bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis and interpretation of the shocklike electrostatic noise observed during the AMPTE Solar Wind Lithium Releases
Authors: Gurnett D. A. , Ma T. Z. , Anderson R. R. , Bauer O. H. , Haerendel G. , Häusler B. , Paschmann G. , Treumann R. A. , Koons H. C. , Holzworth R. , Lühr H.
Published: February 2008

During the Active Magnetospheric Particle Tracer Explorers (AMPTE) solar wind lithium release on September 11, 1984, and again on September 20, 1984, an intense burst of electrostatic noise was observed near the upstream edge of the ion cloud. Comparisons with measurements by the IMP 6 and ISEE 1 spacecraft show that the spectrum and overall features of this noise are very similar to electrostatic noise observed at the earth's bow shock. A stability analysis using realistic parameters shows that the electrostatic noise can be accounted for by an ion beam‐plasma instability caused by the solar wind proton beam streaming through the nearly stationary lithium cloud. The growth rate of this instability is largest when the ion density and solar wind proton density are similar, which explains why the noise only occurs near the outer edge of the ion cloud. The similarity to the noise in the earth's bow shock suggests that a shock may exist in the solar wind plasma flow upstream of the ion cloud. If the noise is associated with a shock, then it must be an electrostatic shock, since the ion cyclotron radii are too small for the existence of a MHD shock. Since the electrostatic instability occurs at phase velocities near the lithium thermal velocity, the electrostatic turbulence may play a role in heating the lithium ions and transferring momentum from the solar wind to the ion cloud. The noise may also play a role in the pitch angle scattering and diffusion of energetic electrons observed in the vicinity of the ion cloud. Because of the similarity to the solar wind interaction with the gaseous envelope of a comet, it is expected that similar types of wave‐particle effects may occur upstream of comets.
Observation of lithium pick‐up ions in the 5‐ to 20‐keV energy range following the Ampte solar wind releases
Authors: Möbius E. , Hovestadt D. , Klecker B. , Scholer M. , Gloeckler G. , Ipavich F. M. , Lühr H.
Published: February 2008

Newly created 5‐ to 20‐keV lithium ions were observed for limited time periods following the first Active Magnetospheric Particle Tracer Explorers (AMPTE) lithium release in the solar wind on September 11, 1984. The detection of these so‐called “pick‐up” ions by the time‐of‐flight spectrometer SULEICA (suprathermal energy ionic charge analyzer) on the AMPTE/IRM satellite depends critically on the orientation of the interplanetary magnetic field with respect to the directions of the solar wind and the spin axis of the IRM spacecraft, which was favorable only during the short time when these ions were seen. Our observations are compatible with a shell‐like expansion of the Li cloud with velocities of about 2.5 km/s. The signatures by which the artificial pick‐up ions are identified can also be used to detect and investigate natural pick‐up ions.
Shock acceleration as explanation for steplike changes and hysteresis in cosmic ray modulation
Authors: Stoker P. H. , Moraal H.
Published: February 2008

When the counting rates of neutron monitors at two different cutoff rigidities are plotted against each other, steplike changes in the rigidity dependence of the modulation are observed, leading to the well‐known hysteresis effect. These steplike changes are generally related to the modulation effects of solar flare‐induced shocks propagating through the heliosphere. Shock acceleration as a mechanism for the steplike changes has however not yet been considered explicitly. Therefore, in this paper it is shown that the acceleration effects of multiple shocks in the outer heliosphere may indeed explain these steps.
Magnetospheric configuration and energetic particle effects associated with a SSC: A case study of the CDAW 6 Event on March 22, 1979
Authors: Wilken B. , Baker D. N. , Higbie P. R. , Fritz T. A. , Olson W. P. , Pfitzer K. A.
Published: February 2008

Three geostationary satellites, GEOS 2, 1976‐059, 1977‐007, located near noon, near midnight, and 0400 LT, respectively, observed the global energetic particle signatures produced by the storm sudden commencement (SSC) at 0826 UT on March 22, 1979. The SSC‐induced magnetopause compression generated a steplike wave which traversed the magnetosphere within 2 min. The associated induced electric fields substantially altered both particle energies and drift motions. Local observations of spectral distributions at all longitudes are compared with predictions from a simple model, thus allowing some inference on the radial properties of the particles' energy distribution function. The nonadiabatic compression during the SSC modified existing drift orbits of energetic particles and increased drift shell splitting. Field‐aligned pitch angle distributions for electrons and protons appearing at and around local midnight are related to an intersection of drift shells with the inward displaced magnetopause. These observations are used to detect displacements of the magnetopause to standoff distances between 6.6 and 9 RE with satellites located in the midnight sector. A combination of the present multipoint measurements with the Olson‐Pfitzer dynamic magnetospheric model allows quantative conclusions on, for example, energetic particle drift times in disturbed fields and the magnetopause standoff distance and its relation to both pitch angle cutoffs and dispersive flux dropout events. The availability of this model made it possible to use particle drift as a medium for remote sensing techniques over global distances.
Ionospheric ion heating by ULF Pc 5 magnetic pulsations
Authors: Lathuillere C. , Glangeaud F. , Zhao Z. Y.
Published: February 2008

Frictional heating of the ions resulting from dc ionospheric electric fields is experimentally and theoretically well known. We extend these results to ion heating due to ULF magnetic pulsations of periods as low as 3 min. Ion temperature fluctuations as measured by the European incoherent scatter facility are very well correlated to magnetic Pc 5 pulsations. We present a method which estimates these ion temperature enhancements from ion velocity measurements.
Ionospheric and thermospheric response over Millstone Hill to the May 30, 1984, annular solar eclipse
Authors: Roble R. G. , Emery B. A. , Ridley E. C.
Published: February 2008

The National Center for Atmospheric Research (NCAR) thermospheric general circulation model (TGCM) is used to calculate the time‐dependent thermospheric response to the May 30, 1984, annular solar eclipse. The path of maximum obscurity begins at sunrise in the Pacific Ocean near 2°N and 135°W. It moves northeastward, passing across central Mexico, the eastern United States, and then the Atlantic before ending near 28°N and 4°E in Algeria. The area of the partial shadow is relatively large, and the total solar flux incident on the dayside of the earth is decreased by about 6% during the eclipse. The TGCM calculates the time‐dependent response of the winds, temperature, and the mass mixing ratios of the major constituents throughout the thermosphere. Perturbations follow the path of the annular eclipse, with maximum deviations occurring near 1700 UT at about 300 km for the temperature and at higher altitudes for the winds and composition. The perturbation winds converge from all directions toward the shadow at speeds reaching 75 m s−1 in the upper thermosphere. The maximum temperature anomaly (−55 K) and vertical wind anomaly (−7 m s−1) occur near the center of the shadow. At a constant altitude of 300 km, both the N2 density and the O density decrease by about 10% and 6%, respectively. The path of maximum obscuration passes within 3° of latitude of the incoherent scatter radar at Millstone Hill, Massachusetts (42.6°N, 71.5°W). The station experiences a maximum solar obscuration of 86% at 1700 UT (1200 LT). A time‐dependent one‐dimensional numerical model of the ionosphere that uses the TGCM‐calculated winds, temperature, and composition at Millstone Hill is used to calculate the electron and ion densities and temperatures and the densities of the odd‐nitrogen species NO, N(4S), and N(²D) during the eclipse. The calculated electron density decreases by about factors of 2 in the F region, 4 in the F1 region, and 3 in the E region compared to a similar control run without an eclipse. The F1 region emerges during the eclipse with an increase in the NO+/O+ ratio. The calculated electron temperature decreases by 460 K during the eclipse but then increases 200 K following the eclipse because of the intense solar heating in a region of reduced electron densities. The calculated ion temperature generally follows the changes in neutral temperature. The calculated thermospheric and ionospheric responses agree well with measurements made by the Millstone Hill incoherent scatter radar.
A quantitative empirical model of the magnetospheric flux transfer process
Authors: Holzer R. E. , McPherron R. L. , Hardy D. A.
Published: February 2008

A simple model for estimating the open flux in the polar cap was based on precipitating electron data from polar orbiting satellites. This model was applied in the growth phase of two substorms on March 27, 1979, to determine the fraction of the flux of the southward IMF which merged at the forward magnetopause, contributing to the polar cap flux. The effective merging efficiency at the forward magnetopause was found to be 0.19±0.03 under average solar wind conditions. The westward electrojet current during the expansion and recovery phases of the same substorms was approximately proportional to the time rate of decrease of polar cap flux due to merging in the tail. An empirical model for calculating polar cap flux changes using the merging at the forward magnetopause for estimating increases and the westward electrojet for decreases was compared with observed changes in the polar cap flux. Agreement between the predicted and observed changes in the polar cap flux was tested over an interval of 8 hours. The advantages and limitations of the method are discussed.
Decay instability of finite‐amplitude circularly polarized Alfven waves: A numerical simulation of stimulated Brillouin scattering
Authors: Terasawa Toshio , Hoshino Masahiro , Sakai Jun‐Ichi , Hada Tohru
Published: February 2008

By means of a numerical simulation, nonlinear evolution of large amplitude dispersive Alfven waves is studied. An energy transfer from the parent wave to two daughter Alfven‐like waves and a soundlike wave is observed (a stimulated Brillouin scattering process). The observed growth rates and propagation characteristics of these daughter waves agree with the analytical results, which we obtain by extending the previous treatments by Goldstein, Derby, Sakai, and Sonnerup. Ions are first trapped by the electrostatic potential of the daughter soundlike waves. Along with the eventual decay (ion Landau damping) of the soundlike waves, ions are phase‐mixed and left heated in the parallel direction. The increased parallel energy of ions is transferred to the perpendicular thermal energy through the nonresonant scattering process in the colliding Alfven waves (parent and daughter waves). We further observe that the daughter Alfven waves, which still have a large amplitude, are also unstable for further decay, and that the wave energy is continuously transferred to the longer wavelength regime (inverse cascading process).
The effect of the ionosphere on the growth of tearing mode instabilities in the magnetotail
Authors: Swift Daniel W.
Published: February 2008

Dispersion relations are derived for collisionless tearing mode instabilities in the magnetotail in which the magnetic field passing through the current sheet connects to the ionosphere. In the absence of the conducting ionosphere, the presence of a component of the magnetic field normal to the current sheet large enough to magnetize the electrons stabilizes the current sheet against the tearing mode. It is shown, however, that height‐integrated ionospheric conductivities in the 0.1‐ to 1.0‐mho range are sufficient to allow the tearing mode instability to grow with e‐folding times of several minutes. The effect of polarization currents is also investigated, and it is found that they are unlikely to have a significant effect. It is pointed out that the connection of the ionosphere to the current sheet would expose the ionosphere to the electric potentials that are generated during the explosive phase of the instability. These potentials may have a role in accelerating auroral electrons.
The inclination of the heliospheric neutral sheet and cosmic ray intensity at the Earth
Authors: Saito Takao , Swinson Derek B.
Published: February 2008

The inclination of the neutral sheet separating the two oppositely directed magnetic polarity hemispheres of the heliosphere is determined from solar K‐corona data from 1971 to 1974. We show that the interplanetary sector structure inferred from these observations agrees well with the interplanetary sector structure observed at the earth over this same time period and demonstrate a strong correlation between the inclination of the neutral sheet and solar wind speed in the ecliptic plane during this period. The inclination of the neutral sheet is compared with the cosmic ray intensity at the earth, recorded by the Mount Washington neutron monitor from 1971 to 1975. There is a general inverse correlation between the cosmic ray intensity at the earth and the inclination of the neutral sheet over this period; the large decreases in cosmic ray intensity which occurred in 1973 and 1974 correlate well with large excursions in the inclination of the neutral sheet occurring some months earlier during these two years.
Numerical simulation of the temperature, electron density, and electric field Distributions near the ionospheric reflection height after turn‐on of a powerful HF wave
Authors: Muldrew D. B.
Published: February 2008

The time variation of the electron temperature profile in the ionosphere following turn‐on of a powerful 1‐s HF pulse is determined numerically from the energy balance equation. Using this and the equations of motion and continuity for a plasma, the effect of heating and the pondermotive force of a powerful HF wave on the electron density and electric field distributions are determined by numerical simulation. The temperature variation and ponderomotive force modify the density distribution, and this new density distribution, in turn, modifies the electric field distribution of the HF wave. The density deviations grow for a few hundred milliseconds after HF turn‐on and then begin to fluctuate in time. At all heights the wave number of the density deviations is approximately twice the wave number of the HF wave. For electric fields near reflection of about 6.0 V/m, the electric field distribution becomes complicated, apparently depending on Bragg scattering of the HF wave from the density deviations. Density impulses propagate away (up and down) from electric field maxima, at the ion thermal velocity, at both turn‐on and turn‐off of the HF wave.
A phase‐bunching mechanism for fine structures in auroral kilometric radiation and Jovian decametric radiation
Authors: Melrose D. B.
Published: February 2008

Fine structures observed in the auroral kilometric radiation (AKR) and in the Jovian decametric radiation (DAM) show remarkable similarities to fine structures in discrete VLF emissions. The feedback model of Helliwell for discrete VLF emissions is modified to apply to ARK and DAM. An important constraint on the model is that the frequency drift must be close to that characteristic of a propagating electron radiating at its cyclotron frequency. For DAM the model fits satisfactorily with the observational data. For AKR it seems necessary to assume that the basic fine structure is unresolved and that the reported fine structures are envelopes of these basic structures drifting at a rate associated with the exciting agency, which is presumed to be a localized parallel electric field. It is argued that these basic fine structures may be drifting rapidly at a rate proportional to the parallel electric field (provided it is >0.1 mV m−1) and that their bandwidth, determined by the relativistic velocity spread, should be less than ≅ 1 kHz. Triggering of AKR by type III bursts can be explained naturally in terms of the model.
Pc 3 pulsations observed near the south polar cusp
Authors: Engebretson Mark J. , Meng Ching‐I. , Arnoldy Roger L. , Cahill Laurence J.
Published: February 2008

We have compared high time resolution search coil magnetometer data near local magnetic noon from South Pole Station, Antarctica, for January and June 1983 with energetic particle data from DMSP and DE 2 satellites and with interplanetary magnetic field data from the IMP 8 satellite. Broadband irregular magnetic pulsations with period range 0.5–40 s (Pi 1) observed at South Pole Station are found to be associated with the proximity of strong >10‐keV electron precipitation, with a somewhat weaker dependence on Kp and the proximity of the cusp. Large‐amplitude Pc 3 pulsations (up to 20 nT peak to peak) also appear frequently in the data and are distinguished by their packetlike structure and their nearly monochromatic character. Pc 3 pulsations show little or no correlation with latitudinal position of the cusp, with magnetic activity, or with the presence of >10‐keV electron precipitation, but their occurrence is strongly correlated with the X component of the interplanetary magnetic field, and their frequency is dependent on the magnitude of this field. Our results suggest that no local sources need be postulated to explain the occurrence of Pc 3 pulsations at cusp latitudes and may suggest that upstream wave energy in the Pc 3 frequency range can reach low altitudes on cusp field lines.
Earth's compressional foreshock boundary revisited: Observations by the ISEE 1 magnetometer
Authors: Greenstadt E. W. , Baum L. W.
Published: February 2008

We introduce a “solar foreshock coordinate” (SFC) system in which the positions of foreshock components can be collated with a minimum of assumptions about the physical processes involved. Location behind the interplanetary magnetic field (IMF) tangent surface to the bow shock and rotational symmetry around the solar wind flow (X) axis are the only presuppositions. We have applied the SFC system to over 300 observations of the boundary of the ULF compressional waves recorded by ISEE 1’s magnetometer in 1978 and 1979. The boundary locations form a coherent pattern in the SFC frame. A selection of those cases for which the cone angle of the IMF was between 40° and 50°, corresponding to the average stream angle, yields a least square line whose mapping back to the solar ecliptic coordinates frame has slope of about 85°, very close to that of the tangent ULF boundary deduced earlier from more primitive methods with entirely different data sets. The line, being parallel to neither the IMF, the typical reflected beam, nor the shock, cannot be compatible with any model of wave production by beam‐solar wind interaction that depends on uniform beam distribution or fixed growth rate. Rather, its tangency suggests the influence of a separate, escaping ion population.
Waves and electric fields associated with the first AMPTE artificial comet
Authors: Gurnett D. A. , Anderson R. R. , Ma T. Z. , Haerendel G. , Paschmann G. , Bauer O. H. , Treumann R. A. , Koons H. C. , Holzworth R. H. , Lühr H.
Published: February 2008

A variety of plasma wave and electric field effects were observed during the AMPTE (Active Magnetospheric Particle Tracer Explorers) solar wind barium release on December 27, 1984. Electron plasma oscillations provided measurements of the electron density during the entire event. Inside the diamagnetic cavity created by the ion cloud, the electron density reached a peak of about 2×105 cm−3 and then decreased approximately as t−2 as the cloud expanded. A static electric field of about 1–2 mV/m was detected in the diamagnetic cavity. This electric field is in the same direction as the solar wind electric field, suggesting that the solar wind electric field may be able to penetrate into the cloud. As the spacecraft passed through the boundary of the diamagnetic cavity, a region of compressed plasma and magnetic field was detected upstream of the ion cloud with a peak density of about 104 cm−3 and magnetic field strength of 130 nT. This region of compressed plasma is believed to be caused by solar wind plasma and magnetic field lines draped around the nose of the ion cloud. Inside the diamagnetic cavity, electrostatic emissions were observed in a narrow band centered on the barium ion plasma frequency and in another band at lower frequencies. These waves are believed to be short‐wavelength ion acoustic waves. Bursts of electrostatic waves were also observed at the boundaries of the diamagnetic cavity, apparently caused by an electron drift current along the boundary. An intense burst of broadband electrostatic noise was observed near the outer boundary of the plasma compression region with intensities of up to 140 mV/m. This noise is apparently associated with a shocklike interaction between the ion cloud and the solar wind. Growth rate computations show that the noise can be accounted for by an electrostatic ion beam‐plasma interaction between the nearly stationary barium ions and the rapidly moving solar wind protons.
ULF signatures of the polar cusp
Authors: Olson John V.
Published: February 2008

Geomagnetic pulsations associated with the polar cusp have been detected at Cape Parry, Northwest Territories, Canada, using flux gate and induction magnetometers. Data from this station show enhanced power almost every day near local noon. It is this enhancement which is taken as the signature of the polar cusp. Maximum signal levels are observed prior to local noon, although the signals are present for several hours on each side of local noon. The spectrum of pulsations near the cusp is broadband, reaching from a few millihertz to above 1 Hz. On average the power spectrum decreases with frequency as f−2.6. Within this general decrease there are often found regions of enhanced power, principally near 5 mHz and near 40 mHz. We have identified the 5‐mHz band with fluctuations in ionospheric currents associated with the cusp boundary and its motions. The 40‐mHz band is presumed to be due to direct penetration of the hydromagnetic radiation in the cusp to the ground. From the measured spectrum we infer an rms fluctuation amplitude of the cusp currents of approximately 3×10³ A, and from this we estimate the total power dissipated by these fluctuations of approximately 4×107 W.
A model of the Schumann‐Runge continuum of O2
Authors: Allison A. C. , Guberman S. L. , Dalgarno A.
Published: February 2008

Ab initio calculations of the B³Σu− potential energy curve of O2 are reported together with the transition moment connecting the B³Σu− and the ground electronic states. Photodissociation cross sections are presented over the wavelength region 127–152 nm. Small adjustments to the potential energy curve and the transition moment lead to a model of the absorption which agrees well with the experimental cross sections and which reproduces the structural features observed on the high‐energy edge. The shoulder at 135.6 nm is attributed to the lowest ³Πu state and the auxiliary maxima to transitions into the B³Σu− state.
The resolved layer of a collisionless, high β, supercritical, quasi‐perpendicular shock wave: 1. Rankine‐Hugoniot geometry, currents, and stationarity
Authors: Scudder J. D. , Mangeney A. , Lacombe C. , Harvey C. C. , Aggson T. L. , Anderson R. R. , Gosling J. T. , Paschmann G. , Russell C. T.
Published: February 2008

A comprehensive set of experimental observations of a high β (2.4), supercritical (Mf = 3.8), quasi‐perpendicular (ΘBn1 ∼ 76°) bow shock layer is presented, and its local geometry, spatial scales, and stationarity are assessed in a self‐consistent, Rankine‐Hugoniot‐constrained frame of reference. Included are spatial profiles of the ac and dc magnetic and electric fields, electron and proton fluid velocities, current densities, electron and proton number densities, temperatures, pressures, and partial densities of the reflected protons. The transformation of the apparent time scales to the actual spatial scales is performed with unprecedented accuracy. The observed layer profile is shown to be nearly phase standing and one dimensional in a Rankine‐Hugoniot frame, empirically determined by the magnetofluid parameters outside the layer proper. One or both of these properties appear to collapse at the time resolution of 1.5 s in the specific geometry considered in this study. Several pieces of evidence are used to show this stationarity: (1) the similarity of the average magnetic structures seen on the two ISEE spacecraft; (2) the close agreement between the electric currents directly determined from the plasma data and those inferred from the magnetic data assuming the layer is one dimensional and time stationary; (3) the close agreement of the empirically determined scale lengths of the most prominent substructures with those determined by numerical simulations and previous laboratory studies; and (4) the close agreement between the theoretical Rankine‐Hugoniot‐determined normal plasma pressure jump and that of the observed electron and proton fluids. The resolved cross‐field electrical currents (with empirical error estimates) are observed to peak within the main magnetic ramp at a level well below the first stabilization threshold for ion acoustic turbulence suggested for low β shocks by Galeev (1976); clear evidence is also provided for smaller parallel currents throughout the main ramp and overshoot, with a predominant sense as if the shock electric field has caused the lighter electrons to lead the ions along the local magnetic field direction. The width of the shock depends on what structures are used to define it. The upstream pedestal or “foot” is nearly two upstream ion skin depths wide, but the main magnetic ramp is only 1/5 the upstream ion skin depth and thus considerably smaller than “conventional wisdom” and most simulations. The ramp scale length is directly corroborated by the current densities determined from the plasma instruments.
The resolved layer of a collisionless, high β, supercritical, quasi‐perpendicular shock wave, 2. Dissipative fluid electrodynamics
Authors: Scudder J. D. , Mangeney A. , Lacombe C. , Harvey C. C. , Aggson T. L.
Published: February 2008

At a high β (2.4), supercritical (Mf ∼ 3.8), perpendicular (ΘBn1 ∼ 76°) shock, we have experimentally established for the first time a number of properties. The energy transformation within the resolved shock layer takes place in three stages: (1) the pedestal where ion gyromechanical energy is increased at the expense of the energy of the flow, (2) the ramp where flow energy is further diverted almost exclusively into magnetic and electron pressure, and (3) the downstream convected ion inertial length within which the ions start to make progress toward “thermalization” of the gyromechanical energy created in the pedestal. The scale of the magnetic ramp is clearly separated from that of the ion skin depth based on either of the Hugoniot asymptotic states. The cross‐shock electrical profile has been determined in both the normal incidence frame (NIF) and in the deHoffman‐Teller frame (HTF) by two different methods; the NIF potential drop was approximately 8 times that in the HTF. Potential overshoots were determined in both frames. The solar wind ion's convected inertial length in the downstream field is 10 times the scale of the magnetic ramp. The solar wind ions are shown to be significantly decelerated by the NIF electric force. Nearly all solar wind electrons have gyroradii less than the scale length of the magnetic field in the ramp; when E ≥ 500 eV this condition is no longer true. The thermal electron plasma remains well magnetized throughout the magnetic profile of the shock. The profile of the electron parallel temperature is closely correlated with that of the nonmonotonic deHoffman‐Teller potential profile, suggesting that the parallel energy change of the electrons is largely reversible. The perpendicular electron temperature is often, but not always, proportional to the magnetic intensity. The average cross‐field resistivity at the magnetic ramp was determined to be η⊥ ∼ 10−7 cgs by three independent methods; the spatial variation of the resistivity through the shock layer is significant, including order of magnitude variations throughout the downstream overshoot structures. The maximum resistivity occurs near the end of the first low‐frequency magnetic overshoot. The parallel “resistivity” is usually negative and concentrated in regimes where the electron's HT potential energy has a local minimum. The cross‐field diffusion of the magnetic field within the ramp balances the steepening of the field profile, as demonstrated by the equality of the magnetic Reynold's length and the exponential scale length of the magnetic ramp.
Electrostatic shocks as nonlinear ion acoustic waves
Authors: Witt E. , Hudson M.
Published: February 2008

We present a one‐dimensional, quasi‐neutral fluid model of the local structure of electrostatic shocks that have been seen in conjunction with ion beams at around one earth radius altitude in the auroral zone. The method is useful when one population of cold ions supports the shock and when one has an idea of how the other particle species behave. The cold ions are described via the ion fluid equations which incorporate a constant magnetic field. The other particle species are described via a plasma model consisting of known expressions, in terms of the electrostatic potential, for the number density of each species. We show how exact time stationary double‐layer solutions may be found when quasi‐neutrality is assumed. We take double‐layer solutions in the wave frame to be possible shock models, with the implications that the cold ions stream into the shocks supersonically, the shock scale length varies with the acoustic Larmor radius, and the shock potential depends only on the incoming parallel cold ion speed, independent of the angle the shock electric field makes with the magnetic field. We examine shock solutions derived from two different plasma models: (1) cold ions and two Boltzmann populations of electrons and (2) cold ions, hot Boltzmann ions, cool Boltzmann electrons, and cold streaming electrons. Assuming reasonable values for the plasma parameters, we find double layers with electric fields of 100–1200 mV/m, widths of 1–4 km, and potential drops of up to 2 kV. This suggests that the electrostatic shocks seen in conjunction with ion beams at one earth radius altitude may be nonlinear ion acoustic waves.
An interplanetary magnetic field dependent model of the ionospheric convection electric field
Authors: Sojka J. J. , Rasmussen C. E. , Schunk R. W.
Published: February 2008

A mathematical model of the magnetospheric electric field imposed upon the ionosphere is presented. The model provides an interplanetary magnetic field (IMF) dependent description of the magnetospheric electric field at ionospheric altitudes for global ionospheric and thermospheric modelers. Although many theoretical and empirical ionospheric convection models have been published, none give both a quantitative and a general Kp, IMF (Bx, By, Bz) dependent description. The need for such a model is particularly pressing with the success of the Dynamic Explorer (DE) mission. As a result of this mission, extensive data sets of thermospheric and ionospheric parameters for well‐defined IMF orientations have been acquired. These data sets, especially for northward IMF orientations, are so complex that global models of both the thermosphere and ionosphere are required to help unravel the physics. Our convection model is an empirical model based upon a synthesis of published observations and current understanding. It describes the convection electric field by a set of simple functions which are dependent on Kp and IMF (Bx, By, Bz). These simple functions create a framework by which current and future empirical data can be used to adjust the model. Since no recent major statistical surveys have been made of ionospheric electric fields, these functions (based upon a few published case studies) are exceedingly simple.
Observations of electric fields near the plasmapause at midnight
Authors: Olsen R. C. , Aggson T. L. , Ledley B. G.
Published: February 2008

We report here static electric field measurements in the equatorial plane from the 100‐m double floating probe experiment carried on the SCATHA (P‐78‐2) satellite. Eclipse measurements on auroral L shells are studied to better understand the change in magnetospheric convection at the plasmapause. The use of eclipse data allows the electric fields to be measured directly without contamination from the spacecraft photoelectron sheath; and it allows the thermal ion population in the outer plasmasphere to be observed, identifying the satellite location with respect to the plasmapause. (Such measurements are limited to near local midnight.) We find that in the corotating frame there is generally an electric field component in the antisolar direction during periods of low magnetic activity which begins at the edge of the plasmasphere and builds in amplitude as the satellite enters the plasma sheet. The amplitude of this electric field varies from 0.05 mV/m to 0.2 mV/m with increasing magnetic activity; the electric field switches to radially inward during periods of high activity with magnitudes up to 2 mV/m. The amplitude of the observed electric field increases with the amount of contribution from east‐west currents in the earth's plasma sheet‐magnetotail current system. Since the electric fields observed on these eclipse passes are radially outward in the midnight meridian during periods of low activity and since they are observed on a near‐synchronous satellite which generally corotates with the earth, they are not included in most modeling studies of the formation of the plasmasphere.
Simultaneous lidar measurements of the sodium layer at the Air Force Geophysics Laboratory and the University of Illinois
Authors: Gardner C. S. , Voelz D. G. , Philbrick C. R. , Sipler D. P.
Published: February 2008

Simultaneous lidar measurements of the mesospheric sodium layer were made at the Air Force Geophysics Laboratory (AFGL) and University of Illinois at Urbana‐Champaign (UIUC) on the nights of August 28, October 9 and October 16, 1985. On these nights the layer centroid height was 1 to 3 km lower at AFGL. In October the altitude of the layer bottomside was near 80 km at AFGL compared to 85 km at UIUC. Gravity wave activity was present in the layer at both sites on all 3 nights. In October, the wave amplitudes were significantly larger at AFGL. The sodium profiles were compared with similar measurements obtained at the Goddard Space Flight Center in October 1981 and at the White Sands Missile Range in October 1984. The data from all four sites indicate that there is a significant longitudinal variation in the layer structure between 70°W and 90°W. It is suggested that these structural differences may be due to dynamics. The most promising mechanism capable of producing the large 1 to 3 km differences in the layer centroid heights between UIUC and AFGL is a small difference in the mean vertical wind velocity. Because the typical residence time for a sodium atom in the layer is approximately 5.8 days, a 0.4 cm s−1 difference in the mean vertical wind velocities at the two sites is capable of inducing a 2‐km difference in the centroid height of the sodium layer.
Stability analysis of double‐peaked proton distribution functions in the solar wind
Authors: Leubner Manfred P. , Viñas Adolfo F.
Published: February 2008

Twelve proton velocity distribution functions as measured for different solar wind speeds by the plasma analyzer at the Helios spacecraft are modelled analytically by a superposition of two bi‐Maxwellians. The stability of these distributions is investigated by solving the linear dispersion equation for parallel propagation of both left‐ and right‐hand polarized modes. Due to the temperature anisotropy of the main proton component the presence of the resonant left‐hand ion cyclotron instability is found to be typical for high‐speed streams and is independent of an ion beam. The results indicate that the ratio of the beam density to total particle density and the beam drift velocity are generally close to the threshold values necessary to drive a highly unstable nonresonant right‐hand mode. This instability is found for one proton distribution and is a consequence of the beam particles. It is concluded that both the ion cyclotron instability and the ion beam instability act as a regulating mechanism on the shape of solar wind double humped proton distribution functions.
Temporal features of the refilling of a plasmaspheric flux tube
Authors: Singh Nagendra , Schunk R. W. , Thiemann H.
Published: February 2008

Time‐dependent hydrodynamic equations were solved in order to study the refilling of plasmaspheric flux tubes depleted during magnetic storms. Depending on the initial density profiles in the depleted flux tube, a variety of shock formations occur during the early stage (∼1 hour) of the refilling. After this early stage, an important feature of the flow is the formation of a pair of shocks, which propagate down, one in each hemisphere. The refilling occurs by the downward propagating shocks with speeds <1.5 km/s and by a simultaneous increase in the plasma density between the two shocks. The time rates of this increase in the density are given for magnetic shells L = 4 and 6.6. These rates depend on the density (N0) at the ionospheric boundaries. Depending on N0, a fair agreement is found between the refilling rates obtained from our calculations for L = 6.6 and those determined from the GEOS 2 observations. The refilling of a flux tube with different densities in the conjugate ionospheres was also considered, and it was found that after the initial stage of about one hour, the filling occurs through the propagation of only one shock from the hemisphere of the weak ionospheric source to that of the strong one. An interesting feature of the temporal evolution of the density of the shocked plasma after the early stage is the persistence of fluctuations with time periods ranging from about 2 to 10 minutes and corresponding wavelengths ranging from about one to several thousand kilometers. These fluctuations appear to be sound waves. Prior to the shock formation, counterstreaming of the ions is expected to occur in the equatorial region. The single‐fluid hydrodynamic model used in the present study is not suited to handle such multiple plasma streams. Therefore, some kinetic considerations for the formation of shocks are given. Results from the particle simulations of counterstreaming plasma expansion show that a potential hill, which eventually slows down the ion streams, leads to the formation of a shock pair in the “equatorial plane.” These shocks propagate in opposite directions in a manner analogous to that obtained with the hydrodynamic model of a geomagnetic flux tube. However, the kinetic calculations show that the shock formation occurs only when the electron temperature Te > 3Ti, where Ti is the ion temperature.
Tangential discontinuities in the solar wind: Correlated field and velocity changes and the Kelvin‐Helmholtz instability
Authors: Neugebauer M. , Alexander C. J. , Schwenn R. , Richter A. K.
Published: February 2008

Three‐dimensional Helios plasma and field data are used to investigate the relative changes in direction of the velocity and magnetic field vectors across tangential discontinuities, (TDs) in the solar wind at solar distances of 0.29–0.50 AU. It is found for tangential discontinuities with both Δv and ΔB/B large that Δv and ΔB are closely aligned with each other, in agreement with the unexpected results of previous studies of tangential discontinuities observed at 1 AU and beyond. It is shown that this effect probably results from the destruction by the Kelvin‐Helmholtz instability of TDs for which Δv and ΔB are not aligned. The observed decrease in the number of interplanetary discontinuities with increasing solar distance may be associated with the growth of the Kelvin‐Helmholtz instability with decreasing Alfvén speed.
Ion composition and upstream solar wind observations at comet Giacobini‐Zinner
Authors: Coplan M. A. , Ogilvie K. W. , A'Hearn M. F. , Bochsler P. , Geiss J.
Published: February 2008

The observations by the ion composition instrument (ICI) on the ICE spacecraft made during the encounter with comet P/Giacobini‐Zinner (Ogilvie et al., 1986) are discussed in detail. Solar wind 4He++ kinetic temperatures, densities, and velocities before, during, and after the encounter are presented. These data combined with 4He++ velocity distributions provide evidence for the existence of a thick diffuse shock. Relative abundances of water group ions and CO+ are derived along with an estimate of the abundance of an ion with M/Q = 24 ± 1 amu/e. The ICI data are compared with electron data from two other experiments (Bame et al., 1986; Meyer‐Vernet et al., 1986) and found to be in reasonable agreement in the region outside the tail. Spectroscopic data for several neutral and ionic species are compared with the ICI results for the water group ions and CO+. The spectroscopic data are also used to eliminate Mg+ and CN+ as candidates for the M/Q = 24 peak. The two most likely candidates are C2+ and Na+, but neither photoionization of parent neutrals nor sputtering from dust grains is sufficient to explain the observed abundance relative to H2O+.
Structure of a slow mode shock observed in the plasma sheet boundary layer
Authors: Feldman W. C. , Tokar R. L. , Birn J. , Hones E. W. , Bame S. J. , Russell C. T.
Published: February 2008

A detailed study of the plasma parameters and magnetic field measured using instrumentation aboard ISEE 2 during the recovery phase of a substorm on April 24, 1979, is presented. The purpose of this study was to determine the nature and structure of the lobe‐plasma sheet boundary layer. The analysis shows that the lobeward edge of the boundary is consistent with a freestanding slow mode shock. This shock is followed by a slow compression wave containing a trailing ion cyclotron wave which also stands in the flow. Measurement of the cross‐tail current in the shock and the current system within the wave gives a shock thickness and wavelength comparable to but larger than both the upstream ion inertial length and the downstream proton gyroradius. Equality of the shock thickness with the standing ion cyclotron wavelength suggests that the steepness of the front is limited by dispersion rather than current‐driven anomalous resistivity.
Satellite sweeping in offset, tilted dipole fields
Authors: Paonessa Mark T. , Cheng Andrew F.
Published: February 2008

We present a theory for the longitudinally averaged satellite sweeping rate in an offset, tilted dipole magnetic field. We include the reductions in the sweeping rate when the moon radius is not large compared to the gyroradius or the azimuthal drift distance during a bounce period. With a large tilt angle between the magnetic and rotation axes, moons make large excursions in dipole L value, and more than one moon can sweep at a given L. The sweeping rate peaks at the minimum L for each moon. If the gyroradius is large, additional peaks can occur when the particle mirrors near the moon latitude. To illustrate the theory, sweeping rates are evaluated for parameters relevant to the observations at Uranus by the Voyager 2 Low Energy Charged Particles Experiment. Calculated sweeping rates for ions and electrons are typically two or three orders of magnitude less than the strong‐diffusion loss rate. The observation of sweeping signatures at Uranus would imply that pitch‐angle scattering there occurs at a rate far below the strong‐diffusion limit, contrasting with the situation for energetic ions in the inner Jovian magnetosphere.
A dynamical‐chemical model of wave‐driven fluctuations in the OH nightglow
Authors: Walterscheid R. L. , Schubert G. , Straus J. M.
Published: February 2008

Wave‐induced temporal fluctuations in the intensity of the OH nightglow are related to the temperature oscillations of the wave field by a model that incorporates a five‐reaction photochemical scheme and the complete dynamics of linearized acoustic‐gravity waves in an isothermal, motionless atmosphere. The intensity I and rotational temperature T oscillations, δI and δT, are conveniently related by the ratio, where the overbar refers to time‐averaged quantities. The ratio η is a complex quantity that depends on the properties of the basic state atmosphere (temperature, thermodynamic parameters, major constituent O2, N2 and minor constituent O, O3, OH, H, HO2 concentrations, and scale heights), chemical reaction rate constants, wave period, horizontal wavelength, and direction of wave energy propagation (upward or downward). The intensity‐temperature oscillation ratio η is evaluated for a nominal case corresponding to an altitude of about 83 km in a nightside model atmosphere with an atomic oxygen scale height of −2.8 km; horizontal wavelength λx is 100 km, and wave energy propagation is upward. Over a broad range of acoustic periods |η| varies between 7 and 8, and η is approximately in phase with the temperature fluctuations. At gravity wave periods, |η| decreases with increasing period from a maximum value of about 7.0; at a period of about 3 hours, |η| is about 1.8. The phase of η and δT are within 45° in the gravity wave regime. The main effect of order of magnitude changes in λx is the modification of the location and width (in period) of evanescent regions. At hour periods, |η| increases as the magnitude of atomic oxygen scale height decreases; at periods of several hours, |η| is about 1/3 greater for an atomic oxygen scale height of −2 km than for the nominal scale height. The amplitude of η is essentially independent of the direction of wave energy propagation, but the phase of η relative to that of δT depends on the upward or downward sense of energy propagation at periods in close proximity to the evanescent regime. The magnitude of η at gravity wave periods can depend sensitively on the altitude of the OH emission layer; higher OH emission heights give smaller values of |η| at 10‐min periods, providing the O3 scale height is not too great. Neglect of minor constituent photochemistry in computing η is a tolerable approximation at acoustic wave periods, but it is entirely inadequate at gravity wave periods. Inclusion of dynamical effects is absolutely essential for a valid assessment of η at any period.