bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion and electron energy dispersion features detected by ISEE 1
Authors: Greenspan M. E. , Williams D. J. , Mauk B. H. , Meng C.‐I.
Published: February 2008

An energetic particle dispersion feature observed by the ISEE 1 medium energy particle instrument is identified as an old phenomenon, injection of hot plasma followed by drift dispersion, seen from a new viewpoint, the highly elliptical ISEE orbit. The feature is characterized by enhancements in the electron and ion fluxes in the energy range 20 keV to 200 keV and is seen between 5 RE and 13 RE. Events with this signature show strong energy dispersion, with the highest energy ions and electrons arriving first. The feature is not always present for both ions and electrons or at both 30° and 90° pitch angles. The species and pitch angle of particle in which it is most likely to occur vary with local time. Because the signature is seen on both outbound and inbound satellite passes, always with high‐energy particles arriving first, it cannot be due to satellite passage through stationary spatial structures set up by steady state convection. Creation of the events can be qualitatively explained by using an injection boundary model with a magnetopause that functions as a particle absorber. Such an absorber is necessary to explain the predominance of electron features and scarcity of 90° ion features in the morning and the predominance of ion features in the afternoon. Signatures seen by satellites with highly elliptical orbits are often interpreted as effects of satellite motion through spatial boundaries. Here, it is shown that the intrinsically time‐dependent injection boundary model can qualitatively explain the features that we see in data from a satellite that makes an almost radial cut through the magnetosphere.
A new source of suprathermal O+ ions near the dayside polar cap boundary
Authors: Lockwood M. , Waite J. H. , Moore T. E. , Johnson J. F. E. , Chappell C. R.
Published: February 2008

A new dayside source of O+ ions for the polar magnetosphere is described, and a statistical survey presented of upward flows of O+ ions using 2 years of data from the retarding ion mass spectrometer (RIMS) experiment on board DE 1, at geocentric distances below 3 RE and invariant latitudes above 40°. The flows are classified according to their spin angle distributions. It is believed that the spacecraft potential near perigee is generally less than +2 V, in which case the entire O+ population at energies below about 60 eV is sampled. Examples are given of field‐aligned flow and of transversely accelerated “core” O+ ions; in the latter events a large fraction of the total O+ ion population has been transversely accelerated, and in some extreme cases all the observed ions (of all ion species) have been accelerated, and no residual cold population is observed (“toroidal” distributions). However, by far the most common type of O+ upflow seen by DE RIMS lies near the dayside polar cap boundary (particularly in the prenoon sector) and displays an asymmetric spin angle distribution. In such events the ions carry an upward heat flux, and strong upflow of all species is present (H+, He+, O+, O++, and N+ have all been observed with energies up to about 30 eV, but with the majority of ions below about 2 eV); hence, these have been termed upwelling ion events. The upwelling ions are embedded in larger regions of classical light ion polar wind and are persistently found under the following conditions: at geocentric distances greater than 1.4 RE; at all Kp in summer, but only at high Kp in winter. Low‐energy conical ions (<30 eV) are only found near the equatorial edge of the events, the latitude of which moves equatorward with increasing Kp and is highly correlated with the location of field‐aligned currents. The RIMS data are fully consistent with a “mass spectrometer effect,” whereby light ions and the more energetic O+ ions flow into the lobes and mantle and hence the far‐tail plasma sheet, but lower‐energy O+ is swept across the polar cap by the convection electric field, potentially acting as a source for the nightside auroral acceleration regions. The occurrence probability of upwelling ion events, as compared to those of low‐altitude transversely accelerated core ions and of field‐aligned flow, suggests this could be the dominant mechanism for supplying the nightside auroral acceleration region, and subsequently the ring current and near‐earth plasma sheet, with ionospheric O+ ions. It is shown that the total rate of O+ outflow in upwelling ion events (greater than 1025 s−1) is sufficient for the region near the dayside polar cap boundary to be an important ionospheric heavy ion source.
Observation of ionospheric source cone enhancements at the substorm injection boundary
Authors: Quinn J. M. , Johnson R. G.
Published: February 2008

A large number of time‐varying electron and ion features, such as those observed in energy‐time spectrograms of data obtained near geosynchronous orbit, have been previously explained through the use of an injection boundary model. This model describes such features in terms of the dispersion signatures of fresh, hot plasma which is “injected” into an extended region tailward of an injection boundary at the time of substorm onset. Using data from the Lockheed ion composition instrument and the University of California, San Diego, electron and ion analyzers on SCATHA, we present two events indicating that the innermost edge of the injection region is an especially important location for the substorm input of ionospheric ions. The injection signatures are identified by comparison of electron and ion data with the dispersion features predicted by various electric and magnetic field models. In both events the ion composition data show intense, narrow‐energy, field‐aligned O+ fluxes on the limiting edge of the dispersing ions. This feature corresponds to ions which can be backtracked to localized positions in the vicinity of the injection boundary at the onset time. We conclude that the injection boundary, which corresponds statistically to the equatorward edge of the auroral oval, is at times the location of direct ionospheric input into the trapped, energetic particle population.
Anomalous absorption and reflection in ionospheric radio modification experiments
Authors: Mjølhus Einar
Published: February 2008

The anomalous absorption of an ordinary polarized radio wave due to magnetic field aligned short‐scale striations is studied. By the method of averaging, a correction term to the cold plasma dielectric tensor can be derived. The correction term behaves singularly at the upper hybrid level, inducing new cutoff and resonance. A situation analogous to the Budden tunneling problem arises. Thus the anomalous absorption is necessarily accompanied by partial reflection at the upper hybrid level. A consequence is that the absorption coefficient has a maximum at a certain striation intensity, with reflection dominating at higher intensities. This is expected to be important for the saturation of the process generating the striations.
Theoretical interpretation of the observed interplanetary magnetic field radial variation in the outer solar system
Authors: Suess S. T. , Thomas B. T. , Nerney S. F.
Published: February 2008

Analysis of interplanetary magnetic field (IMF) data from the outer solar system has shown that the azimuthal component of the IMF falls off more rapidly with radius between 1 and 10 AU than as r−1, where an r−1 dependence is predicted in classical theory. This result is consistent with meridional flow transporting magnetic flux away from the heliographic equator. An identical effect has been predicted to result from the force due to the meridional gradient of the azimuthal component of the IMF. Here, the data are evaluated in the context of the theory and it is shown that the observed flux deficits generally agree with predictions by the MHD model. Furthermore, the MHD interaction is an attractive candidate for explaining the flux redistribution because it is conceptually simple and represents a direct body force on the plasma that does not depend on internal plasma processes. Important ingredients in the theory include the strength of the IMF, the magnitude of the solar wind flow speed, and possible meridional gradients in the flow speed, temperature, density, and radial field strength.
A new VLF method for studying burst precipitation near the plasmapause
Authors: Carpenter D. L. , Inan U. S. , Paschal E. W. , Smith A. J.
Published: February 2008

VLF signals in the 2–4 kHz range transmitted from Siple Station, Antarctica (L ∼ 4.3), and received at various Antarctic locations have been used to detect the occurrence of burst precipitation of electrons (E ≥ 50 keV) into the nighttime lower ionosphere. The receiving stations, each ∼1400 km from Siple, were located to the north at Palmer (L ∼ 2.3), to the east at Halley (L ∼ 4.3), and to the south at South Pole (Λ ∼ 74°). Rapid changes in the received phase and amplitude of the Siple signal (“Trimpi events”) were observed in conjunction with the reception of one‐hop whistlers. In one case involving propagation paths lying poleward of the plasmapause, amplitude decreases by ∼20% in ∼2 s, decaying in ∼7 s, were recorded simultaneously at Halley and South Pole. Post facto analysis of the South Pole records using a new digital processing scheme showed corresponding fast phase advances of ∼15 µs. In a case of phase perturbations at Palmer, the Siple signal path crossed the plasmapause projection, and the associated whistlers propagated in the outer plasmasphere. Phase measurements appear to be a particularly sensitive means of detecting burst precipitation activity under experimental conditions of the kind described. The length and spatial distribution of the signal paths provide a basis for studying the occurrence and approximate location of burst precipitation in regions outside the observing range of most instruments used for detection of precipitation. Direction finding on correlated whistler events as well as dispersion analysis may be used to increase the spatial resolution of the method.
The energization of electrons and ions by electron beams injected in the ionosphere
Authors: Arnoldy R. L. , Pollock Craig , Winckler J. R.
Published: February 2008

When intense beams of 10‐ to 40‐keV electrons are injected into the auroral zone ionosphere, a large suprathermal electron flux of up to 1013 electrons (cm² s sr keV)−1 greater than 10 eV energy appears in the region of space surrounding the beam‐injecting vehicle. The intensity of these electrons increases with altitude and can be quenched by the release of neutral gas. These electrons when measured aboard the beam‐emitting payload are undoubtedly related to the neutralization of this payload. The neutralizing electron current forms a discharge around the accelerator payload during beam emission as measured by photometers. The suprathermal electrons are probably produced by collective plasma effects in this neutralization process. Suprathermal electrons are also observed when relatively low electron beam fluxes reflected from the atmosphere below the rocket pass near the payload after the electron accelerator has been turned off. These electrons are apparently produced by a beam‐plasma interaction. The process of electron beam injection accelerates ions observed on the beam‐emitting vehicle with a spectrum extending to a broad peak at about 0.5 keV seen only in the direction perpendicular to B. The exact nature of the acceleration process is not known. In the thermal ion region (few eV) during beam injection, sporadic fluxes similar to ambient intensities are observed, but immediately after gun turn‐off, only a greatly depleted portion of the spectrum remains. The thermal ions' recovery only after several seconds indicates a space charge region up to 1 km in radius. Evidence that ions could play a major role in the plasma processes accompanying beam injection is presented. Oscillations at or near heavy ion gyroperiods are seen in the payload neutralization current, in the luminous sheath surrounding the payload, and in the intensity of 0.5‐keV suprathermal electrons. The oscillating electron intensities are apparently responsible for the luminous oscillations, and both phenomena are out of phase with the return current which flows radially inward to the vehicle. This may represent an oscillating sheath in which the ions gyrate in phase inward and outward in a purely radial mode. It is speculated that ion interactions might be responsible for partially quenching an intense plasma discharge at each accelerator turn‐on. An attempt is made in this paper to draw a parallel between some of the above mentioned beam injection effects and similar observations relating to natural auroral plasmas.
Parametric excitation of collisional modes in the high‐latitude ionosphere
Authors: Stenflo L.
Published: February 2008

This paper points out that the nonlinear coupling of a large‐amplitude electromagnetic pump wave with convective plasma fluid instabilities is significantly enhanced by pump‐induced temperature changes. It should thus be easy to exceed the threshold values for parametric instabilities in several ionospheric heating experiments.
Bremsstrahlung X ray images of isolated electron patches at high latitudes
Authors: Imhof W. L. , Voss H. D. , Datlowe D. W. , Mobilia J.
Published: February 2008

Small isolated patches of energetic electron precipitation have been observed at high latitudes with a bremsstrahlung X ray imager in the Stimulated Emission of Energetic Particles (SEEP) payload on the polar‐orbiting S81‐1 satellite. Twenty‐nine patches of X rays (>4 keV) with typical widths of ∼200 km were observed in June 1982 at invariant latitudes between 65° and 83° with a median latitude of 72.5°. The majority of X ray patches occurred from dusk until dawn, but a few were present in the early afternoon hours. The observed energy spectra were relatively soft (e fold energies about 1–6 keV) and independent of invariant latitude, magnetic local time, or geomagnetic activity. The occurrence frequency of the patches was somewhat greater at times of high geomagnetic activity. The patches were usually oblong by factors up to 3.7, with a median value of 1.75. No strongly preferred alignment was found. Comparisons of the direct electron measurements and the X ray observations from the same satellite have shown that in some cases the small isolated patches of electron precipitation at high latitudes may undergo significant changes in position on time scales of the order of a few seconds.
Thermospheric and ionospheric structure of the southern hemisphere polar cap on October 21, 1981, as determined from Dynamics Explorer 2 satellite data
Authors: Emery B. A. , Roble R. G. , Ridley E. C. , Killeen T. L. , Rees M. H. , Winningham J. D. , Carignan G. R. , Hays P. B. , Heelis R. A. , Hanson W. B. , Spencer N. W. , Brace L. H. , Sugiura M.
Published: February 2008

The Dynamics Explorer satellite (DE 2) passed over the Southern Hemisphere polar cap on orbit 1174 between 2326 UT and 2345 UT on October 21, 1981. The altitude of the satellite over the polar cap ranged between 325 and 390 km, and the local times were about 2100 LT on the down leg and 0900 LT on the up leg portions of the orbit. The full complement of instruments on the DE 2 satellite were making measurements during this pass. The electron precipitation spectra detected at a pitch angle of 7.5° were averaged over 8‐s intervals (0.5° latitude), and these spectra were used in an auroral model to calculate the ionization rates below the satellite in an atmosphere determined from the neutral temperature and composition measurements. These vertical ionization rate profiles are combined with solar photoionization rate profiles and used in a photochemical equilibrium model with O+ diffusion to calculate the electron and ion densities below the satellite. The electron and ion temperatures are also calculated assuming a local thermal energy balance, and the temperatures and densities are used to calculate the parallel, Pedersen, and Hall electrical conductivities. The total neutral gas heating rate is also calculated from four main sources: (1) particle heating, (2) Joule heating, (3) solar EUV heating, and (4) solar Schumann‐Runge heating. The particle heating is determined by multiplying the particle ionization rate by a particle heating efficiency determined from earlier studies. Joule heating at the satellite altitude is determined from the calculated Pedersen conductivity and the relative difference between the measured ion drifts and the neutral winds. Below the satellite altitude the Joule heating is calculated using the winds from the National Center for Atmospheric Research, Boulder, Colo. (NCAR) thermospheric general circulation model (TGCM) and a mapping of the measured ion drift into the lower ionosphere. The TGCM winds are shown to be in reasonable agreement with the measured winds at the satellite height. For this satellite pass the height‐integrated Joule heating exceeds both the auroral particle heating and the solar heating rates over the entire magnetic polar cap. The neutral gas heating rates peak in the vicinity of the morning auroral oval where the electric field increases abruptly from typical polar cap values of 30 mV m−1 to a high of about 100 mV m−1 just poleward of the dayside cusp aurora. Comparisons are made between the ionospheric properties derived from orbit 1174 and the corresponding properties used as parameterizations for the TGCM.
Model calculations of currents and magnetic fields along a Magsat trajectory
Authors: Dremuhina L. A. , Feldstein Y. I. , Levitin A. E.
Published: February 2008

Recent models have made it possible to obtain distributions of ionospheric and field‐aligned currents at high latitudes from surface magnetic observations. The surface geomagnetic field variations at high latitudes are closely associated with interplanetary medium parameters. As a result, a model has been developed that estimates high‐latitude current distributions directly from the interplanetary magnetic field and solar wind values. Ionospheric and field‐aligned current distributions computed with this technique are compared to the distributions computed directly from the Magsat magnetic field observations by Zanetti et al. [1983]. There are small variations in the two results, which are apparently due to the different resolutions of the two techniques. However, the current distributions computed from the different techniques are similar.
The N II 2143‐Å dayglow from Spacelab 1
Authors: Torr Marsha R. , Torr D. G.
Published: February 2008

During the Spacelab 1 shuttle mission (November 28 to December 7, 1983) spectral measurements were made in the ultraviolet which resolve the N+(5S) doublet at 2143 Å from the NO (1‐0) gamma band at 2148 Å in the upper thermosphere. The measured slant path surface brightness profile of the N+ feature is well explained by photodissociative ionization of N2 with a yield of 0.2. The intensity of the N+ feature relative to the NO (1‐0) gamma band is dependent on the conditions prevailing at the time and location of the measurement. For the near‐twilight mid‐latitude measurements made here, in the upper themosphere the N+(5S) feature would contribute 20% to 75% of a low spectral resolution NO measurement.
Subionospheric VLF/LF phase perturbations produced by lightning‐whistler induced particle precipitation
Authors: Inan U. S. , Carpenter D. L. , Helliwell R. A. , Katsufrakis J. P.
Published: February 2008

New evidence of phase perturbations of subionospheric VLF/LF signals, produced by lightning‐whistler‐induced precipitation of bursts of radiation belt electrons, is reported. Phase changes of 0.1–1.0 µs on a 12.9‐kHz signal arriving at Palmer, Antarctica (L ∼ 2.4), over a ∼2400‐km path are regularly observed with a characteristic signature of a rapid (≤ 1 s) onset followed by a relatively slow (10–30 s) recovery. Event occurrence peaks during equinoctial periods, with typical rates of 1–40 events per hour lasting for several hours per night. The observed phase perturbations can be interpreted to correspond to a rapid reduction of up to ∼0.1–1.0 km in the effective nighttime ionospheric reflection height (∼85 km) for the subionospheric VLF signals. The incident energetic particle fluxes that are required to produce the extra ionization are estimated to be ∼10−3‐10−2 ergs cm−2 s−1. Such flux levels are generally consistent with those estimated using theoretical models of whistler‐particle resonant scattering as well as direct satellite‐based observations of whistler‐induced precipitation. This phenomenon provides a sensitive means for detecting wave‐induced burst particle precipitation. The ionospheric perturbations resulting from such precipitation may cause significant errors in certain global navigation aids, such as the Differential Omega and LORAN‐C systems.
A simulation study of two major events in the heliosphere during the present sunspot cycle
Authors: Akasofu S.‐I. , Fillius W. , Sun Wei , Fry C. , Dryer M.
Published: February 2008

The two major disturbances in the heliosphere during the present sunspot cycle, the event of June–August 1982 and the event of April–June 1978, are simulated by the method developed by Hakamada and Akasofu (1982). Specifically, we attempt to simulate effects of six major flares from three active regions in June–July 1982 and April‐May 1978, respectively. A comparison of the results with the solar wind observations at Pioneer 12 (∼0.8 AU), ISEE 3 (∼1 AU), Pioneer 11 (∼7–13 AU), and Pioneer 10 (∼16–28 AU) suggests that some major flares occurred behind the disk of the sun during the two periods. Our method provides qualitatively some information as to how such a series of intense solar flares can greatly disturb both the inner and outer heliospheres. A long lasting effect on cosmic rays is discussed in conjunction with the disturbed heliosphere.
Energetic electron flux pulsations observed at geostationary orbit: Relation to magnetic pulsations
Authors: Takahashi Kazue , Higbie Paul R. , Baker Daniel N.
Published: February 2008

Energetic electron data (30–300 keV) from Los Alamos National Laboratory charged particle analyzers on board geostationary satellites were compared with magnetic field data from the GOES 3 geostationary satellite to study electron flux pulsations in the Pc 4–5 frequency range. From particle data and magnetic field data obtained with the satellites located only a small spatial distance apart, it is found that 60% of electron flux pulsation events have clearly associated magnetic pulsations. The magnetic pulsations have three different polarization and frequency characteristics: radially polarized Pc 4, azimuthally polarized Pc 5, and compressional Pc 5. Based on theoretical work presented by Southwood and Kivelson, it is concluded that the possible causes of the observed flux modulations are convection of a particle density gradient for the radially polarized Pc 4; the mirror effect, adiabatic acceleration, or convection of a particle density gradient for the azimuthally polarized Pc 5; and the mirror effect for the compressional Pc 5. Using data from geostationary satellites located at different magnetic latitudes, it is also found that the occurrence probability increases with latitude for the Pc 4 electron flux pulsations, whereas the probability is independent of the latitude for the Pc 5 pulsations. This is interpreted as due to the fundamental (Pc 5) and second harmonic (Pc 4) structure of standing waves. The electron flux pulsations which do not accompany magnetic pulsations are attributed to azimuthally polarized fundamental standing waves that have a magnetic node very close to the satellites.
Chatanika radar and S3‐2 measurements of auroral zone electrodynamics in the midnight sector
Authors: Robinson R. M. , Rich F. , Vondrak R. R.
Published: February 2008

Measurements made by the incoherent scatter radar at Chatanika, Alaska, have been combined with S3‐2 satellite data to study the relationships between conductivities, electric fields, and currents near the Harang discontinuity. Three S3‐2 passes were chosen for the study, based on the quality of the radar and satellite data and the availability of supplementary ground‐ and space‐based observations. The radar measured electric fields and conductivities as a function of latitude and local time. The satellite measured the latitudinal distribution of electric field and field‐aligned current during the three polar passes. The dominant field‐aligned current in the midnight sector is upward. Equatorward of this current a downward sheet is observed which is the eastern end of the evening sector region 2 sheet. Poleward of the upward current are several sheets of varying directions and magnitudes. These sheets are associated with active aurora during substorms. The most intense electric fields were located at the poleward and equatorward boundaries of the upward current sheet. A model is presented which demonstrates the self‐consistency of the observed relationships between conductivities, electric fields, and currents.
Deformation of the heliospheric current sheet
Authors: Suess S. T. , Hildner E.
Published: February 2008

A kinematic analysis of the previously neglected effect of velocity inhomogeneity on the topology of the heliospheric current sheet in a radially flowing solar wind shows how the originally smooth current sheet becomes “ruffled.” In the highly idealized case of a totally uniform, radial, steady solar wind, the shape of the current sheet is independent of distance from the sun. However, the real solar wind is inhomogeneous; the velocity varies from point to point along the current sheet, causing a distortion in the current sheet of progressively greater amplitude with increasing distance from the sun. This is true even for purely radial flow. Significant and observable distortion is produced by relatively small gradients in velocity; thus to predict or understand the shape of the heliospheric current sheet it is essential to know the solar wind in which the current sheet is embedded. We give examples of mild velocity gradients which demonstrate the principles, the magnitude, and the character of the effect; deformation of the actual heliospheric current sheet in the highly variable solar wind is expected to be of far greater amplitude and complexity than in the simplified, tutorial examples. We also derive a new expression for the inclination of the current sheet as a function of velocity inhomogeneity and distance from the sun that is easily applied to the interpretation of solar wind data.
A statistical study of solar type III bursts and auroral kilometric radiation onsets
Authors: Farrell W. M. , Gurnett D. A.
Published: February 2008

Simultaneous occurrences of type III solar radio bursts and auroral kilometric radiation were observed by Calvert using ISEE 1 spectrograms. He presented evidence suggesting that the incoming type III burst stimulates the onset of auroral kilometric radiation (AKR). This paper presents a statistical study of the correlation between type III bursts and auroral kilometric radiation. A superposed epoch analysis was performed on as many as 186 type III events. The type III bursts were detected by the ISEE 3 spacecraft on the sunward side of the earth. At the same time the IMP 8 spacecraft was used to detect onsets of kilometric radiation on the nightside of the earth. For each event the intensities measured by ISEE 3 (type III intensities) were subtracted from the intensities measured by IMP 8 (type III and possible AKR intensities). The resulting intensities for each event were then added to determine if kilometric radiation was preferentially observed following a type III burst. This analysis was performed at frequencies of 100, 178, and 500 kHz. The results of this study show that a statistically significant correlation exists between incoming type III bursts from the sun and kilometric radiation from the earth.
Electrical measurements in the atmosphere and the ionosphere over an active thunderstorm: 2. Direct current electric fields and conductivity
Authors: Holzworth R. H. , Kelley M. C. , Siefring C. L. , Hale L. C. , Mitchell J. D.
Published: February 2008

On August 9, 1981, a series of three rockets were launched over an air mass thunderstorm off the eastern seaboard of Virginia while simultaneous stratospheric and ground‐based electric field measurements were made. The conductivity was substantially lower at most altitudes than the conductivity profiles used by theoretical models. Direct current electric fields over 80 mV/m were measured as far away as 96 km from the storm in the stratosphere at 23 km altitude. No dc electric fields above 75 km altitude could be identified with the thunderstorm, in agreement with theory. However, vertical current densities over 120 pA/m² were seen well above the classical “electrosphere” (at 50 or 60 km). Frequent dc shifts in the electric field following lightning transients were seen by both balloon and rocket payloads. These dc shifts are clearly identifiable with either cloud‐to‐ground (increases) or intercloud (decreases) lightning flashes.
Flux loss from the geomagnetic tail
Authors: Hill T. W.
Published: February 2008

The open model of the magnetosphere requires that the magnetic flux in the geomagnetic tail decrease at least linearly with increasing downstream distance. The length scale of this minimum uniform gradient is the tail length, estimated to be of the order of 10³ RE. The distant tail data from ISEE 3, contrary to earlier reports, are fully consistent with the existence of such a gradient.
Magnetospheric responses to the gradient drift entry of solar wind plasma
Authors: Olson W. P. , Pfitzer K. A.
Published: February 2008

Historically, it has been assumed that all solar wind particles are specularly reflected off of the magnetopause. However, because the presence of solar wind plasma is required for the maintenance of many features observed in the ground state magnetopshere, several mechanisms for the transport of energy, mass and momentum through a closed magnetopause have been postulated. In this paper, the consequences of the gradient drift entry (GDE) of charged particles into the magnetosphere are examined qualitatively. It occurs even for particles with solar wind energies because the geomagnetic field at the magnetopause is not precisely uniform and a portion of the incident charged particles are in reality not specularly reflected. This process (which is a direct consequence of particle interactions with a realistically nonuniform geomagnetic field) will, if allowed to operate unimpeded, immediately produce large charge excesses over certain regions of the magnetopause since the GDE process allows only one charge species (either positive ions or electrons) entry to the magnetosphere at a given location. In this paper we attempt to take the first qualitative steps toward a model that will quantitatively and self‐consistently explain the responses of the magnetosphere that may act to limit this charge buildup. Qualitatively, we find the following: (1) The GDE process operates at all times. (2) It provides magnetosheath plasma directly to the equatorial flanks of tail and to the high latitude dayside magnetosphere. (3) This process produces a buildup of excess charge along the flanks of the tail. (4) The direction of current flow in the magnetosphere (to partially dissipate this charge buildup) is always in agreement with observations: dawn to dusk across the tail; along magnetic field lines toward (away from) the ionosphere in the dawn (dusk) hemisphere; and dusk to dawn over the tail lobes. (5) Since the magnetospheric response is not expected to completely get rid of the continuously formed charge buildup, in the steady state electrostatic fields will remain. Their direction is also as observed: dawn to dusk across the tail; dawn to dusk across the polar cap; and dusk to dawn across the low latitude boundary layer. Basically, we find qualitatively that (other than the formation of the magnetopause by the majority of incident solar wind particles which are reflected) many steady state features and processes (plasmas, electric currents and fields) are formed in the magnetosphere in response to the regions of charge excess produced by the gradient drift entry process. The locations and directions of these plasmas, electric currents and fields are all in agreement with those observed in the magnetosphere. Work is in progress on the further definition of this model with emphasis on a quantitative self‐consistent description of the impact of the GDE process on the tail of the magnetosphere.
Nonresonant interaction of heavy ions with electromagnetic ion cyclotron waves
Authors: Berchem Jean , Gendrin Roger
Published: February 2008

The motion of a heavy ion in the presence of an intense ultralow‐frequency electromagnetic wave propagating along the dc magnetic field is analyzed. Starting from the basic equations of motion and from their associated two invariants, the heavy ion velocity‐space trajectories are drawn. It is shown that after a certain time, particles whose initial phase angles are randomly distributed tend to bunch together, provided that the wave intensity, b1 is sufficiently large. The maximum perpendicular velocity υa which the particle reaches during the bunching process can be a fraction of the Alfvén velocity. When the wave frequency f is smaller than the heavy ion gyrofrequency, F, υa is maximum for waves with frequencies slightly smaller than F. When the wave frequency is larger than the cutoff frequency fco, υa is a continuously decreasing function of f. In both cases, υa is proportional to b1/|F ‐ f| when b1 is small and/or |F ‐ f| is large, and it is proportional to (b1/f)1/3 when b1 is large and/or |F ‐ f| is small. The process is nonresonant in the sense that it is efficient however small is the heavy ion initial parallel velocity. A parameter study is done which gives the process efficiency for different wave or particle characteristics. Approximate analytical expressions are given, and they are compared with the results of numerical computations. The importance of these results for the interpretation of the recently observed acceleration of He+ ions in conjunction with the occurrence of large‐amplitude ion cyclotron waves in the equatorial magnetosphere is discussed.
Pulsating aurora and hydrogen emissions
Authors: Viereck R. A. , Stenbaek‐Nielsen H. C.
Published: February 2008

From all‐sky TV and meridian scanning photometer data, obtained at Poker Flat, Alaska, during the 1982/1983 winter, 12 nights with extensive displays of pulsating aurora were selected for analysis. The majority of the pulsations were located near the equatorward edge of the proton aurora as identified by the Hβ emission; however, on two nights, pulsating aurora was also observed embedded in the main region of the proton aurora. The period of the pulsations varied from 3 to 25 s and appeared to be correlated with the Hβ intensity. The short periods corresponded to weak Hβ emissions while no pulsations were observed above 80 R in Hβ. The change in period appeared to be caused mainly by a variation in the time between individual pulses.
Azimuthal propagation of storm time Pc 5 waves observed simultaneously by geostationary satellites GOES 2 and GOES 3
Authors: Lin C. S. , Barfield J. N.
Published: February 2008

Storm time Pc 5 wave events observed simultaneously by the GOES 2 and GOES 3 satellites in the afternoon sector during the 1‐year interval March 1979 to February 1980 are surveyed to learn the wave propagation. Essentially, all storm time Pc 5 waves (∼93%) are found to propagate westward azimuthally with a velocity of 5 to 50 km/s and a wavelength of 1000 km to 9000 km. (Only two of 30 events had eastward propagation with a velocity of about 150 km/s). We conclude that westward propagating waves are excited by ion drift instabilities associated with the ion ring current and that the eastward propagating waves are excited by surface waves on the magnetopause through Kelvin‐Helmholtz instability.
Transverse motion of high‐speed barium clouds in the ionosphere
Authors: Mitchell H. G. , Fedder J. A. , Huba J. D. , Zalesak S. T.
Published: February 2008

Simulation results, based on a field‐line‐integrated, two‐dimensional, electrostatic model, are presented for the motion of a barium cloud injected transverse to the geomagnetic field in the ionosphere at high speeds. It is found that the gross evaluation of injected plasma clouds depends on the initial conditions, as well as the nature of the background coupling. For a massive (M0 ∼ 10 kg), orbital (V0 ∼ 5 km/s) release in the F region (350–450 km), we find that plasma clouds can drift tens of kilometers across the magnetic field in tens of seconds after ionization. This type of release is similar to those which are planned for the Combined Release and Radiation Effects Satellite (CRRES) mission.
Evidence of solar wind energy deposition into the ionosphere of Mars
Authors: Mantas G. P. , Hanson W. B.
Published: February 2008

Suprathermal electron fluxes measured in the ionosphere of Mars by the retarding potential analyzer (RPA) on Viking lander 1 are presented and compared with the photoelectron flux that is produced by the absorption of the solar EUV. The calculation of the equilibrium photoelectron population on Mars is based on the multistream electron transport theory and a model neutral atmosphere and ionosphere that was actually observed by Viking lander 1. From the theoretical equilibrium photoelectron population we compute the expected RPA volt‐ampere characteristic curves and compare them with those recorded by the instrument. The theoretical and the observed RPA currents below ≃170 km are in agreement, confirming that the solar EUV is the main source of suprathermal electrons at these altitudes. Above ≃170 km an additional source of suprathermal electrons is required to explain the observations. We suggest that this source is supplied by the solar wind, either by direct particle entry or by wave‐particle coupling. The rate of attenuation of the topside suprathermal electron flux with altitude indicates that the ionosphere is permeated by a substantially horizontal (dip angle ≃15°) magnetic field.
Broadband Jovian kilometric radiation: New results on polarization and beaming
Authors: Leblanc Yolande , Daigne Gérard
Published: February 2008

Using the Voyager 1 and 2 (V1 and V2) planetary radio astronomy experiment, we have analyzed the data in the kilometric wavelength range from January to December 1979, the period which includes the Jupiter encounters for V1 and V2. Statistical studies of the broadband kilometric radiation (bKOM) reveal new results on the polarization and beaming of the emission. The northern and southern components are right‐hand and left‐hand, respectively polarized, without reversal at encounter. The central meridian longitude occurrence of these two components is dependent on the zenographic latitude of the observer. The shadowing by the Io plasma torus is confirmed, the boundaries of the emission beam have been deduced, and it is shown that the latitudinal beaming of the emission is dependent on local time, from dayside to nightside observations. Our results are discussed in terms of a source radiating in the extraordinary mode. It is suggested that the source regions are at the inner boundary of the Io torus all around the planet and that the emission is beamed into a hollow conical sheet whose axis coincides with the magnetic dipole of the planet. Radiation mechanisms are briefly discussed; the maser synchrotron instability and the non linear conversion of electrostatic waves could contribute to bKOM, each one in a limited frequency range.
ISEE observations of the magnetopause: Reconnection and the energy balance
Authors: Paschmann G. , Papamastorakis I. , Sckopke N. , Sonnerup B. U. Ö. , Bame S. J. , Russell C. T.
Published: February 2008

According to the usual magnetopause reconnection model, plasma flows across the magnetopause current sheet, which is a rotational discontinuity with a nonzero normal magnetic field component Bn, from the magnetosheath into the magnetospheric boundary layer. As the plasma crosses the sheet, which has net current I, it is accelerated by the I × Bn force and flows toward the poles with speeds up to twice the Alfvén speed. In the past a number of ISEE magnetopause crossings in which such plasma jetting was observed have been interpreted in terms of reconnection, on the basis of a quantitative check of the tangential velocity and magnetic field changes across the magnetopause. In this paper we examine the total energy balance for two of these events (August 9 and September 8, 1978) with the objective of obtaining an additional check on the interpretation in terms of reconnection. The results are as follows: (1) To within experimental and other uncertainties the plasma and magnetic field data appear consistent with reconnection. (2) An enthalpy increase comparable to the kinetic energy increase occurs in the magnetopause. Thus substantial dissipation, which we believe to be viscous in nature, is present in the rotational discontinuity. (3) During the September 8 event an ion heat flow associated with a beam of reflected magnetosheath particles carried away 10–20% of the total converted electromagnetic energy. (4) The energy balance is consistent with the previously inferred location of the ISEE spacecraft south of the reconnection line on August 9 and north of it on September 8, 1978. For a third event (December 4, 1977) examined here the magnetopause crossing occurred at a substantial northern latitude, but the plasma momentum change was equatorward rather than poleward, and there was little change in plasma kinetic energy. In this case we infer that normal magnetic field and flow components but no local reconnection electric field were present at the magnetopause.
Electrostatic ion cyclotron waves in a plasma with an ion beam and counterstreaming bulk electrons: Waves in the zero‐frequency band
Authors: Singh Nagendra , Conrad J. R. , Schunk R. W.
Published: February 2008

Electrostatic ion cyclotron (EIC) waves driven by electron currents and ion beams at frequencies near the harmonics of the ion‐cyclotron frequency have been extensively studied in the literature. Recently, however, EIC waves with nearly zero‐frequency in an ion‐beam‐plasma system were seen in numerical simulations. In the simulations, the excitation mechanism was the resonant excitation of the beam‐ion‐cyclotron modes by the relative drift of the target ions. These waves occurred at frequencies near zero in the frame of reference of the target ions because of the downward doppler shift. It is shown here that the counterstreaming background electrons, in addition to the target ions, make an important contribution to the growth rate of the EIC waves in the zero‐frequency band defined by |ωr| < Ωi, where ωi and Ωi are the wave and ion cyclotron frequencies, respectively. The growth mechanism is the Landau interaction of the negative energy (slow) ion‐cyclotron‐beam modes with the electrons. Since the counterstreaming of electrons (upward currents) and ion beams along auroral magnetic field lines is common in the region above parallel electric fields, this growth mechanism may be of relevance to satellite observations of waves and turbulence near zero frequency. It is shown that if the observed narrow‐banded zero‐frequency waves are those seen in the simulations, then the electron currents must be sufficiently weak or the current‐carrying electrons must be sufficiently hot. In that event, the relatively cold ion beams are the source of free energy for exciting the EIC waves. On the other hand, in the presence of sufficiently large currents or cold current‐carrying electrons, the narrow‐banded feature of the zero‐frequency waves is destroyed. Both isotropic and anisotropic ion beams were considered. For cold isotropic ion beams in a warm background plasma, the banded feature of the waves, which is an important characteristic of EIC waves, disappears and the excited waves become broadband. The banded feature appears if the isotropic beam temperature becomes comparable to that of the background plasma temperature or if the beam is anisotropic with the perpendicular temperature much larger than the parallel temperature.
Generation of auroral omega bands by shear instability of the neutral winds
Authors: Lyons L. R. , Walterscheid R. L.
Published: February 2008

Thermospheric neutral wind acceleration via ion drag in the conducting E‐region of the ionosphere is greatly increased by electron precipitation associated with auroras. This increased acceleration can lead to the development of significant horizontal wind shears, which we find are unstable to the Kelvin‐Helmholtz shear instability. Numerical simulation of the neutral response to an intense, postmidnight, diffuse aurora shows the formation of an E‐region “jet stream” within the aurora, with peak winds speeds >700 m/s after one hour. We propose that this jet stream produces unstable Kelvin‐Helmholtz waves, which can drive waves of discrete aurora along the poleward boundary of the preexisting diffuse aurora. We suggest that such auroral waves, driven by the neutral winds, form eastward propagating waves (omega bands) occasionally observed along the poleward boundary of postmidnight diffuse auroras. We also find neutral wind shears that develop in response to discrete auroral arcs to be unstable; however we do not expect the resulting wind waves to drive significant auroral waves along discrete arcs.
Fast and optimal solution to the “Rankine‐Hugoniot problem”
Authors: Viñas Adolfo F. , Scudder Jack D.
Published: February 2008

A new, definitive, reliable and fast iterative method is described for determining the geometrical properties of a shock (i.e., θBn, n, Vs and M A), the conservation constants and the self‐consistent asymptotic magnetofluid variables using the Rankine‐Hugoniot conservation equations. The technique uses the three dimensional magnetic field and plasma observations. The method is well conditioned and reliable at all θBn angles regardless of the shock strength or geometry. Explicit proof of “uniqueness” of the shock geometry solution by either analytical or graphical methods is given. The method is applied to synthetic and real interplanetary shocks, including a bow shock event and the results are then compared with those determined by preaveraging methods and other iterative schemes. A complete analysis of the confidence region and error bounds of the solution is also presented.
Gyrating and intermediate ion distributions upstream from the Earth's bow shock
Authors: Fuselier S. A. , Thomsen M. F. , Gosling J. T. , Bame S. J. , Russell C. T.
Published: February 2008

Study of ISEE 2 fast plasma data reveals that many suprathermal ion events that in previous studies would have been identified as intermediate ion events are actually gyrating ion events. Of 190 apparently intermediate ion events selected on the basis of their signature in energy‐time spectrograms, half are actually found to be gyrating ion events. Using a model bow shock, the shock geometries and spacecraft locations for the observed gyrating and intermediate ion events are compared and found to be quite similar. Both gyrating and intermediate ion events are found to be associated with upstream MHD‐like wave activity. Most gyrating ion events are associated with large‐amplitude, monochromatic, weakly compressive waves, whereas many intermediate ion events are associated with smaller‐amplitude, nonmonochromatic, weakly compressive waves. Some intermediate ion events are found to have no associated waves. Detailed study of the gyrating ion distributions reveals that the distributions are typically gyrotropic within ∼4 RE of the bow shock, whereas at larger distances (up to ∼10 RE) upstream from the shock the distributions are frequently “gyrophase bunched.” In light of these observational characteristics it is concluded that gyrating ion distributions are most likely generated both through coherent wave disruption of field‐aligned beams and through reflection of solar wind ions off the shock.