bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of electrostatic waves by discontinuous electron distributions
Authors: Yin L. , Ashour‐Abdalla M. , Richard R. L. , Frank L. A. , Paterson W. R.
Published: September 2002

This paper presents studies of narrowband electrostatic waves (NEN) in the distant lobe region and electrostatic waves in the bow shock and slow mode shocks. Geotail measurements from the tail lobe region show a two‐humped feature in the low‐energy region of the parallel electron distributions correlated with lobe NEN emissions. Unstable waves were found in our linear dispersion and simulation studies initialized with the measured electron distributions. The wave energy density, wave frequency, and waveform were comparable with those from spacecraft observations. The electron contribution to bow shock and slow mode shock wave spectra was examined with the use of a parallel electron distribution model function that featured flat tops and single peaks drifting with speeds of the order of the effective electron thermal speed. The model assumed a possible discontinuity in the parallel distribution. Results from the model included waves with frequencies above the ion plasma frequency (ωpi) but well below the electron plasma frequency (ωpe) as well as broadband, higher‐frequency waves extending to ωpe. In addition, wave frequencies increased and growth rates and wave energy density decreased as the peak offset speed increased and the peak height decreased during a shock penetration. Dispersions from both linear theory and simulation were obtained in our studies. The unstable waves had a broad k range with kλD exceeding unity. For waves with frequencies well below ωpe, the frequency decreased further during the evolution of the electron distribution.
Energetic particles in the duskside Jovian Magnetosphere
Authors: Krupp Norbert , Dougherty M. K. , Woch J. , Seidel R. , Keppler E.
Published: September 2002

The paper provides a detailed description of energetic ion measurements from the Energetic P article Composition instrument (EPAC) and magnetic field measurements from the dual‐technique magnetometer on board Ulysses made in the duskside Jovian magnetosphere after its Jupiter flyby on February 8, 1992. The Ulysses spacecraft performed these in situ measurements on its outbound trajectory passing through the local time sector between 2100 and 1830 from northern to relatively high southern latitudes. The outbound pass is divided into six different regions, which are differentiated by magnetic field measurements and by the behavior of the particle intensities, ion spectra, and composition, as well as ion anisotropies. At a distance of 21 RJ the energy spectrum of 0.57–1.42 MeV protons suddenly becomes much softer, indicative of a transition between a dipolar‐like inner magnetosphere and the inner edge of the plasma sheet. The EPAC instrument observes a dramatic increase in all particle intensities at distances around 50 RJ at southern magnetic latitudes of 30° S. The intensity levels are as high as those observed during the inbound equatorial plasma sheet crossings at comparable distances. The increase is interpreted as a temporal phenomenon associated with a thickening of the plasma sheet. After the first magnetopause crossings at distances near 80 RJ, EPAC measurements reveal signatures of magnetospheric particles existing in the magnetosheath which imply that the Jovian magnetosphere is open. Following a change in the interplanetary magnetic field orientation, these particles are then no longer observed within the magnetosheath. A further puzzling particle observation along the Ulysses outbound pass is the reentry into the magnetosphere between 115 and 124 RJ at 37° southern magnetic latitude. It impressively shows the high variability of the Jovian magnetosphere.
Dissipation range dynamics: Kinetic Alfvén waves and the importance of βe
Authors: Leamon Robert J. , Smith Charles W. , Ness Norman F. , Wong Hung K.
Published: September 2002

In a previous paper we argued that the damping of obliquely propagating kinetic Alfvén waves, chiefly by resonant mechanisms, was a likely explanation for the formation of the dissipation range for interplanetary magnetic field fluctuations. This suggestion was based largely on observations of the dissipation range at 1 AU as recorded by the Wind spacecraft. We pursue this suggestion here with both a general examination of the damping of obliquely propagating kinetic Alfvén waves and an additional examination of the observations. We explore the damping rates of kinetic Alfvén waves under a wide range of interplanetary conditions using numerical solutions of the linearized Maxwell‐Vlasov equations and demonstrate that these waves display the nearly isotropic dissipation properties inferred from the previous paper. Using these solutions, we present a simple model to predict the onset of the dissipation range and compare these predictions to the observations. In the process we demonstrate that electron Landau damping plays a significant role in the damping of interplanetary magnetic field fluctuations which leads to significant heating of the thermal electrons.
An interhemispheric study of the ground magnetic and ionospheric electric fields during the substorm growth phase and expansion phase onset
Authors: Yeoman T. K. , Lewis R. V. , Milan S. E. , Watanabe M.
Published: September 2002

HF radar data during equinoctial, small IMF By conditions have enabled the substorm growth phase to be studied in both hemispheres. This has revealed highly conjugate behavior during the substorm growth phase. The characteristic equatorward progression of the radar backscatter in both hemispheres is well matched by a calculation of the position of the equatorward boundary of the radar backscatter, based on an estimate of the reconnection rate at the magnetopause and the relationship between the cross polar cap potential and the change in polar cap area. Coincident radar backscatter and DMSP precipitation measurements suggest that there is a close relationship between the location of the radar backscatter and structured nightside precipitation. This nightside relationship appears to be analogous to the close relationship between radar backscatter and the targets provided by precipitation at the cusps on the dayside. The high degree of conjugacy during the growth phase mirrors the high degree of conjugacy known to exist between the substorm electrojets. However, in detail, and during the expansion phase, there are significant non‐conjugacies displayed in, e.g., the degree of HF absorption in the two hemispheres. This nonconjugacy appears similar to that recently observed in interhemispheric optical data.
Evidence of component merging equatorward of the cusp
Authors: Chandler M. O. , Fuselier S. A. , Lockwood M. , Moore T. E.
Published: September 2002

The Polar spacecraft passed through a region near the dayside magnetopause on May 29, 1996, at a geocentric distance of ∼8 RE and high, northern magnetic latitudes. The interplanetary magnetic field (IMF) was northward during the pass. Data from the Thermal Ion Dynamics Experiment revealed the existence of low‐speed (∼50 km s−1) ion D‐shaped distributions mixed with cold ions (∼2 eV) over a period of 2.5 hours. These ions were traveling parallel to the magnetic field toward the Northern Hemisphere ionosphere and were convecting primarily eastward. The D‐shaped distributions are distinct from a convecting Maxwellian and, along with the magnetic field direction, are taken as evidence that the spacecraft was inside the magnetosphere and not in the magnetosheath. Furthermore, the absence of ions in the antiparallel direction is taken as evidence that low‐shear merging was occurring at a location southward of the spacecraft and equatorward of the Southern Hemisphere cusp. The cold ions were of ionospheric origin, with initially slow field‐aligned speeds, which were accelerated upon reflection from the magnetopause. These observations provide significant new evidence consistent with component magnetic merging sites equatorward of the cusp for northward IMF.
Small and very small interstellar grains
Authors: Witt A. N.
Published: September 2002

This review summarizes the observational characteristics of those interstellar grains, which are prevented from entering the solar system by interactions with the heliopause. Such grains are typically <100 nm in radius, and they reveal their presence by interstellar absorption at ultraviolet wavelengths and by nonequilibrium emissions in the red and near‐infrared portions of the spectrum.
The midlatitude ionosphere during the total solar eclipse of March 9, 1997
Authors: Boitman O. N. , Kalikhman A. D. , Tashchilin A. V.
Published: September 2002

The total solar eclipse of March 9, 1997, was visible from some regions of China, Mongolia, and East Siberia during 0045–0130 UT. The eclipse coincided with a relatively long geomagnetically quiet period. During the total solar eclipse, the observations included oblique‐incidence ionograms recording; also measurement the total electron content along specified directions to the visible Global Positioning System satellites and the Doppler sounding on various HF ray paths over the region under consideration were carried out. This paper presents results derived from studying the spatial pattern of midlatitude ionospheric response to this eclipse on the basis of a numerical simulations. Calculations have been executed using a model for ionosphere‐plasmasphere coupling. Comparison of model results with data of all measurements showed a good qualitative and quantitative agreement. It is shown that by and large the behavior of the ionosphere during the eclipse manifests itself as a short‐lasting (∼l‐hour) rearrangement to nighttime conditions with the ion flow directed downward from the plasmasphere, as a rise of the F2 layer maximum by about 20 km, and as a twofold increase in electron density at the height of the maximum during the eclipse's totality phase. The electron temperature decreases by 200–400 K, while the ion temperature drops only slightly. It is found that changes in the spatial distribution of electron density along the HF ray paths during the eclipse give rise to variations of Doppler frequency shift with amplitudes of about 1 Hz and a duration of about 120 min. The findings reported in this paper do not validate the hypothesis that solar eclipses generate atmospheric gravity waves and associated traveling ionospheric disturbances.
A multipoint determination of the propagation velocity of a sudden commencement across the polar ionosphere
Authors: Engebretson M. J. , Murr D. L. , Hughes W. J. , Lühr H. , Moretto T. , Posch J. L. , Weatherwax A. T. , Rosenberg T. J. , Maclennan C. G. , Lanzerotti L. J. , Marcucci F. , Dennis S. , Burns G. , Bitterly J. , Bitterly M.
Published: September 2002

We use magnetic field and riometer data from ground observatories in both the Arctic and Antarctic regions to characterize the high‐latitude propagation of a sudden storm commencement (SC) that occurred at 0901 UT February 21, 1994. (1) High time resolution magnetic field data from both hemispheres indicate extremely rapid propagation of the initial part of the SC signal at high latitudes. An initial inflection point was observed in the data from dawn sector stations in both polar caps nearly simultaneously (Δt <2 s) but ∼3 s earlier in the southern hemisphere. (2) Data from the Magnetometer Array for Cusp and Cleft Studies (MACCS) in Arctic Canada, with stations from 0130 to 0600 magnetic local time, indicate dispersive propagation of the preliminary impulse (PI) at speeds decreasing from ∼150 to ∼50 km/s, directly away from a source near or slightly poleward of the cusp, rather than along the auroral oval. (3) Plots of two‐dimensional, 20‐s resolution equivalent convection vectors in the Northern Hemisphere reveal the imposition and rapid propagation and decay of a short‐lived large‐scale flow pattern opposite to the normal dawn sector flow, followed by an intensification of the original pattern. However, the perturbed flows were not dominated by the localized, tailward propagating vortices predicted in some models of SC events. In both hemispheres, observations of the PI are consistent with the temporary imposition of a field‐aligned current pair antisymmetric about local noon in the polar ionosphere and with horizontal fast mode propagation of a pulse through the ionosphere. (4) Riometer signatures do not match the magnetic variations in either time or intensity, and they propagate with a much lower velocity (∼1 km/s). We infer that the initial magnetic signatures are generated by the arrival of Alfvén waves and associated Birkeland currents at the near‐cusp ionosphere, while the riometer signatures at these high latitudes are generated predominantly by interplanetary particles associated with the causative coronal mass ejection.
The galactic environment of the Sun
Authors: Frisch Priscilla C.
Published: September 2002

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun and constrains the physical characteristics of the interplanetary medium. This paper compares interstellar dust grain properties observed within the solar system with dust properties inferred from observations of the cloud surrounding the solar system. Properties of diffuse clouds in the solar vicinity are discussed to gain insight into the properties of the diffuse cloud complex flowing past the Sun. Evidence is presented for changes in the galactic environment of the Sun within the next 104–106 years. The combined history of changes in the interstellar environment of the Sun, and solar activity cycles, will be recorded in the variability of the ratio of large‐ to medium‐sized interstellar dust grains deposited onto geologically inert surfaces. Combining data from lunar core samples in the inner and outer solar system will assist in disentangling these two effects.
Magnetospheric response to magnetic cloud (coronal mass ejection) events: Relativistic electron observations from SAMPEX and Polar
Authors: Kanekal S. G. , Baker D. N. , Blake J. B. , Klecker B. , Mewaldt R. A. , Mason G. M.
Published: September 2002

In this paper we report on relativistic electron (energies of ≳ 2 MeV) observations using detectors onboard SAMPEX and Polar satellites. The spacecraft orbits are such that a global view of the outer zone is obtained covering a wide range of energy and pitch angle. We have examined the magnetospheric electron effects of nine magnetic cloud events identified using sensors onboard the Wind spacecraft. It is confirmed, as suspected from earlier, more limited work, that the relativistic electron flux enhancements in outer zone show a high degree of coherence that is largely independent of pitch angle,Lshell and energy. Furthermore, the flux enhancements occur over a broad range ofLvalues. The observations imply that the underlying acceleration mechanism(s) are of a global nature operating simultaneously over much of the outer zone.
Structure of the magnetospheric magnetic field during magnetic storms
Authors: Dremukhina L. A. , Feldstein Y. I. , Alexeev I. I. , Kalegaev V. V. , Greenspan M. E.
Published: September 2002

We report the results of a study of the contributions of the largescale magnetospheric currents to the observed Dst variation. Ground‐based magnetometer data during four magnetic storms (January 27–30, 1985; November 23–27, 1986; January 14–16, 1988; and May 6–8, 1988) were used to calculate Dst, and the paraboloid model of the magnetospheric magnetic field [Alexeev et al., 1996] was used to determine the contribution of each magnetospheric current system. Input data for our model were the solar wind plasma parameters, the interplanetary magnetic field (IMF) Bz, DMSP F6, F7, F8, and F9 satellite observations of precipitating auroral particles, and Active Magnetospheric Particle Tracer Explorers (AMPTE)/CCE satellite measurements of the total energy of the ring current ions with energy per charge between 1.5 and 300 keVq−1. We found good agreement between observed and modeled magnetic fields during the main phase of the magnetic storms. Using the paraboloid model, we have determined the contributions to Dst of different magnetospheric current systems including the magnetopause current BCF, the symmetric ring current BR, and the geotail current BT‐Such separation shows that values of BT and BCF are comparable with the value of BR during the main phase of the storms. During the recovery phase the effect of BR predominates.
A kinematic analysis of the role of velocity shear in expanding plasmas
Authors: Roberts D. Aaron , Ghosh Sanjoy
Published: September 2002

We present a kinematic analysis of the effects on waves of the shear due to variations in radial flow and field‐aligned propagation speeds in an expanding medium. We show that although the expansion limits the extent to which wave vectors transverse to the shear flow are produced, shear can be very effective at turning wave vectors and producing off‐radial fluctuations. Any initial wave vector spectrum will become spread in wave vector space with no change in spectral index. For typical spectra of the sheared radial speeds, the small‐scale variability in the speed is more important than the large‐scale in the sense of effectively turning the wave vectors. Radial spectra will be unchanged by stream or microstream shear, and although field‐aligned Alfvén speed changes will produce some observable effects, nonlinear processes are still needed to fully explain observations. This work suggests a model for near‐Sun solar wind turbulence in which modes are “driven” nonlocally at all scales rather than the Kolmogoroff model, in which only large‐scale driving is important; this is consistent with well‐developed turbulence spectra in highly structured regions farther out in the wind.
Coherent EISCAT Svalbard Radar spectra from the dayside cusp/cleft and their implications for transient field‐aligned currents
Authors: Sedgemore‐Schulthess K. J. F. , Lockwood M. , Trondsen T. S. , Lanchester B. S. , Rees M. H. , Lorentzen D. A. , Moen J.
Published: September 2002

Naturally enhanced incoherent scatter spectra from the vicinity of the dayside cusp/cleft, interpreted as being due to plasma turbulence driven by short bursts of intense field‐aligned current, are compared with high‐resolution narrow‐angle auroral images and meridian scanning photometer data. Enhanced spectra have been observed on many occasions in association with nightside aurora, but there has been only one report of such spectra seen in the cusp/cleft region. Narrow‐angle images show considerable change in the aurora on timescales shorter than the 10‐s radar integration period, which could explain spectra observed with both ion lines simultaneously enhanced. Enhanced radar spectra are generally seen inside or beside regions of 630‐nm auroral emission, indicative of sharp F region conductivity gradients, but there appears also to be a correlation with dynamic, small‐scale auroral forms of order 100 m and less in width.
Azimuthal phase speeds of field line resonances driven by Kelvin‐Helmholtz unstable waveguide modes
Authors: Mills Katharine J. , Wright Andrew N.
Published: September 2002

A model for the coupling of Kelvin‐Helmholtz unstable fast cavity modes to field line resonances (FLRs) is presented. We consider a bounded, nonuniform magnetospheric flank separated from a semi‐infinite, field‐free, flowing magnetosheath by an infinitely thin magnetopause. Fast cavity modes may become unstable for sufficiently high flow speeds, and we find that for any flow speed there is a common phase speed at which all the harmonics have their maximum growth rate. The common phase speed is less dependent on the equilibrium structure within the magnetosphere than on the local structure of density ratio and relative velocity jump at the magnetopause. We perform a local analysis of the reflection and transmission of modes at the magnetopause. By requiring the spontaneous radiation of modes from the magnetopause, we may predict a phase speed at which we would expect the maximum growth rate to occur for any set of parameters. These predicted phase speeds are found to be in agreement with both those found by our model and observations of FLRs that are observed simultaneously at different latitudes.
Structure of disturbances in the dayside and nightside ionosphere during periods of negative interplanetary magnetic field Bz
Authors: Solovyev S. I. , Baishev D. G. , Barkova E. S. , Engebretson M. J. , Posch J. L. , Hughes W. J. , Yumoto K. , Pilipenko V. A.
Published: September 2002

By comparing data from a globally distributed set of high‐latitude magnetic observatories with optical data in the nightside auroral ionosphere, we studied the features of short‐term activations (≤10–15 min) during periods of steady magnetospheric convection (SMC) observed between two substorms. We found that the occurrence of local auroral and current structures stretched along the meridian to several hundreds of kilometers is the characteristic feature of activations in the nightside ionosphere. At premidnight and night hours (2100–0100 LT) we observed auroral structures that expand rapidly equatorward (V≥1 km/s) from the discrete auroral oval and become north–south aligned (N–S aurora or auroral streamers). In the night‐morning hours (0100–0500 LT) torch‐like structures form at the poleward boundary of the diffuse auroral oval. Ionospheric currents of local auroral structures responsible for Pi3 magnetic pulsations (T≃5–15 min) are predominantly directed to the north (to the south) for auroral structures drifting azimuthally to the west (to the east). Similar auroral and current structures in the nightside ionosphere are also observed during the expansion and recovery phase of a substorm. At the dayside during SMC events at latitudes of 75°–80°, magnetic pulsations of ƒ ∼0.5–1.0 mHz are excited and are accompanied by enhancements of the DPY equivalent current system. We also present observations which show that the N–S aurora formation is accompanied by fluctuations of the electric field (Ey) and particle fluxes directed earthward (Vx) in the plasma sheet with a quasiperiodicity of ∼5–15 min. On the basis of these observational facts we confirm that (1) auroral streamers are the optical manifestation of high‐speed flow bursts propagating earthward; (2) torch‐like structures are caused by generation of magnetospheric plasma tubes of increased pressure (in comparison with the background level) drifting around the Earth.
Source region of 1500 MLT auroral bright spots: Simultaneous Polar UV‐images and DMSP particle data
Authors: Liou K. , Newell P. T. , Meng C.‐I. , Sotirelis T. , Brittnacher M. , Parks G.
Published: September 2002

We compare auroral images from the Polar ultraviolet imager (UVI) and simultaneous particle observations from the Defense Meteorological Satellite Program (DMSP) in the afternoon (1300 – 1600 MLT) sector along the oval in the northern hemisphere to determine the magnetospheric source region of postnoon auroral bright spots. Auroral bright spots are determined with Polar UVI, while their magnetospheric source regions are determined from DMSP F13 particle data. A total of 65 events of good temporal and spatial coincidence were identified after searching through over 1 year of data, from April 1996 to June 1997. Instances occur of auroral arcs mapping to each of several different regions, including the plasma sheet, the low‐latitude boundary layer, and the plasma mantle. However, our results indicate that ∼2/3 of the time the most prominent auroral arcs are associated with plasma sheet electron precipitation and slightly less than 1/3 of the time they are found to occur near (less than 1° in magnetic latitudes) the boundary between the plasma sheet and other regions.
The nocturnal behavior of the hydroxyl airglow at the equatorial and low latitudes as observed by WINDII: Comparison with ground‐based measurements
Authors: Melo Stella M. L. , Lowe R. P. , Takahashi Hisao
Published: September 2002

Measurements of the hydroxyl nightglow from the Wind Imaging Interferometer (WINDII) satellite‐borne experiment and from ground‐based photometers are compared and combined in order to characterize the hydroxyl airglow nocturnal behavior at 23°S and the equatorial region. Ground‐based observations at Cachoeira Paulista (23°S, 45°W) and at Fortaleza (4°S, 38°W) from 1987 to 1994 and WINDII data from March 1992 to January 1994 are selected, and two periods are studied: the March/April equinox and the December/January solstice. The WINDII results for the equinox/solstice difference and for the nocturnal behavior of the vertically integrated emission rate of the hydroxyl nightglow are found to be in very good agreement with the ground‐based observations. The WINDII measurements revealed two general characteristics of the hydroxyl nightglow altitude variation at the latitudes above. The hydroxyl nocturnal variations are predominantly occurring below 90 km, and the vertically integrated emission rate and the peak height of the volume emission rate show an inverse relationship with seasonal, latitudinal, and inter annual effects. The interpretation of these results in terms of atmospheric tides is then discussed.
Sporadic plasma sheet ion injections into the high‐altitude auroral bulge: Satellite observations
Authors: Sauvaud J.‐A. , Popescu D. , Delcourt D. C. , Parks G. K. , Brittnacher M. , Sergeev V. , Kovrazhkin R. A. , Mukai T. , Kokubun S.
Published: September 2002

We report on a new feature of auroral substorms, namely, the sporadic though recurrent injections of magnetospheric ions throughout the auroral bulge. These injections are interpreted as time of flight dispersed ion structures (TDIS). Our analysis builds on a combination of measurements from Interball‐Auroral, from UV imagery onboard Polar, from ground magnetometers, and also from observations on Geotail and from geostationary spacecraft. Backward tracing of ion trajectories from Interball‐Auroral orbit using realistic three‐dimensional magnetic and electric field models indicates that the injection region can extend over a wide range of radial distances, from ∼7–40 RE in the nearly equatorial magnetosphere. Both hydrogen and oxygen ions are shown to be injected toward the Earth's upper ionosphere. At Interball altitudes we find that ion injections are associated with two types of low‐frequency torsional oscillations of the magnetic field: (1) shear Alfvén waves with a period of a few minutes with the highest amplitude near the bulge front and decreasing amplitude at lower latitudes and (2) higher‐frequency shear Alfvén waves of the PlB type, strictly restricted to the poleward boundary of the surge, with a characteristic period of ∼40 s. The systematic observation of sporadic TDIS during the auroral bulge expansion leads us to conclude that the same physical process is at work throughout the midtail. We also show that ion injections are detected well inside the bulge, which suggests that the injection fronts propagate from the outer to the inner magnetosphere over large distances. This topic is more extensively studied by Sergeev et al. [1999]. We also show that the poleward boundary of the surge is associated with a prominent outflow of ionospheric H+ and O+. These ions in the hundred of eV to the keV range are heated perpendicularly to the local magnetic field and subsequently transported into the magnetotail. The expanding auroral bulge thus forms a significant source of ionospheric ions for the midtail magnetosphere.
Solar wind control of magnetospheric energy content: Substorm quenching and multiple onsets
Authors: Karlsson S. B. P. , Opgenoorth H. J. , Eglitis P. , Kauristie K. , Syrjäsuo M. , Pulkkinen T. , Lockwood M. , Nakamura R. , Reeves G. , Romanov S.
Published: September 2002

In this paper we report coordinated multispacecraft and ground‐based observations of a double substorm onset close to Scandinavia on November 17, 1996. The Wind and the Geotail spacecraft, which were located in the solar wind and the subsolar magnetosheath, respectively, recorded two periods of southward directed interplanetary magnetic field (IMF). These periods were separated by a short northward IMF excursion associated with a solar wind pressure pulse, which compressed the magnetosphere to such a degree that Geotail for a short period was located outside the bow shock. The first period of southward IMF initiated a substorm growth phase, which was clearly detected by an array of ground‐based instrumentation and by Interball in the northern tail lobe. A first substorm onset occurred in close relation to the solar wind pressure pulse impinging on the magnetopause and almost simultaneously with the northward turning of the IMF. However, this substorm did not fully develop. In clear association with the expansion of the magnetosphere at the end of the pressure pulse, the auroral expansion was stopped, and the northern sky cleared. We will present evidence that the change in the solar wind dynamic pressure actively quenched the energy available for any further substorm expansion. Directly after this period, the magnetometer network detected signatures of a renewed substorm growth phase, which was initiated by the second southward turning of the IMF and which finally lead to a second, and this time complete, substorm intensification. We have used our multipoint observations in order to understand the solar wind control of the substorm onset and substorm quenching. The relative timings between the observations on the various satellites and on the ground were used to infer a possible causal relationship between the solar wind pressure variations and consequent substorm development. Furthermore, using a relatively simple algorithm to model the tail lobe field and the total tail flux, we show that there indeed exists a close relationship between the relaxation of a solar wind pressure pulse, the reduction of the tail lobe field, and the quenching of the initial substorm.
Magnetic field and electrode geometry effects on vehicle discharging by neutral gas release
Authors: Walker D. N. , Fernsler R. F. , Amatucci W. E. , Duncan D. , Keskinen M. J.
Published: September 2002

In earlier work we quantified the effect of the Mach number of neutral gas release and neutral gas species on minimum breakdown potential in ionospheric‐like plasmas. The theoretical basis of this work incorporates the Townsend breakdown criterion to the ambient plasma to characterize the discharge. The results of a model based on this theory provide good agreement with the results of experiments in a variety of gases performed in the large Space Physics Simulation Chamber (SPSC) at the Naval Research Laboratory. The experiments in the SPSC used a 10 cm × 10 cm aluminum cylinder which contained a neutral gas release valve and variable Mach number nozzles. The cylinder was charged to high negative potential before neutral gas was released, causing breakdown to the ambient plasma for sufficient valve plenum pressure. We have recently incorporated both electrode geometry design changes and an external magnetic field produced by a permanent magnet in an effort to lower the breakdown voltage required. We have preliminary results which suggest that both an extended smaller cylinder and an external magnetic field can significantly lower the potentials required for breakdown. We are in the process of verifying these results by adding an adjustable constant magnetic field both perpendicular and parallel to the gas release direction.
Intermediate electromagnetic turbulence at comets
Authors: Verheest Frank , Lakhina G. S. , Tsurutani B. T.
Published: September 2002

Low‐frequency electromagnetic turbulence observed in cometary environments mostly peaks at the gyrofrequency of the water‐group ions of cometary origin, because of cyclotron resonance fueled by relative drifts parallel to the interplanetary magnetic field. Nevertheless, some of the observations point to pickup proton cyclotron turbulence, to single‐cycle magnetic pulses or solitary waves at the proton gyrofrequency, and also to intermediate frequencies between the water‐group and the proton gyrofrequencies, The generation of turbulence at such frequencies has been attributed to cascade via wave‐wave interactions, but here an alternative and direct mechanism for the generation of these waves is suggested in an unstable wavelength band when the solar wind is sufficiently mass‐loaded by cometary material. It is shown, for average parameters near comet 1P/Halley, that unstable modes of the intermediate frequency kind can indeed occur up to several million kilometers from the cometary nucleus and are easier to excite in higher‐velocity solar wind flows.
A large‐scale survey of corotating interaction regions and their successors in the outer heliosphere
Authors: Gazis P. R.
Published: September 2002

Corotating interaction regions (CIRs) and their successors play an important role in the structure and dynamics of the outer heliosphere. CIRs, consisting of a forward and reverse shock pair in association with a region of enhanced solar wind density and temperature, are a dominant structure in the solar wind at low heliographic latitudes at heliocentric distances between 2 and 8 AU. At larger heliocentric distances, CIRs spread, merge, and interact to form merged interaction regions (MIRs). MIRs are a dominant structure at low latitudes between 8 and 12 AU. At even larger heliocentric distances, considerable uncertainty remains regarding the small‐scale structure of the solar wind. Solar wind and interplanetary magnetic field observations from the Pioneer 10 and Voyager 2 spacecraft were used to conduct a large‐scale survey of CIRs and their successors over solar cycles 21 and 22 between heliocentric distances of 1 and 50 AU to categorize changes that occur as CIRs were convected outward from the Sun. At heliocentric distances less than 37 AU, similar changes were observed at similar heliocentric distances at different spacecraft during different portions of the solar cycle. These changes may reflect qualitative changes in the dynamics of the solar wind as CIRs spread and merge and the flux of kinetic energy available in solar wind streams declines with respect to the flux of thermal energy. At heliocentric distances greater than 37 AU, Pioneer 10 and Voyager 2 observed different types of structure. Interpretation of these differences is complicated by differences in the trajectories of the two spacecraft, and it remains to be determined whether they are associated with latitudinal gradients, solar cycle variations or the effects of interstellar pickup ions at Voyager 2.
Height‐integrated conductivity in auroral substorms: 1. Data
Authors: Gjerloev J. W. , Hoffman R. A.
Published: September 2002

We present height‐integrated Hall and Pedersen conductivity (conductance) calculations from 31 individual Dynamics Explorer 2 (DE 2) substorm crossings. All are northern hemisphere (except one) nighttime passes which took place from September 1981 to January 1982. Global auroral images are used to select substorms which display a typical bulge‐type auroral emission pattern and to organize the position of individual DE 2 passes with respect to key features in the emission pattern. The Hall and Pedersen conductances are calculated from electron precipitation data obtained by the low altitude plasma instrument (LAPI) carried on DE 2 and the monoenergetic conductance model by Reiff [1984]. This method is shown to effectively minimize undesirable smearing of parameters in statistical substorm studies. Large spatial gradients in the conductance profiles are common in high‐latitude part of the premidnight substorm region. The conductances maximizes in the high‐latitude part of the surge with average Hall and Pedersen conductances of 38 and 18 mho respectively. During six different DE 2 passes we found Hall conductance peaks exceeding 100 mho in the high‐latitude part of the surge or surge horn. These peaks are highly localized with a typical scale size of ∼20 km and are associated with energetic (>10 keV) inverted V events. Except in the low‐latitude part of the auroral oval the Hall to Pedersen ratio equals or exceeds 1.0, and it peaks in the high‐latitude part of the surge where values of 3 or more are common. The latitudinal conductance profiles are strongly asymmetric and have a pronounced local time dependency.
The origin of the near‐Earth plasma population during a substorm on November 24, 1996
Authors: Ashour‐Abdalla M. , El‐Alaoui M. , Peroomian V. , Walker R. J. , Raeder J. , Frank L. A. , Paterson W. R.
Published: September 2002

We investigate the origins and the transport of ions observed in the near‐Earth plasma sheet during the growth and expansion phases of a magnetospheric substorm that occurred on November 24, 1996. Ions observed at Geotail were traced backward in time in time‐dependent magnetic and electric fields to determine their origins and the acceleration mechanisms responsible for their energization. Results from this investigation indicate that during the growth phase of the substorm, most of the ions reaching Geotail had origins in the low‐latitude boundary layer and had already entered the magnetosphere when the growth phase began. Late in the growth phase and in the expansion phase a higher proportion of the ions reaching Geotail had their origin in the plasma mantle. Indeed, during the expansion phase, more than 90% of the ions seen by Geotail were from the mantle. The ions were accelerated enroute to the spacecraft; however, most of the ions' energy gain was achieved by nonadiabatic acceleration while crossing the equatorial current sheet just prior to their detection by Geotail. In general, the plasma mantle from both southern and northern hemispheres supplied nonadiabatic ions to Geotail, whereas the LLBL supplied mostly adiabatic ions to the distributions measured by the spacecraft. Distribution functions computed at the ion sources indicate that ionospheric ions reaching Geotail during the expansion phase were significantly heated. Plasma mantle source distributions indicated the presence of a high‐latitude reconnection region that allowed ion entry into the magnetosphere when the interplanetary magnetic field was northward. These ions reached Geotail during the expansion phase. Ions from the traditional plasma mantle had access to the spacecraft throughout the substorm.
High‐frequency and time resolution rocket observations of structured low‐ and medium‐frequency whistler mode emissions in the auroral ionosphere
Authors: LaBelle J. , McAdams K. L. , Trimpi M. L.
Published: September 2002

High bandwidth electric field waveform measurements on a recent auroral sounding rocket reveal structured whistler mode signals at 400–800 kHz. These are observed intermittently between 300 and 500 km with spectral densities 0–10 dB above the detection threshold of 1.5 × 10−11 V2/m2 Hz. The lack of correlation with local particle measurements suggests a remote source. The signals are composed of discrete structures, in one case having bandwidths of about 10 kHz and exhibiting rapid frequency variations of the order of 200 kHz per 100 ms. In one case, emissions near the harmonic of the whistler mode signals are detected simultaneously. Current theories of auroral zone whistler mode emissions have not been applied to explain quantitatively the fine structure of these signals, which resemble auroral kilometric radiation (AKR) rather than auroral hiss.
Characteristics of energetic (≳30 keV/nucleon) ions observed by the Wind/STEP instrument upstream of the Earth's bow shock
Authors: Desai M. I. , Mason G. M. , Dwyer J. R. , Mazur J. E. , von Rosenvinge T. T. , Lepping R. P.
Published: September 2002

We investigate here the characteristics of energetic ions (0.03–2.0 MeV/nucleon) during 1225 upstream events observed by the Energetic Particles: Anisotropy, Composition, and Transport/Suprathermal Energetic Particle (EPACT/STEP) instrument on board the Wind spacecraft from 1994 day 325 to 1999 day 92. We find that (1) the event occurrence rate showed significant variations with changes in the solar cycle, (2) the occurrence rate increased when both the solar wind speed and the geomagnetic activity index were enhanced, (3) most events were observed within ±80 RE in YGSE and inside ∼100 RE in XGSE, although the events occurred at all locations of the Wind orbit, (4) ∼73% of the events were observed when the interplanetary magnetic field was radial and in the ecliptic plane, and when the spacecraft was most likely magnetically connected to the bow shock, (5) the events lasted typically between 10 min to 3 hours and exhibited strong sunward field‐aligned flow, (6) ∼25% of the ion events were accompanied by 20–48 keV electrons as measured by the Wind/3DP instrument, (7) the energy spectra 100–300 keV protons and 30–300 keV/nucleon He‐Fe during ∼70% of the events obeyed power laws with γ between 3 and 5, while the energy spectra of He and CNO for ∼30% of the events softened above ∼80 keV/nucleon obeyed power laws with γ∼3–5, (8) the total energy ion spectrum above ∼0.5 MeV energy was dominated by heavier ions during the events, (9) a substantial fraction (≳40%) of the spectra for all species extended above ∼150 keV/e, and (10) the heavy ion composition of the events was similar to typical solar wind values. We compare the above findings with the main predictions of the magnetospheric leakage and the Fermi acceleration models and find that neither model can satisfactorily account for our results. We highlight the new challenges and requirements for both models.
Solar wind control of the polar cusp at high altitude
Authors: Zhou X. W. , Russell C. T. , Le G. , Fuselier S. A. , Scudder J. D.
Published: September 2002

The POLAR mission is ideally suited to study the high‐altitude polar cusp. Polar magnetometer data, together with electron and ion measurements from the Hydra and Toroidal Imaging Mass‐Angle Spectrograph (Timas) instruments from March 1996 to December 1997, have been used to identify 459 polar cusp crossings. These crossings are used to study the statistical behavior of the cusp location and its dependence on the solar wind conditions. We find that the invariant latitude of the center of the cusp varies from 70° to 86° as solar wind conditions change and the magnetic local time of the footprints of the cusp magnetic field lines extends from 0800 to 1600 MLT, the cusp being slightly wider for increasing solar wind dynamic pressure. The average latitude of the center of the cusp is at 80.3° invariant latitude at noon and decreases to 78.7° at 0800 and 1600 MLT. The cusp also appears to thicken slightly in invariant latitude with increasing dynamic pressure. The center of the cusp moves equatorward with increasingly southward interplanetary magnetic field (IMF) to 73° invariant latitude for a 10 nT southward IMF. The cusp moves only slightly for northward IMF. This motion is consistent with erosion of dayside magnetic flux for southward IMF but little or no erosion for northward IMF. The cusp is also somewhat wider in invariant latitude with increasingly northward IMF. Consistent with low‐altitude observations, we find that there is a clear MLT shift due to the IMF By for strongly southward IMF. We interpret the motion of the local time of the cusp for southward IMF as a shift of the reconnection site away from the noon meridian when the IMF is not due southward.
Collisional consequences of big interstellar grains
Authors: Grün Eberhard , Landgraf Markus
Published: September 2002

Identification by the Ulysses spacecraft of interstellar grains inside the planetary system provides a new window for the study of diffuse interstellar matter. Dust particles observed by Ulysses and confirmed by Galileo are more massive (≥ 10−13 g) than the “classical” interstellar grains. Even bigger grains (≈ 10−7 g) were observed in form of interstellar meteors. We analyze the consequences of the plentiful existence of massive grains in the diffuse interstellar medium. Astronomically observed classical interstellar grains can be described by a size distribution ranging from ∼ 5 to 250 nm in radius (∼ 10−18 to 10−13 g). Lifetimes of these particles, owing to mutual collisions in interstellar space, can be as short as 105f years, where f = 10 to 1000, is the fraction of total lifetime to the time when grains are exposed to supernova shocks. Shattering is a source of the smallest of these grains, but grains more massive than ∼ 10−16g of the classical interstellar grain population are rapidly destroyed. When applying the same shattering mechanism to the more massive grains found recently, we suggest that collisions of particles bigger than ∼ 10−15 g provide a source for smaller grains. Because massive grains couple to the interstellar gas only over large (100 to 1000 pc) length scales, the cosmic abundance ratio of gas‐to‐dust needs only to be preserved averaged over corresponding volumes of space.
OEDIPUS‐C topside sounding of a structured auroral E region
Authors: Prikryl P. , James H. G. , Knudsen D. J. , Franchuk S. C. , Stenbaek‐Nielsen H. C. , Wallis D. D.
Published: September 2002

The Observations of Electric‐field Distributions in the Ionospheric Plasma—A Unique Strategy C (OEDIPUS‐C) rocket payload was launched from Poker Flat, Alaska, into an evening aurora at 0638 UT, on November 7, 1995. The payload included a tethered HF transmitter‐receiver pair which acted as a topside sounder. The bistatic (two‐point) configuration allowed an in situ calibration of the radiated power. The conditions in the magnetosphere and ionosphere during the experiment were monitored by a ground‐based network of instruments and by instruments on the GOES 7 satellite in a geosynchronous orbit. In this paper we present results of the data analysis of topside ionograms that were obtained during the down‐leg flight of OEDIPUS‐C (OC). The relatively low altitudes through which OC carried out topside sounding make the resulting ionograms a novel data set. Ionospheric reflections of the 10‐W transmissions were detected at payload heights between 780 and 160 km on the down leg. Near apogee at 824 km, extremely low electron densities (∼100 cm−3) were observed. The monotonic rise in electron density at the payload from apogee to reentry clearly showed that there was no ionospheric F layer peak. The topside‐sounding echoes came from all heights between the payload and the E layer peak around 100 km altitude. Strong X‐mode ionospheric reflections plus strong O‐mode ground reflections were observed. OC thus has provided a close‐hand view of a thick, highly structured, auroral E layer sounded at small ranges. The RF signal was efficiently guided along the magnetic field aligned density depletions that were located at the equatorward edges of auroral arcs. Large pulse‐to‐pulse variations in the amplitude of the ionospheric reflection are not explained by ducting in the geometric‐optics sense.