Duskside Magnetosphere Research Articles

Mercury’s plasma environment after BepiColombo’s third flyby

Understanding Mercury’s magnetosphere is crucial for advancing our comprehension of how the solar wind interacts with the planetary magnetospheres. Despite previous missions, several gaps remain in our knowledge of Mercury’s plasma environment. Here, we present findings from BepiColombo’s third flyby, offering a synoptic view of the large scale structure and composition of Mercury’s magnetosphere. The Mass Spectrum Analyzer (MSA), Mass Ion Analyzer (MIA), and Mass Electron Analyzer (MEA) on the magnetospheric orbiter reveal insights, including the identification of trapped energetic hydrogen (H+) with energies around 20 keV e−1 evidencing a ring current, and a cold ion plasma with energies below 50 eV e−1. Additionally, we observe a Low-Latitude Boundary Layer (LLBL), which is a region of turbulent plasma at the edge of the magnetosphere, characterized by bursty ion enhancements, indicating an ongoing injection process in the duskside magnetosphere flank. These observations during cruise phase provide a tantalizing glimpse of future discoveries expected from the Mercury Plasma Particle Experiment (MPPE) instruments after orbit insertion, promising broader impacts on our understanding of planetary magnetospheres.

H+, He+, He++, O++, N+ EMIC Wave Occurrence and Its Dependence on Geomagnetic Conditions: Results From 7 Years of Van Allen Probes Observations

AbstractElectromagnetic ion cyclotron (EMIC) waves are believed to play an important role in the dynamics of the inner magnetosphere, including the ring current, the radiation belts and potentially, the cold plasma. In this work, we investigate their occurrence in the magnetosphere and the geomagnetic and solar wind conditions which lead to their excitation. We use an automated detection algorithm of EMIC waves observed by Van Allen Probes over the entire mission duration between 2012 and 2019. Consistent with earlier studies, we find that the H+ band occurrence maximizes in the dayside magnetosphere during enhancements of solar wind dynamic pressure. Both the H+ and He+ band are also generated along the duskside magnetosphere during disturbed geomagnetic conditions. In addition, to H+ and He+ bands commonly surveyed, we investigate the occurrence of H+ waves above and below 0.5 H+ gyrofrequency, as well as wave occurrence in the N+ and O++ bands. Most H+ waves are observed in the band below 0.5fH+. We find several events in the N+ band, indicative of their very low occurrence. The O++ band is observed during disturbed geomagnetic conditions and high solar wind dynamic pressure at low L‐shells. Its radial localization coincides with the O++ torus. This study provides a comprehensive picture of EMIC wave distribution and insight into ion composition in the inner magnetosphere during variable geomagnetic conditions.

THEMIS observations of compressional Pc5 pulsations in the dawn- and duskside magnetosphere

We present case and statistical studies of compressional Pc5 pulsations observed by the THEMIS spacecraft in the dawn- and duskside magnetosphere from 2007 to 2011. A case study provides evidence for compressional Pc5 pulsations in the dawnside magnetosphere following the arrival of particles injected by a substorm and the subsequent growth of the drift mirror instability on February 27, 2011. The statistical study shows that the Pc5 pulsations occur in a weak or moderately disturbed magnetosphere but rarely develop during strong magnetic activity (i. e., for Dst index below −25 nT). The most striking characteristic of the compressional Pc5 pulsations is their localization in latitude and longitude over many consecutive days. Dawnside Pc5 pulsations occur under quieter conditions, last longer, and attain greater amplitudes than duskside Pc5 pulsations. We attribute compressional pulsations in both sectors to the drift mirror instability, with a warmer, more energized, and gradient-curvature drifting population of substorm-injected ions on the duskside and a colder ExB drifting population of plasma sheet ions on the dawnside.

Structure of Pc 5 Compressional Waves Observed in the Duskside Outer Magnetosphere: MMS Observations

AbstractThe geometrical structure of the Pc 5 compressional wave is important in judging its generation mechanism and the wave‐particle interaction process. In this work, 117 magnetic troughs (where magnetic field strength transiently decreases) identified from 50 Pc 5 compressional wave events in the duskside (15.5–18.5 local time) magnetosphere are studied based on the Magnetospheric Multiscale (MMS) data. We derived the three dimensional geometry of the magnetic trough by including the normal and velocity information at its boundaries from the multi‐spacecraft analysis method. The magnetic trough has a magnetic bottle shape along the magnetic field line with the most probable center (with weakest magnetic field) located at θ = , while the widest part of the magnetic bottle located around θ (θ denotes the angle between spacecraft position vector and the ambient magnetic field). The cross section of the magnetic trough is eccentric and has a “wedge‐like” shape whose average open angle is ∼23° toward radial outward. It is found that the radial component of the current density is the dominant one at the boundaries, and the value is generally proportional to the depth of the magnetic trough. The generation of these Pc 5 compressional waves can be attributed to the drift Alfvén ballooning mirror instability. This work reveals the possible changes of magnetic field configuration caused by the Pc 5 compressional wave in the magnetosphere and may bring new ideas to the interaction way between wave field and ring current particles.

Magnetospheric response to the interaction with the sporadic solar wind diamagnetic structure

We report the results of a study on the movement of the solar wind diamagnetic structure (DS), which is a sequence of smaller-scale microDS being part of the May 18, 2013 coronal mass ejection, from a source on the Sun to Earth’s surface. DS determined from the high negative correlation coefficient (r=–0.9) between the IMF modulus (B) and the SW density (N) on the ACE and Wind satellites at the L1 point, on the THB and THC satellites (r=–0.9) in near-Earth orbit, and on the THA satellite inside the magnetosphere is carried by the solar wind from the Sun to Earth’s orbit, while maintaining its fine internal structure. Having a large size in the radial direction (≈763 Rᴇ, where Rᴇ is the Earth radius), DS flows around the magnetosphere. At the same time, microDS of size ≤13 Rᴇ passes through the bow shock and magnetopause as a magnetized plasmoid in which the ion concentration increases from 10 cm⁻³ to 90 cm⁻³, and the velocity decreases as it moves toward the magnetotail. When a microDS passes through the magnetopause, a pulsed electric field of ~400 mV/m is generated with subsequent oscillations with a period of T~200 s and an amplitude of ~50 mV/m. The electric field accelerates charged particles of the radiation belt and produces modulated fluxes of protons in an energy range 95–575 keV on the day side and electrons in 40–475 keV and protons in 95–575 keV on the night side. In the duskside magnetosphere (19–23 MLT), the substorm activation is observed in geomagnetic pulsations and auroras, but without a magnetic negative bay. In the post-midnight sector (01–05 MLT), a sawtooth substorm occurs without the growth phase and breakup with deep modulation of the ionospheric current and auroral absorption. The duration of all phenomena in the magnetosphere and on Earth is determined by the period of interaction between DS and the magnetosphere (~4 hrs). To interpret the regularities of the magnetospheric response to the interaction with DS, we consider alternative models of the impulsive passage of DS from SW to the magnetosphere and the classical model of reconnection of IMF and the geomagnetic field.

Магнитосферный отклик на взаимодействие с диамагнитной структурой спорадического солнечного ветра

We report the results of a study on the movement of the solar wind diamagnetic structure (DS), which is a sequence of smaller-scale microDS being part of the May 18, 2013 coronal mass ejection, from a source on the Sun to Earth’s surface. DS determined from the high negative correlation coefficient (r=–0.9) between the IMF modulus (B) and the SW density (N) on the ACE and Wind satellites at the L1 point, on the THB and THC satellites (r=–0.9) in near-Earth orbit, and on the THA satellite inside the magnetosphere is carried by the solar wind from the Sun to Earth’s orbit, while maintaining its fine internal structure. Having a large size in the radial direction (≈763 Rᴇ, where Rᴇ is the Earth radius), DS flows around the magnetosphere. At the same time, microDS of size ≤13 Rᴇ passes through the bow shock and magnetopause as a magnetized plasmoid in which the ion concentration increases from 10 cm⁻³ to 90 cm⁻³, and the velocity decreases as it moves toward the magnetotail. When a microDS passes through the magnetopause, a pulsed electric field of ~400 mV/m is generated with subsequent oscillations with a period of T~200 s and an amplitude of ~50 mV/m. The electric field accelerates charged particles of the radiation belt and produces modulated fluxes of protons in an energy range 95–575 keV on the day side and electrons in 40–475 keV and protons in 95–575 keV on the night side. In the duskside magnetosphere (19–23 MLT), the substorm activation is observed in geomagnetic pulsations and auroras, but without a magnetic negative bay. In the post-midnight sector (01–05 MLT), a sawtooth substorm occurs without the growth phase and breakup with deep modulation of the ionospheric current and auroral absorption. The duration of all phenomena in the magnetosphere and on Earth is determined by the period of interaction between DS and the magnetosphere (~4 hrs). To interpret the regularities of the magnetospheric response to the interaction with DS, we consider alternative models of the impulsive passage of DS from SW to the magnetosphere and the classical model of reconnection of IMF and the geomagnetic field.

Statistical study of non-adiabatic energization and transport in Kelvin-Helmholtz vortices at mercury

Non-adiabatic energization and transport of planetary ions in the vicinity of Kelvin-Helmholtz (KH) vortices at Mercury are statistically investigated using a magnetohydrodynamic model combined with a test particle tracing technique. The measurements from the MErcury Surface, Space ENvironment, Geochemistry, and Ranging spacecraft show signatures of KH waves in the magnetospheric flanks, especially on the duskside. We examine here the energization and transport of heavy ions of planetary origin such as Na+ associated with the growth of the KH instability on both the dawn and dusk sides of the magnetosphere, and for both northward and southward interplanetary magnetic field configurations. We find that in all cases those planetary ions in the magnetosphere can be accelerated non-adiabatically with a level of acceleration larger on the dawnside. The transport of those ions is controlled by the convection electric field in the magnetosheath. Those planetary ions when picked up in the duskside magnetosphere where the KH waves have been mainly observed at Mercury stagnate inside the magnetosphere and, hence, are not expected to escape. The present study indicates that these ions may likely stay inside the magnetosphere and sputter the planetary surface on the duskside preferentially, being the source of secondary neutrals from the planetary surface.

Low‐Energy (<200 eV) Electron Acceleration by ULF Waves in the Plasmaspheric Boundary Layer: Van Allen Probes Observation

AbstractWe report observational evidence of cold plasmaspheric electron (<200 eV) acceleration by ultralow frequency (ULF) waves in the plasmaspheric boundary layer on 10 September 2015. Strongly enhanced cold electron fluxes in the energy spectrogram were observed along with second harmonic mode waves with a period of about 1 min which lasted several hours during two consecutive Van Allen Probe B orbits. Cold electron (<200 eV) and energetic proton (10–20 keV) bidirectional pitch angle signatures observed during the event are suggestive of the drift‐bounce resonance mechanism. The correlation between enhanced energy fluxes and ULF waves leads to the conclusions that plasmaspheric dynamics is strongly affected by ULF waves. Van Allen Probe A and B, GOES 13, GOES 15, and MMS 1 observations suggest that ULF waves in the event were strongest on the duskside magnetosphere. Measurements from MMS 1 contain no evidence of an external wave source during the period when ULF waves and injected energetic protons with a bump‐on‐tail distribution were detected by Van Allen Probe B. This suggests that the observed ULF waves were probably excited by a localized drift‐bounce resonant instability, with the free energy supplied by substorm‐injected energetic protons. The observations by Van Allen Probe B suggest that energy transfer between particle species in different energy ranges can take place through the action of ULF waves, demonstrating the important role of these waves in the dynamical processes of the inner magnetosphere.

Electron dropout echoes induced by interplanetary shock: A statistical study

Abstract“Electron dropout echo” as indicated by repeated moderate dropout and recovery signatures of the flux of energetic electron in the outer radiation belt region has been investigated systematically. The electron moderate dropout and its echoes are usually found for higher‐energy (>300 keV) channel fluxes, whereas the flux enhancements are obvious for lower energy electrons simultaneously after the interplanetary shock arrives at the Earth's geosynchronous orbit. The electron dropout echo events are found to be usually associated with the interplanetary shocks arrival. The 104 dropout echo events have been found from 215 interplanetary shock events from 1998 to 2007 based on the Los Alamos National Laboratory satellite data. In analogy to substorm injections, these 104 events could be naturally divided into two categories: dispersionless (49 events) or dispersive (55 events) according to the energy dispersion of the initial dropout. It is found that locations of dispersionless events are distributed mainly in the duskside magnetosphere. Further, the obtained locations derived from dispersive events with the time‐of‐flight technique of the initial dropout regions are mainly located at the duskside as well. Statistical studies have shown that the effect of shock normal, interplanetary magnetic field Bz and solar wind dynamic pressure may be insignificant to these electron dropout events. We suggest that the ∼1 min electric field impulse induced by the interplanetary shock produces a more pronounced inward migration of electrons at the duskside, resulting in the observed duskside moderate dropout of electron flux and its consequent echoes.

Asymmetric magnetospheric compressions and expansions in response to impact of inclined interplanetary shock

AbstractWe use global MHD simulations to model the magnetospheric response to an inclined shock that first strikes the duskside magnetosphere. The simulations predict several phenomena related specifically to the inclined shocks. The magnetospheric compression on the duskside exceeds that on the dawnside, and the geocentric distance to the dusk magnetopause varies in a simple step‐like form. The compression on the dawnside is preceded and followed by expansions. For a moderately strong shock, the expansion magnitude reaches severalREbehind the terminator plane. The magnetopause and cross‐tail currents in the magnetotail are significantly deformed during and after the shock passage. The position of the magnetotail magnetopause moves by more than 10 RE. This asymmetric magnetopause deformation is mainly related to a strong |Vy| downstream from the inclined shock. The magnetospheric expansion results in a decrease in the horizontal magnetic field at low‐latitude stations, as confirmed by observations.

The large-scale energetic ion layer in the high latitude Jovian magnetosphere as revealed by ULYSSES/HI-SCALE cross-field intensity-gradient measurements

ULYSSES investigated the high latitude Jovian magnetosphere for a second time, after Pioneer 11 mission, and gave us the opportunity to search the structure and the dynamics of this giant magnetosphere above the magnetodisc. Kivelson and Williams (1976) and Kennel and Coroniti (1979) reported that Pioneer 11 observed energetic particle intensities at high latitudes at the same level with those measured in the plasma sheet and inferred that they were not consistent with the magnetodisc model. ULYSSES observations supported the idea about a large-scale layer of energetic ions and electrons in the outer high latitude Jovian magnetosphere (Cowley et al., 1996; Anagnostopoulos et al., 2001a). This study performs a number of further tests for the existence of the large scale layer of energetic ions in the outer high latitude Jovian magnetosphere by studying appropriate cross-B field anisotropies in order to monitor the ion northward/southward intensity gradients. In particular, we examined ULYSSES/HI-SCALE observations of energetic ions with large gyro-radius (0.5–1.6MeV protons and>2.5MeV heavy (Z>5) ions) in order to compare instant intensity changes with remote sensing intensity gradients. Our analysis confirms the existence of an energetic particle layer in the north hemisphere, during the inbound trajectory of ULYSSES traveling at moderate latitudes, and in the south high-latitude duskside magnetosphere, during the outbound segment of the spacecraft trajectory. Our ULYSSES/HI-SCALE data analysis also provides evidence for the detection of an energetic proton magnetopause boundary layer during the outbound trajectory of the spacecraft. During ULYSSES flyby of Jupiter the almost permanent appearance of alternative northward and southward intensity gradients suggests that the high latitude layer appeared to be a third major area of energetic particles, which coexisted with the radiation belts and the magnetodisc.

Magnetopause reconnection across wide local time

Abstract. During April to July 2007 a combination of 10 spacecraft provided simultaneous monitoring of the dayside magnetopause across a wide range of local times. The array of four Cluster spacecraft, separated at large distances (10 000 km), were traversing the dawn-side magnetopause at high and low latitudes; the five THEMIS spacecraft were often in a 4 + 1 grouped configuration, traversing the low latitude, dusk-side magnetosphere, and the Double star, TC-1 spacecraft was in an equatorial orbit between the local times of the THEMIS and Cluster orbits. We show here a number of near simultaneous conjunctions of all 10 spacecraft at the magnetopause. One conjunction identifies an extended magnetic reconnection X-line, tilted in the low latitude, sub-solar region, which exists together with active anti-parallel reconnection sites extending to locations on the dawn-side flank. Oppositely moving FTE's are observed on all spacecraft, consistent with the initially strong IMF By conditions and the comparative locations of the spacecraft both dusk-ward and dawn-ward of noon. Comparison with other conjunctions of magnetopause crossings, which are also distributed over wide local times, supports the result that reconnection activity may occur at many sites simultaneously across the sub-solar and flank magnetopause, but linked to the large scale (extended) configuration of the merging line; broadly depending on IMF orientation. The occurrence of MR therefore inherently follows a "component" driven scenario irrespective of the guide field conditions. Some conjunctions allow the global magnetopause response to IMF changes to be observed and the distribution of spacecraft can directly confirm its shape, motion and deformation at local noon, dawn and dusk-side, simultaneously.

THEMIS observations of duskside compressional Pc5 waves

The five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft offer new possibilities to analyze ULF waves in the magnetosphere by means of multipoint measurements. During the coast phase, THEMIS observed many compressional oscillations with periods in the Pc5 range and longer. The observed events occur inside a well‐defined spatial domain in the outer equatorial duskside magnetosphere. We analyze these waves using the unique string‐of‐pearls configuration of the THEMIS constellation to evaluate their phase speed and propagation direction. We find that the waves are propagating sunward (westward) and radially outward, orthogonal to the mean magnetic field, with phase speeds around 30 km/s and higher in the spacecraft frame. In the plasma frame the propagation direction is still sunward, with lower speeds (up to 30 km/s for most events). The oscillations exhibit a strong anticorrelation between the magnetic field and the plasma density. On the basis of this, as well as their low propagation speed, orthogonal to the mean magnetic field propagation direction and almost parallel to the magnetic field maximum variance direction, we conclude that the most likely source of these waves is the drift mirror instability.

Surveys on magnetospheric plasmas based on the Double Star Project (DSP) exploration

The equatorial and polar satellites of the Double Star Project (DSP) were launched successfully on December 29, 2003 and July 25, 2004, respectively, and both of them are operating smoothly. The DSP provides a good opportunity for investigating the structure of the magnetosphere. Based on the DSP data collected during 2004, we have surveyed the distribution of the magnetic fields and plasmas in the magnetosphere. It is found that: (1) Near the Earth’s equatorial plane within geocentric distances of less than 7 RE, the Earth’s magnetic field is dipolar. In the vicinity of the magnetopause, the magnetic field is enhanced by a factor of about 1.5, and on the nightside, the magnetic field can vary significantly from the Earth’s dipole field, likely caused by the presence of the near-Earth tail current sheet. (2) In the day-side magnetosheath, the electron and ion densities are usually both in the range of 10–30 cm−3; the ion and electron temperatures are usually about 200 and 50 eV, respectively. The flow pattern is usually smooth, with a low velocity in the subsolar region and with significantly higher velocities in the dawn and dusk flanks. (3) In the region between the magnetopause and plasmasphere the density is low, approximately 0.5–5 cm−3, and the temperature is high, about 1–10 keV for ions and 0.1–5 keV for electrons. The ion temperature has an apparent anisotropy, with the ratio of the perpendicular and parallel temperatures being about 1.0–1.3 for the night-and dusk-side magnetosphere and about 1.3–2.0 for the day-and dawn-side magnetosphere. There is an evident sunward convection of about 50 km/s in the magnetosphere. On the dawn side, the flow becomes somewhat turbulent, and in the vicinity of the night-noon meridian plane, the convection is rather slow. (4) The high-energy electrons with energies higher than 2 MeV are mainly located in the regions with 3 < L < 4.5; the size of the high-energy electrons area varies with time, it may expand and shrink occasionally according to different solar wind conditions and magnetic activities.

Duskside auroral undulations observed by IMAGE and their possible association with large‐scale structures on the inner edge of the electron plasma sheet

On February 6, 2002 large‐scale undulations along the equatorward edge of the afternoon/dusk auroral oval were observed with the IMAGE FUV/Wideband Imaging Camera (WIC) during the late expansion/recovery phase of a substorm. The undulations are similar to others previously reported, but occur at higher than usual latitudes and map to the outer duskside magnetosphere, 1 to 2 RE beyond a plasmaspheric drainage plume. The mapping suggests that the undulations result from large‐scale fluctuations on the inner edge of the electron plasma sheet. 2.5‐D simulations using representative plasma parameters for this region indicate that such large‐scale coherent structures can be created by a kinetic drift wave driven by the ion pressure gradient in the destabilizing curvature and grad B drift of the plasma sheet ions.

Magnetosheath waves under very low solar wind dynamic pressure: Wind/Geotail observations

Abstract. The expanded bow shock on and around "the day the solar wind almost disappeared" (11 May 1999) allowed the Geotail spacecraft to make a practically uninterrupted 54-h-long magnetosheath pass near dusk (16:30-21:11 magnetic local time) at a radial distance of 24 to 30 RE (Earth radii). During most of this period, interplanetary parameters varied gradually and in such a way as to give rise to two extreme magnetosheath structures, one dominated by magnetohydrodynamic (MHD) effects and the other by gas dynamic effects. We focus attention on unusual features of electromagnetic ion wave activity in the former magnetosheath state, and compare these features with those in the latter. Magnetic fluctuations in the gas dynamic magnetosheath were dominated by compressional mirror mode waves, and left- and right-hand polarized electromagnetic ion cyclotron (EIC) waves transverse to the background field. In contrast, the MHD magnetosheath, lasting for over one day, was devoid of mirror oscillations and permeated instead by EIC waves of weak intensity. The weak wave intensity is related to the prevailing low solar wind dynamic pressures. Left-hand polarized EIC waves were replaced by bursts of right-hand polarized waves, which remained for many hours the only ion wave activity present. This activity occurred when the magnetosheath proton temperature anisotropy (= ) became negative. This was because the weakened bow shock exposed the magnetosheath directly to the (negative) temperature anisotropy of the solar wind. Unlike the normal case studied in the literature, these right-hand waves were not by-products of left-hand polarized waves but derived their energy source directly from the magnetosheath temperature anisotropy. Brief entries into the low latitude boundary layer (LLBL) and duskside magnetosphere occurred under such inflated conditions that the magnetospheric magnetic pressure was insufficient to maintain pressure balance. In these crossings, the inner edge of the LLBL was flowing sunward. The study extends our knowledge of magnetosheath ion wave properties to the very low solar wind dynamic pressure regime.

Cluster observes the Earth’s magnetopause: coordinated four-point magnetic field measurements

Abstract. The four-spacecraft Cluster mission has provided high-time resolution measurements of the magnetic field from closely maintained separation distances (200–600 km). Four-point coverage of the Earth’s magnetopause began on the 9 and 10 November 2000 when all spacecraft first exited the dusk-side magnetosphere at about 19:00 LT, providing extensive coverage of the near flank magnetosheath and magnetopause boundary layer on re-entry to the magnetosphere. The traversals on this occasion were caused by the arrival of an intense CME at the Earth, which produced a large compression of the magnetopause and high magnetic activity. The magnetopause traversals represent an unprecedented data set, allowing detailed analysis of the local magnetic structure (gradients) and dynamics of the magnetopause boundary. By performing minimum variance analysis (MVA) on the magnetic field data from all four spacecraft, we demonstrate that the magnetopause was planar on the scale of the spacecraft separation scales and that the transverse scale size of the magnetopause boundary layer was 1000–1100 km. We also show that the motion of the boundary (defined by the magnetic shear at the current layer), is changing over the sequence of spacecraft crossings so that acceleration of the magnetopause can be very high in this region of the magnetosphere. Indeed, the magnetopause speed reaches the order of 300 km/s in response to the arrival of the interplanetary shock. Using MVA coordinates, we have identified a number of magnetospheric and magnetosheath FTE signatures, which are sampled simultaneously by all spacecraft at different distances from and on either side of the magnetopause. The signatures show a variation of scale with distance from the boundary.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers) Space plasma physics (discontinuities; magnetic reconnection)

Large-scale energetic particle layers in the high latitude Jovian magnetosphere

This study presents an analysis of long lasting (∼2– 3 h ) energetic (≳60 keV) ion and (≳40 keV) electron events observed by the HISCALE instrumentation on board Ulysses in the high latitude Jovian magnetosphere. The high latitude events in the prenoon dayside (d 36–38, 1992) and the south duskside (d 40–43, 1992) magnetosphere are different from the magnetodisk plasma sheet events; they are characterized by: (a) a rigidity dependent flux dispersion, (b) softening of the spectrum of energetic ions and electrons at flux minima (and of low energy ions at flux maxima) and (c) proximity of the spacecraft to the high latitude magnetopause. The spectral index peaks which correspond to the high latitude particle events show a ∼10 h (or ∼5 h ) periodicity and a phase shift of ∼7 h between the inbound and the outbound measurements. The HISCALE data are consistent with the existence of large scale layers of energetic ions and electrons in the high latitude Jovian magnetosphere. The proposed concept of the high latitude magnetospheric large scale energetic particle layers provide us with the possibility of a new synthesis of a variety of Jovian observations.

Periodic variations of magnetosheath energetic electron flux associated with global Pc5 pulsations

Measurements from the Wind spacecraft in the solar wind, the Geotail spacecraft in the magnetosheath, and multiple magnetometers on the ground are combined to study a unique electron flux modulation event in the magnetosheath that occurred during an interval of global Pc5 waves. The electron event is characterized by a Pc5‐band oscillation occurring in the magnetic‐field‐aligned component of the electron flux (energy &gt; 38 keV) while the local magnetic field and plasma density remained unperturbed. During this event the whole magnetosphere oscillated as inferred from magnetic field recorded at the CANOPUS, IMAGE, and 210° MM chains. At the ground stations that are mapped to the dayside and duskside magnetosphere, we find a one‐to‐one correspondence of the peaks in the horizontal component to those in the electron flux. At the stations mapped to the dawnside magnetosphere the observed frequency is twice that of the electron flux oscillation. The time‐lagged solar wind density and velocity at Wind were constant, which leads us to exclude the possibility that the waves were driven by ram pressure variations upstream of the bow shock. The Kelvin‐Helmholtz (K‐H) instability on the magnetopause is the more probable source of the Pc5 waves because (1) the solar wind velocity was ∼730 km s−1, well above the average value; (2) the ground‐based observations show that the Pc5 amplitude decreases with distance from the magnetopause; and (3) the dawnside and duskside magnetospheric flanks show oppositely polarized waves. The electron flux oscillation in the magnetosheath can be explained by intermittent magnetic connection between the spacecraft and the dawnside pulsating magnetopause. The ∼60 keV protons are continuously streaming throughout the whole interval, providing evidence for a continuously active source and permanent leakage through a tangential magnetopause discontinuity. It is worth noticing that at progressively higher energies the energetic particle angular distributions are gradually more isotropic because at higher energies the particles are strongly scattered in the magnetosheath.

Bulk flows of hot plasma in the Jovian magnetosphere: A model of anisotropic fluxes of energetic ions

Since the Ulysses flyby of Jupiter in February 1992, a consistent picture of the bulk flows of hot plasma has yet to be formed. The present study reports a comprehensive analysis of energetic particle anisotropies from the Ulysses mission. We present an empirical model which separates flow from gradient anisotropies. The model employs a multidimensional minimization routine to fit simultaneously 13 free parameters using 98 measurements. The large number of independent measurements is possible because the Ulysses Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energy (HI‐SCALE) has nearly full angular coverage at high time resolution and moderately high angular resolution. The model uses the full energy range (∼50–3000 keV) of the low‐energy magnetic spectrometers and also the pure proton channels of the composition aperture on the instrument. We present flow results during the inbound pass of Ulysses in which the radial velocity component shows a persistent radial outflow. The azimuthal component is in the sense of planetary rotation but generally below rigid corotation, and the azimuthal velocity is greater near the plasma current sheet than at higher magnetic latitudes. Outbound, the flows in the high‐latitude duskside magnetosphere inferred from the particle anisotropies indicate, surprisingly, sunward flows opposite to planetary rotation. We find evidence of gradient anisotropies especially near the magnetospheric current sheet on the dayside. We present a picture of the global magnetic field configuration and flows of hot plasma, consistent with our model results, dominated by subcorotation at low latitudes but by sunward flow at high latitudes.