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Nowadays, it is so important in saving our economic activity and evading the disasters caused by terrestrial electromagnetic effects to predict both temporal and spatial scales of the geomagnetic d...

The terrestrial magnetosphere is perpetually exposed to and significantly deformed by the interplanetary magnetic field (IMF) in the solar wind. This deformation is typically detected at discrete locations by space‐ and ground‐based observations. Earth's aurora, on the other hand, is a globally distributed phenomenon that may be used to elucidate magnetospheric deformations caused by IMF variations, as well as plasma supply from the deformed magnetotail to the high‐latitude atmosphere. We report the utilization of an auroral form known as the transpolar arc (TPA) to diagnose the plasma dynamics of the globally deformed magnetosphere. Nine TPAs examined in this study have two types of a newly identified morphology, which are designated as “J”‐ and “L”‐shaped TPAs from their shapes and are shown to have antisymmetric morphologies in the Northern Hemisphere and Southern Hemisphere, depending on the IMF polarity. The TPA‐associated ionospheric current profiles suggest that electric currents flowing along the magnetic field lines (field‐aligned currents [FACs]), connecting the magnetotail and the ionosphere, may be related to the “J”‐ and “L”‐shaped TPA formations. The FACs can be generated by velocity shear between fast plasma flows associated with nightside magnetic reconnection and slower background magnetotail plasma flows. Complex large‐scale TPA FAC structures, previously unraveled by an magnetohydrodynamic (MHD) simulation, cannot be elucidated by our observations. However, our interpretation of TPA features in a global context facilitates the usage of TPA as a diagnostic tool to effectively remote sense globally deformed terrestrial and planetary magnetospheric processes in response to the IMF and solar wind plasma conditions.

In this study, we try to explore the feasibility on whether or not the magnetospheric processes under northward Interplanetary Magnetic Field (IMF) conditions can be diagnosed using two different a...

Since we discovered the newly morphological transpolar arc (TPA), whose nightside end got distorted toward pre- or post-midnight, identified as “nightside distorted TPAs”, their fundamental charact...

The terrestrial magnetosphere is perpetually exposed, and significantly deformed by the Interplanetary Magnetic Field (IMF) in the solar wind. This deformation is typically detected at discrete loc...

Although the responses of the transpolar arcs (TPAs) to the north-south or dawn-dusk interplanetary magnetic field (IMF) orientations are relatively well known, the effects of the Sun-Earth IMF component on the TPA formation are still poorly understood. On 29 October 2005, the IMF pointed nearly earthward over seven hours from 08:20 to 15:40 UT. In this time interval, the Defense Meteorological Satellite Program (DMSP) satellite and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite observed two clear TPA structures (one near the magnetic pole and the other near the dawnside auroral oval) in the northern hemisphere and one clear TPA structure in the dawnside southern hemisphere. Precipitating particle data reveal that the TPA in the southern hemisphere and that near the dawnside auroral oval in the northern hemisphere are associated with precipitating electrons and ions, but the TPA near the magnetic pole in the northern hemisphere is associated with electron-only precipitation. These observational results imply that the formation of TPAs is not limited to northward IMF conditions and that the TPAs could be located not only on open field lines connected to the northward draped IMFs over one hemisphere magnetopause, but also on closed field lines rooted on both hemispheres even under the radial IMF conditions.

The Advanced Small Analyzer for Neutrals (ASAN) on board the Chang’E-4 Yutu-2 rover first detected energetic neutral atoms (ENAs) originating from the lunar surface at various lunar local times on the lunar farside. In this work, we examine the ENA energy spectra, obtained in the first 23 lunar days from 2019 January 11 to 2020 October 12, and find a higher ENA differential flux on the lunar dawnside than on the duskside. Combined with Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) data, we analyze the correlation between the ENA differential flux and solar wind parameters, such as flux, density, dynamic pressure, and velocity, for each ASAN energy channel on the dawnside and duskside. The results show that ENA differential flux is positively correlated with solar wind flux, density, and dynamic pressure and relatively lower on the duskside than on the dawnside. To determine the relationship between solar wind energy and ENA energy, we analyze the correlation between solar wind energy and ENA cutoff energy and temperature on the dawnside and duskside. The results show that the ENA cutoff energy and temperature are lower on the duskside than on the dawnside at the same solar wind energy. The difference between the ENA–solar wind observation on the dawnside and duskside is possibly caused by solar wind deflection and deceleration on the duskside, which can be attributed to the interaction between solar wind and the lunar magnetic anomalies located nearby in the northwestern direction of the Chang’E-4 landing site.

Magnetic holes (MHs), with a scale much greater than \r{ho}i (proton gyroradius), have been widely reported in various regions of space plasmas. On the other hand, kinetic-size magnetic holes (KSMHs), previously called small size magnetic holes (SSMHs), with a scale of the order of magnitude of or less than \r{ho}i have only been reported in the Earth's magnetospheric plasma sheet. In this study, we report such KSMHs in the magnetosheath whereby we use measurements from the Magnetospheric Multiscale (MMS) mission, which provides three-dimensional (3D) particle distribution measurements with a resolution much higher than previous missions. The MHs have been observed in a scale of 10 ~ 20 \r{ho}e (electron gyroradii) and lasted 0.1 ~ 0.3 s. Distinctive electron dynamics features are observed, while no substantial deviations in ion data are seen. It is found that at the 90{\deg} pitch angle, the flux of electrons with energy 34 ~ 66 eV decreased while for electrons of energy 109 ~ 1024 eV increased inside the MHs. We also find the electron flow vortex perpendicular to the magnetic field, a feature self-consistent with the magnetic depression. Moreover, the calculated current density is mainly contributed by the electron diamagnetic drift, and the electron vortex flow is the diamagnetic drift flow. The electron magnetohydrodynamics (EMHD) soliton is considered as a possible generation mechanism for the KSMHs with the scale size of 10 ~ 20 \r{ho}e., Comment: The paper need to be removed as some data is not corrected

Ultralow frequency (ULF) waves play an important role in the transport of the solar wind energy to the magnetosphere. In this paper, we present a ULF wave event in the dayside magnetosphere which shows a sudden decrease in frequency from 3.1 to 2.3 mHz around 0756 UT on 11 January 2010, when a solar wind dynamic pressure drop (from ∼5 to ∼2 nPa) was observed simultaneously. The wave exits globally. The phase differences between electric and magnetic fields indicate that the compressional mode wave is standing before and after the wave frequency decrease. This result suggests that the ULF wave should be associated with a cavity mode and the frequency decrease might be induced by the change of the cavity size. A theoretical calculation was made to estimate the cavity mode frequency. The calculated wave frequency before/after the negative impulse is 3.8/2.6 mHz, which is consistent with the observations.

Using the Cluster data during the period from January to April between 2001 and 2006, we find an observation of solar wind entry due to magnetic reconnection occurred in the terrestrial high-latitude magnetospheric lobes, tailward of the cusps under northward Interplanetary Magnetic Field (IMF). Occurrence rate of solar wind entry events in this study is of the same order as that for the Cluster orbital interval from August to October between the years of 2002 and 2004 as reported by Shi et al [2013]. In this paper, we further study the role of the IMF Bx and By components in the control of solar wind plasmas entry based on the investigations of different magnetic dipole tilt variations between our database and Shi et al. [2013]. This study shows that the asymmetry distribution of solar wind entry events in the northern and southern lobes could be caused by the variation of magnetic dipole tilt, which could influence the locations of the reconnection site on the high latitude lobe magnetopause. On the other hand, IMF Bx can also affect the solar wind plasma entry rate, which is also consistent with previous results. Therefore, we conclude that the “north-south asymmetry” of solar wind entry events in the lobes could be the combined result of magnetic dipole tilt and IMF Bx. In addition, the IMF By component can influence the entry events in conjunction with the variation of IMF Bx component, which is in line with the Parker Spiral of the IMF.

A transpolar arc (TPA), which extended from postmidnight to prenoon, was seen on 16 September 2001 in the Northern Hemisphere under northward interplanetary magnetic field (IMF)-Bz and weakly dawnward IMF-By conditions. Super Dual Auroral Radar Network detected significant westward plasma flows just equatorward of the poleward edge of the midnight sector auroral oval. These plasma flows were confined to closed field lines and are identified as the ionospheric plasma flow signature of tail reconnection during IMF northward nonsubstorm intervals (TRINNIs). These TRINNI flows persisted for 53 min from prior to the TPA appearance to the cessation of TPA growth. They are usually observed before (and during) intervals when TPAs are present, but in this case, subsided after the TPA was completely connected to the dayside. Additional slower flows across the open/closed polar cap boundary were seen at the TPA onset time in the same magnetic local time sector as the nightside end of the TPA. These ionospheric flows suggest that magnetotail reconnection significantly contributed to the TPA formation, as proposed by Milan et al. (, https://doi.org/10.1029/2004JA010835). We propose a possible scenario for an absence of the TRINNI flows during the TPA brightening by considering the relation between the extent of the magnetotail reconnection line mapped onto nightside auroral oval and the TPA width; TRINNI flows would subside when the extent of X-line is comparable to the TPA width. Therefore, our results suggest that the fate (absence or presence) of TRINNI flows on closed field lines during the TPA formation would be closely related with magnetotail reconnection extent.

The conventional Grad-Shafranov (GS) method is designed to reconstruct a two-dimensional magnetohydrostatic structure with isotropic pressure. In this work, we developed a new GS solver (GS-like) t ...

Based on multi-satellite and ground observations, we investigated an influence of long-lasting and gradual enhancements of magnetic flux transport rate on the magnetotail fast flow duration. On March 10th, 2009, THEMIS-B, which was located in the central plasma sheet of middle distant magnetotail (XGSM ~−25.8 RE), observed the fast flows with the velocity exceeding 300 km/s, lasting over 3 h for intense southward Interplanetary Magnetic Field (IMF) period. During long-lasting fast flows, AL index variations were very extensive and their recovery was much slow. Pi 2 waves were observed at the ground observatories around the THEMIS׳s footpoints and at low-/mid-latitudes. The aspect for these AL variations suggests Steady Magnetospheric Convection (SMC), but clear substorm signatures were also observed. Further magnetic dipolarization was detected by THEMIS-A at XGSM ~−8.2 RE and its nearby THEMIS-E. Only THEMIS-A observed the associated energetic electron flux enhancements. Therefore, the fast flows occurred during substorm with energetic particle injections at “imitative” SMC, which would be driven by prolonged intense southward IMF. The cumulative transport rates of magnetic and Poynting fluxes consecutively and gradually enhanced. On the other hand, THEMIS-C detected much shorter fast flows with the duration of 37 min at XGSM ~−18.1 RE and weak/gradual substorm-associated dipolarization. However, the cumulative magnetic flux transport rate was enhanced only during the fast flow interval and was saturated after the fast flows. From different magnetic transport rate profiles at THEMIS-B and THEMIS-C, the realms of dipolar-configured field lines expanded to near THEMIS-C׳s position responsible for long-lasting fast flow-associated consecutive and gradual magnetic flux pileup. Because the resultant “high-speed flow braking” region was retreated into a few RE tailward direction, long-lasting fast flows were almost stemmed. These results suggest that the cumulative magnetic flux transport rate is one of the important factors to determine “fate” (duration) of the magnetotail fast flows.

Detailed features of the near-Moon pickup ions under different interplanetary magnetic field (IMF) conditions are investigated using data obtained from the solar wind ion detector (SWID-B) onboard Chang'E-1. In the event studied, Chang'E-1 was on a noon-midnight meridian orbit and the field-of-view of the SWID-B was in the satellite orbital plane. The observations show that the pickup energy detected depends not only on where these particles are detected but also on their incident angles. As the spacecraft moved into the wake from the South Pole along the midnight meridian, wider incident angle distributions were measured. When IMF B-x was significant, the pickup ions had a strong velocity component parallel to the magnetic field, and the efficiency of acceleration was reduced when the IMF B-y decreased. The back tracking calculations show that the possible source of the pickup ions is solar wind ions scattered/reflected on the lunar surface in a wide area over the dayside of the Moon, from both magnetic and nonmagnetic anomaly regions. A three dimensional analysis performed on the asymmetric properties of the pick-up ions can explain most of the particle behavior observed near the Moon under different IMF conditions. (C) 2013 Elsevier Ltd. All rights reserved.

The relationship between the orientation of the interplanetary magnetic field (IMF), represented by the clock angle which is the angle defined by IMF-B y and -B z components, and the AL and AU indices is examined at various dipole tilt angles for the period of 1978–1988. We use the IMF data obtained from the IMP 8 satellite, AL and AU indices with corrected seasonal variations, and the dipole tilt angle, which is the dipole magnetic latitude of the subsolar point calculated as a function of the day of year and universal time. For both positive (dipole tilted to the Sun) and negative dipole tilt angles, the values of | AL | and AU decrease as the IMF clock angle moves away from 180 ∘ , becoming more northward. The indices also tend to become smaller for larger dipole tilt angle, either toward or away from the Sun. This dependence on dipole tilt angle enhances the semiannual variation of geomagnetic activity.

An understanding of the transport of solar wind plasma into and throughout the terrestrial magnetosphere is crucial to space science and space weather. For non-active periods, there is little agreement on where and how plasma entry into the magnetosphere might occur. Moreover, behaviour in the high-latitude region behind the magnetospheric cusps, for example, the lobes, is poorly understood, partly because of lack of coverage by previous space missions. Here, using Cluster multi-spacecraft data, we report an unexpected discovery of regions of solar wind entry into the Earth's high-latitude magnetosphere tailward of the cusps. From statistical observational facts and simulation analysis we suggest that these regions are most likely produced by magnetic reconnection at the high-latitude magnetopause, although other processes, such as impulsive penetration, may not be ruled out entirely. We find that the degree of entry can be significant for solar wind transport into the magnetosphere during such quiet times.

[1] This paper presents THEMIS measurements of two substorm events to show how the substorm current wedge (SCW) is generated. In the late growth phase when an earthward flow burst in the near-Earth magnetotail brakes and is diverted azimuthally, pressure gradients in the X- and Y-directions are observed to increase in the pileup and diverting regions of the flow. The enhanced pressure gradient in the Y-direction is dawnward (duskward) on the dawnside (duskside) where a clockwise (counter-clockwise) vortex forms. This dawn-dusk pressure gradient drives downward (upward) field-aligned current (FAC) on the dawnside (duskside) of the flow, which, when combined with the FACs generated by the clockwise (counter-clockwise) vortex, forms the SCW. Substorm auroral onset occurs when the vortices appear, Near-Earth dipolarization onset is observed by the THEMIS spacecraft (probes) when a rapid jump in the Y-component of pressure gradient is detected. The total FACs from the vortex and the azimuthal pressure gradient are found to be comparable to the DP-1 current in a typical substorm.

[1] We examined the magnetospheric magnetic field and plasma responses to an encounter of a discontinuity in the Bx component of interplanetary magnetic field (IMF). The striking variations of simultaneous solar wind dynamic pressure and IMF-Bz were not observed. Furthermore, we found that this IMF-Bx discontinuity was a heliospheric current sheet, separating two high-speed solar wind streams with different velocity and magnetic polarity. In this study, the magnetic field and plasma data were obtained from Time History of Events and Macroscale Interactions during Substorms (THEMIS), Cluster, and GOES to investigate the magnetospheric responses, and those were taken from ACE and Geotail to monitor the solar wind conditions. Simultaneous geomagnetic field variations from the ground observatories and aurora activity from Polar were also examined. When the discontinuity encountered the magnetosphere, THEMIS-D, -E, and THEMIS-A observed abrupt and transient magnetic field and plasma variations in the dawnside near-Earth magnetotail and tail-flank magnetopause. Significant magnetic field perturbations were not observed by Cluster as located in the duskside magnetotail at this time interval. Although simultaneous dipolarization and negative bay variations with Pi2 waves were observed by GOES and the ground observatories, global auroral activities were not found. Around the dawnside tail-flank magnetopause, THEMIS-C and -A experienced the magnetopause crossings due to the magnetopause surface waves induced by Kelvin-Helmholtz instability. These results suggest that the magnetic field and plasma variations in the near-Earth magnetotail and tail-flank magnetopause were caused by moderate substorm-like phenomena and magnetopause surface waves. They also indicate that clear magnetospheric disturbances can be brought even without significant variations in the solar wind.

[1] The magnetopause is the boundary where the reduced solar wind dynamic pressure is equal to the magnetic pressure of the Earth's outer magnetosphere. With hundreds of magnetopause crossings identified from the THEMIS data, we estimate a ratio (f) of the compressed magnetic field just inside the subsolar magnetopause to the purely dipolar magnetic field. Previous theoretical studies reported that the ratio f was nearly independent of the subsolar standoff distance (r0). Here we report that the ratio f is linearly proportional to r0 for both northward and southward interplanetary magnetic field (IMF). The proportionality constant for southward IMF is larger than that for northward IMF, implying that the compression level of the magnetic field by inward magnetopause for southward IMF is smaller than that for northward IMF.

[1] With unique simultaneous observations both in the magnetosheath and magnetosphere by the THEMIS probes, Alfvenic variations in the plasma velocity are observed at the inner edge of low-latitude boundary layer (LLBL) and are induced by the mirror mode waves in the magnetosheath near the subsolar magnetopause on 31 July 2007. These Alfvenic variations appeared as the wavy perturbations in the V x and V y components observed by THEMIS C, D, and E, which had the same periodicity as associated magnetic field variations. Simultaneously, THEMIS B observed the mirror mode waves in the magnetosheath. The periodicities of the magnetic and plasma pressure variations of mirror modes in the magnetosheath were consistent with those of the Alfvenic wavy variations in the LLBL. Therefore, the mirror mode waves can induce the magnetopause undulations, launchingAlfven waves, and resultant Alfvenic variations are observed in the LLBL. Also, in the succeeding magnetosheath interval by THEMIS B, we examined whether the mirror mode waves occurred and associated Alfvenic variations were observed in the LLBL. However, no clear evidence for an existence of the mirror mode waves was obtained, and THEMIS C, D, and E do not also observe associated magnetic field and plasma Alfvenic responses in the LLBL. These results suggest that the Alfvenic variations in the LLBL are strongly related to the mirror mode waves in the magnetosheath. On the basis of these results, we emphasize that the magnetosheath energy is transmitted and transported into the magnetosphere via magnetopause surface waves.

This paper describes the ion properties within the subsolar magnetopause current layer (MPCL) under the northward and southward IMF. This study was based on the magnetic field and plasma data measured by the GEOTAIL spacecraft on November 10, 1995 and January 3, 1996. An interesting signature of a “collimated” ion distribution was found under the southward IMF. This can be interpreted as evidence that the ions originating from the magnetosheath were distributed along the open field lines formed by the magnetic reconnection on the MPCL. Under the northward IMF the low energy ions were found to be coexisting (or mixing) with energetic magnetospheric ions on the outer edge of the magnetosphere. This result indicates that the LLBL existed under the northward IMF.

On the basis of our recent studies (Sakurai, 1999a, 1999b and 2001) the present paper is intended to review oscillation and propagation characteristics of Pc 3 and Pc 5 ULF waves observed near the dayside magnetopause by the Geotail satellite. These characteristics are studied on the basis of the simultaneous observations of the magnetic and electric fields, and low energy plasmas measured with the excellent instruments on board the satellite. The study reveals that the dominant ULF waves observed near the dayside magnetopause are Pc 3 and Pc 5 oscillations. The Pc 3 oscillations appear with a peak power around noon at the frequency of 25 mHz in the azimuthal component of the magnetic field. This frequency component shows clear resonant oscillations. In addition fast mode earthward propagation is recognized. The Poynting flux of Pc 3 waves is about 1-10 nW/m2on average, the strongest being along the magnetic field-line. Pc 5 oscillations are also dominant, and are observed mainly in the dawn and dusk-side flanks. They appear as clear oscillations in the radial component of the electric field, suggesting that resonant oscillations along the magnetic field-line are well established. The Poynting flux of Pc 5 can be estimated as 10 - 100 nW/m2in both directions across and along the magnetic field-line. This result suggests that Pc 5 wave energy is carried into both the ionosphere and the inner magnetosphere during an hour with the energy of 1010- 1013J, which is one or two orders of magnitude less than the substorm energy. By taking into account the continuous activation of ULF waves in the outer magnetosphere, these waves should play an important role in the energetics of the magnetosphere.

The GEOTAIL satellite observed an interesting oscillation phenomenon of low energy plasma (LEP) in the dawnside outer magnetosphere. The oscillation was taking place with a frequency double that of the transverse oscillation of Pc 5 pulsations. The double-frequency oscillation appeared in the plasma density and temperature, clearly showing an out-of-phase relationship between them. However, this phenomenon is revealed to be an instrumental effect of the LEP detector, which has a low energy threshold of measuring an ion population at 32 eV/Q. The imbedded ion population is found to be composed of cold ions with an energy of less than the threshold. They are convected past the LEP detector by the Pc 5 wave and enter the detector energy window twice per wave period. Plasma bulk parameters calculated using the detected ions produce an oscillation that has a frequency exactly double that of the Pc 5 wave. However, it should be noted that this phenomenon is observed with a large amplitude electric field oscillation only in intervals when the satellite passes through the dawnside outer magnetosphere under very quiet magnetic conditions, i.e., periods of the northward interplanetary magnetic field.