Magnetospheric Configuration Research Articles

The anomalous state of Uranus’s magnetosphere during the Voyager 2 flyby

AbstractThe Voyager 2 flyby of Uranus in 1986 revealed an unusually oblique and off-centred magnetic field. This single in situ measurement has been the basis of our interpretation of Uranus’s magnetosphere as the canonical extreme magnetosphere of the solar system; with inexplicably intense electron radiation belts and a severely plasma-depleted magnetosphere. However, the role of external forcing by the solar wind has rarely been considered in explaining these observations. Here we revisit the Voyager 2 dataset to show that Voyager 2 observed Uranus’s magnetosphere in an anomalous, compressed state that we estimate to be present less than 5% of the time. If the spacecraft had arrived only a few days earlier, the upstream solar wind dynamic pressure would have been ~20 times lower, resulting in a dramatically different magnetospheric configuration. We postulate that such a compression of the magnetosphere could increase energetic electron fluxes within the radiation belts and empty the magnetosphere of its plasma temporarily. Therefore, the interpretation of Uranus’s magnetosphere as being extreme may simply be a product of a flyby that occurred under extreme upstream solar wind conditions.

Unexpected STEVE Observations at High Latitude During Quiet Geomagnetic Conditions

AbstractStrong Thermal Emission Velocity Enhancement (STEVE), is a captivating optical phenomenon typically observed in the mid‐latitude ionosphere. This paper presents an intriguing observation of a STEVE event at high‐latitudes, approximately 10 degrees poleward of previously documented observations. This event was recorded in Yellowknife, Canada, by a TREx RGB imager and a citizen scientist. Swarm satellites traversed the latitude of the observation, measuring extreme westwards ion drift velocities exceeding 4 km/s. Such velocities are more typically associated with the subauroral region located at mid‐latitudes, rather than at the high‐latitudes reported here. Significantly, this event occurred without a substorm, which differs from previous STEVE observations. While high‐latitude radars detected fast ionospheric equatorward flows, GOES satellite did not record any injections. These observations suggest that the inner magnetosphere is highly inflated. This unique case study raises new questions surrounding subauroral dynamics and the influence of magnetospheric configurations on ionospheric responses.

Identifying the Magnetospheric Drivers of Giant Undulations: Global Modeling of the Evolving Inner Magnetosphere and Its Auroral Manifestations

AbstractWe present the first global geospace simulation to reproduce auroral giant undulations (GUs). To identify their magnetospheric drivers, we employ the MAGE (Multiscale Atmosphere‐Geospace Environment) model in a case study of a geomagnetic storm for which there were spacecraft‐ and ground‐based observations of GUs. The model reproduces the spatial and temporal scales of the GUs as well as the presence of duskside subauroral polarization streams (SAPS) and plasmapause undulations. Based on our modeling, we are able to identify the magnetospheric drivers of GUs as mesoscale ring current injections which, after drifting westward, create inverted regions of flux‐tube entropy (FTE) and subsequent interchange instability. Outward‐protruding interchange fingers disrupt shielding of the inner magnetosphere, creating longitudinally localized ripples in magnetospheric convection equatorward of the magnetospheric instability, which structure the plasmapause and duskside diffuse precipitation. While not causal, SAPS and plasmapause undulations are a consequence of the unstable magnetospheric configuration.

Mesoscale Structure and Properties of the Terrestrial Magnetotail Plasma Sheet From the Magnetospheric Multiscale Mission

AbstractUsing Magnetospheric Multiscale mission (MMS) orbits in the Earth's magnetotail from 2017 to 2020, plasma conditions and the 3D spatial structure of inner‐magnetotail plasma environments (with a focus on the plasma sheet (PS)) are studied with different approaches. Threshold conditions for distinguishing the PS, PS boundary layers, and lobes are derived from the statistical properties of background plasma parameters. Our results support previous studies that employed similar methods using Cluster data. However, stronger currents are observed in both the lobes and PS, likely due to the smaller spacecraft separation (≲70 km) that can resolve thin electron‐scale currents. Threshold conditions are used together with magnetic field and electric field measurements to image the spatial structure of the PS. Results are in good agreement with a global neutral sheet model based on solar wind conditions and magnetospheric configurations. Furthermore, the Earth's dipole tilts toward the Sun around June solstice, which warps the magnetotail as much as ∼2–4 RE in Z geocentric solar magnetospheric. This warping effect is relaxed toward September equinox. Consequently, as MMS travels through the magnetotail from dawn to dusk during this period, there is an apparent dawn‐dusk asymmetry in plasma conditions between June and September. Kink‐like flapping waves and interplanetary magnetic field twisting are other mesoscale processes attributed with a few RE of flaring near the flanks. These findings reveal important insights into the mesoscale structure and dynamics of the magnetotail.

Impact of Changing Stellar and Planetary Magnetic Fields on (Exo)planetary Environments and Atmospheric Mass Loss

The magnetic activity of a star—which modulates the stellar wind outflow—shapes the immediate environments of orbiting (exo)planets and induces atmospheric loss, thereby impacting their habitability. We perform a detailed parameter space study using three-dimensional magnetohydrodynamic simulations to understand the effect of changing stellar wind magnetic field and planetary magnetic field strengths on planetary magnetospheric topology and atmospheric losses. It is observed that the relative strengths of stellar and planetary magnetic fields play a significant role in determining the steady-state magnetospheric configuration and atmospheric erosion. When the stellar field is strengthened or the planetary field is weakened, stellar magnetic field accumulation occurs at the dayside of the planet, forcing the magnetopause to shift closer to its surface. The magnetotail opens up, leading to the formation of Alfvén wings in the nightside wake region. We demonstrate how reconnection processes and wind conditions lead to the bifurcation of the magnetotail current sheet. With increasing stellar wind magnetic field strength, the dayside reconnection point approaches the planet, thereby enhancing mass loss. We establish an analytic equation relating the atmospheric mass-loss rates to stellar and planetary magnetic field strengths, which successfully explains the modeled behavior. Our results are relevant for understanding how the interplay of stellar and planetary magnetism influence (exo)planetary environments and their habitability in star–planet systems with differing relative magnetic field strengths or in a single star–planet system over the course of their evolution with age.

Relativistic coronal mass ejections from magnetars

ABSTRACT We study dynamics of relativistic coronal mass ejections (CMEs), from launching by shearing of foot-points (either slowly – the ‘Solar flare’ paradigm, or suddenly – the ‘star quake’ paradigm), to propagation in the preceding magnetar wind. For slow shear, most of the energy injected into the CME is first spent on the work done on breaking through the overlaying magnetic field. At later stages, sufficiently powerful CMEs may lead to the ‘detonation’ of a CME and opening of the magnetosphere beyond some equipartition radius req, where the decreasing energy of the CME becomes larger than the decreasing external magnetospheric energy. Post-CME magnetosphere relaxes via the formation of a plasmoid-mediated current sheet, initially at ∼req, and slowly reaching the light cylinder. Both the location of the foot-point shear and the global magnetospheric configuration affect the frequent/weak versus rare/powerful CME dichotomy – to produce powerful flares, the slow shear should be limited to field lines that close in near the star. After the creation of a topologically disconnected flux tube, the tube quickly (at ∼ the light cylinder) comes into force-balance with the preceding wind and is passively advected/frozen in the wind afterward. For fast shear (a local rotational glitch), the resulting large amplitude Alfvén waves lead to the opening of the magnetosphere (which later recovers similarly to the slow shear case). At distances much larger than the light cylinder, the resulting shear Alfvén waves propagate through the wind non-dissipatively.

On the Particle Motion in Paleo‐Magnetosphere During the Geomagnetic Polarity Reversal

AbstractDuring the Earth's magnetic reversal, the dipole component of the magnetic field weakens, and the non‐dipole component becomes dominant, resulting in a far more complex magnetospheric topology than that of a dipole. In this study, we used a particle tracing technique to investigate the motion of ions within an irregular magnetosphere during the Matuyama‐Brunhes magnetic polarity reversal. Compared to the scenario in which the geomagnetic field is dominated by a dipole component, earthward‐moving particles can be hardly “trapped” in the inner magnetosphere when the geomagnetic field experiences the polarity reversal, and particles can directly precipitate into the Earth's atmosphere on a global scale. It suggests that under an irregular magnetospheric configuration, the traditional trapped region of particles (e.g., radiation belt or ring current) no longer exists.

Drivers of rapid geomagnetic variations at high latitudes

Abstract. We have examined the most intense external (magnetospheric and ionospheric) and internal (induced) |dH/dt| (amplitude of the 10 s time derivative of the horizontal geomagnetic field) events observed by the high-latitude International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers between 1994 and 2018. While the most intense external |dH/dt| events at adjacent stations typically occurred simultaneously, the most intense internal (and total) |dH/dt| events were more scattered in time, most likely due to the complexity of induction in the conducting ground. The most intense external |dH/dt| events occurred during geomagnetic storms, among which the Halloween storm in October 2003 featured prominently, and drove intense geomagnetically induced currents (GICs). Events in the prenoon local time sector were associated with sudden commencements (SCs) and pulsations, and the most intense |dH/dt| values were driven by abrupt changes in the eastward electrojet due to solar wind dynamic pressure increase or decrease. Events in the premidnight and dawn local time sectors were associated with substorm activity, and the most intense |dH/dt| values were driven by abrupt changes in the westward electrojet, such as weakening and poleward retreat (premidnight) or undulation (dawn). Despite being associated with various event types and occurring at different local time sectors, there were common features among the drivers of most intense external |dH/dt| values: preexisting intense ionospheric currents (SC events were an exception) that were abruptly modified by sudden changes in the magnetospheric magnetic field configuration. Our results contribute towards the ultimate goal of reliable forecasts of dH/dt and GICs.

Magnetosphere Distortions During the “Satellite Killer” Storm of February 3–4, 2022, as Derived From a Hybrid Empirical Model and Archived Data Mining

AbstractA pair of relatively mild geomagnetic storms of February 3–4, 2022, resulted in the loss of 38 Starlink satellites. In this work we reconstruct a sequence of magnetospheric configurations during that event, based on the largest ever archive of historical data, a new magnetic field model, and the nearest‐neighbor method of mining the solar wind, magnetosphere, and ground activity data. The model is constructed as a combination of main modular framework, explicitly representing magnetic effects of principal current systems, and a high‐resolution superstructure, based on expanding the field of equatorial currents into a sum of quasi‐orthogonal harmonics, whose purpose is to correct residual inaccuracies of the modular component. In addition, the variable penetration of the interplanetary magnetic field (IMF) into the magnetosphere is taken into account in the form of a potential field, parameterized by the observed IMF components. Despite relatively modest intensity of the event in terms of Sym‐H peak values, surprisingly strong transient distortions of the global magnetic field are found. Whereas under quiet pre‐storm conditions the midnight segment of synchronous orbit and the dayside cusps mapped, respectively, to ∼67° and ∼77° of corrected latitude, at the peak of the storm their footpoints shifted equatorward to as low as ∼63° and ∼67°–68°, with formation of entangled flux‐rope‐like structures and magnetic neutral lines at distances R ∼ 12–15 RE on the nightside. At nearly the same time, a deep magnetic depression and, possibly, an island of reversed field polarity forms even closer, in the post‐dusk sector of geosynchronous orbit.

Thin Filaments in an Average Magnetosphere: Pure Interchange Versus Ballooning Oscillations

AbstractThis paper describes magnetospheric waves of very long wavelength in thin magnetic filaments. We consider an average magnetospheric configuration with zero ionospheric conductance and calculate waves using two different formulations: classic interchange theory and ideal magnetohydrodynamic (MHD) ballooning. Classic interchange theory, which is developed in detail in this paper, is basically analytic and is relatively straightforward to determine computationally, but it cannot offer very high accuracy. The eigenfrequencies from the two formulations cover a range of a factor of seven and generally agree with a root‐mean‐square difference between the common logarithms of interchange and MHD frequencies to be ∼0.054. The pressure perturbations in the classic interchange theory are assumed constant along each field line, but the MHD computed pressure perturbations along the field line vary in a range ∼30% in the plasma sheet but are larger in the inner magnetosphere. The parallel and perpendicular displacements, which are very different in the plasma sheet and inner magnetosphere, show good qualitative agreement between the two approaches. In the plasma sheet, the perpendicular displacements are strongly concentrated in the equatorial plane, whereas the parallel displacements are spread through most of the plasma sheet away from the equatorial plane; and can be regarded as buoyancy waves. In the inner magnetosphere, the displacements are more sinusoidal and are more like conventional slow modes. The different forms of the waves are best characterized by the flux tube entropy PVγ.

Neptune’s Pole-on Magnetosphere: Dayside Reconnection Observations by Voyager 2

Abstract The “pole-on” configuration occurs when the polar magnetosphere of a planet is directed into the solar wind velocity vector. Such magnetospheric configurations are unique to the ice giant planets. This means that magnetic reconnection, a process that couples a magnetosphere to the solar wind, will be different at the ice giants when they are pole-on compared to other planets. The only available in situ measurements of a pole-on magnetosphere are from the Neptune flyby by Voyager 2, which we analyze in this paper. We show that dayside magnetopause conditions were conducive to magnetic reconnection. A plasma depletion layer in the magnetosheath adjacent to the magnetopause was observed. Plasma measurements inside the magnetospheric cusp show evidence of multiple reconnection taking place at the magnetopause before the spacecraft crossed the open–closed field line boundary. A possible traveling compression region from a nearby passing flux rope was also observed, providing further supporting evidence that multiple X-line reconnection occurred during the flyby. During a perfectly pole-on configuration, reconnection will not depend on the orientation of the interplanetary magnetic field, as is the case at other planetary magnetospheres. The rate of reconnection will not vary because the area of the dayside magnetopause where antiparallel shears occur will be approximately equal for all interplanetary magnetic field orientations. Therefore, we suggest that rotating into and out of the pole-on configuration will likely drive the “on–off”/“switch-like” dynamics observed in simulations. Consequently, the pole-on configuration is most likely an important rotational phase for driving ice giant magnetospheric dynamics.

The Case for a New Frontiers–Class Uranus Orbiter: System Science at an Underexplored and Unique World with a Mid-scale Mission

Abstract Current knowledge of the Uranian system is limited to observations from the flyby of Voyager 2 and limited remote observations. However, Uranus remains a highly compelling scientific target due to the unique properties of many aspects of the planet itself and its system. Future exploration of Uranus must focus on cross-disciplinary science that spans the range of research areas from the planet’s interior, atmosphere, and magnetosphere to the its rings and satellites, as well as the interactions between them. Detailed study of Uranus by an orbiter is crucial not only for valuable insights into the formation and evolution of our solar system but also for providing ground truths for the understanding of exoplanets. As such, exploration of Uranus will not only enhance our understanding of the ice giant planets themselves but also extend to planetary dynamics throughout our solar system and beyond. The timeliness of exploring Uranus is great, as the community hopes to return in time to image unseen portions of the satellites and magnetospheric configurations. This urgency motivates evaluation of what science can be achieved with a lower-cost, potentially faster-turnaround mission, such as a New Frontiers–class orbiter mission. This paper outlines the scientific case for and the technological and design considerations that must be addressed by future studies to enable a New Frontiers–class Uranus orbiter with balanced cross-disciplinary science objectives. In particular, studies that trade scientific scope and instrumentation and operational capabilities against simpler and cheaper options must be fundamental to the mission formulation.

Effects of the IMF Direction on Atmospheric Escape From a Mars‐like Planet Under Weak Intrinsic Magnetic Field Conditions

AbstractDirection of the upstream interplanetary magnetic field (IMF) significantly changes the magnetospheric configuration, influencing the atmospheric escape mechanism. This paper investigates effects of IMF on the ion escape mechanism from a Mars‐like planet that has a weak dipole magnetic field directing northward on the equatorial surface. The northward (parallel to the dipole at subsolar), southward (antiparallel), and Parker‐spiral IMFs under present solar wind conditions are compared based on multispecies magnetohydrodynamics simulations. In the northward IMF case, molecular ions escape from the high‐latitude lobe reconnection region, where ionospheric ions are transported upward along open field lines. Atomic oxygen ions originating either in the ionosphere or oxygen corona escape through a broader ring‐shaped region. In the southward IMF case, the escape flux of heavy ions increases significantly and has peaks around the equatorial dawn and dusk flanks. The draped IMF can penetrate into the subsolar ionosphere by erosion, and the IMF becomes mass‐loaded as it is transported through the dayside ionosphere. The mass‐loaded draped IMF is carried to the tail, contributing to ion escape. The escape channels in the northward and southward IMF cases are different from those in the Parker‐spiral IMF case. The escape rate is the lowest in the northward IMF case and comparable in the Parker‐spiral and southward IMF cases. In the northward IMF case, a weak intrinsic dipole forms a magnetosphere configuration similar to that of Earth, quenching the escape rate, while the Parker‐spiral and southward IMFs cause reconnection and erosion, promoting ion escape from the upper atmosphere.

Ice giant system exploration in the 2020s: an introduction.

The international planetary science community met in London in January 2020, united in the goal of realizing the first dedicated robotic mission to the distant ice giants, Uranus and Neptune, as the only major class of solar system planet yet to be comprehensively explored. Ice-giant-sized worlds appear to be a common outcome of the planet formation process, and pose unique and extreme tests to our understanding of exotic water-rich planetary interiors, dynamic and frigid atmospheres, complex magnetospheric configurations, geologically-rich icy satellites (both natural and captured), and delicate planetary rings. This article introduces a special issue on ice giant system exploration at the start of the 2020s. We review the scientific potential and existing mission design concepts for an ambitious international partnership for exploring Uranus and/or Neptune in the coming decades. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.

The Effects of Field Line Curvature (FLC) Scattering on Ring Current Dynamics and Isotropic Boundary

AbstractIn the ring current dynamics, various loss mechanisms contribute to the ring current decay, including losses to the upper atmosphere through particle precipitation. This study implements the field line curvature (FLC) scattering mechanism in a kinetic ring current model and investigates its role in precipitating ions into the ionosphere during the 17 March 2013 storm. Simulation results indicate that (1) the FLC scattering process exerts on energetic ions on the nightside where the magnetospheric configuration is more stretching. It is more effective on heavy ions (e.g., O+). These ion losses thereafter lead to a faster recovery of the ring current. (2) The FLC‐associated ion precipitation mainly occurs in the outer region (L > 5 for protons and L > 4.5 for oxygen ions) on the nightside. The O+ precipitation takes places in a wider region than protons although its intensity is much lower. Comparisons with POES observations suggest that more proton precipitation is needed in the inner region. This is probably caused by the less stretched configuration in the simulation that prevents more precipitation. It may also imply that other loss process is required in the model such as wave‐particle interactions. (3) The storm time precipitating proton flux of tens of keV due to the FLC scattering sometimes becomes comparable to that of electrons on the nightside, although electrons usually dominate the ionospheric energy deposition from the midnight eastward toward the dayside. (4) The FLC scattering process seems to be capable of explaining the formation of isotropic boundary in the ionosphere during the investigated event.

Use of the L1 Constellation as a Multispacecraft Solar Wind Monitor

AbstractA novel multispacecraft solar wind monitor is developed, which expands on the forecasting ability of OMNI by giving spatially resolved predictions. The prediction algorithm ingests all the data from the current fleet of three L1 monitors, allowing gradients in the solar wind to be resolved on scale sizes similar to the magnetosphere. Understanding structure of the solar wind is vital to determine the global magnetospheric configuration, which is important in both real time as a space‐weather product and data users wanting to know upstream conditions when interpreting observations. The model is validated by comparing the predictions with other spacecraft observing the solar wind in situ. We perform a statistical study with thousands of hours of magnetospheric multiscale observations in the solar wind, comparing the prediction accuracy of the multispacecraft monitor to all of the OMNIWeb single‐spacecraft monitors. The multispacecraft monitor shows improvement over all three of the single‐spacecraft predictions for 44% of the cases and also outperforms both ACE and Wind, which are the primary magnetic field contributors to the OMNI IMF prediction, 55% of the time. We propose that the realistic structure of the solar wind that is resolved with multiple solar wind monitors could be vitally important to implement as upstream conditions in global magnetospheric simulations.

Magnetosphere of an orbiting neutron star

We conduct force-free simulations of a single neutron star undergoing orbital motion in flat spacetime, mimicking the trajectory of the star about the center of mass on a compact binary system. Our attention is focused on the kinetic energy being extracted from the orbit by the acceleration of the magnetic dipole moment of the neutron star and, particularly, on how this energy gets distributed within its surrounding magnetosphere. A detailed study of the resulting magnetospheric configurations in our setting is presented, incorporating as well the effects due to neutron star spin and the misalignment of the magnetic and orbital axes. We find many features resembling those of pulsar magnetospheres for the orbiting neutron star---even in the absence of spin-of particular interest being the development of a spiral current sheet that extends beyond the light cylinder. Then, we use recent advances in pulsar theory to estimate electromagnetic emissions produced at the reconnection regions of such current sheets.

Characterizing Mars's Magnetotail Topology With Respect to the Upstream Interplanetary Magnetic Fields

AbstractThe 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.

Second Braking Index of Intermittent Pulsar and Nulling Pulsar**This work was funded by Xin Jiang Autonomous Region Science and Technology Department Natural Science Fund Youth Project under No. 2017D01B02.

The braking index parameter of intermittent pulsar would provide important insight into the pulsar slowdown and emission mechanism. In previous work, we presented the first braking index of the intermittent pulsar B1931+24, J1841−0500, J1832+0029 and nulling pulsar B0823+26, by using their observed spin frequency first derivatives in “on” and “off” states. In this paper, to improve and justify our method for studying the braking mechanism of intermittent pulsars, we continue to formulate a method in which the second braking indices, , of these pulsars can also be given with only the observed spin frequency first derivatives and . This paper will discuss, according to the emission and spin-down property of intermittent pulsars, three different magnetospheric configuration changes in the polar cap region. We find our approach produces feasible values of the second braking index of intermittent pulsar. Our calculations of the second braking indices are in close agreement with predicted second braking indices m = n(2n − 1), which are given by simple spin-down law of pulsar spin evolution, resulting in indirect observational support to our model.

Using PC indices to predict violent GIC events threatening power grids

The aim of the present contribution is to investigate the timing relations between enhancements in the Polar Cap (PC) indices and power grid disturbances related to geomagnetically induced currents (GIC). The polar cap indices, PCN (North) and PCS (South), are based on measurements of geomagnetic variations in the central polar caps. These variations are strongly related to the transpolar convection of plasma and magnetic fields driven by the solar wind. During cases of enhanced merging processes at the front of the magnetosphere and subsequent tailward convection of plasma and embedded magnetic fields, the magnetospheric tail configuration may accumulate excess energy, which upon release may cause violent substorm activity. Earlier reports have disclosed remarkably lengthy intervals, ranging up to several hours, of elevated PC index values preceding GIC-related power grid disruptions. The present investigation has shown that the delays of typically 3–4 h between increases in the PC indices and GIC-related power grid disturbances are related to displacements of the substorm processes responsible for strong GIC events to subauroral latitudes where vulnerable power grids reside. The results have shown that PC index values remaining above an “alert level” of 10 mV/m through more than 1 h indicate a high risk for violent GIC events that may threaten power grids and other vulnerable technical systems. These results support the application of real-time PC indices in space weather monitoring and forecast services.