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Mercury is surrounded by a tenuous neutral exosphere composed primarily of sodium atoms, which can be continuously ionized. The production of sodium ions is concentrated on the dayside, and these ions can subsequently be transported to the magnetotail and flanks. MESSENGER spacecraft observations revealed dawn‐dusk asymmetric distributions of sodium ions Na+$N{a}^{+}$. In this study, we investigate the Na+$N{a}^{+}$circulation, distribution, and its influence on global magnetospheric convection with a two‐fluid MHD model, which is coupled with an empirical sodium exosphere profile as the source of Na+$N{a}^{+}$. In particular, we aim to investigate if the dawn‐dusk asymmetries in Na+$N{a}^{+}$distributions near the equator can be driven by internal mechanisms within the magnetosphere. Our findings indicate that (a) the observed dawn‐dusk asymmetric Na+$N{a}^{+}$distributions can be driven by the separation of H+${H}^{+}$and Na+$N{a}^{+}$flows, and (b) the Hall‐driven global convection preferentially transporting Na+$N{a}^{+}$ions to the morning sector. Mercury's weak magnetic field and proximity to the Sun make its magnetosphere much smaller and more dynamic than Earth's. With no substantial ionosphere, the magnetosphere is dominated by solar wind protons rather than planetary ions. However, Mercury has a tenuous sodium exosphere, and these neutral sodium atoms can become ionized on the dayside. This study uses a two‐fluid MHD model that couples magnetospheric plasma flows with Mercury's neutral sodium exosphere to study the transport and distribution of the sodium ions. It shows the Hall effect and the velocity separation between the proton fluid and sodium fluid can produce dawn‐dusk asymmetric distributions of sodium ions. Developed a multi‐fluid MHD model to study the dawn‐dusk asymmetric distributions of sodium ions in Mercury's magnetosphereVelocity separation between proton and sodium ion fluids can drive sodium ion dawn‐dusk asymmetric distributionsHall effects can transport more sodium ions to the morning sector Developed a multi‐fluid MHD model to study the dawn‐dusk asymmetric distributions of sodium ions in Mercury's magnetosphere Velocity separation between proton and sodium ion fluids can drive sodium ion dawn‐dusk asymmetric distributions Hall effects can transport more sodium ions to the morning sector

We report a rare regime of Earth's magnetosphere interaction with sub‐Alfvénic solar wind in which the windsock‐like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low‐beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter‐streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic‐cloud and Alfvén‐wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub‐Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars. Like supersonically fast fighter jets creating sonic shocks in the air, planet Earth typically moves in the magnetized solar wind at super‐Alfvénic speeds and generates a bow shock. Here we report unprecedented observations of Earth's magnetosphere interacting with a sub‐Alfvénic solar wind brought by an erupted magnetic flux rope from the Sun, called a coronal mass ejection (CME). The terrestrial bow shock disappears, leaving the magnetosphere exposed directly to the cold CME plasma and the strong magnetic field from the Sun's corona. Our results show that the magnetosphere transforms from its typical windsock‐like configuration to having wings that magnetically connect our planet to the Sun. The wings are highways for Earth's plasma to be lost to the Sun, and for the plasma from the foot points of the Sun's erupted flux rope to access Earth's ionosphere. Our work indicates highly dynamic generation and interaction of the wing filaments, shedding new light on how sub‐Alfvénic plasma wind may impact astrophysical bodies in our solar and other stellar systems. MMS observed a rare regime of magnetosphere interaction with unshocked low‐beta CME plasmaWing filaments represent dynamical channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux ropeCold CME ions observed on closed field lines, likely generated by dual‐wing reconnection MMS observed a rare regime of magnetosphere interaction with unshocked low‐beta CME plasma Wing filaments represent dynamical channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope Cold CME ions observed on closed field lines, likely generated by dual‐wing reconnection

Using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we explore the plasma properties of Martian magnetotail current sheets (CS), to further understand the solar wind interaction with Mars and ion escape. There are some CS exhibit energetic oxygen ions that show narrow beam structures in the energy spectrum, which primarily occurs in the hemisphere where the solar wind electric field (Esw) is directed away from the planet. On average, these CS have a higher escaping flux than that of the CS without energetic oxygen ion beams, suggesting different roles in ion escape. The CS with energetic oxygen ion beams exhibits different proton and electron properties to the CS without energetic oxygen ion beams, indicating their different origins. Our analysis suggests that the CS with energetic oxygen ion beams may result from the interaction between the penetrated solar wind and localized oxygen ion plumes. Ion escape into space, driven by solar wind interactions with Mars, plays a pivotal role in the evolution of the Martian atmosphere. An important escape channel of planetary oxygen ions is the current sheet in the nightside magnetotail. Yet, our existing understanding of plasma characteristics within this magnetic structure remains quite limited. Based on the MAVEN observations, we find the current sheets can be categorized into two distinct types according to the energy distribution patterns of oxygen ions: one is with the appearance of energetic oxygen ions with narrow beam structure, the other one is not. On average, the current sheets with energetic oxygen ion beams have a higher escaping flux than those without, suggesting different roles in ion escape. Furthermore, the two types of current sheets exhibit markedly distinct plasma properties, indicating that they have different origins. Here we suggest that the current sheet with energetic oxygen ion beams arise from the interaction between the penetrated solar wind and localized oxygen ion plumes. Martian magnetotail current sheets occasionally exhibit energetic oxygen ions that show beam structures in the energy spectrumThe current sheets with energetic oxygen ion beam usually have a higher escaping flux than those withoutPlasma properties in current sheets differ significantly differences between those with and without energetic oxygen ion beams Martian magnetotail current sheets occasionally exhibit energetic oxygen ions that show beam structures in the energy spectrum The current sheets with energetic oxygen ion beam usually have a higher escaping flux than those without Plasma properties in current sheets differ significantly differences between those with and without energetic oxygen ion beams

For the first time, we explore the tightly coupled interior‐magnetosphere system of Mercury by employing a three‐dimensional ten‐moment multifluid model. This novel fluid model incorporates the nonideal effects including the Hall effect, electron inertia, and tensorial pressures that are critical for collisionless magnetic reconnection; therefore, it is particularly well suited for investigating collisionlessmagnetic reconnection in Mercury's magnetotail and at the planet's magnetopause. The model is able to reproduce the observed magnetic field vectors, field‐aligned currents, and cross‐tail current sheet asymmetry (beyond magnetohydrodynamic approach), and the simulation results are in good agreement with spacecraft observations. We also study the magnetospheric response of Mercury to a hypothetical extreme event with an enhanced solar wind dynamic pressure, which demonstrates the significance of induction effects resulting from the electromagnetically coupled interior. More interestingly, plasmoids (or flux ropes) are formed in Mercury's magnetotail during the event, indicating the highly dynamic nature of Mercury's magnetosphere. The new model can reproduce observations beyond MHD including dawn‐dusk asymmetries in Mercury's magnetotail and field‐aligned currentsThe new model is essential for capturing the electron physics associated with collisionless magnetic reconnection in Mercury's magnetosphereThe induction response arising from the electromagnetically coupled interior plays an important role in solar wind‐Mercury interaction

We report the first global, time‐dependent simulation of the Mars upper atmospheric responses to a realistic solar flare event, an X8.2 eruption on 10 September 2017. The Mars Global Ionosphere‐Thermosphere Model runs with realistically specified flare irradiance, giving results in reasonably good agreement with the Mars Atmosphere and Volatile EvolutioN spacecraft measurements. It is found that the ionized and neutral regimes of the upper atmosphere are significantly disturbed by the flare but react differently. The ionospheric electron density enhancement is concentrated below ∼110‐km altitude due to enhanced solar X‐rays, closely following the time evolution of the flare. The neutral atmospheric perturbation increases with altitude and is important above ∼150‐km altitude, in association with atmospheric upwelling driven by solar extreme ultraviolet heating. It takes ∼2.5 hr past the flare peak to reach the maximum disturbance and then additional ∼10 hr to generally settle down to preflare levels. Ionospheric perturbation follows the flare in time and is concentrated mostly below 110‐km altitudeNeutral atmospheric perturbation increases with altitude and is important above 150‐km altitudeIt takes the neutral atmosphere 2.5 hr to reach the perturbation peak and 10 more hours to generally recover

Understanding how the Mars plasma environment responds to space weather events provides insights into the early Sun‐Mars interaction and helps constrain the extrapolation of atmospheric loss back in time. The 2003 Halloween interplanetary coronal mass ejection (ICME) event is one of the most extreme space weather events encountered by Mars during the last two decades. Mars Global Surveyor's circular orbit at ∼400 km allows us to observationally study the magnetic topology response to this extreme event globally for the first time. We analyze the suprathermal electron data and magnetic field measurements from Mars Global Surveyor to infer magnetic topology before, during, and after this ICME event and quantify the variation of the topology over both weak and strong crustal regions and correlate the variation with the upstream dynamic pressure. Over weak crustal regions, more draped field lines and fewer closed field lines are observed under high dynamic pressures, implying a deeper interplanetary magnetic field penetration during the ICME event. Over dayside strong crustal regions, the dominant magnetic topology switches from closed field lines during quiet periods to open field lines during disturbed periods, suggesting more reconnection occurring between the crustal magnetic fields and interplanetary magnetic field. This mixed magnetic topological response is consistent with predictions from magnetohydrodynamic simulations for ICME events in previous studies. We analyze Martian magnetic topology response to the 2003 Halloween ICME event and correlate the variation with upstream driversA deeper IMF penetration is found over weak crustal regions but more open field lines over strong crustal regions during the eventThis mixed magnetic topological response confirms previous predictions from MHD simulations for ICME events

We study a large interplanetary coronal mass ejection event impacting Mars in mid‐September 2017 numerically. During this time period, MAVEN remained inside the Martian bow shock and therefore could not measure the solar wind directly. We first simulate the event using three steady state cases with estimated solar wind conditions and find that these cases were able to reproduce the general features observed by MAVEN. However, these time‐stationary runs cannot capture the response of the system to large variations in the solar wind associated with the event. To address this problem, we derive a solar wind proxy based on MAVEN observations in the sheath region and their comparison with steady state magnetohydrodynamic model results. The derived solar wind proxy is then used to drive a time‐dependent magnetohydrodynamic model, and we find that the data‐model comparison is greatly improved, especially in the magnetosheath. We are able to reproduce some detailed structures observed by MAVEN during the period, despite the lack of a direct measurement of the solar wind, indicating that the derived solar wind conditions are reliable. Finally, we examine in detail the impact of the event on the Martian system: including variations of the three typical plasma boundaries and the ion loss rates. Our results show that these plasma boundary locations varied drastically during the event, and the total ion loss rate was enhanced by more than an order of magnitude. A large interplanetary coronal mass ejection event impacted on Mars in mid‐September 2017. We use a numerical model to study in detail about the effect of the interplanetary coronal mass ejection on the Mars plasma environments. The model results are in good agreement with MAVEN observations, despite the lack of a direct measurement of the solar wind. We also examine in detail variations of typical plasma boundaries and the ion loss rates and found that the plasma boundary locations varied drastically during the event, and the total ion loss rate was enhanced by more than an order of magnitude. A solar wind proxy method is developed and validated for the 2017 September ICME eventTime‐dependent MHD model reproduces detailed structures observed by MAVEN for the ICME eventModel predicts drastic variation of plasma boundaries and large enhancement of ion loss rates during the event

We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind‐Mars interaction. We employ a four‐species multifluid magnetohydrodynamic model to simulate the Martian ionosphere and magnetosphere. The coldthermosphere background is taken from the Mars Global Ionosphere Thermosphere Model, and the hot oxygen exosphere is adopted from the Mars exosphere Monte Carlo model—Adaptive Mesh Particle Simulator. A total of four cases with the combination of 1‐D (globally averaged) and 3‐D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1‐D and 3‐D atmospheres are similar; however, the latter are required to adequately reproduce the ionospheric observations by the Mars Atmosphere and Volatile EvolutioN mission. In addition, our simulations show that the 3‐D hot oxygen corona plays an important role in preventing planetary molecular ions (O 2+and CO 2+) escaping from Mars, mainly resulting from the mass loading of the high‐altitude exospheric O+ions. The coldthermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O+ion escape during the relatively weak solar cycle 24. Despite the similar ion loss rate calculated from 1‐D and 3‐D atmospheres, the latter are required to adequately reproduce MAVEN observationsThe hot oxygen corona plays an important role in protecting the Martian ionosphere/thermosphere from the solar wind erosionThe thermospheric oxygen atom is the primary neutral source for O+ion escape during the relatively weak solar cycle 24

We examine for the first time the flare‐induced effects on the Martian hot O corona. The rapid ionospheric response to the increase in the soft X‐ray flux (~800%) facilitates more hot O production at altitudes below the main ionospheric peak, but almost all of these atoms are thermalized before escape. In response to the increase in the extreme ultraviolet (EUV) flux (~170%), the overall upper ionospheric and thermospheric densities are enhanced, and the peak thermospheric responses are found ~1.5 hr later. The photochemical escape rate is predicted to increase by ~20% with the increases in the soft X‐ray and EUV fluxes but decrease rapidly by ~13% about 2.5 hr later before recovering the preflare level. Since escaping hot O atoms are mostly produced at high altitudes where ionization by the EUV flux is the greatest, the main contributor to the 20% increase in escape rate is the enhancement in the EUV flux. We present for the first time the flare‐induced effects on the loss of neutral O atoms from the atmosphere of Mars. This study found that the main contributor to the sudden increase in the O loss rate is the increase in the solar extreme ultraviolet flux during the flare event, which induces more energetic O atoms at high altitudes where they can easily escape to space. Our investigation will contribute to the earlier works on the atmospheric loss from Mars by providing additional knowledge about the variability of the neutral escape. We examine for the first time the flare‐induced effects on the Martian hot O corona and photochemical escapeThe photochemical escape rate increases by ~20% in the case that describes the peak response time of the ionosphere during the flare eventWe found that the main contributor to the increase in escape rate is the enhancement in the EUV flux

Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45° twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross‐tail current sheet is rotated away from the expected location for a Venus‐like induced magnetotail based on nominal IMF draping. Data‐model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth. This study investigates the magnetic environment of Mars in order to understand how its structure is different from that of other planets. In the past, it was thought that the Sun's magnetic field interacts with Mars in a similar way to a comet or Venus. This would imply that the magnetic field geometry could be easily predicted; however, recent investigations have found that this is not the case. This work includes both simulation and MAVEN data to determine that the magnetic environment of Mars is much different than this original picture. The conclusions find that these fields are twisted from their expected geometry, suggesting a difference in the interaction between Mars and the Sun. Because atmospheric particles are able to travel along these magnetic fields, this unique geometry may have great implications for atmospheric loss at Mars. MAVEN data and simulations confirm that a twisted field configuration is present in the Martian magnetotail that is highly dependent on IMF BYOpen fields, likely created by magnetic reconnection between Mars crustal fields and the IMF, occupy a majority of the twisted tail lobesComparisons with Earth suggest that the dipolar component of Mars' crustal fields play a crucial role in altering the magnetotail structure

Global models of the interaction of the solar wind with the Martian upper atmosphere have proved to be valuable tools for investigating both the escape to space of the Martian atmosphere and the physical processes controlling this complex interaction. The many models currently in use employ different physical assumptions, but it can be difficult to directly compare the effectiveness of the models since they are rarely run for the same input conditions. Here we present the results of a model comparison activity, where five global models (single‐fluid MHD, multifluid MHD, multifluid electron pressure MHD, and two hybrid models) were run for identical conditions corresponding to a single orbit of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We find that low‐altitude ion densities are very similar across all models and are comparable to MAVEN ion density measurements from periapsis. Plasma boundaries appear generally symmetric in all models and vary only slightly in extent. Despite these similarities there are clear morphological differences in ion behavior in other regions such as the tail and southern hemisphere. These differences are observable in ion escape loss maps and are necessary to understand in order to accurately use models in aiding our understanding of the Martian plasma environment. Various Martian plasma models show clear morphological differences in the state of the global plasmaComparing these models with MAVEN data shows what physics is necessary to model different physical regionsModeled escape rates compare well with each other and with estimates from data, despite morphological differences in escaping ion flux maps

The magnetic field draping pattern in the magnetosheath of Mars is of interest for what it tells us about both the solar wind interaction with the Mars obstacle and the use of the field measured there as a proxy for the upstream interplanetary magnetic field (IMF) clock angle. We apply a time‐dependent, global magnetohydrodynamic model toward quantifying the spatial and temporal variations of the magnetic field draping direction on the Martian dayside above 500‐km altitude. The magnetic field and plasma are self‐consistently solved over one Mars rotation period, with the dynamics of the field morphology considered as the result of the rotation of the crustal field orientation. Our results show how the magnetic field direction on the plane perpendicular to the solar wind flow direction gradually departs from the IMF as the solar wind penetrates toward the obstacle and into the tail region. This clock angle departure occurs mainly inside the magnetic pileup region and tailward of the terminator plane, exhibiting significant dawn‐dusk and north‐south asymmetries. Inside the dayside sheath region, the field direction has the greatest departure from the IMF‐perpendicular component direction downstream of the quasi‐parallel bow shock, which for the nominal Parker spiral is over the dawn quadrant. Thus, the best region to obtain an IMF clock angle proxy is within the dayside magnetosheath at sufficiently high altitudes, particularly over subsolar and dusk sectors. Our results illustrate that the crustal field has only a mild influence on the magnetic field draping direction within the magnetosheath region. According to the classic magnetic field draping theory, when the solar wind plasma encounters unmagnetized planetary bodies, the entrained interplanetary magnetic field (IMF) would pile up and drape around as the flow is diverted. Under this approximation, the draped field lines maintain an orientation similar to the upstream IMF in the plane perpendicular to the solar wind flow direction. However, the real morphology of the magnetic field draping at Mars has been poorly understood. In this study, we apply a state‐of‐the‐art global model to investigate the degree of distortion of the draped field lines when the complex Mars‐solar wind interaction is self‐consistently accounted for. Our results illustrate that when the IMF penetrates the magnetosheath edge into lower altitudes, the magnetic field lines may be so distorted and bent that their directions significantly deviate from the expectation from the classic field draping scenario. Our study reinforces the need to change any remaining notion of Mars in field line draping as a nonmagnetic planet. Moreover, this work presents a practical approach for inferring the IMF direction when direct measurements of the pristine solar wind are not available. The clock angle of the field within the dayside magnetosheath is a reasonable proxy for the IMFThe magnetic field clock angle departure increases with decreasing altitude and increasing SZAThe draping direction departure is the greatest downstream of the quasi‐parallel bow shock

We studied the role of electron physics in 3‐D two‐fluid 10‐moment simulation of Ganymede's magnetosphere. The model captures nonideal physics like the Hall effect, electron inertia, and anisotropic, nongyrotropic pressure effects. A series of analyses were carried out: (1) The resulting magnetic field topology and electron and ion convection patterns were investigated. The magnetic fields were shown to agree reasonably well with in situ measurements by the Galileo satellite. (2) The physics of collisionless magnetic reconnection were carefully examined in terms of the current sheet formation and decomposition of generalized Ohm's law. The importance of pressure anisotropy and nongyrotropy in supporting the reconnection electric field is confirmed. (3) We compared surface “brightness” morphology, represented by surface electron and ion pressure contours, with oxygen emission observed by the Hubble Space Telescope. The correlation between the observed emission morphology and spatial variability in electron/ion pressure was demonstrated. Potential extension to multi‐ion species in the context of Ganymede and other magnetospheric systems is also discussed. Jupiter's moon, Ganymede, is revealed by many space missions to have a dipole magnetic field, much like the Earth's. Unlike the Earth's strong dipole field, however, Ganymede is much smaller in size and its dipole field is also much weaker. Consequently, a great portion of energetic particles, accelerated in a process called “magnetic reconnection” near Ganymede, are able to travel at high speed and impact the moon's surface, exciting a bright aurora, in the polar regions. During this process, high‐energy electrons are supposed to play an important role, but their detailed dynamics have been rarely studied. We performed computational modeling of Ganymede, for the first time, revealing how electrons are accelerated near the moon and impact the polar regions of the moon. They turn out to be quite important in transporting the Jovian energy and materials to near Ganymede and might have a substantial influence on the strength and location of the bright aurora. The lessons we learned here can also help us to understand the space weather near the Earth, which is greatly controlled by the same magnetic reconnection process and where electron physics can also be critical. Nongyrotropic electron pressure tensor effects are important in Ganymede's collisionless magnetic reconnectionElectrons and ions form highly asymmetric and distinct drift patterns in the magnetosphereSome key features of the observed oxygen emission morphologies are reproduced by the model

This study investigates the role of solar EUV intensity at controlling the location of the Mars magnetotail current sheet and the structure of the lobes. Four simulation results are examined from a multifluid magnetohydrodynamic model. The solar wind and interplanetary magnetic field (IMF) conditions are held constant, and the Mars crustal field sources are omitted from the simulation configuration. This isolates the influence of solar EUV. It is found that solar maximum conditions, regardless of season, result in a Venus‐like tail configuration with the current sheet shifted to the −Y(dawnside) direction. Solar minimum conditions result in a flipped tail configuration with the current sheet shifted to the +Y(duskside) direction. The lobes follow this pattern, with the current sheet shifting away from the larger lobe with the higher magnetic field magnitude. The physical process responsible for this solar EUV control of the magnetotail is the magnetization of the dayside ionosphere. During solar maximum, the ionosphere is relatively strong and the draped IMF field lines quickly slip past Mars. At solar minimum, the weaker ionosphere allows the draped IMF to move closer to the planet. These lower altitudes of the closest approach of the field line to Mars greatly hinder the day‐to‐night flow of magnetic flux. This results in a buildup of magnetic flux in the dawnside lobe as the S‐shaped topology on that side of the magnetosheath extends farther downtail. The study demonstrates that the Mars dayside ionosphere exerts significant control over the nightside induced magnetosphere of that planet. Mars, which does not have a strong magnetic field, has an induced magnetic environment from the draping of the interplanetary magnetic field from the Sun. It folds around Mars, forming two “lobes” of magnetic field behind the planet with a current sheet of electrified gas (plasma) behind it. The current sheet is not directly behind the planet but rather shifted toward the dawn or dusk direction. It is shown here that one factor controlling the location of the current sheet is the dayside ionosphere. At solar maximum, the ionosphere is dense, the magnetic field slips easily by the planet, and the current sheet is shifted toward dawn. At solar minimum, the ionosphere is relatively weak, the magnetic field slippage is slowed down, and the current sheet shifts toward dusk. There is a systematic Y(i.e., dawn‐dusk) asymmetry in the location of the Martian magnetotail current sheet in modified MSE coordinatesThe asymmetry is controlled by ionospheric conditions, shifting to the dawn (‐Y) during solar maximum and to the dusk during solar minimumThe shift found in this study is not a function of crustal fields, which were omitted, or solar wind conditions, which were held constant

We present results from a global Mars time‐dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3‐D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic changes with time. We develop a physics‐based, empirical algorithm to effectively summarize the multidimensional crustal field distribution. It is found that by organizing the model results using this new approach, the Mars crustal field shows a clear, significant influence on both the IMB and the BS. Specifically, quantitative relationships have been established between the field distribution and the mean boundary distances and the cross‐section areas in the terminator plane for both of the boundaries. The model‐predicted relationships are further verified by the observations from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our analysis shows that the boundaries are collectively affected by the global crustal field distribution, which, however, cannot be simply parameterized by a local parameter like the widely used subsolar longitude. Our calculations show that the variability of the intrinsic crustal field distribution in Mars‐centered Solar Orbital itself may account for ∼60% of the variation in total atmospheric loss, when external drivers are static. It is found that the crustal field has not only a shielding effect for atmospheric loss but also an escape‐fostering effect by positively affecting the transterminator ion flow cross‐section area. The inhomogeneous crustal magnetic field at Mars has important controlling effects on the Mars‐solar wind interaction and has both shielding and escape‐fostering effects on atmospheric erosion. The Mars crustal field has a clear, significant influence on both the IMB and the BSThe global crustal field distribution collectively affects IMB and BS locationsThe crustal field has both shielding and escape‐fostering effects for atmospheric loss

This study analyzes results from a multifluid MHD simulation to investigate the shape and structure of the pressure and composition boundaries at Mars, which can provide physical insight for the observational analysis. These boundaries are examined via the unity contours and gradients of the plasma ß, as well as ß*, which includes the dynamic pressure in the numerator, and the ion mass and number density ratios. It is found that unity contours are well aligned with the gradient extrema, indicating that the unity contour is a topological boundary. In addition, these two transitions of pressure and composition are of a thickness of 0.05–0.1 RMnear the subsolar region to 1–1.5 RMin the tail. The comparison of the pressure and composition boundaries indicates that the two are very similar and that not only the plasma sheet but also the full volume of the lobes are dominated by planetary ions. It suggests that the tail escape for ions not only concentrates in the central plasma sheet but also the magnetic lobes. It is also worthy pointing out that the ion number density ratio unity contour is found to be systematically smaller than other unity boundaries, which calls for attention when the ion number density is used to identify such boundaries. Finally, the comparison between the boundaries of this study and two analytical fittings is carried out. We found a good agreement with the Vignes fitting, with little flaring in the tail, in contrast to a larger flaring angle from the Trotignon fitting. The pressure and composition boundaries are very similarNot only the plasma sheet but also the full volume of the lobes are dominated by planetary ionsThe boundary layers are about 1–1.5 RMthick in the near-tail region, and this thickness increases with distance down the tail

We investigate Mars‐ward planetary ions (O+and O2+) in the Martian magnetotail that potentially reduce the amount of escaping ions. The global properties of Mars‐ward flows in the Martian magnetotail are characterized, based on over 13‐years of ion data (May 2007–December 2020) collected by the Analyzer of Space Plasma and Energetic Atoms instrument on Mars Express. We find that Mars‐ward flows are frequently observed in the vicinity of the crustal fields, implying that crustal fields may play a key role in producing such flows. The occurrence rate and sunward flux are found higher during solar maximum than solar minimum. However, the occurrence rate and flux of Mars‐ward flows are relatively low. This is different from the case at Venus, where the planetward flows can significantly decrease the total escape rates of ions. Without the protection of an intrinsic magnetic field, solar wind can interact directly with the Martian atmosphere and drive ion escape, which plays a vital role in the evolution of the planetary atmosphere. It was shown that, on average, all Martian ions accelerated by the solar wind flow downstream and escape to interplanetary space. However, some planetary ions can flow sunward or Mars‐ward in the tail, possibly reducing total ion escape. The mechanism and role of these Mars‐ward ions remain unclear. Here, we present a statistical analysis that reveals the global properties of Mars‐ward flows at Mars based on over 13 years of Mars Express data. Our results suggest that crustal fields may play a role in driving Mars‐ward flows. We also show that Mars‐ward flows might have negligible influence on total ion escape at Mars regardless of solar activity level. This finding can help us understand ion escape and tail dynamics at Mars. Mars‐ward ion flows in the magnetotail occur more frequently and with a higher flow flux during solar maximumThe occurrence rate and flux of planetward flows at Martian magnetotail are relatively lower than the case at Venusian magnetotailA strong correlation between crustal fields and Mars‐ward flows is identified Mars‐ward ion flows in the magnetotail occur more frequently and with a higher flow flux during solar maximum The occurrence rate and flux of planetward flows at Martian magnetotail are relatively lower than the case at Venusian magnetotail A strong correlation between crustal fields and Mars‐ward flows is identified

We study the solar wind interaction with the Martian upper atmosphere during the 8 March 2015 interplanetary coronal mass ejection (ICME) by using a global multifluid MHD model. Comparison of the simulation results with observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft shows good agreement. The total ion escape rate is increased by an order of magnitude, from 2.05 × 1024s−1(pre‐ICME phase) to 2.25 × 1025s−1(ICME sheath phase), during this time period. Two major ion escape channels are illustrated: accelerated pickup ion loss through the dayside plume and ionospheric ion loss through the nightside plasma wake region. Interestingly, the tailward ion loss is significantly increased at the ejecta phase. Both bow shock and magnetic pileup boundary (BS and MPB) locations are decreased from (1.2RM, 1.57RM) at the pre‐ICME phase to (1.16RM, 1.47RM), respectively, during the sheath phase along the dayside Mars‐Sun line. Furthermore, both simulation and observational results indicate that there is no significant variation in the Martian ionosphere (at altitudes ≲ 200 km, i.e., the photochemical region) during this event. The total ion escape rate is increased by an order of magnitude during the 8 March ICMEThe tailward ion loss is significantly increased at the ejecta phaseThere is no significant variation in the Martian ionosphere (at altitudes ≲ 200 km)

Prior to the arrival of the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft at Mars, the only available measurements of the composition of the planet's ionosphere were those acquired by the two Viking Landers during their atmospheric entries. Many numerical models of the composition of the ionosphere of Mars have been developed, but these have only been validated for species, altitudes, and conditions for which Viking data exist. Here we compare the ionospheric composition and structure predicted by 10 ionospheric models at solar zenith angles of 45–60° against ion density measurements acquired by the MAVEN Neutral Gas and Ion Mass Spectrometer (NGIMS). The most successful models included three‐dimensional plasma transport driven by interactions with the surrounding space environment but had relatively simple ionospheric chemistry. Topside composition is mixture of O+and O2+Few models predict topside composition accuratelyMost successful models simulated interactions with surrounding space environment

Mars is typically viewed as a member of the category of weakly magnetized planets, with a largely induced magnetosphere and magnetotail produced by the draped fields of the solar wind interaction. However, selected Mars Atmosphere and Volatile EvolutioN Mission (MAVEN) suprathermal electron and magnetic field observations in the near wake, sampled along its elliptical orbit during the early prime mission at altitudes ranging from its ~150 km periapsis to the tail magnetosheath, reinforce a picture seen in an MHD model where magnetic fields are rooted in the planet throughout much of the Martian magnetotail. Mars' solar wind interaction is often viewed as an induced magnetosphere typeMHD models of the interaction suggest much of its wake magnetic flux is instead rooted in MarsMAVEN measurements show some support for this alternate picture, at least at the present epoch

An interesting characteristic of magnetospheric chorus is the presence of a frequency gap at ω≃0.5Ωe, where Ωeis the electron cyclotron angular frequency. Recent chorus observations sometimes show additional gaps near 0.3Ωeand 0.6Ωe. Here we present a novel nonlinear mechanism for the formation of these gaps using Hamiltonian theory and test particle simulations in a homogeneous, magnetized, collisionless plasma. We find that an oblique whistler wave with frequency at a fraction of the electron cyclotron frequency can resonate with electrons, leading to effective energy exchange between the wave and particles. Recent observations of chorus show multiple bandsNonlinear wave‐particle resonances can occur at subcyclotron frequenciesSubcyclotron resonance may lead to formation of gaps in banded chorus

The crustal remnant field on Mars rotates with the planet at a period of 24 h 37 min, constantly varying the magnetic field configuration interacting with the solar wind. Until now, there has been no self‐consistent modeling investigation on how this varying magnetic field affects the solar wind plasma interaction. Here we include the rotation of this localized crustal field in a multispecies single‐fluid MHD model of Mars and simulate an entire day of solar wind interaction under normal solar wind conditions. The MHD model results are compared with Mars Global Surveyor (MGS) magnetic field observations and show very close agreement, especially for the field strength along almost all of the 12 orbits on the day simulated. Model results also show that the ion escape rates slowly vary with rotation, generally anticorrelating with the strength of subsolar magnetic crustal sources, with some time delay. In addition, it is found that in the intense crustal field regions, the densities of heavy ion components enhance significantly along the MGS orbit, implying strong influence of the crustal field on the ionospheric structures. Model results closely agree with MGS observationsIon escape rates slowly vary with rotationCrustal field has strong influence on the ionospheric structures

The 3‐D multifluid Block Adaptive Tree Solar‐wind Roe Upwind Scheme (BATS‐R‐US) MHD code (MF‐MHD) is coupled with the 3‐D Mars Thermospheric general circulation model (MTGCM). The ion escape rate from the Martian upper atmosphere is investigated by using a one‐way coupling approach, i.e., the MF‐MHD model incorporates the effects of 3‐D neutral atmosphere profiles from the MTGCM model. The calculations are carried out for two cases with different solar cycle conditions. The calculated total ion escape flux (the sum of three major ionospheric species, O+, O2+, and CO2+) for solar cycle maximum conditions (6.6×1024s−1) is about 2.6 times larger than that of solar cycle minimum conditions (2.5×1024s−1). Our simulation results show good agreement with recent observations of 2–3×1024s−1(O+, O2+, and CO2+) measured near solar cycle minimum conditions by Mars Express. An extremely high solar wind condition is also simulated which may mimic the condition of coronal mass ejections or corotating interaction regions passing Mars. Simulation results show that it can lead to a significant value of the escape flux as large as 4.3×1025s−1. To better predict the ion escape rate from Martian upper atmosphereTo understand the long‐term evolution of Mars atmosphere over its historyTo support MAVEN spacecraft mission planning and data analysis (2013–2016)

Abstract: Information feedback strategy, serving as the critical part of intelligent traffic systems, has been treated with growing emphasis. In recent years, a variety of feedback strategies have been proposed. Despite the fact that these strategies have been proved to enhance the traffic efficiency, we find that the road capacity has not been saturated and there is still plenty of room for improvement. Based on the analytic approximations, we found the reason why corresponding angle feedback strategy is superior to weighted congestion coefficient feedback strategy. Given that the sharp decay of the weighted coefficient is the key point, we proposed an efficient feedback strategy called the exponential function feedback strategy (EFFS). We applied it to both the symmetrical two-route model with two exits and that with a single exit. The simulation results indicate that, compared with other strategies, EFFS has decided numerical advantages in average flow, a physical quantity used for depicting the road capacity. Even more importantly, EFFS stands out for its convenient application as well as its fitness for modeling the rugged roads. [Copyright &y& Elsevier]

Abstract: Optimization of information feedback technologies is very important for many socioeconomic systems such as stock markets and traffic systems aiming to make full use of resources. In this paper, we propose an adaptive weight method, which has potential value for a variety of information processing contexts. We apply this adaptive weight method to an intelligent transportation system (ITS) as a case study. A feedback strategy named Improved Congestion Coefficient Feedback Strategy (ICCFS) is introduced based on a two-route scenario in which dynamic information can be generated and displayed on the roadside in order to enable drivers to make an informed route decision. Our model incorporates the effects of adaptability into the cellular automaton models of traffic flow. Simulations demonstrate that adopting this optimal information feedback strategy provides a high efficiency in controlling spatial distribution of traffic patterns when compared with the three other information feedback strategies, i.e., Travel Time Feedback Strategy (TTFS), Mean Velocity Feedback Strategy (MVFS) and Congestion Coefficient Feedback Strategy (CCFS). [Copyright &y& Elsevier]

Abstract: The optimal information feedback has a significant effect on many socioeconomic systems like stock market and traffic systems aiming to make full use of resources. In this paper, we study dynamics of traffic flow with real-time information. The influence of a feedback strategy named vehicle number feedback strategy (VNFS) is introduced, in which we only calculate the vehicle number of first 500 route sites from the entrance. Moreover, the two-route traffic system has only one entrance and one exit, which is different from those in the previous work. Our model incorporates the effects of adaptability into the cellular automaton models of traffic flow, and simulation results by adopting this optimal information feedback strategy have demonstrated higher efficiency in controlling spatial distribution of traffic patterns than the other three information feedback strategies, i.e., TTFS, MVFS and CCFS.

Superthermal electron precipitation is one of the main sources supporting the Mars nightside ionosphere. It is expected that solar wind electron fluxes are to increase significantly during interplanetary coronal mass ejections (ICMEs) and therefore an enhanced nightside ionospheric density. This study is to quantify the variation of the precipitating and deposited electron fluxes during five extreme ICMEs encountered by Mars Global Surveyor (MGS). We find that energy fluxes correlate better with the upstream dynamic pressure proxy than number fluxes and electron fluxes increase more at high energies, which means that electrons tend to have a lower peak production altitude during storm times. The precipitating and net/deposited fluxes are increased up to an order of magnitude from low to high dynamic pressures. The estimated total electron content (TEC) is a few times of 1014m−2for quiet times and on the order of 1015m−2for storm times, with an enhancement up to an order of magnitude locally near strong crustal fields. Crustal magnetic fields have an effect on the deposited fluxes with more prominent magnetic reflection over strong magnetic fields during quiet periods, which is significantly reduced during storm times. Lastly, we estimate a global energy input from downward fluxes of 1.1 × 108and 5.5 × 108W and the globally deposited energy from net fluxes of 2.0 × 107and 1.6 × 108W for quiet and storm time periods, a factor of 5 and 8 enhancement globally, respectively, but up to an order of magnitude locally near strong crustal fields. We quantify the variation of nightside precipitating and deposited electron fluxes during five extreme ICME events encountered by MGSThe estimated TEC is on the order of 1014m−2for quiet periods and 1015m−2for storm periods because of enhanced electron precipitationCrustal magnetic fields reduce deposited fluxes during quiet time because of magnetic reflection, which is largely reduced during storm time

We examine here for the first time the effects of both global and regional dust storms on the formation of the Martian hot O corona and associated photochemical loss of O. Our study is conducted by utilizing our integrated model framework, which couples our Martian hot O corona model with a multifluid magnetohydrodynamic model for Mars for the dusty and clear atmospheric condition cases. We present our results with the most up‐to‐date cross sections for the O(3P)‐CO2collisions. The main effect of dust storms on the ionosphere is the upward shift of the ionosphere on the dayside, which results in an increase in production of hot O at all altitudes above the ionospheric peak. However, the dust‐induced inflation of the neutral upper atmosphere results in an enhancement in collisional loss of hot O and thus effectively suppresses the hot O density, reducing the global photochemical loss rate by ~28% for the global dust storm scenario. The relative density structure of the hot O corona does not show any significant changes, while its magnitude decreases at all altitudes. We investigated the effect of dust storms on photochemical escape from Mars using up‐to‐date cross sections for O‐CO2collisionsThe storm‐induced upward shift of the ionosphere causes increased production of hot O and efficient thermalization occurs by the inflated thermosphereThe net result is a global photochemical escape rate that is suppressed by ~28% during the global dust storm scenario

The canonical picture of the magnetotail of unmagnetized planets consists of draped interplanetary magnetic fields (IMFs) forming opposite‐directed lobes, separated by the current sheet. DiBraccio et al. (2018, https://doi.org/10.1029/2018GL077251) showed that Mars's magnetotail has a twist departing from this picture. Magnetohydrodynamic (MHD) results suggest that the asymmetry in how open field lines connected to the planet populate the tail causes the apparent twist. To validate this interpretation, we compare the tail topology determined from MHD simulations to that inferred from data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, in particular, how each topology responds to the upstream IMF orientation. The occurrence rates for open topology from both data and MHD vary with IMF polarities in a similar fashion as the tail twisting. This suggests that Mars's crustal fields have a global effect on the magnetosphere configuration, supporting the picture of a “hybrid” magnetotail that is partly induced/draped and partly intrinsic/planetary in origin. The interaction of the solar wind with unmagnetized planets, such as Venus, results in an induced magnetotail, which is formed by the interplanetary magnetic field lines draping around the planet, forming opposite‐directed lobes. Mars is similar to Venus in many aspects and was thought to have a similar tail configuration. A recent study, however, shows that Mars has a twist in its tail lobes and that modeling results suggest this twist is caused by the effects of its crustal magnetism. In this study, we use the superthermal electron measurements from MAVEN to infer the magnetotail topology resulting from the interaction between the solar magnetic fields and Mars's crustal fields, which is compared with the global magnetohydrodynamic model topology. Our results support the hypothesis that magnetic reconnection between crustal magnetic sources and the solar wind is responsible for the observed twist in Mars's tail lobes. This study provides a detailed mapping of tail magnetic topology at Mars, which is dominated by draped and open magnetic field linesBoth the MHD model and data show significant changes in Martian tail topology with respect to east/west IMFsIt implies that Mars's crustal fields have a global effect on the magnetosphere configuration, supporting the picture of a hybrid magnetotail

Mars regional and global dust storms are able to impact the lower/upper atmospheres through dust aerosol radiative heating and cooling and atmospheric circulation. Here we present the first attempt to globally investigate how the dust impact transfers from the neutral upper atmosphere to the ionosphere and the induced magnetosphere above 100‐km altitude. This is achieved by running a multifluid magnetohydrodynamic model under nondusty and dusty atmospheric conditions for the 2017 late‐winter regional storm and the 1971–1972 global storm. Our results show that the dayside main ionospheric layer (below ∼250‐km altitude) undergoes an overall upwelling, where photochemical reactions dominate. The peak electron density remains unchanged, and the peak altitude shift is in accordance with the upper atmospheric expansion (∼5 and ∼15 km for the regional and global storms, respectively). Controlled by the day‐to‐night transport, the nightside ionosphere responds to the dust storms in a close connection with what happens on the dayside but not apparently with the ambient atmospheric change. At higher altitudes, dust‐induced perturbations propagate upward from the ionosphere to the magnetosphere and extend from the dayside to the nightside, within a broad region bounded by the induced magnetospheric boundary. It is found that the global dust storm is able to dramatically enhance the CO 2+loss by a factor of ∼3, which amounts to an increase of ∼20% or more for total carbon loss (in the forms of neutrals and ions). Strong dust storms are a potentially important factor in atmospheric evolution at Mars. The dayside main ionosphere is lifted in accordance with dust‐induced atmospheric expansion, with peak electron densities unchangedDust‐induced perturbations propagate upward from the ionosphere to the magnetosphere and extend from the dayside to the nightsideStrong dust storms may enhance CO 2+loss by a factor of ∼3 and increase total carbon loss (neutrals and ions) by ∼20% or more