Solar Wind Protons Research Articles

Investigating the variations in the composition and heating of interacting ICMEs

Interacting coronal mass ejections (CMEs) have been commonly reported during the STEREO era. With the interaction of CMEs in the heliosphere, it is expected that the participating CMEs will either merge to form a single interplanetary CME (ICME) or will arrive as distinct entities or ICMEs at 1 AU. Previous studies have focused on in situ observations of solar wind, i.e., plasma and magnetic field properties to understand the nature of the CME–CME interaction and its impact. In this study, we examine the observations of composition parameters of those ICMEs that resulted due to the interaction of two CMEs during their propagation between the Sun and the Earth. We report two events of the CME–CME interaction observed in 2012, of which one led to a merged structure after the interaction, as observed at 1 AU. The second interaction event was reported to arrive at L1 as two distinct structures. Our analysis reveals distinct composition signatures in the form of ion charge state enhancements. The results improve our understanding of the signatures of ICMEs and different complex structures formed after the interaction. The study reveals that compression can occur due to the passage of the shock associated with the following CME through the preceding CME and not due to the CME–CME interaction. The results also highlight the importance of the comparison of solar wind proton velocity data with the expected temperature data, in particular, to understand the ICME–ICME interaction processes.

Formulation of a high-fidelity multibody dynamical model for an electric solar wind sail

E-sail technology enables a continuous propulsion system based on the repulsive force exerted by solar wind protons on a set of positively charged tethers. Diverse methods have been explored within the last two decades to investigate the dynamics of E-sail. This work introduces a dynamic multibody model combining Absolute Nodal Coordinate Formulation (ANCF) and Natural Coordinates (NC) to describe flexible and rigid bodies, respectively. A complete formulation for cable elements considering nonlinear bending and internal damping is provided. Coulomb propulsive forces are included and the expressions for the integration of the resulting Differential Algebraic Equation (DAE) system are given. Based on the simulation results obtained from the proposed model, the convenience of considering bending stiffness to accurately capture the dynamics is proven. The in-plane and out-of-plane oscillations of the tethers are reported and explained. By means of the Power Spectral Density (PSD) representation, the relevant role on the E-sail dynamics of the spin, bending and axial modes, associated to the well-known problem of a rotating cable with a tip mass, is described. The force and perturbation moments transmitted to the central body are compared to the generated thrust, and its complexity and instability under non-null sailing angle operation is established.

Super rogue waves at Venusian ionosphere and mantle

Formation of super rogue ion-acoustic wave is suggested as a physical catalyst for the photochemical reaction to form the Venusian ionosphere and its mantle. Based on the observed data at Venus by Pioneer Venus Orbiter (PVO) and Venus Express (VEX), we constructed our models. The plasma model of the ionosphere consists of two positive ions fluid (H+andO+) and Maxwellian distributed ionospheric electrons. Whereas, the plasma mantle comprises streaming solar wind (SW) protons and Maxwellian SW electrons in addition to H+,O+ and electrons. To define precisely the existence regions and the features of super rogue waves (SRWs), we studied numerically the effect of the plasma parameters on the instability of the propagating pulses. At Venus’ ionosphere, we found that the increase of the ionospheric density ratio (nH0/nO0) enhances the energy of the SRWs. Whereas, in the mantle region, we found that the nonlinearity of the system is enhanced by the effect of the streaming SW proton, through its density and velocity, which leads to amplifying of the SRWs amplitude. Thus, the enhancement in the density of ionospheric particles and SW protons contributes to enhancing the photochemical reaction in the ionosphere and the mantle region.

Dynamical Response of Solar Wind Charge Exchange Soft X-Ray Emission in Earth’s Magnetosphere to the Solar Wind Proton Flux

This work studies the dynamic response of solar wind charge exchange (SWCX) soft X-ray emission in the Earth’s magnetosphere to the solar wind proton flux. Unlike previous studies that attempted to use complex magnetohydrodynamic models to match the details of observed SWCX of a necessarily limited number of cases, this work focuses on determining the changes over individual observations in a much larger sample. To provide the cleanest test, we selected XMM-Newton observations when the solar wind proton flux changed suddenly by a factor greater than 1.5 and calculated the correlation coefficient between the SWCX emission in the 0.5–0.7 keV band and the proton flux. We find that the dynamical response is weak when the solar wind proton flux is low (<10,000 n*km/cc/s) because its variation is smaller than the uncertainty due to other emission components, but this response increases with the proton flux and its change value. The response is improved when the valence state of solar wind ions is high, as a higher abundance of ions generating SWCX can produce a greater correlation even though the proton flux is relatively low. It is conducive to the study of interplanetary coronal mass ejections (ICMEs) because ions in ICMEs are usually highly ionized. For XMM-Newton, the 0.5–0.7 keV band shows the strongest correlation, as the instrumental response decreases at lower energies and the SWCX emission decreases at higher energies. Moreover, the closer the satellite line of sight is to the subsolar magnetopause with the strongest SWCX emissivity, the better the correlation.

The Polytropic Behavior of Solar Wind Protons as Observed by the Ulysses Spacecraft during Solar Minimum

We analyze proton bulk parameters derived from Ulysses observations and investigate the polytropic behavior of solar wind protons over a wide range of heliocentric distances and latitudes. The large-scale variations of the proton density and temperature over heliocentric distance indicate that plasma protons are governed by subadiabatic processes (polytropic index γ < 5/3), if we assume protons with three effective kinetic degrees of freedom. From the correlation between the small-scale variations of the plasma density and temperature in selected subintervals, we derive a polytropic index γ ∼ 1.4 on average. Further examination shows that the polytropic index does not have an apparent dependence on the solar wind speed. This agrees with the results of previous analyses of solar wind protons at ∼1 au. We find that the polytropic index varies slightly over the range of the heliocentric distances and heliographic latitudes explored by Ulysses. We also show that the homogeneity of the plasma and the accuracy of the polytropic model applied to the data points vary over Ulysses' orbit. We compare our results with the results of previous studies that derive the polytropic index of solar wind ions within the heliosphere using observations from various spacecraft. We finally discuss the implications of our findings in terms of heating mechanisms and the effective degrees of freedom of the plasma protons.

Direct observation of solar wind proton heating from in situ plasma measurements

Aims. We determine the perpendicular and parallel proton heating rate in the solar wind, which is one of the primary goals of the Parker Solar Probe mission. Methods. To estimate the perpendicular and parallel proton heating rates from direct particle measurements by the SPAN electrostatic analyzers, the strong correlation between the proton temperature and the solar wind speed must be removed. This speed dependence is removed by normalization factors that convert the instantaneous temperature to the value it would have if the solar wind speed were 400 km s−1. One-hour and five-hour averages of the normalized perpendicular and parallel temperatures, measured on orbits 6–9, between 20 and 160 solar radii, are compared to the radial dependence they would have if there were no heating. Results. For the first time, perpendicular proton heating has been measured between 20 and 160 solar radii while there is neither heating nor cooling of the parallel protons below 70 solar radii. The extrapolated proton perpendicular temperature at one AU in a 400 km s−1 solar wind is 25 eV, which compares well with several earlier measurements. This result attests to the quality of the temperature measurements made by the particle detectors on the Parker Solar Probe. The heating rates, in ergs cm−3 s−1, that produced the observed perpendicular temperature are 6e−12 at 20 solar radii, 1e−13 at 50 solar radii, and 5e−14 at 160 solar radii.

Forces, electric fields and currents at the subsolar martian MPB: MAVEN observations and multifluid MHD simulation

The Martian MPB (Magnetic Pileup Boundary) is a key boundary in the Mars/Solar Wind interaction as it is here that part of the momentum and energy from the solar wind plasma are transferred to the planetary plasma. Since this interaction is for the most part collisionless, the transfer is mediated by electric and magnetic fields. The acceleration processes and the interaction of particles with electromagnetic fields operate at spatial scales determined by the ambient particle populations. In particular, in regions with sizes of the order of the ion inertial length (ion scales), the Hall electric field is expected to be dominant.In the present work we combine data from the MAVEN spacecraft along one orbit around Mars and multifluid MHD simulation results to study the role of electric fields, currents and forces at the MPB at ion scales. In particular, we find that the current densities deduced from MAVEN data (J ∼ 238 nA/m2) of the same order as the values obtained in the simulation (J ∼ 56-156 nA/m2) and that the Hall electric force points sunward in both cases. In addition, we find that in the subsolar MPB current layer the Hall electric field (∼3.2 mV/m) dominates over the solar wind convective electric field (∼0.4 mV/m) and electron pressure gradient (∼0.8 mV/m). These values are consistent with previous results suggesting that the MPB thickness is of the order of the solar wind proton inertial length and support the idea that non ideal terms in Ohm’s law must be considered when analysing the dynamics of particles around plasma boundaries with ion scale thicknesses.

Variations of Signal Strength during Solar Bursts: A Probable Coronal and Surface Effects of the Sun

Variations of signal strengths during solar bursts recorded at Kalyani corresponding to two different frequencies, 406.7 MHz and 100 MHz are reported. The amplitude of the signals received at 406.7 MHz is found larger and that the flares analyzed are mostly of M-type. The signal strengths of the coronal effect at such times were very high compared to the surface effect of the Sun. The signal level of surface effect of the Sun at the peak activity varies in amplitude from 0.06 volts to 0.1 volt while those related to solar corona vary in between 7.0 to 7.2 volts. Both the solar wind velocity and proton density are found to increase in the dates of severe bursts and there are sudden disturbances in the arrival direction of solar wind particles. Also the geomagnetic indices are enhanced at the time of solar bursts when the DST index reduces rapidly.

5‐Species MHD Study of Martian Proton Loss and Source

AbstractAlthough photochemistry‐enabled escape of oxygen is a dominant atmospheric loss process at Mars today, ion outflow plays an essential role in the long‐term evolution of Mars' atmosphere. Apart from heavy planetary ions such as O+, O2+, and CO2+, the loss of planetary protons is also important because it could be related to water loss. To study planetary proton loss due to solar wind interaction, we improve the 4‐species (O+, O2+, CO2+, and H+) single‐fluid magnetohydrodynamic (MHD) model of Mars, to a 5‐species (separating planetary protons and solar wind protons) MHD model so that the two types of protons can be tracked separately. The global distributions of solar wind protons and planetary ions at low altitudes are investigated. The calculated planetary proton escape rates are larger than heavy ion loss rates and solar wind proton inflows for both solar maximum and minimum conditions. Planetary proton escape rates are 1–2 orders less than neutral hydrogen loss, suggesting that planetary protons could contribute to no &gt;10% of the hydrogen loss under current conditions. By comparing normal cases with cases for which H‐O charge exchange reactions or electron impact ionizations are switched off, we find that H‐O charge exchange mainly affects densities at low altitudes, while impact ionizations exert great influence on escape rates at high altitudes. The overall results suggest the specific treatment of proton origins in models of Mars atmosphere escape provides better insight into the contributing processes, and should be included in future studies focusing on water's fate.

Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov-Gerasimenko.

The plasma environment at a comet can be divided into different regions with distinct plasma characteristics. Two such regions are the solar wind ion cavity, which refers to the part of the outer coma that does not contain any solar wind ions anymore; and the diamagnetic cavity, which is the region of unmagnetized plasma in the innermost coma. From theory and previous observations, it was thought that under usual circumstances no solar wind ion should be observable near or inside of the diamagnetic cavity. For the first time, we report on five observations that show that protons near solar wind energies can also be found inside the diamagnetic cavity. We characterize these proton signatures, where and when they occur, and discuss possible mechanisms that could lead to protons penetrating the inner coma and traversing the diamagnetic cavity boundary. By understanding these observations, we hope to better understand the interaction region of the comet with the solar wind under nonstandard conditions. The protons detected inside the diamagnetic cavity have directions and energies consistent with protons of solar wind origin. The five events occur only at intermediate gas production rates and low cometocentric distances. Charge transfer reactions, high solar wind dynamic pressure and a neutral gas outburst can be ruled out as causes. We suggest that the anomalous appearance of protons in the diamagnetic cavity is due to a specific solar wind configuration where the solar wind velocity is parallel to the interplanetary magnetic field, thus inhibiting mass-loading and deflection.

Coupled H, H2, OH, and H2O lunar exosphere simulation framework and impacts of conversion reactions

Numerical models of the lunar exosphere have been available for several decades to allow investigations of the Moon’s tenuous atmosphere beyond the few measurements made by satellite or ground-based experiments. We present a novel approach to modeling a system of elements, namely the hydrogen-bearing species H, H2, OH, and H2O, in a multi-element simulation, implementing exospheric and geochemical conversion reactions to connect the different species through their loss and source processes. The model resembles the lunar water cycle, including several source and sink mechanisms like the solar wind proton influx and the eventual loss through Jean’s escape, photodissociation, or cold trapping. Unknown and uncertain parameters have been modeled using probability distributions that propagate their uncertainty through the system to allow subsequent statistical analysis of the predictions. In eight studies we varied the reactivity of the lunar environment and investigated the response of the exosphere’s densities and dynamics. The results show that the new framework is able to reproduce many published values for the surface number densities and reported dynamics like the H2 dawn-dusk asymmetry, even with a very simple approach to many of the complex input parameters. The most diverging results can be found for the hydroxyl and water predictions. Nonetheless, we show that the multi-element approach using conversion reactions offers an alternative explanation to the observed H and H2 exosphere without having to assume these volatiles as condensable species.

On the Evaluation of Solar Wind's Heating Rates

AbstractSolar wind heating rates have often been calculated by fitting plasma and magnetic field data with a set of model functions. In this letter, we show that the rates obtained by such an approach strongly depend on the rather arbitrary choice one makes for these model functions. An alternative approach, consisting in monitoring the radial evolution of the adiabatic invariants, based on locally and consistently measured plasma and magnetic field parameters, is free from such a flaw. We apply this technique to a recently released Helios proton data set, and confirm the existence of a clear perpendicular heating of solar wind's protons. On the other hand, no significant change in the parallel adiabatic invariant is visible in the data. We conclude that to date, and in the distance range of 0.3–1 AU, no clear observation of a deviation of solar wind's protons from parallel adiabaticity has ever been made.

Effects of Force in the Martian Plasma Environment With Solar Wind Dynamic Pressure Enhancement

AbstractDisturbed solar wind dynamic pressure is one of the important external drivers which could cause significant impacts on Martian plasma environment. In this study, a 3D multifluid multispecies numerical model is established to simulate the interaction between solar wind and Mars. Functions of electromagnetic forces applied on different ion species were analyzed. We found that the total electromagnetic force peaks near bow shock (BS) and magnetic pileup boundary (MPB) with clear asymmetry features, acting to decelerate solar wind plasma across boundary layers, and compresses heavy ions toward the planet inside the MPB. For solar wind protons, electron pressure gradient force dominates near BS and Hall electric field force dominates near MPB, controlling the location of plasma boundary. Furthermore, the morphology of motional electric field force shows clear north‐south asymmetry, leading to the formation of asymmetric structures and plasma flow in Martian space environment. The response of BS, MPB to a solar wind dynamic pressure enhancement event, as well as the effects of electromagnetic forces in this process are also investigated. After the arrival of solar wind pulse, the magnitudes of electromagnetic forces increased simultaneously to balance the enhanced solar wind dynamic pressure, while the peaks of forces moved inward with BS and MPB. The magnitudes and peaks of ion velocity in subsolar region show similar variations as well, with the greater enhancement of forces leading to the greater increase of ion velocities, indicating that the changes of forces influence boundary layers through the variation of plasma speed.

Determining the Ionization Rates of Interstellar Neutral Species Using Direct-sampling Observations of Their Direct and Indirect Beams

A good understanding of the ionization rates of neutral species in the heliosphere is important for studies of the heliosphere and planetary atmospheres. So far, the intensities of the ionization reactions have been studied based on observations of the contributing phenomena, such as the solar spectral flux in the EUV band and the flux of the solar wind protons, alpha particles, and electrons. The results strongly depend on absolute calibration of these measurements, which, especially for the EUV measurements, is challenging. Here, we propose a novel method of determining the ionization rate of neutral species based on direct sampling of interstellar neutral gas from two locations in space distant to each other. In particular, we suggest performing observations from the vicinity of Earth’s orbit and using ratios of fluxes of interstellar neutral He for the direct and indirect orbits of interstellar atoms. We identify the most favorable conditions and observations geometries, suitable for implementation on the forthcoming NASA Interstellar Mapping and Acceleration Probe mission.

Solar Control of the Pickup Ion Plume in the Dayside Magnetosheath of Venus

AbstractUsing the 8.5‐year Venus Express measurements, we demonstrate the asymmetric plasma distributions in the Venusian magnetosheath. An escaping plume is formed by pickup oxygen ions in the hemisphere where the motional electric field points outward from Venus, while the velocity of solar wind protons is faster in the opposite hemisphere. The pickup O+ escape rate is estimated to be (3.6 ± 1.4) × 1024 s−1 at solar maximum, which is comparable to the ion loss rate through the magnetotail, and (1.3 ± 0.4) × 1024 s−1 at solar minimum. The increase of O+ fluxes with extreme ultraviolet (EUV) intensity is significant upstream of the bow shock, partially attributed to the increase of exospheric neutral oxygen density. However, the solar wind velocity just has a slight effect on the pickup O+ escape rate in the magnetosheath, while the effect of solar wind density is not observed. Our results suggest the pickup O+ escape rate is mainly controlled by EUV radiation.

Solar wind H+ fluxes at 1 AU for solar cycles 23 and 24

The solar wind consists of electrons and ion species having kinetic energy ≲10 keVs. Ion stream is mainly composed of protons. Their flux magnitude is especially important for radiation hardness assurance scientists who qualify materials for future space missions. Materials irreversibly degrade as soon as are exposed to solar radiation. Hence, proton differential and integral flux spectra play a crucial role in properly estimating radiation loads deposited within satellite functional components. Up to now, the wind fluxes were read out, e.g., from figures made for specific periods of a solar cycle. This method is not effective and is a source of a flux, and further on, a fluence uncertainty. The objective of this work was to calculate and tabulate the solar wind differential and integral proton fluxes, which can be used further on to evaluatespace mission proton fluence spectra. Solar wind proton bulk velocity and number density from four space solar observatories (SOHO, ACE, WIND, and DSCOVR) were numerically processed to achieve that goal. Fluxes were tabulated and represented in calendar year periods.Now, the radiation hardness assurance community can quickly access, compute and compare SW proton fluxes from different energy ranges, calendar years, and satellite data sources. Proton fluxes presented here indicate magnitude variations along with the solar cycle period. A correlation between the number of sunspots and the proton average flux was found, i.e., the larger the number of spots, the larger the flux magnitude. More importantly, it was discovered that proton fluxes indicate huge variations in magnitude for a selected year based on different satellite data sources. For some years, the difference reaches 240%. This value is reported for the first time and shows that to have a complete picture of the SW proton stream population, one must compare data from all four satellites. Also, it is reported that satellites, for a given calendar year, record different ranges of proton velocity and number density values. This finding, even stronger, suggests a necessity of comparing SW data from as many solar observatories as possible. The spread in the proton flux magnitude (240%) has a direct implication for planning and executing satellite material on-ground radiation test campaigns. Not carefully choosing a proton flux may result in a false impression of how examined material would degrade under an interplanetary space radiation environment. In this article, recommendations for selecting proper proton spectra are given.

Role of solar wind on the ionic escaping from Venus upper ionosphere via plasma wakefield

According to the observations that detected significant ionospheric escape from Venus, a test charge approach is suggested to explain the ionic loss caused by the solar wind (SW) interaction with the Venusian upper ionosphere. The proposed plasma system consists of two positive planetary ions (H + and O +) with isothermal electrons and streaming SW protons, with Maxwellian electrons. The electrostatic Debye screening and wakefield potentials caused by a moving test charge as well as the modified dielectric constant of the ion-acoustic waves (IAWs) created in the model are derived. The normalized Debye potential is found to decrease exponentially with the axial distance. Whereas the amplitude of the wakefield potential is amplified with the altitudes and decreases with increasing the density of either planetary oxygen or the SW protons but it is enhanced by SW electrons number density. However, the wakefield amplitude is not affected by the SW protons velocity or their temperatures because the SW protons velocity is fast compared with the velocity of the plasma system. Thus, the properties of the ions escaping are affected by the velocity variations within a certain range called the velocity scale window. The obtained results are found to be in a good agreement with the observed data.

The Mini Induced Magnetospheres at Mars

AbstractWe report on observations made by the Mars Atmosphere and Volatile EvolutioN spacecraft at Mars, in the region of the ion plume. We observe that in some cases, when the number density of oxygen ions is comparable to the density of the solar wind protons interaction between both plasmas leads to formation in the magnetosheath of mini induced magnetospheres possessing all typical features of induced magnetospheres typically observed at Mars or Venus: a pileup of the magnetic field at the head of the ion cloud, magnetospheric cavity, partially void of solar wind protons, draping of the interplanetary magnetic field around the mini obstacle, formation of a magnetic tail with a current sheet, in which protons are accelerated by the magnetic field tensions. These new observations may shed a light on the mechanism of formation of induced magnetospheres.

Solar Wind Protons Forming Partial Ring Distributions at Comet 67P

AbstractWe present partial ring distributions of solar wind protons observed by the Rosetta spacecraft at comet 67P/Churyumov‐Gerasimenko. The formation of ring distributions is usually associated with high activity comets, where the spatial scales are larger than multiple ion gyroradii. Our observations are made at a low‐activity comet at a heliocentric distance of 2.8 AU on 19 April 2016, and the partial rings occur at a spatial scale comparable to the ion gyroradius. We use a new visualization method to simultaneously show the angular distribution of median energy and differential flux. A fitting procedure extracts the bulk speed of the solar wind protons, separated into components parallel and perpendicular to the gyration plane, as well as the gyration velocity. The results are compared with models and put into context of the global comet environment. We find that the formation mechanism of these partial rings of solar wind protons is entirely different from the well‐known partial rings of cometary pickup ions at high‐activity comets. A density enhancement layer of solar wind protons around the comet is a focal point for proton trajectories originating from different regions of the upstream solar wind. If the spacecraft location coincides with this density enhancement layer, the different trajectories are observed as an energy‐angle dispersion and manifest as partial rings in velocity space.

Analysis of Geoeffective Impulsive Events on the Sun During the First Half of Solar Cycle 24

A coronal mass ejection (CME) is an impulsive event that emerges rapidly from the Sun. We observed a quiet Sun without many spectacular episodes during the last decade. Although some fast halo and partial halo CMEs had taken place, among them was the backside CME on 23 July 2012. In this work, we verify the link between the variability of solar-wind, heliospheric and geomagnetic parameters and the transmission grid failures registered in southern Poland during 2010 – 2014 when many geomagnetic storms appeared, caused by halo and partial halo CMEs. We aim to apply three machine learning methods: Principal Components Analysis, Self-Organizing Maps, and Hierarchical Agglomerative Clustering to analyze sources on the Sun and the impacts of the intense geomagnetic storms in the first half of Solar Cycle 24. The conducted analyzes underline the importance of solar-wind proton temperature and point out other solar-wind and geomagnetic parameters independently indicated by all the methods used in this study.