of water in the lunar regolith

The source of water (H2O) and hydroxyl radicals (OH), identified on the lunar surface, represents a fundamental, unsolved puzzle. The interaction of solar-wind protons with silicates and oxides has been proposed as a key mechanism, but laboratory experiments yield conflicting results that suggest that proton implantation alone is insufficient to generate and liberate water. Here, we demonstrate in laboratory simulation experiments combined with imaging studies that water can be efficiently generated and released through rapid energetic heating like micrometeorite impacts into anhydrous silicates implanted with solar-wind protons. These synergistic effects of solar-wind protons and micrometeorites liberate water at mineral temperatures from 10 to 300 K via vesicles, thus providing evidence of a key mechanism to synthesize water in silicates and advancing our understanding on the origin of water as detected on the Moon and other airless bodies in our solar system such as Mercury and asteroids.

Kelvin‐Helmholtz Waves Magnetic Curvature and Vorticity: Four‐Spacecraft Cluster Observations

Abstract[1] Magnetopause Kelvin‐Helmholtz (KH) waves are rich in complex magnetic and flow structures which are key to understand the role of these waves in facilitating the solar wind plasma transport into the Earth's magnetosphere. Four spacecraft in tetrahedral configuration provide the tools necessary for characterizing in situ magnetic geometry and vortical flow. We apply the tools on KH waves observed by Cluster inside an electron boundary layer on the duskside magnetopause. Magnetic curvature and flow vorticity properties of the KH waves are obtained for various solar wind conditions. Smaller curvature radius and higher‐positive vorticity are found for longer wavelength. Changes in KH wavelengths observed with relatively fixed tetrahedron size allow us to resolve magnetic curvature in multiscales. For the first time in a space plasma, we report the dependence of the curvature radius measurement on the ratio of the tetrahedron size to the wavelength, consistent with nonlinear spatial variations of magnetic structures that would be resolved by nested cross‐scale spacecraft tetrahedrons. Negative vorticity is found to develop in the rolled‐up vortex, adjacent to positive vorticity in the vortex core. The strength of negative vorticity is found to increase with the solar wind proton density and proton bulk flow speed. This study provides observational evidence of multiscale magnetic structures and is useful for understanding the development of rolled‐up vortex signatures during various stages of solar wind‐controlled KH wave evolution.

Potentials of a moving test charge during the solar wind interaction with dusty magnetosphere of Jupiter

The electrostatic Debye screening and wakefield potentials caused by a test charge are investigated in a positively charged dusty plasma. A modified dielectric constant of the dust-acoustic waves to account for the beam electrons and protons from solar wind is employed and analyzed the electrostatic potentials both analytically and numerically. This model is essentially applied to Jupiter’s magnetosphere that contains positively charged dust grains, Maxwellian electrons and ions, as well as solar wind streaming electrons and protons. The normalized Debye potential decreases exponentially by variation of axial distance while the normalized wakefield potential is strongly influenced by the plasma temperatures and streaming speeds of solar wind electrons and protons.

Modeling the superstorm in the 24th solar cycle

The St. Patrick’s Day phenomenon is a geomagnetic storm that deserves serious discussion because of its intensity and effectiveness. This study focuses on the St. Patrick’s Day storm on March 17, 2015, which is the first big storm of the 24th solar cycle. The data obtained from various spacecrafts observing the ionosphere reveal the reputation and the strength of the storm. The author tries to discuss the event as a whole with all its parameters. Variables of the study are the solar wind parameters and zonal geomagnetic indices. Models with solar wind pressure, proton density and magnetic field may aid in making the dynamic structure of the phenomenon more understandable. The obtained models are able to give the reader an idea of the results even if the storm prediction percentage is low. The author has endeavored to obey the cause–effect relationship without ignoring the physical principles when establishing mathematical models. Despite the fact that the relations between variables have poor correlation or have low statistical significance, in order to introduce the physical point of view they have not been ignored. This study puts forth a new mathematical perspective by discussing and visualizing what happened in the phenomenon.s

Propulsive Force in Electric Solar Sails for Missions in the Heliosphere

An electric solar sail (E-sail) is a recent propulsion technology concept capable of reaching the edge of the Heliosphere. An E-sail consists of a set of bare tethers at high positive/negative bias capable of deflecting solar wind protons to produce thrust. The propulsive force calculation for a single tether was focused on outer planet missions, considering the characteristic plasma ambient at 1 astronomical unit. However, both ion and electron temperature and plasma density cover a wide range of values within the Heliosphere. Propulsive forces are determined here for the solar wind plasma within the entire Heliosphere. Results show that propulsive forces increase with ion temperature, whereas decrease with electron temperature. In addition, propulsive forces do increase with plasma density despite the sheath decreases.

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

AbstractThe solar wind implants protons into the top 20–30 nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan‐1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017, https://doi.org/10.1126/sciadv.1701471). The model reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U0 = 0.5 eV, UW = 0.078–0.1 eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons.

Suzaku detection of enigmatic geocoronal solar wind charge exchange event associated with coronal mass ejection

Abstract Suzaku detected an enhancement of the soft X-ray background associated with solar eruptions on 2013 April 14–15. The solar eruptions were accompanied by an M6.5 solar flare and a coronal mass ejection with magnetic flux ropes. The enhanced soft X-ray background showed a slight variation over half a day and then a clear one in a few hours. The former spectrum was composed of oxygen emission lines, while the later one was characterized by a series of emission lines from highly ionized carbon to silicon. The soft X-ray enhancement originated from geocoronal solar wind charge exchange. However, there appeared to be no significant time correlation with the solar wind proton flux measured by the ACE and WIND satellites. From other solar wind signatures, we considered that an interplanetary shock associated with the coronal mass ejection and a turbulent sheath immediately behind the shock compressed the ambient solar wind ions and then resulted in the soft X-ray enhancement. Furthermore, the enriched emission lines were presumed to be due to an unusual set of ion abundances and ionization states within the coronal mass ejection. We found a better time correlation with the solar wind alpha flux rather than the solar wind proton flux. Our results suggest that the solar wind proton flux is not always a good indicator of geocoronal solar wind charge exchange, especially associated with coronal mass ejections. Instead, the solar wind alpha flux should be investigated when such a soft X-ray enhancement is detected in astronomical observations.

On heating of solar wind protons by the parametric decay of large-amplitude Alfvén waves

Abstract. By three-dimensional hybrid simulations, proton heating is investigated starting from a monochromatic large-amplitude Alfvén wave with left-handed circular polarization launched along the mean magnetic field in a low-beta plasma. We find that the perpendicular scattering is efficient in three dimensions and the protons are heated by the obliquely propagating waves. The thermal core proton population is heated in three dimensions as well in the longitudinal and parallel directions by the field-aligned and obliquely propagating sound waves out of the parametric decay. The astrophysical context is discussed.

Time-of-day-dependent behavior of surficial lunar hydroxyl/water: Observations and modeling

In this study we determine the depth of the absorption band around 3 µm wavelength, which indicates the presence of OH/H2O in a thin surficial layer of the lunar regolith, for 18 lunar highland regions observed by the Moon Mineralogy Mapper (M3) instrument at 4–8 different local times of day. For removing the thermal emission component, a physically motivated thermal equilibrium based method is used, which also takes into account the roughness of the regolith surface. We propose a continuity equation based model of the time-of-day-dependent column densities of surficial atomic hydrogen (H) and hydroxyl (OH). The considered source processes for H are implantation of solar wind protons and photolysis of OH, and for OH the reaction H+O→OH. Sink processes are diffusive loss for H and OH, and photolysis for OH. Sputtering of H and OH is found to be negligible in comparison to the other sink processes. Additionally, we suggest a similar differential equation based model to describe the time-of-day-dependent behavior of micrometeoroid-delivered OH and H2O. The observed 3 µm band depth values indicate that the surficial OH/H2O does not vanish even at local midday at low latitudes, while the model predicts nearly complete removal of surficial OH/H2O at midday. This apparent contradiction between model and observations is reconciled by adding to the model a region-specific “offset” OH component which is assumed to be stable against diffusive loss and photolysis and is therefore interpreted as a strongly bounded OH component. Meteoroid bombardment is found to be negligible in comparison with the solar wind source of OH. Fitting the model to the observed 3 µm band depth values allows for estimating the H activation energy, the OH photolysis time, region-specific values of the offset OH component, and the proportionality factor between OH column density and 3 µm band depth. The observed time-of-day-dependent behavior of the 3 µm band depth at low and high latitudes can be explained convincingly by the modeled source and sink processes. The best-fit OH photolysis time is much shorter than the lunar day and corresponds to 1–3 times the gas-phase value, which indicates that photolysis is a mechanism of high relevance for the behavior of solar wind induced surficial OH. The surface roughness assumed in the M3 data analysis does not have a major influence on the modeling results. The strongly bounded OH component is nearly latitude-independent for low latitudes but decreases sharply for high latitudes. As a possible mode of origin, we suggest slow diffusion of solar wind induced OH to depths inaccessible for ultraviolet photons and into binding states of higher energy, counteracted by sputtering.

Near‐Earth Solar Wind: Plasma Characteristics From ARTEMIS Measurements

AbstractThe interaction between the solar wind and Earth's magnetosphere is the main driver of magnetosphere dynamics because many important processes in Earth's inner and outer magnetosphere can be considered as responses to solar wind parameter variations. Therefore, accurate measurements of these parameters (density, velocity, ion, and electron temperature) in the near‐Earth solar wind is critical for understanding and forecasting magnetosphere dynamics. Moreover, the solar wind is a natural laboratory for investigation of plasma turbulence, including the configuration and dynamics of coherent plasma structures (such as large‐amplitude waves, discontinuities, and interplanetary shocks). A major solar wind parameter database, the OMNI database, consists of solar wind proton characteristics and magnetic field parameters but does not provide electron characteristics. We consider a supplementary solar wind data set compiled by observations of the two Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) probes. We compare characteristics available in both the ARTEMIS and OMNI data sets. We also describe characteristics of solar wind electron components measured by ARTEMIS (density, temperature, and anisotropy). Finally, we discuss opportunities for investigation of the near‐Earth solar wind provided by the ARTEMIS data set.

Solar wind dynamics around a comet

Aims. We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometary atmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics. Methods. We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-state is assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced by individual solar wind protons during the interaction. Results. A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to a comet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r2. The solar wind deflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular region is found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, together with the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of the Rosetta mission. Conclusions. The qualitative match between the model and the in situ data highlights how dominant the motional electric field is throughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic description of how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical model for a systematic quantitative comparison to the data.

Lyman-α emission in the Martian proton aurora: Line profile and role of horizontal induced magnetic field

Enhancements of the dayside Lyman-α emission by as much as ∼50% have been observed between 120 and 130 km in the lower Martian thermosphere from the Mars Express and MAVEN satellites, usually following solar events such as coronal mass ejections and corotating interaction regions. They have been assumed to be optical signatures of proton aurora related to an increase in the solar wind proton flux hitting Mars’ bow shock. We present model simulations of the Lyman-α line profiles at different altitudes. These are partly guided by in situ measurements of the energy spectrum of protons in the magnetosheath region by the SWIA instrument on board the MAVEN spacecraft. We show that the auroral Lyman-α line profile is significantly broader than the hydrogen core of the planetary thermal H atom. Consequently, most of the auroral emission is produced outside the optically thick hydrogen core and creates the observed intensity enhancement. Simulations with incident energetic hydrogen atoms (H ENAs) produce a somewhat broader line profile. Monte Carlo calculations are made separately for incident solar wind protons and H ENAs produced by charge exchange in the hydrogen corona. Absorption by CO2 along the line of sight significantly affects the intensity distribution in the lower thermosphere. The calculated altitude of the peak emission for both types of incident particles is consistent with the observed characteristics of the proton aurora. We show that the presence of a horizontal induced magnetic field somewhat increases the line width and decreases the altitude of the emission peak as a consequence of the magnetic barrier effect on proton precipitation. The brightness of the Lyman-α emission also drops as a result of increased magnetic shielding of the protons.