bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐E × B ordered ion beams upstream of the Earth's bow shock
Authors: Gurgiolo C. , Parks G. K. , Mauk B. H. , Lin C. S. , Anderson K. A. , Lin R. P. , Reme H.
Published: February 2008

The unexpected appearance of spin modulations in our fixed voltage electrostatic analyzer detectors on ISEE 1 and 2 has given us the opportunity to investigate the plasma properties of the upstream ions in high time resolution. The detectors are narrowly collimated and point southward, antiparallel to the satellite spin axis covering a region in phase space not viewed by the other plasma experiments on the satellites. The count rate modulations (up to three orders of magnitude) are due to the convolution of the anisotropic detector response function with the local plasma distribution function and reflect the existence of strong velocity gradients in the local distribution function. By assuming a form for this distribution function, we can simulate the output of any of our detectors. Comparing the simulated and observed count rates, we can then estimate several of the local plasma parameters. This of course is dependent upon the distribution function chosen. Using an isotropic ‘flowing’ Maxwellian distribution (which should be thought of as a ‘local’ approximation to the actual distribution near the region in phase space occupied by our detector response functions), we have obtained estimates of the local plasma temperature and three‐dimensional flow velocity of the upstream ion population we observe. We find that in almost all of our observations of upstream particles there exist beam‐like ions with temperatures in the range 5–80 eV. They are extremely dynamic in velocity with changes of 200–300 km/s occurring in 3–6 s being common. Most significantly, their ‘flow’ velocities cannot be ordered by E × B. This last point separates these observations from the previously reported reflected and diffuse populations of upstream ions. Mechanisms that can gyrophase bunch the ions reflected at the bow shock are discussed as a method of explaining the data.
Disappearing solar filaments: A useful predictor of geomagnetic activity
Authors: Joselyn J. A. , McIntosh P. S.
Published: February 2008

Disappearing solar filaments have long been suspected as an indicator of terrestrial magnetic disturbances. However, because filament disappearances are a common solar event and because they failed as a candidate source for M region (recurrent) magnetic disturbances, their potential utility as a forecasting aid for geomagnetic storms has largely been neglected. A search for possible solar sources of geomagnetic storms from June 1976 through June 1979 has revealed that a significant number of the storms, including the two largest, can only be associated with filament disappearances. This result is supported by the many recent papers studying SKYLAB and other observations of coronal transients which always find a strong correlation between those transients and eruptive prominences. By analyzing the physical characteristics of those disappearances which precede magnetic storms and those which do not, some tentative guidelines for forecasting geomagnetic disturbances have been developed based on evidence of a significant restructuring of the implied coronal magnetic field which could release solar wind plasma favorably positioned to impact the earth.
Organization of solar wind plasma properties in a tilted, heliomagnetic coordinate system
Authors: Zhao Xue‐Pu , Hundhausen A. J.
Published: February 2008

We have used a superposed epoch analysis to examine the variation in solar wind properties observed in 1974 in a ‘heliomagnetic’ coordinate system tilted with respect to the solar equator. A tilt of 30°±10° was found to produce the best ‘organization’ of these properties in such a coordinate system. The solar wind speed increased with heliomagnetic latitude, while the proton density and the proton flux density decreased. These variations are qualitatively consistent with those inferred from coronal hole and other interplanetary observations.
Mercury: Magnetospheric processes and the atmospheric supply and loss rates
Authors: Goldstein B. E. , Suess S. T. , Walker R. J.
Published: February 2008

Magnetospheric processes at Mercury are investigated to determine how they affect the source and loss rates of the neutral He and H atmosphere. The atmospheric source rate caused by direct impact of the solar wind on the planetary surface is estimated by using a model that included the effect of the large planetary core upon the compressibility of the magnetosphere. As the nonconducting planetary surface could inhibit Birkeland currents that cause erosion of the dayside magnetosphere, the impact of the solar wind on the surface is modeled with and without the effects of erosion. The solar wind impacts the surface, at most, only about 6% of the time, and the resulting atmospheric supply rate is negligible. The flux on closed dayside field lines is estimated to be roughly comparable to the flux to the surface along open dayside field lines in the polar cap region. The flux to the surface from the plasma sheet is estimated as being about three times either of these sources, provided that all sunward convected particles in the tail precipitate to the surface. A comparison of the flux available from convection with the flux that would precipitate to the ‘auroral zones’ under the assumption of strong pitch angle scattering shows that the strong pitch angle scattering assumption may be invalid at Mercury, owing to the large size of the loss cone. Observations of a correlation between the lunar atmosphere He content and Kp, and consideration of surface processes, suggest that a significant fraction of the He striking the surface eventually enters the atmosphere. Loss mechanisms are also investigated. The extent to which magnetospheric convection recycles photoions (created at both high and low latitudes) back to the planetary surface, and to a lesser extent the uncertainty in the number of atoms exposed to sunlight, leads to considerable uncertainty in atmospheric loss estimates. An examination of atmospheric losses caused by electron impact ionization in the ‘auroral zone’ indicates that this mechanism does not compete with photoionization. The estimated solar wind supply of He to the surface is in the range 3.9 × 1022−2.3 × 1023 s−1, the estimated radiogenic supply is between 6.9 × 1021 and 4.6 × 1022 s−1, and the loss rate is estimated as between 1.2 × 1022 and 1.1 × 1023 s−1.
Energetic ion beams at the edge of the plasma sheet: ISEE 1 observations plus a simple explanatory model
Authors: Williams D. J.
Published: February 2008

The ISEE 1 satellite experienced numerous encounters with the plasma sheet on May 3, 1978, during the period 0400–2000 hours UT. ISEE 1 was in the dusk‐midnight quadrant of the tail and ranged in geocentric distance from 22 to 16 RE. We have examined the energetic ion (≥24 keV) three‐dimensional distributions during this period and find a multitude of energetic ion beams, generally observed within two gyroradii of the plasma sheet edge. Beam characteristics include E−γ spectra, single‐peaked energy spectra with peak energies dependent on time and pitch angle and ranging upwards of 100 keV, double‐peaked energy spectra having peaks at tens and hundreds of keV, streaming directions parallel and antiparallel to B, and streaming directions at arbitrary angles to B. The time evolution of these energetic ion energy and angular distributions indicates that the plasma sheet edge is dynamic and not an equilibrium situation. From a close study of the data we conclude that all the observed energetic ion beam characteristics are explained by single‐particle motion along B under conservation of the first adiabatic invariant µ =E⊥/B. Thus, for example, tailward streaming beams are simply the result of mirror point reflection of an earthward moving ion population. Round‐trip distances of 35–40 RE are observed, implying unimpeded travel to low‐altitude mirror points and back. Energetic ion beams at arbitrary angles to B are simply azimuthal asymmetries around B due to the sharp energetic ion density gradient at the plasma sheet edge. A sporadic source of the general form of a Maxwellian plus an E−γ high‐energy tail is required on the ISEE 1 flux tube. The variable nature of the source can be due to either an intrinsic source property or intermittent contact of the satellite flux tube with the source. The observations and analysis indicate that the existence of energetic beams propagating at apparently arbitrary directions through lower‐energy plasmas is a natural result of single‐particle dynamics. Large, positive phase space density velocity gradients, ∂f/∂υ ≫0, naturally develop at all energies and pitch angles, dependent on spatial location with respect to the source. These results can unify a variety of previous energetic ion streaming observations in the tail and relate them to a common source.
Escaping nonthermal continuum radiation
Authors: Kurth W. S. , Gurnett D. A. , Anderson R. R.
Published: February 2008

New observations by the ISEE 1 plasma wave receiver reveal heretofore unreported details of the nonthermal continuum radiation from the earth. In particular, the higher frequency escaping component shows temporal and spectral features which are quite different from those of the lower frequency trapped emission. The higher frequency component is often clearly separated in frequency from the trapped component and high resolution spectrograms show that the escaping radiation consists of numerous narrowband emissions which drift slowly in frequency with time. The higher frequency component also exhibits greater temporal and spatial variability in both amplitude and frequency although the temporal variations are still quite smooth when compared to the more intense and higher frequency auroral kilometric radiation. Evidence is presented which clearly shows a direct connection between intense electrostatic emissions near the upper hybrid frequency and the escaping continuum radiation and strongly suggests the latter electromagnetic emission is generated through mode coupling with the upper hybrid waves. The new ISEE observations of the escaping continuum radiation from the earth strongly suggest a close correspondence with the newly reported narrowband kilometric radiation from Jupiter. Both emissions are relatively narrowband and show slow variations in amplitude with time. In both cases, the narrowband radiation lies above the trapped continuum radiation and below the intense extraordinary mode emissions (auroral kilometric radiation at the earth and decametric radiation at Jupiter). Evidence from both planets suggests the radiation is generated by intense electrostatic waves near the upper hybrid resonance frequency in the vicinity of the plasmapause at the earth and at the outer edge of the Io plasma torus at Jupiter.
Simulations on lower hybrid drift instability and anomalous resistivity in the magnetic neutral sheet
Authors: Tanaka Motohiko , Sato Tetsuya
Published: February 2008

An investigation of microinstabilities in a field reversal plasma is made by using a two‐dimensional magnetostatic particle code for application to the magnetospheric tail. The reversed magnetic field is provided by the electron and ion diamagnetic currents, and the ion temperature is assumed to be higher than the electron temperature. It is observed that a flute instability is generated in a local region with a steep density gradient apart from the neutral sheet; the frequency is about the lower hybrid frequency, and the wavelength is roughly the electron Larmor radius. The observed dispersion relation suggests that the instability must be the lower hybrid drift (LHD) instability. The initial diamagnetic current rapidly decreases in association with formation of E × B electron vortices, and simultaneously, particles are accelerated on the neutral line. In the magnetic null region, where the plasma beta is extremely large, an unstable electromagnetic mode is observed to develop in the nonlinear stage of the LHD instability, whereby the magnetic neutral line is deformed into a meandering structure. Anomalous resistivity and plasma transport are observed during the evolution of the LHD instability; it is to be noted that even on the neutral line a small but finite resistivity is generated. It is found that the resistivity η increases as η ∝ (Vdi/υthi)1.9, where Vdi is the drift speed of ions and υthi is the ion thermal speed. Also, significant electron heating is observed around the neutral line. This process may be relevant to electron heating in the neutral sheet of the magnetotail.
Spatial distribution of energetic particles in the distant magnetotail
Authors: Meng C.‐I. , Lui A. T. Y. , Krimigis S. M. , Ismail S. , Williams D. J.
Published: February 2008

The spatial distribution of energetic particles in the distant magnetotail is examined by using identical sets of two complementary energetic particle experiments aboard the IMP 7 and 8 spacecraft. The combined IMP 7 and 8 data set provides nearly 10 years of satellite observation. The quantitative distributions of energetic electrons in two energy ranges (30 keV ≤Ee ≤100 keV, 220 keV ≤Ee ≤2.5 MeV) and energetic protons (50 keV ≤Ep ≤220 keV, 290 keV ≤Ep ≤500 keV) are presented in terms of occurrence frequency and the average particle flux intensity over an 80 RE × 70 RE plane perpendicular to the sun‐earth line. The θ‐shaped particle distribution over the solar magnetospheric YZ plane in the antisolar direction is clearly demonstrated at all energies and for both species. The ‘O’ part of the θ corresponds to the magnetosheath region, and the cross bar is the average plasma sheet configuration. A distinct, species dependent, dawn‐dusk asymmetry in particle distribution is observed in the plasma sheet and to a lesser extent also in the magnetosheath. Energetic electrons are observed most often in the morningside of the plasma sheet and protons in the evening side. The degree of asymmetry differs for electrons and protons and is energy dependent. Geomagnetic activity affects the particle distribution substantially. At high geomagnetic activity, the occurrence frequency increases by about a factor of 2 and the average flux intensity is enhanced by approximately one order of magnitude.
The effect of plasma instabilities on the ionospherically reflected wave from a high‐power transmitter
Authors: Fejer J. A. , Kopka H.
Published: February 2008

Observations of the reflected radio wave from a high‐power transmitter show at times of not too high ionospheric absorption a drop of signal strength of typically almost 10db in the first few milliseconds after the arrival of the ionospheric echo following switching on a transmitter with 130 MW equivalent power. This decrease in signal strength is attributed to the excitation of the parametric decay instability. During about the next 5 s a further drop in signal strength by typically almost 10 db is observed. This decrease is attributed to the excitation of short‐scale field‐aligned irregularities which scatter the incident radio wave into Langmuir waves. These preliminary observations tend to confirm the theoretical threshold of the parametric decay instability. There are also indications that the formation of short‐scale field‐aligned irregularities inhibits the excitation of the parametric decay instability, as was previously inferred from the ‘overshoot’ effect in the Arecibo radar observations.
The Martian twilight
Authors: Kahn Ralph , Goody Richard , Pollack James
Published: February 2008

The changing sky brightness during the Martian twilight as measured by the Viking lander cameras is shown to be consistent with data obtained from sky brightness measurements. An exponential distribution of dust with a scale height of 10 km, equal to the atmospheric scale height, is consistent with the shape of the light curve. Multiple scattering resulting from the forward scattering peak of large particles makes a major contribution to the intensity of the twilight. The spectral distribution of light in the twilight sky may require slightly different optical properties for the scattering particles at high levels from those of the aerosol at lower levels.
Propagating substorm injection fronts
Authors: Moore T. E. , Arnoldy R. L. , Feynman J. , Hardy D. A.
Published: February 2008

The geosynchronous ATS 6 environmental measurements experiment was operated during 15 evening passes when the SCATHA spacecraft was within 1–2 RE and both spacecraft were very near the geomagnetic equator. Numerous, well‐defined substorm injections were recorded at both spacecraft with varying local time and radial separations. Accurate delay timing was possible since these events exhibit abrupt and essentially dispersionless (to within 10 s) plasma flux changes which replace cool preexisting plasma with hot quasi‐Maxwellian distributions. The hot plasma propagates earthward in close association with an equally abrupt magnetic field increase at velocities in the range of 10–100 km/s. On this basis we identify the agent of injection as the induced electric field of the earthward propagating compression wave observed by Russell and McPherron (1973), and we refer to the propagating particle structure as the injection front. These dramatic synchronous orbit electron injection signatures are produced mainly by a boundary motion rather than by local acceleration of plasma. However, we find some evidence that the plasma sheet electrons are weakly ‘heated’ by the passage of each compression wave, the energy appearing mainly in the high‐energy tail of the distribution. The spectral change we observe argues convincingly that the boundary in question is a precipitation‐flow boundary layer (Kennel, 1969) and that the near‐earth plasma sheet is significantly degraded in average energy by the addition of ionospheric plasma, especially secondary electrons emitted by the ionosphere due to precipitating energetic electrons. The presence of significant ∂B/∂t requires that a change of mapping occur between the equatorial plane and the ionosphere, the sense being such as to map the inward moving injection front to a relatively fixed latitude in the ionosphere. Such an earthward plasma injection would not therefore require equatorward auroral motion.
Nighttime observations of 0.2‐ to 26‐keV electrons in the South Atlantic Anomaly made by Atmosphere Explorer C
Authors: Gledhill J. A. , Hoffman R. A.
Published: February 2008

The high‐energy background radiation in the South Atlantic Anomaly makes it difficult to measure the fluxes and spectra of the low‐energy particles with any degree of certainty, and as a result no values for the energy range below 30 keV are to be found in the literature. We have found that the flux of low‐energy ions is much smaller than that of the electrons. This has enabled us to use the low‐energy ion detector on AE‐C to monitor the high‐energy background and to correct the response of the low‐energy electron detector for this. The electron spectra can be represented by a power law in the range 0.2–26 keV, with the spectral index close to −1. Maps are shown of downward energy flux in this range over the South Atlantic Anomaly. The mean energy flux carried by electrons in the middle of the anomaly is found to be about 3 × 10−3 erg cm−2 s−1 and may reach 5 times this value on occasions. A surprising result is that this energy flux decreases as Kp increases.
Compression of Jupiter's magnetosphere by the solar wind: Reexamination via MHD simulation of evolving corotating interaction regions
Authors: Smith Z. K. , Dryer M. , Fillius R. W. , Smith E. J. , Wolfe J. H.
Published: February 2008

We examine the major changes in the solar wind before, during, and after the Pioneer 10 and 11 encounters with the Jovian magnetosphere during 1973 and 1974, respectively. In an earlier study, Smith et al. (1978) concluded that the Jovian magnetosphere was subjected to large‐scale compression during at least three of four intervals during which it appeared that the spacecraft had reentered the solar wind or magnetosheath near 50 RJ after having first entered the magnetosphere near 100 RJ. They based this suggestion on the observations of the sister spacecraft, which indicated—on the basis of a kinematic translation of corotating interaction regions (CIR's)—that these structures would be expected to arrive at Jupiter at the appropriate beginning of these three intervals. Our reexamination of this suggestion involved the numerical simulation of the multiple CIR evolutions from one spacecraft to the sister spacecraft. This approach, considered to be a major improvement, confirms the suggestion by Smith et al. (1978) that Jupiter's magnetosphere was compressed by interplanetary CIR's during three out of four of these events. Our MHD simulation also suggests that Jupiter’s magnetosphere reacts to solar wind rarefactions in the opposite way—by expanding. A previously unexplained pair of magnetopause crossings on the Pioneer 11 outbound pass may simply be due to a delayed reexpansion of Jupiter's magnetosphere from a compression that occurred during the inbound pass.
Instabilities of low frequency, parallel propagating electromagnetic waves in the Earth's foreshock region
Authors: Sentman D. D. , Edmiston J. P. , Frank L. A.
Published: February 2008

We compute the electromagnetic dispersion relation for right‐ and left‐hand circularly polarized low frequency waves propagating parallel and antiparallel to the upstream interplanetary magnetic field in the presence of both reflected and diffuse suprathermal ions. The ion distribution function is modeled after three‐dimensional observations of reflected and diffuse ions made upstream of the quasiparallel bowshock crossing of December 8, 1977, while the electron distribution function is based on concurrent three‐dimensional observations of low energy electrons. It is found that the reflected ions destabilize the plasma most strongly at ω ∼0.1Ωi by way of a resonant ion beam instability for waves propagating upstream, and by way of a nonresonant firehose‐like instability for waves propagating downstream. The diffuse ion population also destabilizes the plasma most strongly at ω ∼ .1Ωi by way of resonant instability of both right‐ and left‐hand polarized waves propagating away from the bow shock. The growth times of the unstable waves are roughly 60 s and 150 s for those associated with the reflected and diffuse ions, respectively, during which time the waves would be carried several earth radii downstream.
Charge exchange in the Venus ionosphere as the source of the hot exospheric hydrogen
Authors: Hodges R. Richard , Tinsley Brian A.
Published: February 2008

A global Monte Carlo model of the exosphere of Venus, simulating the normal exospheric processes, as well as the production of a ‘hot’ hydrogen component by charge exchange of H+ with H and O, has been computed. The resulting altitude profiles of atomic hydrogen concentration over both the day and night hemispheres are in reasonable agreement with Mariner 5 and Mariner 10 observations of Lyman α showing that the ionospheric charge exchange reactions are a significant source of ‘hot’ hydrogen, possibly the dominant source. However, the uncertainties in the available atomic hydrogen data allow for production of a similar amount of nonthermal H by chemical processes involving H2 as suggested by Kumar and Hunten (1974).
The Voyager mission through the Jupiter encounters
Authors: Stone E. C.
Published: February 2008

The Voyager mission is a major element in NASA's program of exploration of the outer solar system. Objectives of the Voyager mission include comparative studies of the Jovian and Saturnian planetary systems and exploratory studies of the interplanetary medium at increasing distances from the sun. With the successful Saturn encounter in November 1980, the objectives of the mission have been extended to include an exploration of Uranus and interplanetary studies to beyond 20 astronomical units.

The papers in this special issue represent the first comprehensive report of the detailed analysis of data from the initial phase of the mission, extending from launch through the Jupiter encounters. Voyager 1 was launched on September 5, 1977, and arrived at Jupiter on March 5, 1979, while Voyager 2 was launched on August 20, 1977, and arrived at Jupiter on July 9, 1979.
Observations of the magnetic field and plasma flow in Jupiter's magnetosheath
Authors: Lepping R. P. , Burlaga L. F. , Klein L. W. , Jessen J. M. , Goodrich C. C.
Published: February 2008

Large scale (many minutes to 10 hours) magnetic field structures consisting predominantly of nearly north‐south field directions have been discovered in Jupiter's magnetosheath from the data of Voyagers 1 and 2 and Pioneer 10 during their outbound encounter trajectories. The Voyager 2 data, and those of Voyager 1 to a lesser extent, show evidence of a quasi‐period of 10 hours (and occasionally 5 hours) for these structures. For all three spacecraft the changes in the field throughout these structures for many tens of hours are approximately restricted to a plane parallel to Jupiter's local magnetopause, according to a variance analysis of the field. Similar directional changes in the field occurred in the inbound magnetosheath for the Voyager spacecraft, but the occurrence was much less frequent, no quasiperiodicity was apparent, and the scale lengths were on average much shorter. The north‐south components of the field and plasma velocity are strongly correlated in the outbound magnetosheath as observed by Voyagers 1 and 2, and the components orthogonal to the north‐south direction show weak correlations. For both Voyager encounters the sense (positive or negative) of the north‐south correlations has been directly related to the direction of the ecliptic plane component of the interplanetary magnetic field (IMF) using the field and plasma measurements of the non‐encountering spacecraft. Some outbound magneto pause and bow shock crossings, on Voyager 2 especially, are phase locked in system III with some of the large scale magnetosheath field and plasma structures. These structures may be accounted for in terms of field line draping around the magnetopause of the convected IMF and solar wind, where the temporal properties are controlled by the motion and shape of a flattened magnetosphere which, in turn, depend on the rapid rotation of the current sheet within the magnetosphere.
Characteristics of hot plasma in the Jovian magnetosphere: Results from the Voyager spacecraft
Authors: Krimigis S. M. , Carbary J. F. , Keath E. P. , Bostrom C. O. , Axford W. I. , Gloeckler G. , Lanzerotti L. J. , Armstrong T. P.
Published: February 2008

The low‐energy charged particle (LECP) experiment on the Voyager 1 and 2 spacecraft made measurements of the intensity, energy spectra, angular distributions, and composition of ions (30 keV ≲E ≲150 MeV) and electrons (14 keV ≲E ≲10 MeV) during encounters with the Jovian magnetosphere in 1979. Detailed analysis of the multicomponent (H, He, O, S) low‐energy (∼30 keV to ∼4 MeV) ion population reveals the Jovian environment to be dominated by magnetospheric ions to distances ≳200 RJ upstream and ≳350 RJ downstream from the planet. Inside the magnetosphere, ions move generally in the sense of corotation to the dayside magnetopause, and on the nightside to distances of ∼130–150 Rj, beyond this distance, but inside the magnetopause, ion flow abruptly changes to an antisunward, anti‐Jupiter direction and continues to large (>350 RJ) radial distances outside the magnetosphere. The ion particle spectrum is characterized by a nonthermal power law (E−γ) component for E ≳200 keV, and a convected Maxwellian for E ≲200 with characteristic temperatures (kT) of ∼20‐45 keV. Temperature maxima generally coincide with crossings of the Jovian plasma sheet, while at higher energies spectra become softer at the equator. The ion spectra and composition are affected strongly by convective flows in all parts of the magnetosphere. By using the observed spectra and angular distributions, density and pressure profiles are produced for ions measured above the lowest LECP detector threshold (E ≳30 keV) and are compared with reported ambient total electron densities and magnetic field pressures. The particle pressures are found to be comparable to magnetic field pressures to at least ∼10 RJ, i.e., Jovian magnetosphere dynamics are determined by pressure variations in a high β plasma. Energetic ion densities are found to be comparable with the total electron densities in the outer (≳40 RJ) dayside magnetosphere but are generally lower at smaller radial distances and exhibit substantial variability. We interpret the hot plasma outflow on the nightside of Jupiter as a ‘magnetospheric wind' and estimate the mass and energy loss through this region at ∼2 × 1027 ions/s and ∼2 × 1020 ergs/s, respectively. We find the plasma source from the active volcanoes on Io to be adequate for supplying the mass outflow; only the rotational kinetic energy of Jupiter is sufficient to provide the energy in the flow, although energy from the solar wind interaction can perhaps contribute a significant fraction. A phenomenological model of Jupiter's magnetosphere is presented which accounts for the observations.
Positive ion observations in the middle magnetosphere of Jupiter
Authors: McNutt R. L. , Belcher J. W. , Bridge H. S.
Published: February 2008

We consider the positive ion data gathered by the Voyager Plasma Science experiment in the middle magnetosphere of Jupiter. The experiment measures positive ions with energies per charge between 10 and 5950 V. The observations are analyzed to obtain the mass and charge densities, velocity components, and temperatures of the low‐energy plasma population. The reduced data set is discussed in the context of the outstanding questions concerning this plasma population and its dynamics. We find that on the dayside, there exists a transonic to highly supersonic positive ion population which tends to move azimuthally but does not rigidly corotate with the planet. These ions provide the inertia of the magnetospheric plasma inside of ∼40 RJ. The mass density is everywhere dominated by heavy ions, and the mass density gradient is consistent with outward diffusion from the Io plasma torus via flux tube interchange. The ions tend to be concentrated in a plasma sheet which is associated with the current sheet inferred from the magnetic field observations. The plasma in the sheet is relatively cool (∼20 eV) in comparison with plasma at higher magnetic latitudes (≳100 eV). In addition to the azimuthal flow pattern, we find a local time asymmetry in the data which we interpret as flow away from the current sheet on the dayside and toward the current sheet on the nightside. This dynamic expansion and contraction of the plasma sheet is presumably driven by the asymmetry in the magnetosphere due to the solar wind interaction.
Low‐energy charged particle observations in the 5–20 RJ region of the Jovian magnetosphere
Authors: Armstrong T. P. , Paonessa M. T. , Brandon S. T. , Krimigis S. M. , Lanzerotti L. J.
Published: February 2008

Ion (>0.5 MeV) and electron (>30 keV) measurements made by the low‐energy charged particle instrument during the Voyager 1 and 2 traversais of the 5–20 RJ region of the Jovian magnetosphere are presented. The spatial morphology of particle intensities, energy spectra, and composition is emphasized. Diffusive radial transport is also discussed. The Jovian magnetopshere seemed to be much more disturbed during the Voyager 2 passage than during that of Voyager 1. Significant inbound‐outbound asymmetries of the radial profiles of intensities are observed; an appropriate magnetic field model to provide closure has not been found. Low‐energy electrons are not enhanced or depleted in the Io torus region except at the inner edge, about 5.2 RJ, where they sharply decrease. This may be due to enhanced electron loss associated with a region of increased plasma density.
Factors governing the ratio of inward to outward diffusing flux of satellite ions
Authors: Richardson John D. , Siscoe George L.
Published: February 2008

The primary loss process for the ionized component of satellite debris in Jupiter's magnetosphere appears to be radial transport, which carries the satellite‐derived ions away from the source satellite. Cross L (interchange) diffusion is a likely candidate for the radial transport mechanism. Many consequences are predicted to result from satellite ions that reach regions close to and remote from Jupiter. The ratio of the inward to outward flux of diffusing ions from a given satellite is therefore important as an input to the estimates of the magnitudes of expected consequences. In the formal analysis of cross L diffusion, the flux ratio depends on poorly known boundary conditions and on a poorly determined diffusion coefficient. We present here an analysis of the sensitivity of the flux ratio to the uncertainties in the mentioned parameters. The main result is that if the diffusion is driven externally, for example by winds in Jupiter's ionosphere, the inward flux exceeds or is of the same order of magnitude as the outward flux. On the other hand, if the diffusion is driven locally by the centrifugal interchange instability, as one interpretation of Voyager plasma data suggests, the outward flux can be one or two orders of magnitude greater than the inward flux. Fits to the Voyager in situ plasma torus data obtained from solutions to the transport equations appropriate to wind driven and centrifugally driven diffusion are compared. In both cases, good fits are obtained. Both require a substantial discontinuity in the diffusion coefficient at Io's orbit, and both require an onset of ion injection a finite time prior to Voyager encounter. The values of the source strength, the duration of injection, and the percentage of inward flux transport, determined thereby differ by a factor of four or less between the two types of diffusion.
On the arc structure of the DAM Jupiter emission
Authors: Leblanc Y.
Published: February 2008

An analysis of the dynamic spectra of the Jovian DAM emission (1.3–40 MHz) has been made from Voyager data; it appears that the different Jovian ‘sources’ can be defined by spectral characteristics, rather than by occurrence probability. The non‐Io emission consists of two families: vertex early arcs (VEA) and vertex late arcs (VLA). These two families are superimposed at all longitudes, but one is always more intense than the other. The characteristics of the two families are specified; in particular, it is shown that the VEA family is more stable in time than the VLA family. The Io‐controlled emission consists of the four sources already known from the ground‐based observations in addition to a new source, (Io‐A')sp, identified by its dynamic spectrum alone. All of the sources are partially superimposed on non‐Io emission. The (Io‐B)sp and (Io‐A')sp sources are made up of low‐curvature arcs having low‐frequency limits above 5 MHz. The high‐frequency limit of the (Io‐B)sp source is strongly modulated by Io‐phase. The (Io‐A)sp source has a spectrum similar to the non‐Io VLA emission. The other two sources, (Io‐C)sp and (Io‐D)sp, are not structured into well‐defined arcs. A comparison is made between the occurrence of these sources in the Io‐CML plane with the sources defined from ground observations by probability of occurrence. Local time effects are observed only in the non‐Io emission when compared before and after encounter. Before encounter, the VEA family is very weak and the VLA family very intense. After encounter, the opposite effect is observed. The Io‐controlled sources are not affected by these local time effects.
The Jovian S burst sources
Authors: Leblanc Y. , Genova F.
Published: February 2008

By using the high resolution observations of Nançay observatory, we have been able to identify the S burst emission on the planetary radio astronomy (PRA) records of Voyager. It is shown that the S bursts occur in two regions of the ΦIO‐CML plane (S‐IoB and S‐IoA'C regions). In these regions the S burst emission is arranged into a pattern of repetitive features, drifting negatively. These features could be incomplete vertex late arcs. We show that the S burst pattern is distinct from the pattern of the Io‐controlled emission. These results are discussed in the frame of Goldstein and Thieman's arc model.
A heuristic model for Jovian decametric arcs
Authors: Pearce Jeffrey B.
Published: February 2008

A field line emission cone model is proposed that fits the frequency‐time profiles of decametric arcs emitted by the Jupiter system. Four parameters (latitude of the observer, longitude of the excited flux tube, emission cone angle, and field line L shell value) can be varied to fit most of the observed radiation.
Spatial color variations in the volcanic plume at Loki, on Io
Authors: Collins Stewart A.
Published: February 2008

Multicolor Voyager 1 photographs of the Loki volcanic plume, on Io, have been analyzed to determine the nature and quantity of the scattering material within the plume. This work indicates that there are two particle populations. The first population consists of particles with radius of 0.001–0.01 µ m, while the second population, which is concentrated near the source, comprises particles with radius greater than 1 µ m;. The population of smaller particles includes most of the particulate mass in the plume. This work increases the previously estimated particulate mass (Johnson et al., 1979) and suggests that the SO2 gas spectroscopically identified by Pearl et al. (1979) may represent transient flow from the volcano instead of an atmosphere in stable equilibrium with the local surface.
Visible and infrared observations of Jovian plumes during the Voyager encounter
Authors: Hunt Garry E. , Conrath Barney J. , Pirraglia Joseph A.
Published: February 2008

Observations by the Voyager imaging instrument has shown an organized train of features moving in a westerly current at 9°N with a zonal speed of 100–120 m s−1. The measurement reports show that the number of plumes varied between 13 at the time of the Voyager 1 encounter, and 11 at the time of the second spacecraft passage. The infrared interferometer spectromer (Iris) measurements suggest that the effect of these plume features propagates throughout the Jovian troposphere. A mechanism is suggested for the origin of the plumes in terms of wave interactions with the Jovian flow.
Numerical study of explosive tearing mode instability in one‐component plasmas
Authors: Terasawa Toshio
Published: February 2008

A numerical simulation is performed to investigate the nonlinear phase of the collisionless tearing mode instability. The results are found consistent with the expectation from the theory by Galeev, Coroniti, and Ashour‐Abdalla, who predicted the existence of an explosive phase of the instability caused by the magnetization of particles by the perturbed component of the magnetic field normal to the neutral sheet. Since electrostatic effects on the evolution of the instability are neglected a priori in the present numerical simulation, we do not obtain the final answer. But there seems to be a good possibility of the explosive evolution of the tearing mode instability in its nonlinear stage. It is argued that for a sufficiently long‐wavelength perturbation the nonlinear explosive evolution can become faster than the nonlinear coalescence mode. It is further noted that the particles are heated adiabatically within the magnetic islands by the one‐dimensional compression process.
Corotating magnetospheric convection
Authors: Hill T. W. , Dessler A. J. , Maher L. J.
Published: February 2008

The longitudinal asymmetry of the Io plasma torus, as predicted by the magnetic‐anomaly model and observed by Earth‐based optical astronomy, provides a driving mechanism for a corotating convection system in Jupiter's magnetosphere. Here we deduce some qualitative properties of this convection system from the general equations that govern a steady state corotating convection system (although we expect that time‐dependent effects may also have to be included for a complete description of Jovian convection). The corotating convection system appears capable of providing both the dominant radial transport mechanism (with a time scale possibly as short as a few rotation periods) and the dominant mechanism for extracting energy from Jupiter's rotation (at a rate ∼1015 W) for driving a wide variety of magnetospheric phenomena. A similar corotating convection system may occur in other rotation‐dominated magnetospheres, for example, those of pulsars and Saturn.
Steepening, soliton, and landau damping of large‐amplitude magnetosonic waves: Particle code computer simulation
Authors: Matsumoto Hiroshi , Nagai Keisuke
Published: February 2008

In order to understand and interpret the large‐amplitude hydromagnetic fluctuations in the solar wind plasma, a particle code computer simulation is carried out for a study of nonlinear characteristics of large‐amplitude magnetosonic waves in a magnetized high β plasma. Not only magnetohydrodynamic features such as steepening, shock formation, and soliton production, but also kinetic effects such as Landau damping are observed. The time evolution of a large‐amplitude magnetosonic wave is as follows: It first exhibits steepening because of nonlinear propagation characteristics and shows a forward tilting of its magnetic field profile. Comparison with an an existing nonlinear kinetic theory (Barnes, 1979b) for the nonlinear propagation velocity and the steepening time shows a good agreement between the theory and the simulation up to a time of shock formation. The measured Landau damping rate in the simulation agrees well with the linear kinetic theory (Barnes, 1966) even for large‐amplitude magnetosonic waves. This is the case when the steepening time is much shorter than the particle trapping time. After a shock condition is reached, solitary spikes are observed from the vicinity of the wave peak which eventually changes the feature of the steepening. The final waveform within the present computation shows a backward tilting of its magnetic field component.
Observations of field‐aligned ion and electron beams from SCATHA (P78‐2)
Authors: Richardson J. D. , Fennell J. F. , Croley D. R.
Published: February 2008

Intense field‐aligned beams of ions and electrons have been observed by electrostatic analyzers on the SCATHA (P78‐2) satellite. The beans have peaked energy spectra with energies ranging from tens of eV to several keV. These beams show a strong local time dependence, with occurrence frequencies peaking near local midnight. The occurrence frequencies of these beams are also positively correlated with Kp. Comparisons have been done with S3‐3 observations of field‐aligned ion fluxes, suggesting a direct relationship between acceleration of ions at low altitude in the auroral region and the observations of field‐aligned beams at the equator near synchronous orbit.
Mars atmospheric opacity effects observed in the northern hemisphere by Viking Orbiter Imaging
Authors: Thorpe Thomas E.
Published: February 2008

Observations of changing Mars contrasts by Viking orbiter television cameras have provided a description of changing atmospheric opacity in the Southern Hemisphere (paper 1). This report extends those measurements into the Northern Hemisphere over a greater time period and provides a detailed description of photometric changes at the lander sites as seen from orbit. Reflectivity changes compared with optical depth increases produced by four dust storms indicate mean particle scattering changes with storm evolution as well as substantial opacity in the Northern Hemisphere for the duration of nearly a Martian year.
Combined effect of cold H+ and He+ ions on the proton cyclotron electromagnetic instability
Authors: Gomberoff L. , Cuperman S.
Published: February 2008

Observations aboard GEOS 1 and 2 show a correlation between generation of strong ion‐cyclotron ULF waves below the proton gyrofrequency and an increase in the cold He+ ion concentration. The amplification process due to one cold species seems to be well understood and has been thoroughly discussed. Nevertheless, the amplification process when two cold species are present has not been so far properly studied. The GEOS experiments have also shown a close association between the occurrence of ion‐cyclotron ULF waves and the presence of thermal He+ ions in the equatorial region of the magnetosphere (Young et al., 1979). Thus we study here the combined effect of cold H+ and He+ ions on the proton cyclotron electromagnetic instability.
Coupling instability of the shear Alfvén wave in the magnetosphere with the ionospheric ion drift wave, 2. Numerical analysis
Authors: Miura A. , Ohtsuka S. , Tamao T.
Published: February 2008

In the present paper we describe in detail results of numerical calculations for eigen oscillations of the shear Alfvén wave coupled with the ionospheric ion drift wave in the presence of the steady electric field. The instability mechanism has been discussed in a companion paper (Tamao and Miura, this issue). For a model magnetosphere with a nonuniform density distribution along dipole magnetic field lines, together with ionospheric boundary conditions through which the coupling with the ion drift wave is taking place, we have solved numerically a system of differential equations describing the localized torsional oscillations of field lines. Dependences of the eigenfrequency and the growth (or damping) rate of oscillations on the height‐integrated ionospheric conductivity are examined, and it is shown that the nighttime oscillations exhibit a stronger instability than those for daytime. There is a minimum threshold intensity of the steady electric field and a maximum scale length in the north‐south direction of the localized oscillation in the ionosphere for occurrence of the instability. These are ten to a few tens of mV/m and a few tens of kilometers, respectively. The maximum scale length decreases with decreasing invariant latitude of the field line, while the peak value of the growth rate increases. Eigen function distributions along the field line are also determined, which makes it possible to infer dependences of perturbations at the level just above the ionosphere on the Pedersen conductivity in the ionosphere.
Titan's upper atmosphere: Composition and temperature from the EUV solar occultation results
Authors: Smith Gerald R. , Strobel Darrell F. , Broadfoot A. L. , Sandel B. R. , Shemansky D. E. , Holberg J. B.
Published: February 2008

The temperature and composition of the upper atmosphere of Titan have been inferred by observing an occultation of the sun by Titan, using the Voyager 1 ultraviolet spectrometer. The temperature is 176±20 K near the evening terminator and 196±20 K near the morning terminator. The major constituent is N2 with a density of 2.7±0.2 × 108 cm−3 at 3840 km. The mixing ratio of CH4 is 8±3% at a radial distance of 3700 km near the evening terminator where [CH4] ≃1.2 × 108 cm−3. On the morning terminator the [CH4] ≃ 1.2 × 108 cm−3 level is about 20 km lower in the atmosphere. The acetylene mixing ratio above 3400 km is measured at the 1 to 2% level. Below 3300 km it decreases to between 0.1 and 0.3%. A layer of absorbing molecules, possibly polymers, is present at both morning and evening terminators. Near the evening terminator the layer is located between 3350 and 3600 km. Near the morning terminator it is located about 100 km lower in the atmosphere. A simple photochemical model suggests that the homopause is located at 3500 ± 70 km with an eddy diffusion coefficient of 1−0.7+2 × 108 cm² s−1, which decreases to ∼10³ cm² s−1 in the lower stratosphere as [N2]−2/3.
Simultaneous observations of energetic electrons and dawnside chorus in geosynchronous orbit
Authors: Isenberg Philip A. , Koons H. C. , Fennell J. F.
Published: February 2008

We present the first simultaneous observations of chorus activity and energetic particles from near‐geosynchronous orbit by using data from the Aerospace Corporation VLF receiver and the UCSD charged particle detector on the SCATHA satellite. We find that, for the 5 days studied, June 23–27, 1979, every encounter with injected clouds of energetic electrons was accompanied by chorus activity. We conclude that dawnside chorus is generated by substorm‐injected, anisotropic clouds of electrons with energies between 10 and 100 keV.