Jovian Electrons Research Articles

Solar wind control of Jovian electron flux: Pioneer 11 analysis

The relations between Jovian electron flux and the solar wind were investigated using energetic particle and solar wind parameter data from Pioneer 11. The cross‐correlation study disclosed that the flux change of Jovian electrons observed in interplanetary space showed an anti‐correlation with the solar wind variation, suggesting that the release of Jovian electrons was controlled by the solar wind at the Jovian magnetosphere. It was also confirmed from simulation models that the modulation of the electron flux in interplanetary space was the result of both the above “source modulation” by the solar wind in the outer magnetosphere of Jupiter and the “barrier effect” induced by the co‐rotating interaction region (CIR) in the solar wind.

Self-consistent model of clock event in outer Jovian electron radiation belts

The work considers nonlinear nonstationary processes in the outer Jupiter electron radiation belts, which are alternating stages of accumulation of particles and their precipitation in the ionosphere during a whistler radiation pulse. The cyclotron instability dynamics of the plasma magnetospheric maser are described by the relativistic system of quasilinear equations. This system takes into account the diffusion of particles in adiabatic invariant space, synchrotron losses and electromagnetic radiation evolution. Analysis shows the importance of the effect of global resonance, i.e. the eigenfrequencies of oscillations of the radiation belt parameters are practically independent of the magnetic shell and coincide with the planet's angular rotation velocity. Considerations show that it is the 10 h dynamics of outer Jovian electron radiation belts that provide the coefficient of particle radial diffusion, which is necessary for global resonance. In this sense, the outer Jovian radiation belts work like a pump accumulating energetic electrons from the periphery of the magnetosphere.

Jovian electron propagation in three dimensions of the heliosphere: The Ulysses Investigations

We report investigations of Jovian relativistic electrons in the interplanetary medium that provide new insights into both the physical processes by which the Jovian magnetosphere releases its trapped, relativistic electrons into the interplanetary medium, and the modes of their interplanetary propagation. These studies were dependent on the unique postencounter trajectory for Ulysses. The spacecraft remained close to the radial distance of Jupiter (∼5.2 AU) and moved southward on the duskside by only ∼12° in heliographic latitude and <8° in heliographic azimuth relative to Jupiter for the period of ∼100° days of this study. During this period the nominal Parker spiral interplanetary magnetic field with its alternating polarities sector structure established direct magnetic field line connections frequently between Jupiter and the spacecraft. These unique conditions made it possible to investigate in detail, for approximately four solar rotations, both the Jovian electron burst phenomenon and the continuous, diffusive interplanetary propagation of Jovian electrons. The Jovian electron burst phenomenon in the energy range 1‐20 MeV, with flux increasing up to 50 times the diffusive Jovian electron flux are now discovered to occur in both multiples of the planetary rotation period (∼10 hours) and occasionally in half rotation periods, namely, in sequences of 5‐, 10‐, 20‐, or 40‐hour intervals. Electrons in the burst are shown to stream from the magnetosphere and not the magnetotail to the spacecraft during times when the interplanetary magnetic field vector direction includes both Jupiter and the spacecraft. Over 90% of all electron bursts lasting ≥6 hours occurred during the positive magnetic field sector. The few bursts occurring in a negative sector (<10%) were associated with rapid changes in magnetic field orientation near a sector boundary. We found that the time for these burst sequences corresponded to either the dawnside or the duskside tilt of the magnetic dipole. This dawn‐dusk dipole tilt is in a plane approximately orthogonal to the Sun‐Jupiter line and aligned with the average interplanetary magnetic field direction at ∼5 AU. To interpret these measurements, we assumed that the release mechanism is intermittent reconnection of the interplanetary magnetic field with the opposite polarity of a component of the polar magnetospheric field. These experimental results appeared to exclude some models for electron release such as the magnetic anomaly model where the electrons are released into the magnetotail. The diffusive Jovian electron flux continuously present in the interplanetary medium confirmed the “10‐hour clock” variations of the differential energy spectral index found by Pioneer 10 in 1973. Present evidence indicates that this continuum of Jovian electrons with its 10‐hour rocking spectrum may be associated with the same release mechanism as the electron bursts.

Electron distributions in the inner Jovian magnetosphere: Voyager 1 observations

Using several improvements in the analysis of the observations of the Low Energy Charged Particle (LECP) experiment on Voyager 1, electron phase space densities in the inner Jovian magnetosphere (5‐10 RJ) were first calculated at constant first and second invariants (represented by µ and K, respectively), based on the LECP measurements. The calculated electron phase space density profiles show that in the inner Jovian magnetosphere there exist evident time and longitude variations, energetic electron injections, and present radial transport and distributed losses. To study the radial and pitch angle diffusions of Jovian electrons, we have calculated the phase space densities in the K‐L space. It is found that the electron population in the inner Jovian magnetosphere seems to consist of two components: electrons radially diffusing from a main external source and electrons generated from local sources. The radially diffusing electrons have a relatively time stationary and isotropic distribution, while the locally created electrons mainly concentrate around the equatorial plane and have relatively lower energies, in comparison with the inward diffusing electrons. Consequently, the sources of precipitation losses to the ionosphere must be primarily electrons transported from outer sources, and the major precipitations occur in the inner magnetosphere (L < 7.5 RJ). In the inner Jovian magnetosphere (L = 5 ∼ 10 RJ) it is estimated that for electrons with magnetic moment µ = 300 MeV/G, the diffusion coefficient D is roughly 10−8 ∼ 10−6 RJ2 s−1, and the lifetime against the diffusion losses is of the order of 104 ∼ 106 s.

Relativistic electron flux anisotropies in the duskside Jovian magnetosphere: a test for source location and escape mechanism

Results of anisotropy analyses of >∼ 3 MeV electron flux data obtained by the high-energy telescope of the COSPIN experiment on Ulysses are presented for the period from day 40 to day 45 of 1992, when the spacecraft was outbound from Jupiter in the duskside high-latitude magnetosphere and magnetosheath. At small L-shells or minimum magnetic latitudes near the planet, the electron pitch-angle distributions are peaked at α = 90° and have net inward flows to the South Pole of the magnetic dipole. A majority of the high-latitude magnetosphere regions are dominated by electrons with field-aligned bidirectional distributions. The electron flows are essentially directed outward from the southern polar region, but inward electron flows which come from the northern polar region have also been detected, particularly near the magnetospheric boundary. The pattern of electron angular distributions in the magnetosphere is compatible with Nishida's model for recirculation of magnetospheric energetic particles by diffusion at low altitudes. Mechanisms for electron acceleration in the magnetosphere are discussed on the basis of our new observations. In the magnetosheath, alternating field-aligned electron flows are present. The observations suggest that electrons escape from the magnetosphere to the interplanetary space through diffusion across closed magnetic field lines on the boundary. It is found that at least a significant fraction of the interplanetary Jovian electrons (>∼ 10 26s −1) may escape the magnetosphere in this way.

Propagation of jovian electrons in and out of the ecliptic

Since its switch-on in Oct. 90, the Kiel Electron Telescope onboard Ulysses has detected many quiet time increases of the flux of 3–30 MeV electrons, known to originate from Jupiter. We report on the long term variations of this flux for the Ulysses ecliptic journey, and at the beginning of the out of ecliptic phase. They are well accounted for by a simple convection-diffusion model, with diffusion coefficients along and perpendicular to the magnetic field of ∼ 5.1022 and 8.1020 cm2s−1 respectively. In addition to the long term flux variations, several short bursts of electrons were detected, particularly after the Jupiter fly-by at southern latitudes. Their duration is about 1 hour or less, and they show a very strong anisotropy in the general direction of Jupiter. They are more numerous and are found at larger distances after encounter (23 of them, up to 0.86 AU from Jupiter), than before (3, up to 0.40 AU).

Long‐term changes in Jovian synchrotron radio emission: Intrinsic variations or effects of viewing geometry?

A long‐term decadal scale variation of Jovian decimetric radio emission has been reported that could indicate intrinsic time variability in the Jovian radiation belts and/or magnetic field. However, the strong beaming of the radiation by trapped relativistic electrons in the complex Jovian magnetic field can also result in apparent decimetric radiation changes due to the evolving viewing geometry of Jupiter during its 11.9‐year orbit. To investigate this problem, radial diffusion models of Jovian trapped electron fluxes at relevant energies are first constructed to simulate possible causes of intrinsic variations. Results indicate several inconsistencies with observations. For example, an increase in diffusion rate with other parameters held constant results in an inward displacement of the peak emission radial distance that is not observed. Second, effects of viewing geometry changes are examined. The possible importance of such effects is suggested by a correlation between the total decimetric radio flux and the Jovigraphic latitude of the Earth, DE, which varies between −3.3° and +3.3° during one Jovian orbital period. Because the Jovian central meridian longitudes where the magnetic latitude passes through zero during a given Jovian rotation change substantially with DE and since significant longitudinal asymmetries exist in both the volume emissivity and the latitudinal profile of the beam, the total intensity should be at least a partial function of DE. Thus variations of viewing geometry associated with Jupiter's orbital motion should be more fully accounted for if long‐term intrinsic variability of Jovian synchrotron radiation is to be unambiguously detected.

Magnetised Wave Collapse in Solar System Plasmas

AbstractClumpy, intense wave packets observed in situ in the Jovian and terrestrial electron foreshocks, and in the Earth’s auroral acceleration zone, point to the existence of non-linear plasma turbulence in these regions. In non-linear turbulence, wave packets collapse to short scales and high fields, stopping only when coherent wave-particle interactions efficiently dissipate the energy in the waves. The purpose of this paper is to examine the shortest scales and highest fields achieved during collapse in a strongly magnetised plasma, and identify parts of the solar system where the magnetised aspects of wave collapse are important.

Heliospheric effects on cosmic-ray electrons

view Abstract Citations (34) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heliospheric Effects on Cosmic-Ray Electrons Moraal, H. ; Jokipii, J. R. ; Mewaldt, R. A. Abstract Motivated by the success of current modulation models in interpreting the solar modulation of Galactic cosmic-ray nuclei, several effects on cosmic-ray electrons which are new or which have not yet been fully explored are considered. Among these are the contribution of Galactic positrons to the total electron flux, the production of secondary electrons from solar system objects, and the possibility of electrons being accelerated at the solar wind termination shock. It is found that the first of these provides a natural interpretation of the time variations of Galactic cosmic-ray electrons. Jovian electrons and thermal solar wind electrons may be accelerated to cosmic-ray energies at the termination shock. Such acceleration effects may alter the time-intensity profiles of electrons at earth, further modifying the interpretation of the electron modulation. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169617 Bibcode: 1991ApJ...367..191M Keywords: Electron Acceleration; Galactic Cosmic Rays; Heliosphere; Milky Way Galaxy; Solar Electrons; Solar Wind; Magnetic Field Configurations; Solar Cycles; Solar System; Space Radiation; COSMIC RAYS: GENERAL; PARTICLE ACCELERATION full text sources ADS |

Monte Carlo simulation of energization of jovian trapped electrons by recirculation

The recirculation model for particle acceleration in the Jovian magnetosphere is studied by means of Monte Carlo simulation. The recirculation model combines the conventional radial and pitch angle diffusion processes with the essentially energy‐conserving latitudinal diffusion in low altitudes and the pitch angle scattering in the plasma disc. This process has been proposed to explain the pitch angle and spectral characteristics of MeV electrons observed by Pioneer spacecraft in the Jovian magnetosphere. The simulation confirms that the dumbbell type anisotropy and the high‐energy tail of the energy spectrum can be produced from the recirculation process if the rate of the low‐altitude cross‐L diffusion is comparable to that of the conventional radial diffusion. The required low‐altitude diffusion rate corresponds to roughly 10−2 times the Bohm diffusion rate for 1‐MeV electrons, and it is suggested that the fluctuating electric field of the ULF turbulence confined to low altitudes is responsible for this high diffusion rate. The dumbbell type anisotropy observed also for MeV range electrons in the Earth's and Saturnian magnetospheres could also be the consequence of the recirculation process.

Relativistic electrons at geosynchronous orbit, interplanetary electron flux, and the 13‐month Jovian synodic year

We report the results of a search to determine the correlation, if any, between the temporal behaviors of ≳ 0.2‐7 MeV electrons at geosynchronous orbit (∼6.6 Re) and 6‐10 MeV electrons in the interplanetary region near Earth at the period of the jovian synodic year (∼13 months). The ∼13‐month intensity variation results from the synodic interplanetary magnetic field connection of Earth to Jupiter. Direct comparison of intensity‐time flux profiles for the years 1976‐1984, ∼7 synodic jovian electron seasons, shows that the intensity envelope of peak electron flux at ∼6.6 Re6 does not appear to be correlated to the observed ∼13‐month intensity envelope of relativistic electron flux in the interplanetary region near Earth. A persistent ∼13‐month variation of geosynchronous orbit flux is not obvious, thus indicating that the intensity of electron flux at ‐6.6 Re is not directly and solely related to the intensity of jovian electron flux near Earth. We conclude that dynamic energization and redistribution processes in Earth‧s magnetosphere must be invoked to produce the intensity variations of relativistic electron flux at ∼6.6 Re and not interplanetary magnetic field connection to Jupiter.

Magnetic helicity of the IMF and the solar modulation of cosmic rays

Using interplanetary magnetic field data acquired at 1 AU, we show that the distribution of magnetic helicity in the heliosphere is asymmetric about the current sheet, in accord with recent theoretical predictions. Such an asymmetric distribution of helicity can in principle explain the sensitivity of the solar modulation of cosmic rays to the sun's magnetic polarity, as observed in charge sign dependent modulation, Jovian electrons, and anomalous 4He.

Possible calorimetric effects at mercury due to solar wind‐magnetosphere interactions

As a result of the solar wind interaction with the magnetosphere of Mercury, we expect several effects which may be observable with ground‐based and/or near‐earth radio and infrared telescopes: (1) there may be direct interaction of the solar wind with the surface of Mercury which could produce measurable heating effects; (2) substormlike magnetotail processes within Mercury's magnetosphere may precipitate particles carrying from 1010 to 1012 W (or more) of power into narrow latitudinal bands on the cold (≲ 130 K) darkside of Mercury, producing surface‐heated “auroral” zones; and (3) the presence of Jovian electrons within the inner Hermean magnetosphere may produce transient, very low frequency synchrotron‐emitting radiation belts. Hence remote radio and infrared observations hold substantial promise for providing information about the intrinsic properties of Mercury's magnetic field, about the planetary surface, and about the dynamical interaction of the Hermean magnetosphere with the solar wind at ∼0.4 AU.

Jovian electrons at 1 AU - 1978-1984

Data on Jovian electrons sensed with a spectrometer on board the ISEE spacecraft at 1 AU are studied in terms of intensity variations over time and shape and variations of the electron spectra with time. Design and performance features of the electron spectrometer are described. The analyses cover solar cycle modulation of intensity, the synodic intensity modulation, micromodulation over a period of days, and adiabatic deceleration of electrons propagating in the expanding solar wind. Emphasis is placed on the effects of maximum solar activity on Jovian electron emission and propagation, noting a confirmed 13 mos intensity variation in the Jovian electrons.

Jovian electron populations in the magnetosphere of Mercury

A mechanism to explain the existence of two distinctly different kinds of energetic electron bursts within the Hermean magnetosphere is presented. The spectrally‐soft, very intense increases of energetic electrons observed in situ by Mariner 10 are ascribed to "substorm‐like" dissipation events due to magnetic reconnection in Mercury's magneto tail. The other type of electron bursts observed in Mercury's magnetosphere, characterized by lower peak intensities and much harder energy spectra, are attributed to Jovian electrons which first enter and are subsequently confined in the Hermean system. This Jovian electron model at Mercury is closely analogous to a similar model of such Jovian electron effects within the terrestrial magnetosphere. Such a model eliminates the need for the Hermean magnetosphere to produce highly relativistic electron bursts by internal generation mechanisms.

Propagation of Jovian Electrons in the Interplanetary Space

Propagation of Jovian Electrons in the Interplanetary Space

Origins of the low-energy relativistic interplanetary electrons

view Abstract Citations (47) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Origins of the low-energy relativistic interplanetary electrons Eraker, J. H. Abstract Pioneer 10 observations of electrons in the energy range from 1.75 to 25 MeV over the heliocentric radial distance 1.0-21.5 AU are presented. The minimum intensity levels of 1-25 MeV electrons about 4.5 AU upwind of Jupiter and about 16.5 AU downwind of Jupiter's orbit are of Jovian origin. The expected galactic electron flux at 1 AU is found to be a factor of 50 or more below the observed quiet-time 12 MeV electron flux, and the evidence confirms the hypothesis advanced by Teegarden et al. (1974) that Jupiter is the source of the approximately 1-25 MeV quiet-time electrons near 1 AU. No evidence was found to support the hypotheses that electrons of either solar or galactic origin contribute significantly to the quiet-time flux inside of 22 AU at low heliographic latitudes. Publication: The Astrophysical Journal Pub Date: June 1982 DOI: 10.1086/160036 Bibcode: 1982ApJ...257..862E Keywords: Electrons; Interplanetary Medium; Jupiter (Planet); Planetary Radiation; Relativistic Particles; Astronomical Models; Background Radiation; Electron Energy; Electron Flux Density; Particle Telescopes; Pioneer 10 Space Probe; Astrophysics full text sources ADS |

Transport coefficients of low‐energy cosmic rays in interplanetary space

The propagation of energetic particles along and across the interplanetary magnetic field is governed by the large‐scale field geometry and by scattering in small‐scale turbulent fields. Values of the scattering mean free path parallel to the field, λ∥(R), are reviewed in prompt solar bursts and nonimpulsive (corotating) events. Analysis of intensity and anisotropy profiles in combination is a powerful tool for elucidating λ∥(R). A consensus is found: at 1 AU, λ∥ = 0.08–0.3 AU over a wide range of rigidity, R = 5 × 10−4 to 5 GV. Efforts to explain the discrepancy between empirical values of λ∥ and scattering theory are discussed. Quantitative measures of λ∥ in rare scatter‐free events, where λ∥ ≳ 1 AU, are discussed because they can provide important details of the scattering process and the magnetic power spectra. Cross‐field diffusion due to random walk of field lines is revisited. Recent values deduced from magnetic power spectra in interplanetary space, magnetic diffusion at the sun, Jovian electron propagation, and cosmic ray events are evaluated. Again, a consensus is sought, and a reasonable mean is K⊥r/β = 1021 cm² s−1. Previous arguments against a significant K⊥r are reassessed, including the problem of the persistence of intensity fluctuations in cosmic ray events. Combining the consensus for K⊥r/β with that for λ∥ gives K⊥r/K∥ < 0.1 at 1 AU, and thus neglect of K⊥r in the modeling of solar cosmic ray events appears justified (although account needs to be taken of coronal propagation). The outlook for the future includes better empirical values of λ∥ down to Ep ∼ 10 keV and Ee ∼ 1 keV, comparison with scattering theories at these energies, and comparison between empirical and theoretical λ∥ in other regions such as the magnetosheath and upstream solar wind.

Jovian auroral secondary electrons and their influence on the Io plasma torus

A direct coupling is proposed between Jovian auroral energy dissipation (estimated to be as much as 1014 W) and ultraviolet emissions (≈ 2.5 × 1012 W) from the heavy ion torus surrounding Io. This association was motivated by the realization that there are serious discrepancies in all previous theories for either the auroral input or the energy source required to maintain hot electrons (> 10 eV) in the emitting torus. It is demonstrated that both problems can be resolved by adopting the plausible assumption that the dominant auroral precipitation occurs in an energy range yet to be reported, in particular heavy ions below 500 KeV. As these enter the atmosphere a dominant fraction of their energy is dissipated in producing secondary electrons with mean energy in the range 20‐40 eV. Most of the secondary electrons subsequently yield their energy to further ionization or excitation. However, those produced above an altitude where the atmospheric density is ∼ 1010 cm−3 can escape into the magnetosphere. The electron heat flux to the magnetosphere can exceed 1% of the auroral dissipation if the dominant precipitation flux consists of heavy ions (O+ or S+) with an energy between 100 to 1000 KeV. This could provide the source of electron energy required to balance radiative loss from the Io torus and it would inject ionospheric H+ ions into the magnetosphere at a rate (≈ 2 × 1029 sec−1) comparable to the upper estimates of heavy ion injection near Io.

The propagation of Jovian electrons to Earth

Jovian electron flux increases are observed by the University of Chicago experiment on the earth‐orbiting satellite Imp 8 throughout five ∼13‐month Jovian synodic years during the period from launch of the satellite in late 1973 to 1979. A detailed analysis of these data is presented to define the characteristics of Jovian electron propagation to earth. Corotating interaction regions (CIR) that form at the leading edges of fast solar wind streams continue to modulate the propagation of MeV electrons from Jupiter to the orbit of earth to produce ∼27‐day recurrent variations in the Jovian electron flux intensity. Between these CIR's, both the spatial distribution of Jovian electrons around earth's orbit and the time‐intensity profiles of the Jovian electron flux induced by the CIR modulation effect are shown to be consistent with the predictions of a simple diffusion model calculation, assuming that Jupiter's magnetosphere is a ‘point’ source of electrons. A new and significant result of this study is that these time‐intensity profiles are more accurately described not by the assumption that Jupiter is a constant source of electrons, but rather by assuming that electron emission is initiated with each passage of a CIR by Jupiter with the emission continuing for several days only. A measurement of the spatial gradient of these electrons demonstrates that there is a significant reduction in the Jovian electron flux between Jupiter and earth even when earth is aligned with Jupiter along the average direction of the interplanetary magnetic field. This observation is inconsistent with ‘scatter‐free’ propagation.