bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock drift acceleration of energetic (E ≥ 50 keV) protons and (E ≥ 37 keV/n) alpha particles at the Earth's bow shock as a source of the magnetosheath energetic ion events
Authors: Anagnostopoulos G. C. , Kaliabetsos G. D.
Published: February 2004

We present simultaneous energetic proton (E ≥ 50 keV), alpha particle (E ≥ 37 keV/n) and electron (E ≥ 220 keV) observations obtained by the spacecraft IMP 8 and IMP 7 for an extended time period on May 2 and 3, 1976. During that time period, IMP 8 crossed successively the quasi‐perpendicular duskside of the bow shock in the presence of high fluxes of the ambient solar energetic particle population and under solar wind conditions which implied in a large value of the induced electric field E and a small ratio rG/Rc of the initial proton gyroradius to the local radius of curvature. The observations indicate that three different types of energetic ion populations can be distinguished inside the magnetosheath for the time period examined: (1) energetic ions of solar origin accelerated at (quasi‐)perpendicular regions of the bow shock via the shock drift acceleration (SDA) process, (2) energetic ions of solar origin not affected by the bow shock, and (3) energetic ions of magnetospheric origin. Protons and alpha particles accelerated and transmitted downstream from the bow shock conserve the same spectral index of the ambient solar population at low energies (50 ≤ E ≤ 360 keV) and present small values of the peak‐to‐background intensity ratio p/b ranging between 2.1 and 3.8 in the cases examined. A characteristic signature of the SDA, the double‐peaked anisotropy of the angular distributions of the particle intensities is not always observable in the low‐energy range (50 ≤ E ≤ 290 keV), because of the influence of the plasma flow in the magnetosheath, but is always observed in the high‐energy range (E ≥ 290 keV). Acceleration effects in the vicinity of the (quasi‐)perpendicular (θBn ≃ 79°‐90°) bow shock are observed in the intensities of the energetic protons with energies as high as E ≃ 4 MeV. Protons of magnetospheric origin present values of the ratio p/b as high as ∼6 × 10² and softer energy spectra (γ ≥ 4) than those of the protons accelerated at the bow shock.
Substorm time constants
Authors: Weimer D. R.
Published: February 2004

We show that during magnetospheric substorms there is a clear tendency for the westward electrojet current to follow a characteristic curve that can be matched with an exponential equation. The substorm recovery phase has a characteristic timescale, or exponential time constant, that does not vary substantially from one substorm to the next. There is a slight trend toward shorter substorms as the peak magnitude of the electrojet current increases. This behavior can be explained by a simple model of the coupling between the currents and electric fields in the magnetotail and ionosphere. We derive an equation for the evolution of the substorm currents, including those in the magnetotail, using fundamental physical principles. There is good agreement between the measured and predicted time constants. This model is also consistent with other reported measurements of plasma flows and magnetic perturbations in the magnetotail.
Localized injection of large‐amplitude Pc 1 waves and electron temperature enhancement near the plasmapause observed by DE 2 in the upper ionosphere
Authors: Iyemori T. , Sugiura M. , Oka A. , Morita Y. , Ishii M. , Slavin J. A. , Brace L. H. , Hoffman R. A. , Winningham J. D.
Published: February 2004

The relation between electron temperature enhancement and large amplitude Pc 1 wave injections in the upper ionosphere is investigated using the data obtained by the Dynamics Explorer 2 spacecraft. Results can be summarized as follows: (1) The region of the temperature enhancement coincides with that of the wave injection which is latitudinally very narrow ( < 100 km) in comparison with the wavelength along the ambient magnetic field (several hundred kilometers). (2) The duration of the wave injection (or the temperature enhancement) seems to be less than a few hours even under quiet geomagnetic conditions, and/or the injection seems to be very localized, not only latitudinally, but also longitudinally. (3) The appearance and the magnitude of temperature enhancement depend on both the wave amplitude and the satellite altitude. (4) Two of the 22 events that were analyzed show a clear enhancement of low‐energy electron flux (5‐30 eV) at the wave injection, and the flux is field‐aligned both downward and upward. The region of the temperature enhancement coincides with that of the downward electron flux. From these results, it is suggested that the temperature enhancement which accompanies large‐amplitude waves with Pc 1 pulsation frequencies (0.2‐5 Hz) is caused by the direct acceleration of thermal electrons at low altitudes by the parallel electric field (0.01‐0.001 mV m−1) of the ion‐cyclotron waves (kinetic Alfvén waves) having an oblique wave normal.
Modeling of convection boundaries seen by CRRES in 120‐eV to 28‐keV particles
Authors: Kerns K. J. , Hardy D. A. , Gussenhoven M. S.
Published: February 2004

We show how often a simple convection model can explain the structure seen in 120‐eV to 28‐keV particles at the inner boundary of the Earth's plasma sheet. A total of 1346 samples of the boundary were made over a 14‐month period using the low‐energy plasma analyzer on the CRRES satellite. The cutoff energy below which enhanced fluxes of electrons are seen during the passage into the boundary increased with L shell; the opposite was observed for ions. Forty to 50 percent of the cutoffs sampled on the nightside of the Earth were consistent with those derived from a convection model with one variable parameter. The model was normally inconsistent with cutoffs measured during increasing activity and with those made on the day side. For consistent cases a correlation of ∼0.9 was found between the zero energy Alfvén layer at midnight and the midnight equatorward boundary measured by the DMSP satellite.
Auroral plasma transport processes in the presence of kV potential structures
Authors: Ganguli Supriya B. , Mitchell H. G. , Palmadesso P. J.
Published: February 2004

We have simulated plasma transport processes in the presence of a quasi‐ two‐dimensional current filament, that generated kV potential structure in the auroral region. The simulation consists of a set of one‐dimensional flux tube simulations with different imposed time‐dependent, field‐aligned currents. The model uses the 16 moment system of equations and simultaneously solves coupled continuity and momentum equations and equations describing the transport along the magnetic field lines of parallel and perpendicular thermal energy and heat flows for each species. The lower end of the simulation is at an altitude of 800 km, in the collisional topside ionosphere, while the upper end is at 10RE in the magnetosphere. The plasma consists of hot electrons and protons of magnetospheric origin and low‐energy electrons, protons, and oxygen ions of ionospheric origin. The dynamical interaction of the individual current filaments with ionospheric and magnetospheric plasma generates a potential structure in the horizontal direction and kilovolt field‐aligned potential drops along the field lines. The side‐by‐side display exhibits the evolution of the implied potential structure in the horizontal direction. In the presence of this potential structure and parallel electric field the ionospheric plasma density is depleted and velocity is reduced, while density enhancement and increased velocity is observed in magnetospheric plasma. The ionospheric and magnetospheric electron temperatures increase below 2RE due to magnetic mirror force on converging geomagnetic field lines. The primary cross‐field motion produced by the horizontal E field (E × B drift) is perpendicular to both of the significant spatial directions and is thus ignorable in this geometry. The effects of other cross‐field drift processes are discussed. The simulation thus provides insight into the dynamical evolution of two‐dimensional potential structures driven by an imposed finite width, field‐aligned current profile.
Boundary structure of low‐energy ions associated with the nightside convection reversal
Authors: Liu Chao , Perez J. D. , Moore T. E. , Chappell C. R.
Published: February 2004

The low‐energy H+data with 6‐s resolution from the retarding ion mass spectrometer instrument on DE 1 have been used to reveal an ion boundary structure at midaltitudes that is associated with the nightside convection reversal. The convection reversal provides a free energy source for the perpendicular ion heating that generates ion conics. A detailed analysis of a Y shape distribution observed in the spin‐spectrogram (Plates 1‐4) shows that the altitude of the ion heating decreases monotonically as latitude decreases along the satellite orbit. This suggests that the convection boundary makes an angle of approximately 3° to 10° with the magnetic field line. Near the convection reversal, the nonlinear transverse heating leads to a local charge separation, which forms a double layer along the boundary. The observations of dc electric field are fitted by a model with a Gaussian charge distribution.
An explicit bounce average calculation of adiabatic particle drifts
Authors: Liu W. William
Published: February 2004

The explicit method of bounce averaging the adiabatic drift of a charged particle is generalized, and the relationship of this method to earlier results derived from more implicitly based approaches is briefly discussed.
What is a geomagnetic storm?
Authors: Gonzalez W. D. , Joselyn J. A. , Kamide Y. , Kroehl H. W. , Rostoker G. , Tsurutani B. T. , Vasyliunas V. M.
Published: February 2004

After a brief review of magnetospheric and interplanetary phenomena for intervals with enhanced solar wind‐magnetosphere interaction, an attempt is made to define a geomagnetic storm as an interval of time when a sufficiently intense and long‐lasting interplanetary convection electric field leads, through a substantial energization in the magnetosphere‐ionosphere system, to an intensified ring current sufficiently strong to exceed some key threshold of the quantifying storm time Dst index. The associated storm/substorm relationship problem is also reviewed. Although the physics of this relationship does not seem to be fully understood at this time, basic and fairly well established mechanisms of this relationship are presented and discussed. Finally, toward the advancement of geomagnetic storm research, some recommendations are given concerning future improvements in monitoring existing geomagnetic indices as well as the solar wind near Earth.
Solar activity and coronal mass ejections on the western hemisphere of the Sun in mid‐August 1989: Association with interplanetary observations at the ICE and IMP 8 spacecraft
Authors: Richardson I. G. , Farrugia C. J. , Winterhalter D.
Published: February 2004

During the 10‐day period from August 12 to 21, 1989, a sequence of coronal mass ejections (CMEs) was observed above the west limb of the Sun by the Solar Maximum Mission (SMM) coronagraph. Most of these CMEs apparently originated in the vicinity of one particularly active region during its passage from near central meridian to behind the west limb of the Sun. We present observations made at 1 AU during this period by the ICE (formerly ISEE 3) and IMP 8 spacecraft which were separated by ∼75° in heliolongitude. Following CMEs on August 12 associated with solar events at ∼W40°, IMP 8 (in Earth orbit) detected a strong shock followed by signatures in magnetic field, solar wind plasma, and energetic ion data which suggest that CME‐related material (“ejecta”) forming the shock driver engulfed the spacecraft. This spacecraft only observed weak shocks, and no ejecta, from later CMEs originating further west of the spacecraft. In contrast ICE, off the west limb at ∼W75°, observed the shock from the W40° event but failed to encounter the shock driver, whereas clear ejecta signatures were observed following events further west, closer to the spacecraft heliolongitude. The disappearance of these signatures (which include bidirectional energetic ion flows, bidirectional solar wind heat fluxes, quiet, enhanced magnetic fields and anomalously cool plasma) at IMP 8 and their emergence at ICE as the solar source region moved westward supports the association of such signatures with ejecta related to CMEs. The dual‐spacecraft observations are also consistent with the conclusion of Richardson and Cane (1993) that ejecta at 1 AU typically extend ∼50° in longitude from the solar source. Some plausible associations between particular intervals of ejecta signatures at ICE and individual CMEs are made. However, these associations are complicated by the large number of CMEs present, by intermittent ICE data coverage, and by uncertainties in the ejecta propagation speeds to the spacecraft.
Self consistent one‐dimensional hybrid code simulations of a relaxing field reversal
Authors: Richardson Alan , Chapman Sandra C.
Published: February 2004

We present the results of self‐consistent one‐dimensional hybrid code (kinetic ions and fluid electrons) simulations of a dipolarizing field reversal. Local ion energization processes are studied in terms of both the ion kinetics and bulk plasma behavior. We demonstrate evolution of the system through two phases: (1) a quasi‐static “trapping” phase, during which inflowing ions are trapped in the reversal structure at early times and (2) a dynamic “escape” phase, during which trapped ions escape from the reversal after an increase in P∥. We perform simulations with different linking field component (GSE Bz) to reversing component (GSE Bx) ratios and show that this parameter controls the details of the ion energization. This study suggests a characteristic signature in the magnetic field (a bipolar By) and bulk plasma parameters (an increase in P∥) associated with this behavior which should be observable in in situ data. Our results are applicable for times earlier than the midtail to ionosphere Alfvén travel time.
Electron distribution function behavior during localized transverse ion acceleration events in the topside auroral zone
Authors: Lynch K. A. , Arnoldy R. L. , Kintner P. M. , Vago J. L.
Published: February 2004

The Topaz3 auroral sounding rocket made the following observations concerning the transfer of precipitating auroral electron energy to transverse ion acceleration in the topside auroral zone. During the course of the flight, the precipitating electron beam was modified to varying degrees by interaction with VLF hiss, at times changing the beam into a field‐aligned plateau. The electron distribution functions throughout the flight are classified according to the extent of this modification, and correspondences with ion acceleration events are sought. The hiss power during most of this rocket flight apparently exceeded the threshold for collapse into solitary structures. At the times of plateaued electron distributions, the collapse of these structures was limited by Landau damping through the ambient ions, resulting in a velocity‐dependent acceleration of both protons and oxygen. This initial acceleration is sufficient to supply the number flux of upflowing ions observed at satellite altitudes. The bursty ion acceleration was anticorrelated, on 1‐s or smaller timescales, with dispersive bursts of precipitating field‐aligned electrons, although on longer timescales the bursty ions and the bursty electrons are correlated.
Steepened structures in equatorial spread F: 1. New observations
Authors: Hysell D. L. , Kelley M. C. , Swartz W. E. , Pfaff R. F. , Swenson C. M.
Published: February 2004

Sounding rocket data from the 1990 CRRES/EQUIS equatorial spread F campaign on Kwajalein Atoll are presented. Two Terrier Malamute sounding rockets were launched into active spread F conditions on July 30 and August 2, respectively, and achieved apogee slightly below 500 km, just above the F peak. Plasma frequency probes aboard both rockets showed that the unstable nighttime F region is characterized by propagating steepened structures. Power density spectra for the structures typically exhibit two regions that obey k−n scaling, where n is approximately equal to 2 at wavelengths greater than 80‐100 m and approximately equal to 5 at shorter wavelengths. These spectral indices are quite variable, and the long‐wavelength spectral index in particular seems to decrease with increasing amplitude of density fluctuations. The rocket payloads also measured vector electric fields in the plane perpendicular to B over wavelengths ranging from over 60 km to less than 6 m. Both vector components of the perpendicular electric field are proportional to δn/n at wavelengths longer than 300 m but assume a Boltzmann relationship (with |δE|² ∼ k²|δn/n|²) at smaller scales. The perturbed zonal electric field, δEx, dominates the vertical field, δEz, at long wavelengths, but the situation is reversed at smaller scales.
Two‐dimensional simulations for the impulsive penetration of a solar wind filament into the magnetosphere
Authors: Dai Wenlong , Woodward Paul R.
Published: February 2004

In order to understand the penetration process of a solar wind filament into the magnetosphere in detail, a simplified two‐dimensional PPMMHD code for ideal MHD is applied to the penetration. The filament is modeled as a field‐aligned cylinder impinging on the dayside magnetosphere. The initial magnetopause is considered as a purely tangential discontinuity without width. The results in this paper show that a plasma filament in the magnetosheath with excess momentum density will penetrate through the magnetopause and become irregularity inside in the magnetosphere. This paper presents detailed pictures for the distribution and the evolution of the plasma mass density, thermal pressure, flow velocity, and magnetic field around the filament. The results in this paper confirm our expectation that the penetration in the case with antiparallel magnetic fields happens in the same way as in the case with parallel magnetic fields in the initial situations both without and with a diamagnetic current flowing on the surface of a filament under the approximation of two‐dimensional ideal MHD.
Galactic cosmic ray modulation and interplanetary medium perturbations due to a long‐living active region during October 1989
Authors: Bavassano B. , Iucci N. , Lepping R. P. , Signorini C. , Smith E. J. , Villoresi G.
Published: February 2004

During October 1989, three very energetic flares were ejected by the same active region at longitudes 9° E, 32° W, and 57° W, respectively. The shape of the galactic cosmic ray variations suggests the presence of large magnetic cloud structures (Nagashima et al., 1990) following the shock‐associated perturbations. In spite of long data gaps the interplanetary observations at IMP 8 (near the Earth) and ICE (∼1 AU, ∼65° W) confirm this possibility for the event related to the 9° E flare; the principal axes analysis shows that the interplanetary magnetic field variations at both spacecraft locations are mainly confined on a meridian plane. This result suggests that the western longitudinal extension of this cloud is indeed very large (≥75°). The nonnegligible depression in the cosmic ray intensity observed inside the possible cloud related to the 57° W flare indicates that also the eastern extension could be very wide. The analysis of neutron monitor data shows clearly the cosmic ray trapping effect of magnetic clouds; this mechanism seems to be responsible for the enhanced diurnal effect often observed during the recovery phase of Forbush decreases. We give an interpretation for the anisotropic cosmic ray peak occurring in the third event, and, related to that, we suggest that the Forbush decrease modulated region at the Earth's orbit could be somewhat wider than the magnetic cloud, as already anticipated by Nagashima et al. (1990). By this analysis, based mainly on cosmic ray data, we show that it is possible to do reasonable inferences on the large‐scale structure of flare‐related interplanetary perturbations when interplanetary medium data are not completely present.
Solar wind velocity and temperature in the outer heliosphere
Authors: Gazis P. R. , Barnes A. , Mihalov J. D. , Lazarus A. J.
Published: February 2004

At the end of 1992, the Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were at heliocentric distances of 56.0, 37.3, and 39.0 AU and heliographic latitudes of 3.3°N, 17.4°N, and 8.6°S, respectively. Pioneer 11 and Voyager 2 are at similar celestial longitudes, while Pioneer 10 is on the opposite side of the Sun. All three spacecraft have working plasma analyzers, so intercomparison of data from these spacecraft provides important information about the global character of the solar wind in the outer heliosphere. The averaged solar wind speed continued to exhibit its well‐known variation with solar cycle: Even at heliocentric distances greater than 50 AU, the average speed is highest during the declining phase of the solar cycle and lowest near solar minimum. There was a strong latitudinal gradient in solar wind speed between 3° and 17°N during the last solar minimum, but this gradient has since disappeared. The solar wind temperature declined with increasing heliocentric distance out to a heliocentric distance of at least 20 AU; this decline appeared to continue at larger heliocentric distances, but temperatures in the outer heliosphere were surprisingly high. While Pioneer 10 and Voyager 2 observed comparable solar wind temperatures, the temperature at Pioneer 11 was significantly higher, which suggests the existence of a large‐scale variation of temperature with heliographic longitude. There was also some suggestion that solar wind temperatures were higher near solar minimum.
Simulation of dusty plasmas near surfaces in space
Authors: Gatsonis N. A. , Erlandson R. E. , Meng C. ‐I.
Published: February 2004

A two‐dimensional particle‐in‐cell/Monte Carlo simulation code is developed and used to examine the electrodynamics of a finite‐size dust (particulate) plasma. The model that can be applied to a dusty plasma bounded by surfaces or to a dust cloud embedded in an unbounded plasma accounts for the dynamics of plasma and dust particles, includes the collisional absorption of plasma species by the dust with the use of a multistep Monte Carlo algorithm, and solves Poisson's equation for the electric fields. Charging of isolated particulates is compared with estimates based on orbital motion‐limited current collection. The charge and potential structure of finite‐length dust clouds embedded in a plasma are examined, and the results are compared to previous one‐dimensional solutions. The average dust charge is found to decrease with increasing dust density. Low‐density dust clouds do not perturb the potential and their average charge approaches that of isolated particulates. In the case of dense dust clouds the potential forms a sheathlike structure while the charge forms a double layer with the negative charge residing on the outer boundary of the cloud. Dust clouds initialized in the sheath of a surface biased to a potential are also examined. It is found that the dusty plasma electrodynamics is affected by the applied surface potential, plasma drift energy, and dust density. Collective effects in high‐density clouds alter the sheath, which can expand or collapse. It is found that particulates can be charged negatively or positively depending on the drift energy and the applied surface potential.
MHD simulations of boundary layer formation along the dayside Venus ionopause due to mass loading
Authors: McGary J. E. , Pontius D. H.
Published: February 2004

A two‐dimensional MHD simulation of mass‐loaded solar wind flow around the dayside of Venus is presented. For conditions appropriate to a low‐altitude ionopause the simulations show that mass loading from the pickup of oxygen ions produces a boundary layer of finite thickness along the ionopause. Within this layer the temperatures exhibit strong gradients normal to and away from the ionopause. Furthermore, there is a shear in the bulk flow velocity across the boundary layer, such that the (predominantly tangential) flow decreases in speed as the ionopause is approached and remains small along the ionopause, consistent with Pioneer Venus observations. The total mass density increases significantly as the flow approaches the ionopause, where the contribution of O+ to the total number density is a few percent. Numerical simulations are carried out for various mass addition rates and demonstrate that the boundary layer develops when oxygen ion production exceeds approximately 2 × 105 m−3 s−1. For the upstream solar wind parameters and mass loading rates chosen for these simulations, the results are consistent with observations made on the dayside of Venus for average ionopause conditions near 300 km.
Field‐aligned Poynting Flux observations in the high‐latitude ionosphere
Authors: Gary J. B. , Heelis R. A. , Hanson W. B. , Slavin J. A.
Published: February 2004

We have used data from Dynamics Explorer 2 to investigate the rate of conversion of electromagnetic energy into both thermal and bulk flow particle kinetic energy in the high‐latitude ionosphere. The flux tube integrated conversion rate E·J can be determined from spacecraft measurements of the electric and magnetic field vectors by deriving the field‐aligned Poynting flux, S
, where
is in the direction of the geomagnetic field. Determination of the Poynting flux from satellite observations is critically dependent upon the establishment of accurate values of the fields and is especially sensitive to errors in the baseline (unperturbed) geomagnetic field. We discuss our treatment of the data in some detail, particularly in regard to systematically correcting the measured magnetic field to account for attitude changes and model deficiencies. S∥ can be used to identify the relative strengths of the magnetosphere and thermospheric winds as energy drivers and we present observations demonstrating the dominance of each of these. Dominance of the magnetospheric driver is indicated by S∥ directed into the ionosphere. Electromagnetic energy is delivered to and dissipated within the region. Dominance of the neutral wind requires that the conductivity weighted neutral wind speed in the direction of the ion drift be larger than the ion drift, resulting in observations of an upward directed Poynting flux. Electromagnetic energy is generated within the ionospheric region in this case. We also present observations of a case where the neutral atmosphere motion may be reaching a state of sustained bulk flow velocity as evidenced by very small Poynting flux in the presence of large electric fields.
Langmuir turbulence in the auroral ionosphere: 2. Nonlinear theory and simulations
Authors: Newman D. L. , Goldman M. V. , Ergun R. E.
Published: February 2004

A theoretical interpretation of sounding rocket measurements of intense Langmuir wave fields (≤ 500 mV/m) driven by a stream of 20 eV ‐ 4 keV electrons in the lower auroral zone is developed. This interpretation is based on the ability of the 10 µs sampling rate of the wave detector to temporally resolve the structure of the Langmuir wave field envelope. A modified form of the Zakharov equations is used to numerically study beam‐driven Langmuir turbulence in the presence of a moderate magnetic field (Ωe ≈ ωpe). Strong Landau damping on observed nonthermal scattered electrons, which is treated in a companion paper (Newman et al., this issue), plays an important role by inhibiting backscatter cascade and the development of strong turbulence. A parameterized model of the linear electron stream‐driven wave instability is introduced, which incorporates limited quasilinear plateau formation. A reasonable set of parameters is found that yields semiquantitative agreement between observed properties of the Langmuir fields and the results of Zakharov equation simulations, including the amplitude and characteristic frequency of the electric field envelope modulations.
Radar interferometric imaging studies of long‐duration meteor echoes observed at Jicamarca
Authors: Chapin Elaine , Kudeki Erhan
Published: February 2004

A large number of long‐duration (≥15 s) meteor echoes were detected at the Jicamarca Radio Observatory on two nights in early August 1990 during an evening electrojet experiment. Using an interferometric imaging technique, we were able to measure a zonal velocity profile for each meteor trail. Our analysis procedure differs from conventional meteor wind methods in that it provides instantaneous profiles rather than long‐term average information. Significant altitudinal and temporal variabilities of the horizontal velocities were noted. Zonal speeds of up to 100 m s−1, large vertical shears of up to 20 m s−1/km, and rapid temporal variations of up to 50 m s−1 over an hour interval were observed. Spectral analysis indicates the presence and decay of asymmetrical high‐frequency signal components. Possible explanations for the observed high‐frequency components are discussed as are the angle of arrival of and the scattering mechanism responsible for the meteor echoes.
Mode properties of low‐frequency waves: Kinetic theory versus Hall‐MHD
Authors: Krauss‐Varban D. , Omidi N. , Quest K. B.
Published: February 2004

In fluid theory, the ordering of low‐frequency modes in a homogeneous plasma is based on the phase velocity, since modes do not intersect each other in dispersion diagrams as a function of wavenumber or other parameters. In linear kinetic theory, modes cross each other. Thus a consistent and useful classification should be based on the physical properties of the modes instead. This paper attempts such a classification by documenting the dispersion and general mode properties of the low‐frequency waves (ω « (ΩciΩce)1/2, where Ωci, Ωce are the cyclotron frequencies of the ions and electrons, respectively) in kinetic theory, and by comparing them to the results of two‐fluid theory. Kinetic theory gives a separate Alfvén/ion‐cyclotron (A/IC) wave with phase speed ω/k ≈ υAcosθ for ω « Ωci, where υA is the Alfvén velocity and θ the angle of propagation between wave vector k and background magnetic field Bo. For a given wavenumber, the magnetosonic mode is a double‐valued solution with a singular point in θ, β parameter space, where β is the ratio of thermal pressure to magnetic pressure. It is shown that a branch cut starting at the singular point θ ∼ 30°, β ∼ 3 and leading to larger β gives a practical and consistent separation of this double‐valued magnetosonic solution. Selection of this branch cut results in a moderately damped fast/magnetosonic and a heavily damped slow/sound wave. A comprehensive review of the polarization, compressibility and other mode properties is given and shown to be consistent with the selected branch cut. At small wavenumbers, the kinetic mode properties typically start to deviate significantly from their fluid counterparts at β ∼ 0.5. At larger β, there is no longer a consistent correspondence between the fluid and kinetic modes. Kinetic theory also dictates the use of different mode properties to distinguish between them in observational data. For example, the phase between the density and magnetic field perturbations may become useless at high β, whereas the direction of the magnetic field perturbation with respect to k and Bo remains a useful characteristic. Two quantities based on this characteristic are suggested and are shown to be useful also to distinguish between the mirror mode and A/IC waves in a plasma with temperature anisotropy.
Growth‐phase thinning of the near‐Earth current sheet during the CDAW 6 substorm
Authors: Sanny Jeff , McPherron R. L. , Russell C. T. , Baker D. N. , Pulkkinen T. I. , Nishida A.
Published: February 2004

The thinning of the near‐Earth current sheet during the growth phase of the CDAW 6 magnetospheric substorm is studied. The expansion onset of the substorm occurred at 1054 UT, March 22, 1979. During the growth phase, two spacecraft, ISEE 1 and ISEE 2, were within the current sheet approximately 13RE from the Earth and obtained simultaneous high‐resolution magnetic data at two points in the current sheet. Plasma data were also provided by the ISEE spacecraft and solar wind data by IMP 8. To facilitate the analysis, the GSM magnetic field data are transformed to a “neutral sheet coordinate system” in which the new x axis is parallel to the average magnetic field above and below the neutral sheet and the new y axis lies in the GSM equatorial plane. A model based on the assumption that the current sheet is a time‐invariant structure fails to predict neutral sheet crossing times. Consequently, the Harris sheet model, which allows one to remove the restriction of time invariancy, is used instead. It is found that during the growth phase, a model parameter corresponding to the thickness of the current sheet decreased exponentially from about 5RE to 1RE with a time constant of about 14 min. In addition, the ISEE 1 and ISEE 2 neutral sheet crossings after expansion onset indicate that the neutral sheet was moving upward at 7 km/s relative to the spacecraft. Since both crossings occurred in approximately 80 s, the current sheet thickness is estimated to be about 500 km. These results demonstrate that the near‐Earth current sheet undergoes dramatic thinning during the substorm growth phase and expansion onset.
Global, quasi‐steady dynamics of the distant solar wind, 1. Origin of north‐south flows in the outer heliosphere
Authors: Pizzo V. J.
Published: February 2004

Regular, large amplitude north‐south flow deflections were observed near the heliographic equator by Voyager 2 in the outer heliosphere in 1986. We present results of numerical simulations supporting the idea that these motions are driven by interplanetary dynamical interactions occurring at quasi‐steady stream fronts associated with the tilted‐dipole coronal magnetic configuration at solar minimum. It is shown that under these conditions the coronal geometry is deeply impressed upon the large scale flow and it determines the disposition and orientation of solar wind structures to great heliocentric distances. The observed predominance of the north‐south flow deflections (relative to the east‐west deflections) and their observed quasiperiodicity are seen to be a natural consequence of the two‐sector tilted‐dipole stream structure in which the fronts of successive corotating interaction regions have opposing north‐south tilts.
Large‐scale convection patterns observed by DMSP
Authors: Rich Frederick J. , Hairston Marc
Published: February 2004

We present a comprehensive compilation of the average distribution of the electrostatic potential across the high‐latitude ionosphere. The averages are compiled from potential along the satellite path calculated from thermal ion drift data from instrumentation on the Defense Meteorological Satellite Program (DMSP) flights 8 and 9 satellites. Data were collected from the DMSP F8 satellite during the period September 1987 to December 1990 and from the DMSP F9 satellite during the period March 1988 to December 1990. The potential distributions are separated by geomagnetic position, season, and orientation of the interplanetary magnetic field (IMF), and then averages of the distributions are calculated. The average potential distributions clearly show the displacement of polar cap convection contours to the dusk or dawn flanks under the influence of the IMF By component. The cross‐cap potential decreases as IMF Bz changes from southward to northward. The average distributions indicate that the development of more than two convection cells for northward IMF is either uncommon or nonexistent. For IMF Bz > 0 and Bz > |By|, a distorted pattern is observed in the average potential distribution, not a four‐cell pattern as some previous studies suggest it should be. For all orientations of the IMF, the convection reversal boundary at the poleward edge of the auroral zone is observed in the average distributions to be a rotational boundary. It is not a shear boundary as suggested by some previous investigations. On average, the Harang discontinuity (convection reversal in the auroral zone near midnight) is observed to exist weakly or not at all. When examining individual passes, a strong eastward flow is present sometimes in the region of the Harang discontinuity, especially on the poleward boundary, but not at all times as implied by the Heppner‐Maynard model.
A global magnetohydrodynamic simulation of the response of the magnetosphere to a northward turning of the interplanetary magnetic field
Authors: Ogino Tatsuki , Walker Raymond J. , Ashour‐Abdalla Maha
Published: February 2004

We have used a global magnetohydrodynamic simulation model to investigate the time series of events which occur in the magnetosphere when the interplanetary magnetic field (IMF) changes from southward to northward. Within 15 min of the northward turning the magnetopause reconnection site moves from the subsolar point to the high‐latitude tail. The high‐latitude reconnection converts tail lobe field lines into closed dayside field lines and new field lines in the IMF. The removal of lobe flux plus continuing reconnection at the near‐Earth neutral line cause the field lines which thread the plasma sheet to relax to a more dipolar state and a very slow tailward retreat of the near earth neutral line. The newly closed dayside field lines are convected around the flanks of the magnetosphere and into the tail. The closed flux convected from the dayside to the tail is the main source of closed flux into the tail. As a result, the plasma sheet recovers first along the flanks of the magnetosphere and then nearer midnight. The near‐Earth neutral line shrinks toward midnight and then moves rapidly tailward.
Patches in the polar ionosphere: UT and seasonal dependence
Authors: Sojka J. J. , Bowline M. D. , Schunk R. W.
Published: February 2004

The seasonal and UT dependencies of patches in the polar ionosphere are simulated using the Utah State University time dependent ionospheric model (TDIM). Patch formation is achieved by changing the plasma convection pattern in response to temporal changes in the interplanetary magnetic field (IMF) By component during periods of southward IMF. This mechanism redirects the plasma flow from the dayside high‐density region, which is the source of the tongue of ionization (TOI) density feature, through the throat and leads to patches, rather than a continuous TOI. The model predicts that the patches are absent at winter solstice (northern hemisphere) between 0800 and 1200 UT and that they have their largest seasonal intensity at winter solstice between 2000 and 2400 UT. Between winter solstice and equinox, patches are strong and present all day. Patches are present in summer as well, although their intensity is only tens of percent above the background density. These winter‐to‐equinox findings are also shown to be consistent with observations. The model was also used to predict times at which patch observations could be performed to determine the contributions from other patch mechanisms. This observational window is ± 20 days about winter solstice between 0800 and 1200 UT in the northern hemisphere. In this observational window the TOI is either absent or reduced to a very low density. Hence the time dependent electric field mechanism considered in this study does not produce patches, and if they are observed, then they must be due to some other mechanism.
Multiple, discrete arcs on sunward convecting field lines in the 14‐15 MLT region
Authors: Moen J. , Sandholt P. E. , Lockwood M. , Egeland A. , Fukui K.
Published: February 2004

Ionospheric plasma flow measurements and simultaneous observations of thin (∼0.2° invariant latitude (ILAT)), multiple, longitudinally extended auroral arcs of transient nature within 74°‐76° ILAT and 1030‐1130 UT (∼14‐15 MLT) on January 12, 1989, are reported. The auroral structures appeared within the luminous belt of strong 630.0‐nm emissions located predominantly on sunward convecting field lines equatorward of the convection reversal boundary as identified by the European Incoherent Scatter UHF radar. The events occurred during a period of several hours quasi‐steady solar wind speed (∼ 700 km s−1) and a radially orientated interplanetary magnetic field (IMF) with a weak northward tilt (IMF Bz>0). These typical dayside auroral features are related to previous studies of auroral activity related to the upward region 1 current in the postnoon sector. The discrete auroral events presented here may result from magnetosheath plasma injections into the low‐latitude boundary layer (LLBL) and an associated dynamo mechanism. An alternative explanation invokes kinetic Alfvén waves, triggered either by Kelvin‐Helmholtz instability at the inner (or outer) edge of the LLBL or by pressure pulse induced magnetopause surface waves.
Low and middle altitude cusp particle signatures for general magnetopause reconnection rate variations: 1. Theory
Authors: Lockwood M. , Smith M. F.
Published: February 2004

We present predictions of the signatures of magnetosheath particle precipitation (in the regions classified as open low‐latitude boundary layer, cusp, mantle and polar cap) for periods when the interplanetary magnetic field has a southward component. These are made using the “pulsating cusp” model of the effects of time‐varying magnetic reconnection at the dayside magnetopause. Predictions are made for both low‐altitude satellites in the topside ionosphere and for midaltitude spacecraft in the magnetosphere. Low‐altitude cusp signatures, which show a continuous ion dispersion signature, reveal "quasi‐steady reconnection" (one limit of the pulsating cusp model), which persists for a period of at least 10 min. We estimate that “quasi‐steady” in this context corresponds to fluctuations in the reconnection rate of a factor of 2 or less. The other limit of the pulsating cusp model explains the instantaneous jumps in the precipitating ion spectrum that have been observed at low altitudes. Such jumps are produced by isolated pulses of reconnection: that is, they are separated by intervals when the reconnection rate is zero. These also generate convecting patches on the magnetopause in which the field lines thread the boundary via a rotational discontinuity separated by more extensive regions of tangential discontinuity. Predictions of the corresponding ion precipitation signatures seen by midaltitude spacecraft are presented. We resolve the apparent contradiction between estimates of the width of the injection region from midaltitude data and the concept of continuous entry of solar wind plasma along open field lines. In addition, we reevaluate the use of pitch angle‐energy dispersion to estimate the injection distance.
Electron heat flow in the auroral ionosphere inferred from EISCAT‐VHF observations
Authors: Blelly P. ‐L. , Alcaydé D.
Published: February 2004

At auroral latitudes the electron heat flow resulting from solar EUV heating, as well as magnetospheric energy input, are important parameters which drive the thermal electron structure of the upper ionosphere. A method is presented which allows a determination from EISCAT‐VHF observations of the heat flow at two altitudes, typical of the collision‐dominated F2 region and of the topside ionosphere. EISCAT midwinter and near‐summer observations are used to illustrate the method: diurnal and seasonal variations of solar origin are evidenced, with peculiar enhancements at sunrise and sunset that are interpreted as a delay between the F2 level and topside terminator passage. Perturbations of magnetospheric origin are then discussed. One of them is characteristic of low‐altitude energy inputs. Others correspond to high‐altitude energy inputs through heat flow variations and are interpreted as upward currents of the order of 14 µA m−2.
An examination of the structure and dynamics of the outer plasmasphere using multiple geosynchronous satellites
Authors: Moldwin Mark B. , Thomsen Michelle F. , Bame Samuel J. , McComas David J. , Moore Kurt R.
Published: February 2004

The structure and the dynamics of the plasmaspheric bulge are examined using in situ three‐dimensional plasma observations from magnetospheric plasma analyzers onboard multiple geosynchronous satellites. We identify the plasmasphere by the presence of high fluxes of low‐energy (≈ few eV) ions (corresponding to densities of ≈10s up to ≈100 cm−3). The results from one year (1991) of nearly continuous plasma measurements from two longitudinally and latitudinally separated spacecraft are presented. This study corroborates many of the features and statistical behavior of the plasmaspheric bulge evidenced in past ground‐based and single spacecraft data sets, except we often find a more complex outer plasmasphere than earlier studies have suggested. By using multipoint, simultaneous observations to separate spatial from temporal changes, this study extends previous examinations of the plasmasphere at synchronous orbit. We find that the width and location of the plasmaspheric bulge can differ significantly for the two spacecraft (separated by 6‐8 hours in time), particularly during quiet geomagnetic conditions. The very different plasmaspheric morphologies seen by the two spacecraft lead us to conclude that the outer plasmasphere is often highly structured even during steady geomagnetic conditions and that the simple teardrop model of the bulge rarely, if ever, adequately describes the duskside plasmasphere.
Origin of flux ropes in Venus' ionosphere
Authors: Cole Keith D.
Published: February 2004

The joule dissipation inside flux ropes in Venus' ionosphere is so great that they must be formed near, and maintained at, the place where they are observed. Thus ropes are not formed by a Kelvin‐Helmholtz instability of the ionopause. The hypothesis that ropes may be formed by the dynamo action of internal gravity waves in Venus' thermosphere (Luhmann and Elphic, 1985; Cole, 1993) is strengthened by discussion of a magnetic evolution equation which includes neutral air motion. However, the dynamo process would work only at altitudes at which νin ≥ ωi. At altitudes or parts of a rope where νin ≪ ωi, the process does not work. A solar wind dynamo is therefore examined to account for the ropes. Thereby a major new heat source for ions of the Venus ionosphere associated with the ropes is uncovered.
Magnetotail views at 33RE: IMP 8 magnetometer observations
Authors: Kaymaz Zerefsan , Siscoe George L. , Tsyganenko Nikolai A. , Lepping Ronald P.
Published: February 2004

This paper presents magnetic field vector (B) maps, electric current vector (curl B) maps, magnetic force (J×B) contour maps, and total field contour maps covering the full tail cross section in the yz plane. The maps are based on 16 years of 5‐min averages of IMP 8 magnetic field data. During this time, IMP 8 traversed the tail between −25RE and −40RE in the x direction. Its average x distance was −33RE. For this average distance we show separate maps for low and high dipole tilts, corresponding to equinox and northern hemisphere summer seasons. The low‐tilt (equinox) maps show symmetrical field and current patterns; the high‐tilt (solstice) maps show the cross‐tail current sheet arcing above the equatorial diagonal in the center and dipping below it on the flanks. The shape of warped current sheet fits Fairfield's (1980) displaced ellipse model fairly well. The distance at which the current sheet is hinged to the magnetic equator is found to be 9.88RE and is independent of kp. The z profile of current density shows a central peak, 3RE full width at half maximum, and smaller, flanking shoulders. A Harris sheet profile with a 7RE thickness fits the Bx profile. Though these are magnetic field data, the J×B maps clearly outline the plasma sheet. This approach also gives a 7RE thickness. Many of the average field and current features inferred and demonstrated in earlier studies are confirmed here; some of them are seen for the first time in full cross‐section view. Among new features revealed are a large current vortex in the winter hemisphere lobe, a dawn‐dusk asymmetry in the J×B force in the plasma sheet (it is stronger on the duskside), and a separation of the cross‐tail current sheet into core and wing parts.