Search

Understanding the interaction between Mars and the solar wind is crucial for comprehending the atmospheric evolution and climate change on Mars. To gain a comprehensive understanding of the Martian plasma environment, global numerical simulations are essential in addition to spacecraft observations. However, there are still discrepancies among different simulation models. This study investigates how these discrepancies stem from the considered physical processes and numerical implementations. We compare two global multispecies MHD models: the "Sun model" based on the BATS‐R‐US code and the "Sakata model" based on a newly developed multifluid model MAESTRO. By employing the same typical upstream conditions and the same neutral atmosphere for current Mars, along with similar numerical implementations such as inner boundary conditions, we obtain simulation results that exhibit unprecedented agreement between the two models. The dayside results are nearly identical, especially along the subsolar line, indicating the robustness of MHD models to predict dayside interaction under given upstream conditions and ionosphere assumptions. The escape rates of planetary ions are also in good agreement. However, discrepancies remain in the terminator and nightside regions. Detailed numerical implementations, including inner boundary conditions, magnetic field divergence control methods, and radial resolutions, are shown to influence certain aspects of the results greatly, such as magnetotail configuration and ion diffusion. Key Points: The same physical assumptions are employed for two different global multispecies MHD modelsThe results for the dayside interaction and planetary ion escape are in unprecedented good agreementDetails of the numerical implementations influence the results, especially on the nightside [ABSTRACT FROM AUTHOR]

Dayside magnetosphere interactions are essential for energy and momentum transport between the solar wind and the magnetosphere. In this study, we investigate a new phenomenon within this regime. Sudden enhancements of ion fluxes followed by repeating dropouts and recoveries were observed by Magnetospheric Multiscale on 5 November 2016, which is the very end of the recovery phase from a moderate geomagnetic storm. These repetitive flux variations display energy‐dispersive characteristics with periods relevant to ion bounce motion, suggesting they are corresponding echoes. Alongside the flux variations, bipolar electric field impulses originating from external sources were detected. We traced the source region of the initial injection and found it is located near the spacecraft's position. To elucidate the underlying physics, a test‐particle simulation is conducted. The results reveal that radial transport resulting from impulse‐induced acceleration can give rise to these echoes. Observations demonstrate dayside magnetosphere interactions are more common than we previously considered, which warrants further research. Plain Language Summary: In spacecraft observations, the quasi‐periodical motion of particles in the geomagnetic field can generate repeating signals known as "echoes". Examining the relationship between the periods of echoes and the particle's energy is necessary for determining their types. The present study reports a novel mechanism responsible for generating echoes that arise from the ion bounce motion along magnetic field lines. Observations from both ground‐based stations and spacecraft, as well as numerical simulations, suggest these echoes can result from the acceleration and radial diffusion of ions responding to external field variations. These findings extend the current understanding of interactions in the dayside outer magnetosphere. Key Points: Ion acceleration and corresponding bounce echoes were observed by MMS in the dayside outer magnetosphereObservations and simulations suggest these echoes are driven by the accompanied electric field impulsesImpulse‐induced ion radial transport with positive phase space density radial gradient leads to the observed pattern [ABSTRACT FROM AUTHOR]

Extreme (>20 nT/s) geomagnetic disturbances (GMDs, also denoted as MPEs—magnetic perturbation events)—impulsive nighttime disturbances with time scale ∼5–10 min, have sufficient amplitude to cause bursts of geomagnetically induced currents (GICs) that can damage technical infrastructure. In this study, we present occurrence statistics for extreme GMD events from five stations in the MACCS and AUTUMNX magnetometer arrays in Arctic Canada at magnetic latitudes ranging from 65° to 75°. We report all large (≥6 nT/s) and extreme GMDs from these stations from 2011 through 2022 to analyze variations of GMD activity over a full solar cycle and compare them to those found in three earlier studies. GMD activity between 2011 and 2022 did not closely follow the sunspot cycle, but instead was lowest during its rising phase and maximum (2011–2014) and highest during the early declining phase (2015–2017). Most of these GMDs, especially the most extreme, were associated with high‐speed solar wind streams (Vsw >600 km/s) and steady solar wind pressure. All extreme GMDs occurred within 80 min after substorm onsets, but few within 5 min. Multistation data often revealed a poleward progression of GMDs, consistent with a tailward retreat of the magnetotail reconnection region. These observations indicate that extreme GIC hazard conditions can occur for a variety of solar wind drivers and geomagnetic conditions, not only for fast‐coronal mass ejection driven storms. Plain Language Summary: Geomagnetically induced currents (GICs) can give rise to the most extreme space weather impact of disrupting electric power distribution. GICs can be driven by extreme geomagnetic disturbances (GMDs) that are observed as large amplitude (several hundred nT amplitude) and rapid (5–10 min period) changes in the geomagnetic field. We found that extreme high‐latitude GMDs occur throughout the solar cycle, but are preferentially observed during the declining phase of the solar cycle (the several year interval just past solar maximum) and in conjunction with high‐speed solar wind streams. They also all occur within 80 min of a geomagnetic substorm, but are not directly related to its explosive onset. These GMDs are most often observed to propagate poleward consistent with tailward retreat of magnetotail reconnection regions. These results show that extreme GMDs and hence large GICs can be driven by a variety of solar wind conditions and not just fast coronal mass ejections. Key Points: Most large (6 nT/s) and extreme (>20 nT/s) high latitude geomagnetic disturbances (GMDs) occurred during the declining phase of the sunspot cycleMost extreme GMDs occurred during high‐speed solar wind streams and often within 25 min after a substorm onset, but seldom within 5 minMany extreme GMDs showed a poleward progression, consistent with the tailward retreat of the magnetotail reconnection region [ABSTRACT FROM AUTHOR]

Foreshock transient (FT) events are frequently observed phenomena that are generated by discontinuities in the solar wind. These transient events are known to trigger global‐scale magnetic field perturbations (e.g., ULF waves). We report a series of FT events observed by the Magnetospheric Multiscale mission in the upstream bow shock region under quiet solar wind conditions. During the event, ground magnetometers observed significant Pc1 wave activity as well as magnetic impulse events in both hemispheres. Ground Pc1 wave observations show ∼8 min time delay (with some time differences) from each FT event which is observed at the bow shock. We also find that the ground Pc1 waves are observed earlier in the northern hemisphere compared to the southern hemisphere. The observation time difference between the hemispheres implies that the source region of the wave is the off‐equatorial region. Key Points: Magnetospheric Multiscale observed a series of foreshock transients near the Earth's bow shockPc1 waves and magnetic impulse events are observed by ground magnetometers in both hemispheres following the foreshock transientsThe difference in observation times between hemispheres implies that Pc1 waves are generated in the off‐equatorial region [ABSTRACT FROM AUTHOR]

Turbulence is ubiquitous within space plasmas, where it is associated with numerous nonlinear interactions. Magnetospheric Multiscale (MMS) provides the unique opportunity to decompose the electric field (E) dynamics into contributions from different linear and nonlinear processes via direct measurements of the terms in generalized Ohm's law. Using high-resolution multipoint measurements, we compute the magnetohydrodynamic ( E MHD ), Hall ( E Hall ), electron pressure ( E P e ), and electron inertia ( E inertia ) terms for 60 turbulent magnetosheath intervals, to uncover the varying contributions to the dynamics as a function of scale for different plasma conditions. We identify key spectral characteristics of the Ohm's law terms: the Hall scale, k Hall , where E Hall becomes dominant over E MHD ; the relative amplitude of E P e to E Hall , which is constant in the sub-ion range; and the relative scaling of the nonlinear and linear components of E MHD and of E Hall , which are independent of scale. We find expressions for the characteristics as a function of plasma conditions. The underlying relationship between turbulent fluctuation amplitudes and ambient plasma conditions is discussed. Depending on the interval, we observe that E MHD and E Hall can be dominated by either nonlinear or linear dynamics. We find that E P e is dominated by its linear contributions, with a tendency for electron temperature fluctuations to dominate at small scales. The findings are not consistent with existing linear kinetic Alfvén wave theory for isothermal fluctuations. Our work shows how contributions to turbulent dynamics change in different plasma conditions, which may provide insight into other turbulent plasma environments. [ABSTRACT FROM AUTHOR]

There have been a number of theories proposed concerning the loss of relativistic electrons from the radiation belts. However, direct observations of loss were not possible on a number of previous missions due to the large field of view of the instruments and often high‐altitude orbits of satellites that did not allow researchers to isolate the precipitating electrons from the stably trapped. We use measurements from the ELFIN‐L suit of instruments flown on Lomonosov spacecraft at LEO orbit, which allows us to distinguish stably trapped from the drift loss cone electrons. The sun‐synchronous orbit of Lomonosov allows us to quantify scattering that occurred into the loss cone on the dawn‐side and the dusk‐side magnetosphere. The loss at MeV energies is observed predominantly on the dawn‐side, consistent with the loss induced by the chorus waves. The companion data publication provides processed measurements. Plain Language Summary: There have been a number of models proposed concerning the loss of relativistic electrons from radiation belts. However, the direct observations of loss have been missing, as for most of the previous missions; the large aperture telescopes could not isolate the precipitating electrons from being stably trapped. In this study, we use measurements from ELFIN‐L on Lomonosov that allow for such separation and allow us to distinguish stably trapped from precipitating particles. We can also identify the particles that will be lost within one drift around the Earth, the so‐called drift loss cone. For understanding the loss processes and differentiating between them, it's crucially important to quantify where in local magnetic time these electrons will be scattered into the drift loss cone. Measurements from the ELFIN‐L instrument show that the loss at MeV energies is observed predominantly on the dawn side, consistent with the loss induced by the so‐called chorus plasma waves. Key Points: ELFIN‐L measurements allow comparing scattering into the loss cone on the dawn and dusk sideProcessed Level‐3 measurements are provided in the data publicationMost of the relativistic electrons are scattered into the drift loss cone on the dawn side [ABSTRACT FROM AUTHOR]

Pulsating auroras are usually observed with ultralow-frequency (ULF) waves in the Pc 3–5 band (period 10–600 s). These auroras are thought to result from interactions between energetic electrons and chorus waves, but their relationship with ULF waves remains an open question. In this study, we investigated this question by conducting a comparative study on two ULF wave events with pulsating auroras observed near the magnetic footprints. Conjugate observations from the Magnetospheric Multiscale mission and the Chinese Yellow River Station were used. In both events, lower-band chorus waves were observed, which were suggested to be connected with the auroral pulsations by wavelet analysis. The intensity of these waves oscillates at the period of the ULF waves, but the physics laid behind them differs by events. During the event of 22 January 2019, compressional ULF waves changed the threshold for the whistler anisotropy instability periodically, affecting the emission of chorus waves. In the event on 10 January 2016, poloidal ULF waves modulated the chorus wave generation by regulating electron temperature anisotropy through drift resonance. ULF waves in these events may originate from perturbations in the solar wind. We highlight the role of ULF waves in the solar wind–magnetosphere–ionosphere coupling, which requires further study. [ABSTRACT FROM AUTHOR]

The objective of the Psyche Magnetometry Investigation is to test the hypothesis that asteroid (16) Psyche formed from the core of a differentiated planetesimal. To address this, the Psyche Magnetometer will measure the magnetic field around the asteroid to search for evidence of remanent magnetization. Paleomagnetic measurements of meteorites and dynamo theory indicate that a diversity of planetesimals once generated dynamo magnetic fields in their metallic cores. Likewise, the detection of a strong magnetic moment (> 2 × 10 14 Am 2 ) at Psyche would likely indicate that the body once generated a core dynamo, implying that it formed by igneous differentiation. The Psyche Magnetometer consists of two three-axis fluxgate Sensor Units (SUs) mounted 0.7 m apart along a 2.15-m long boom and connected to two Electronics Units (EUs) located within the spacecraft bus. The Magnetometer samples at up to 50 Hz, has a range of ± 80 , 000 nT , and an instrument noise of 39 pT axis − 1 3 σ integrated over 0.1 to 1 Hz. The two pairs of SUs and EUs provide redundancy and enable gradiometry measurements to suppress noise from flight system magnetic fields. The Magnetometer will be powered on soon after launch and acquire data for the full duration of the mission. The ground data system processes the Magnetometer measurements to obtain an estimate of Psyche's dipole moment. [ABSTRACT FROM AUTHOR]

A collisionless shock is a self-organized structure where fields and particle distributions are mutually adjusted to ensure a stable mass, momentum and energy transfer from the upstream to the downstream region. This adjustment may involve rippling, reformation or whatever else is needed to maintain the shock. The fields inside the shock front are produced due to the motion of charged particles, which is in turn governed by the fields. The overshoot arises due to the deceleration of the ion flow by the increasing magnetic field, so that the drop of the dynamic pressure should be compensated by the increase of the magnetic pressure. The role of the overshoot is to regulate ion reflection, thus properly adjusting the downstream ion temperature and kinetic pressure and also speeding up the collisionless relaxation and reducing the anisotropy of the eventually gyrotropized distributions. [ABSTRACT FROM AUTHOR]

Although 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 >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. [ABSTRACT FROM AUTHOR]