bluuebunny/crossref_metadata_2025 huggingface dataset:
The magnitude and composition of the outflow of energetic ions from the ionosphere
Authors: Collin H. L. , Sharp R. D. , Shelley E. G.
Published: February 2008

Data from the Lockheed ion mass spectrometer on the polar‐orbiting satellite S3‐3 were used to determine the outflow from the high‐latitude ionosphere of terrestrial ions in the energy range of 0.5 to 16 keV during magnetically quiet times (Kp ≤ 3) and magnetic storms (minimum Dst < −80nT). Populations of ions with different histories were separated on a statistical basis to allow the use of all available data rather than just data in which outflowing ions were conspicuous. The major constituents of the outflow were H+ and O+. A small component (<5%) of He+ could be detected but was too weak to be measured reliably. Both the intensity of the outflow and its composition showed marked dependence on magnetic activity. During quiet times the total outflow in this energy range from both hemispheres was ∼1.3×1025 s−1 with the ratio O+/H+ = 0.25. During storms the total outflow was higher, ∼7.2×1025 s−1 with a much larger O+ component, O+/H+ = 1.4.
Upgoing ion beams: 2. Fluid analysis and magnetosphere‐ionosphere coupling
Authors: Kaufmann Richard L. , Kintner Paul M.
Published: February 2008

Measurements made on the S3‐3 satellite within upgoing ion beams are used to determine what role the beam regions play in ionosphere‐magnetosphere coupling and auroral particle acceleration. Numerical integrations over the measured electron and ion distribution functions provide estimates of the contributions of these energetic particles to bulk properties of the auroral plasma. It is found that energetic ions carry most of the parallel momentum flux and that energetic electrons carry most of the energy flux and field‐aligned current within ion beam regions. We conclude that these energetic electrons carry upward field‐aligned current all the way from the dense ionosphere to the distant magnetotail. The net current density carried by energetic electrons is associated with non‐Maxwellian anisotropies (e.g., loss cones) in the electron distribution functions. These electrons are not well approximated by a drifting Maxwellian distribution. Microscopic stability analysis shows that the observed EHC waves can be driven by an ion beam. From the analysis, we find that there probably are very few cold electrons near the satellite when ion beams and EHC waves are detected. It also is suggested that the cold ion density may be maintained at a very low level within ion beams, although at larger density than that of the cold electrons. Cold electrons are likely to carry much of the downward field‐aligned current adjacent to ion beams, where ion conies and higher frequency waves are observed. It is noted that some field‐aligned current also could be transferred to cold electrons at the lower border of the acceleration region. Finally, momentum fluxes are used to investigate forces exerted by the acceleration process and the way these forces are transmitted from the ionosphere to the magnetosphere. The ion beam carries a substantial momentum flux away from the acceleration region. This momentum flux must be provided from below by another particle species. If hot (10 e V to 100 eV) secondary electrons with a density of 10 to 100 cm−3 are trapped below the acceleration region, these electrons can supply the upward force needed to produce stable acceleration. Otherwise, either the whole acceleration region or structures within it will be accelerated. More complete measurements at the lower edge of the acceleration region are required to distinguish between these possibilities.
The production of ion conics by oblique double layers
Authors: Borovsky Joseph E.
Published: February 2008

Magnetized test ions are subjected to acceleration through a numerically simulated oblique double layer in order to determine whether they emerge with velocity vectors aligned with or oblique to the ambient magnetic field. A criterion for oblique alignment, depending on the double‐layer parameters and on the external magnetization, is obtained. When it is applied to observed and theoretical auroral double layers, this criterion predicts that accelerated heavy ions will be substantially less magnetic field aligned than will accelerated hydrogen ions, thus suggesting auroral double layers as a source of high‐energy ion conies. Test particle simulations are also used to investigate the perpendicular heating of ions at low altitudes by the electric fields associated with moving auroral arcs. The rapid motion of small‐scale structures in the arcs is suggested as a source of low‐energy conical ion distributions, and the slow drifts of the entire arc forms are inferred to heat ionospheric ions.
Acceleration of thermal electrons by ICW's propagating in a multicomponent magnetospheric plasma
Authors: Roux A. , Cornilleau‐Wehrlin N. , Rauch J. L.
Published: February 2008

Norris et al. [1983] have recently shown that thermal (∼1 eV) electrons are accelerated along field lines (up to tens of electron volts) when intense ion cyclotron waves (ICW's) are simultaneously present in the equatorial magnetosphere. In the present paper a mechanism that explains these observations is proposed. It is shown that, owing to the small but finite parallel electric field developed by ICW's in a multicomponent plasma (e.g., containing minor He+ ions), electrons having parallel velocities close to the Alfven velocity (at the equator) can be trapped in the potential troughs of this ICW. Then, taking into account the inhomogeneity along geomagnetic field lines, it is shown that the increase of the parallel phase velocity of the ICW as it leaves the equator implies a parallel acceleration of these trapped electrons. The maximum parallel energy that is reached (a few tens of electron volts) is in agreement with observations; it is obtained by matching the trapping force (proportional to E⫽) to the detrapping force due to the inhomogeneity along field lines.
Observation of high‐frequency turbulence induced by an artificial ion beam in the ionosphere
Authors: Pottelette R. , Illiano J. M. , Bauer O. H. , Treumann R.
Published: February 2008

High‐frequency electrostatic waves have been studied during the injection into the ionosphere of an artificial xenon ion beam in a direction quasi‐perpendicular to the magnetic field. The xenon ion plasma source was situated on a small ejectable payload, and the main characteristics of the beam were recorded on the central payload when the separation distance was increasing. Both active and passive methods of observation have been used. The electron density and temperature inside the beam have been derived from the active method of measurement, based on the propagation of artificial waves. The high‐frequency turbulence, detected with the passive method, appeared to be mainly electrostatic and was localized in two main different regions. At small distances from the source the strongest signals were recorded in the region of large‐density gradients situated in the leading edge of the beam. Then the spiky structure of the high‐frequency turbulence can be interpreted as resulting from the coupling between the lower hybrid drift instability and the Langmuir plasma waves. At larger distances from the source, another type of high‐frequency turbulence was set up in regions of low density situated in front of the beam. This last turbulence resulted from the destabilization of electron cyclotron harmonic waves and was localized inside a well‐defined density dip situated in front of the beam.
Formation and dynamics of large‐scale magnetic structures in the ionosphere of Venus
Authors: Cloutier P. A.
Published: February 2008

In this paper, we examine the formation and dynamics of large‐scale magnetic structures in the ionosphere of Venus. We show that such structures must be the result of steady state convection of interplanetary field lines into the ionosphere by the small amount of solar wind plasma (≲1–5%) absorbed by the planetary atmosphere below the ionopause, rather than isolated remnants of large fields persisting for long periods without connection to the solar wind induced current and convection pattern. In particular, we demonstrate that the magnetic diffusion of such structures would result in their dissipation with time scales of 1–10 min, if they were not steady state structures in convective and diffusive equilibrium. It is shown that the equations governing the diffusion of these magnetic structures are similar to those governing diffusion of a gas out of an enclosed chamber with a porous wall, and a simple analog is illustrated. The application of these results to magnetic fields of astrophysical plasmas is discussed.
Ohmic heating of the polar F region by HF pulses
Authors: Shoucri Merit M. , Morales G. J. , Maggs J. E.
Published: February 2008

A study of the modifications produced by high‐power, high‐frequency (HF) waves in the F region of a quiet (low solar cycle) polar ionosphere is presented. In the polar geometry, maximum ohmic heating occurs producing significant changes to the zero‐order electron temperature and density profiles. The temporal and spatial aspects of these changes are calculated, and their effects on relevant ionospheric parameters, such as the dc conductivity tensor, are found. An interesting result is the generation of a density depression at the reflection point of the HF waves. The dependence of ohmic heating on HF pump parameters and peak background density is considered.
Relative abundance of the light ions in the winter nighttime topside ionosphere
Authors: Sanatani S. , Breig E. L.
Published: February 2008

Ion concentration measurements with the retarding potential analyzer onboard OGO 6 satellite have served as basis for investigation of the distribution of the light ions, H+ and He+, relative to that of O+ in the 500‐ to 800‐km height range in the winter nighttime ionosphere. This concentration ratio exhibits distinct large‐scale horizontal variations, with a relative depression in the ratio observed over a broad region about −45° longitude northward of ∼40° dip latitude. The lower ratios are associated primarily with well‐defined relative increases in the abundance of O+, and occur in the same longitude sector that has been characterized in an earlier study by both an observed concurrent relative enhancement in ion temperature and the presence of large fluxes of energetic electrons. Comparisons are presented for the altitude distributions of the concentration ratio between regions representing extremes of the horizontal variation. A simple diffusive‐equilibrium model demonstrates that the effects of ion temperature on the O+ vertical distribution are a significant factor leading to the observed variation of the concentration ratio.
Fine structure in electrostatic emission bands between electron gyrofrequency harmonics
Authors: Koons H. C. , Fennell J. F.
Published: February 2008

In the 1½ years of broadband VLF data available from the receiver aboard the SCATHA satellite, the majority of observations of electrostatic emissions show fine structure. This fine structure consists of several distinct emission bands between electron gyrofrequency (fc) harmonics. Typically three fine structure bands comprise one emission band. Most of the SCATHA observations include only the passband between fc and 2fc. However, a few observations obtained in regions of lower geomagnetic field intensity show similar fine structure in emission bands up to the passband between 3fc and 4fc. This short note reports the observation of fine structure in electron cyclotron harmonic waves and the corresponding in situ electron distribution functions. A significant number of these observations (∼70%) occurred at times when the electron pitch angle distribution had a pronounced minimum at 90° in one or more energy channels in the 1‐ to 10‐keV range.
Velocity shear stabilization of the current convective instability
Authors: Satyanarayana P. , Ossakow S. L.
Published: February 2008

A nonlocal theory of the current convective instability in the presence of a transverse velocity shear is developed. It is found that the velocity shear stabilizes the short wavelength modes and preferentially excites a long wavelength mode. Application to east‐west structure in the high latitude auroral F layer plasma enhancements is discussed.
Power spectral signatures of interplanetary corotating and transient flows
Authors: Goldstein M. L. , Burlaga L. F. , Matthaeus W. H.
Published: February 2008

Recent studies of the time behavior of the galactic cosmic ray intensity have concluded that long term decreases in the intensity are generally associated with systems of interplanetary flows that contain flare‐generated shock waves, magnetic clouds, and other transient phenomena. In this paper the magnetic field power spectral signatures of such flow systems are compared to power spectra obtained during times when the solar wind is dominated by stable corotating streams that do not usually produce long‐lived reductions in the cosmic ray intensity. We find that the spectral signatures of these two types of regimes (transient and corotating) are distinct. However, the distinguishing features are not the same throughout the heliosphere. The transient flows at 1 AU tend to have smaller correlation lengths and larger magnetic helicity scale lengths than do the corotating flows. In data collected beyond 1 AU, the primary differences are in the power spectra of the magnitude of the magnetic field rather than in the power in the field components. Consequently, decreases in cosmic ray intensity are very likely due to magnetic mirror forces and gradient drifts rather than to pitch angle scattering.
Intense fluxes of low‐energy electrons at geomagnetic latitudes above 85°
Authors: Hardy David A.
Published: February 2008

A systematic survey was performed to determine the frequency of occurrence of intense fluxes of electrons above the level of the polar rain at geomagnetic latitudes ≥85° and their relationship to the orientation of the interplanetary magnetic field, the density and velocity of the solar wind, and geomagnetic activity. These intense fluxes we identify as the “polar showers” and “polar squalls” reported by Winningham and Heikkila (1974). For the study, 452 orbits of data from the SSJ/3 sensor on the DMSP F2 satellite were used. The orbits selected satisfied the criteria that the satellite attained a geomagnetic latitude ≥85° during the orbit and that interplanetary magnetic field (IMF) and solar wind data were available both for the hour in which the satellite passed over the northern hemisphere and for the previous hour. The key result of the study is that in 50% of the cases studied an electron flux exceeding the level of the polar rain was found in both hemispheres at geomagnetic latitudes ≥85° and that such occurrences are dependent predominantly, if not exclusively, on the Bz component of the IMF being positive. Unlike visible polar cap arcs, a positive value of the IMF Bz component appears to be both a necessary and a sufficient condition for the occurrence of such fluxes above 85° geomagnetic latitude. Occurrence is independent of the IMF Bx and By components. The occurrence is strongly skewed toward Kp = 0, but an occurrence exceeding 30% is found up to a Kp = 4. The occurrence is independent of the number density or velocity of the solar wind. The values of the peak energy flux and number flux observed above 85° are roughly logarithmically distributed over the ranges from 3×106 to 3×109 keV/cm² s sr and 107 to 1010 el/cm² s sr, respectively. Average energies of the peak fluxes are typically between 50 and 300 eV. The maximum energy flux and number flux above 85° appear to lie above a threshold dependent on the IMF Bz component magnitude but are independent of the solar wind flux nV. The maxima in integral number flux and energy flux above 85° fall in a continuum of values consistent with visible polar cap arcs being cases near the maximum of the continuum.
Structure of the November 12, 1978, quasi‐parallel interplanetary shock
Authors: Kennel C. F. , Edmiston J. P. , Scarf F. L. , Coroniti F. V. , Russell C. T. , Smith E. J. , Tsurutani B. T. , Scudder J. D. , Feldman W. C. , Anderson R. R. , Mozer F. S. , Temerin M.
Published: February 2008

An objective of this paper is to determine the jump in plasma parameters across the November 12, 1978, interplanetary shock, sufficiently accurately to test in a subsequent paper a major prediction of shock acceleration theory: the dependence of the energetic ion spectral index upon the density compression ratio. We use ISEE 1 and 3 measurements of the magnetic field and electron and proton densities, temperatures, and bulk velocities, as well as ISEE 3 alpha particle measurements, and confirm the ISEE 1 electron densities using plasma wave measurements. We solve for the shock normal using four independent methods and show that the upstream and downstream flow parameters are consistent to better than 10% with γ = 5/3 Rankine‐Hugoniot jump conditions. We conclude that the November 12, 1978, shock was a high‐speed (612 km s−1), supercritical, quasi‐parallel (θBn = 41°) shock of moderate strength (fast Mach number of 2.8) propagating into an upstream plasma whose total β was 1.14 and whose electron‐to‐proton temperature ratio was 2.8. This shock had three dissipative scale lengths one of a few Larmor radii associated with its magnetic field jump, one of about 10 RE associated with electron equilibration, and one of about 30 RE associated with an energetic proton foreshock.
Comparison of induced magnetospheres at Venus and Titan
Authors: Verigin M. I. , Gringauz K. I. , Ness N. F.
Published: February 2008

Considerable evidence exists from data obtained by artificial satellites of Venus describing the detached bow shock wave which develops at Venus due to the interaction of the super‐Alfvenic, supersonic solar wind. However, there is no such direct evidence for any bow shock wave at Titan due to the interaction with the corotating Saturnian magnetosphere. This is because the fast mode MHD Mach number was less than unity at the time of Voyager 1 close flyby. In spite of this difference in plasma regimes, there is a certain striking similarity in these two interactions. (1) Both obstacles to plasma flow have appreciable ionospheres and are globally nonmagnetic, (2) Downstream from both obstacles, an induced bipolar magnetic tail is formed with a central field reversal region which is analogous to the earth's neutral sheet‐plasma sheet region. This paper will discuss plasma and magnetic field data from the Venera 9 and 10 spacecraft at Venus and from Voyager 1 at Titan which lead to new conclusions regarding the magnetic tail structure of their induced magnetospheres: (3) There appears to be evidence for magnetic merging in these induced tails so that magnetic reconnection between the oppositely directed tail lobes occurs. The single tail crossing at Titan shows evidence of merging while the repeated tail crossings at Venus indicate that similarly observed merging there is not a permanent feature.
Harmonic structure of Pc 3–5 magnetic pulsations observed at the Syowa‐Husafell conjugate pair
Authors: Tonegawa Y. , Fukunishi H.
Published: February 2008

Strong evidence for the harmonic structure of Pc 3–5 magnetic pulsations observed on the ground has been provided by extracting coherent oscillations from magnetic pulsation data recorded at the Syowa‐Husafell conjugate pair near L = 6 and then calculating the phase difference of the H components between the conjugate points as a function of local time. The model calculation suggests that the Pc 4/5 band observed in the frequency range ∼3–10 mHz is the fundamental mode of standing shear Alfvén waves near L = 6, while the Pc 3 band with multiple harmonic structure observed in the frequency range ∼20–100 mHz is the higher harmonics (usually third to sixth harmonics). The second harmonic is not notable in comparison with other harmonics. It is found further that the fundamental mode and the higher harmonics are not always excited simultaneously. Therefore it is likely that when the frequency of the external driving source is in the Pc 3 range, it excites higher harmonics of standing shear Alfvén waves near L = 6, while when the frequency of the external driving source is in the Pc 4/5 range, it excites the fundamental mode.
Observations of an ionospheric perturbation arising from the Coalinga Earthquake of May 2, 1983
Authors: Wolcott J. H. , Simons D. J. , Lee D. D. , Nelson R. A.
Published: February 2008

An ionospheric peturbation that was produced by the Coalinga earthquake of May 2, 1983, was detected by a network of high‐frequency radio links in northern California. The ionospheric refraction regions of all five HF propagation paths, at distances between 160 and 285 km (horizontal range) from the epicenter, were affected by a ground‐motion‐induced acoustic pulse that propagated to ionospheric heights. The acoustic pulse was produced by the earthquake‐induced seismic waves rather than the vertical ground motion above the epicenter. These observations appear to be the first ionospheric disturbances to be reported this close to an earthquake epicenter.
Predictions of lithium interactions with Earth's bow shock in the presence of wave activity
Authors: Decker R. B. , Vlahos L. , Lui A. T. Y.
Published: February 2008

We present the results from a test‐particle simulation designed to study how lithium tracer ions injected upstream of the earth's bow shock interact with the bow shock when waves are present in the shock's upstream and downstream vicinity. The wave activity is assumed to consist of parallel and antiparallel propagating Alfvén waves characterized by a frequency power spectrum P(f) ∼ f−1 within a frequency interval and range of amplitudes defined separately in the upstream and downstream regions. At a “single encounter” (defined in this paper as the time during which an ion remains within ∼2 gyroradii of the shock) the waves act mainly to perturb an ion's orbit, leading to an increase (or decrease) in the number of orbital shock crossings, and therefore increase (or decrease) the energy gain (via drift along the U × B electric field) relative to the situation when waves are absent. Complete transmission of the injected ion distribution is predicted with and without wave activity present when the angle ψ1 between the shock normal and the nominal upstream magnetic field satisfies 70° ≲ ψ1 ≤ 90°. A wave field of sufficient amplitude should increase ion transmission for 45° ≲ ψ1 ≲ 70°, where significant reflection (∼ 50%) is possible in the absence of waves. At a fixed ψ1, increasing wave activity yields larger average energy gains, reduced pitch angle anisotropies, and increased spatial dispersion on the bow shock for both the reflected ions and those transmitted to the magnetosheath.
Acceleration of lithium test ions in the quiet time geomagnetic tail
Authors: Chapman Sandra C. , Cowley S. W. H.
Published: February 2008

One of the active experiments to be performed as part of the Active Magnetospheric Particle Tracer Explorers mission involves the release of lithium ions in the geomagnetic tail and their subsequent detection after earthward convection into the nightside outer ring current region. In this paper we have used the guiding center approximation to integrate ion trajectories in a simple two‐dimensional model of the quiet time nightside magnetosphere in order to estimate expected ion properties at the latter location. Our principal conclusion is that under typical quiet time conditions these ions will predominantly form a field‐aligned beam (∼5°–20° pitch angle) at energies from a few hundred eV to ∼1 keV.
High‐altitude observations of an intense inverted V event
Authors: Huang C. Y. , Frank L. A. , Eastman T. E.
Published: February 2008

Inverted V events which generally occur in the premidnight sector over the auroral zone are frequently associated with reversals in the convection electric field. Such a reversal is observed by the University of Iowa quadrispherical LEPEDEA on board ISEE 1 at an altitude of 13 RE on May 1, 1978. The bulk flow of the plasma shows a large shear over a 5‐minute interval. The associated change in the convection electric field is 5.1 mV m−1. Large values of the field‐aligned current are simultaneously detected. The potential structure appears to extend to the satellite location. Using a theoretical model, we have calculated the field‐aligned current due to the electric field discontinuity. The magnitude of the parallel potential drop and width of the inverted V region are consistent with observation.
Ion resonances and ELF wave production by an electron beam injected into the ionosphere: Echo 6
Authors: Winckler J. R. , Steffen J. E. , Malcolm P. R. , Erickson K. N. , Abe Y. , Swanson R. L.
Published: February 2008

The interaction with the ionospheric plasma of two separately controllable electron beams injected from the Echo 6 sounding rocket in the auroral zone has been studied using orthogonal electric double probes and other instruments on a separate plasma diagnostics payload. The gun pulses produced a myriad of large electric probe signals covering the entire ion gyro range between dc and 1250 Hz. In particular a signal driven at the 1‐kHz gun frequency and a naturally occurring resonance at 840 Hz near the 799‐Hz proton gyrofrequency were studied. The 1‐kHz signal decreased by a factor of 100 between 45 and 90 m from the beam field line but was detectable in the 1‐mV/m range at 120 m, confirming previous findings that pulsed electron beams may serve as ELF wave sources in space. The 840‐Hz resonance was excited by a beam injected parallel to the magnetic field but could be quenched by the addition of a transverse beam in what appears to be a case of controlled damping. The 840‐Hz and 1‐kHz signals were superposed on large‐amplitude fluctuations and were extracted using power spectral analysis. The data contain a large variety of ion gyro range frequencies which are under study. The paper discusses the interpretation of the electric probe responses and large turbulent payload floating potential effects produced by the hot plasma generated by the beams.
O+ acceleration due to resistive momentum transfer in the auroral field line plasma
Authors: Mitchell H. G. , Palmadesso P. J.
Published: February 2008

Low‐frequency electric fields maintained in a plasma by resistivity (either collisional or wave induced) imply a balance between the momentum transferred to the electrons by the electric field and that transferred by the resistivity from the electrons to other particle species. As a result, the electrons do not experience a net acceleration due to the electric field. If the plasma contains only one ion species, the momentum balance is the same for the ions, and the ion species is not accelerated either. If a second ion species is present which does not participate in the resistive momentum transfer, it may be accelerated by the electric field while the participating ions experience an acceleration opposite to the field. This mechanism may be applied to the auroral field line plasma in the presence of a current along the magnetic field. Significant resistivity between the electrons and the hydrogen ions may accelerate the oxygen ions provided that the resistivity has the appropriate characteristics. We have used an existing auroral field line plasma simulation to dynamically model this effect. This simulation is a one‐dimensional multimoment dynamic model of a three‐species plasma (e−, H+, and O+) along about 10 RE of field line above an altitude of 800 km.
DE 1 observations of type 1 counterstreaming electrons and field‐aligned currents
Authors: Lin C. S. , Sugiura M. , Burch J. L. , Barfield J. N. , Nielsen E.
Published: February 2008

In this paper we report that the Dynamics Explorer 1 satellite frequently detected type 1 counterstreaming electrons in the region of field‐aligned currents at high altitudes in the nighttime auroral zone. Type 1 counterstreaming electrons are generally detected at energies below a few hundred electron volts in association with energetic (> keV) precipitating electron fluxes. The plasma and magnetic field measurements from DE 1 are used to investigate the relative contributions of energetic precipitating electron fluxes and counterstreaming electrons to the field‐aligned current density. The current density is computed by integrating the two‐dimensional electron distribution functions in two energy ranges: 18–235 eV and 18–10,000 eV. In the case of downward current, low‐energy (18 < E < 235 eV) electrons are found to carry more than 40% of the total plasma current density integrated above 18 eV, while higher‐energy electrons carry the rest. In the case of upward currents, less than 50% of the total plasma current density integrated above 18 eV is found to be contributed by low‐energy (18 < E < 235 eV) electrons. In general, the observed pitch angle distributions show that fluxes of counterstreaming electrons are enhanced at both small (<40°) and large (>140°) pitch angles. The energy spectra of counterstreaming electrons in the field‐aligned directions are frequently found to be characterized by Maxwellian functions and occasionally by spectral peaks. It is thus concluded that counterstreaming electrons contribute to field‐aligned current density mostly because of imbalances in the flux enhancement in the upward and downward directions. The Scandinavian Twin Auroral Radar Experiment radar simultaneous observations indicated that the field‐aligned current observed by DE 1 was closed through Pedersen currents in the ionosphere.
The height dependence of TID and gravity wave parameters
Authors: Tedd B. L. , Morgan M. G. , Ballard K. A.
Published: February 2008

The height dependence of amplitude and both horizontal and vertical phase trace speeds, for individual spectral components of F region TID's, are obtained for the first time by means of a three‐station network of rapid‐run ionosondes. The corresponding causative gravity wave parameters are derived using a previously developed inversion technique, which is extended by incorporating the effects of dissipation and ion diffusion. Reasonable agreement is achieved between the height variation of the real part of the vertical component of the gravity wave phase propagation vector, kzr, obtained from the inversion process, and solutions of a dissipative dispersion relation for kzr at different heights. Height dependent values of the imaginary part of the vertical component of the gravity wave phase propagation vector, kzi, which are required for the inversion, are computed from the dissipative dispersion relation. Values of kzi obtained from analytic formulae which assume an isothermal atmosphere and small dissipation yield erroneous results for the waves considered, suggesting that care should be exercised when interpreting previous theoretical results that have employed these assumptions.
Thermospheric circulation, temperature, and compositional structure of the southern hemisphere polar cap during October–November 1981
Authors: Roble R. G. , Emery B. A. , Dickinson R. E. , Ridley E. C. , Killeen T. L. , Hays P. B. , Carignan G. R. , Spencer N. W.
Published: February 2008

Thermospheric temperature, composition, and winds at F region heights over the southern hemisphere polar cap have been measured by the Dynamics Explorer 2 (DE 2) satellite during October–November 1981. Perigee of the DE 2 satellite during this period was over the southern hemisphere polar cap, and measurements made along 0900–2100 local time polar passes are used to determine the average universal time dependence of thermospheric properties for this local time slice. The F region wind vector is derived from the meridional wind component measured by the Fabry‐Perot interferometer (FPI) and the zonal wind component measured by the wind and temperature spectrometer (WATS) instruments on board DE 2. The neutral gas temperature is derived from FPI and WATS measurements, and the compositional structure is determined from the neutral atmosphere composition spectrometer instrument. The measured temperature, composition, and winds along the 0900–2100 local time polar passes all display a universal time dependence that is due to the displacement between geomagnetic and geographic poles. The temperature and molecular nitrogen densities are enhanced, and the atomic oxygen density is reduced in the magnetic polar cap, in comparison with lower‐latitude regions. The neutral wind pattern follows the pattern of ion drift associated with magnetospheric convection. The National Center for Atmospheric Research thermospheric general circulation model (TGCM) is used to calculate the temperature, composition, and winds over the southern hemisphere polar cap region for conditions similar to those of October 1981. The TGCM includes displaced geomagnetic poles. The temperature, composition, and winds are determined along the DE 2 satellite track for various universal times. The calculated winds are in general agreement with the observed winds, both having a two‐cell pattern of magnetospheric convection. The calculated and observed composition patterns are also in general agreement with predictions made by the mass spectrometer and incoherent scatter radar 1983 empirical model when models and observations are normalized to the same constant pressure surface. The calculated and observed maximum compositional variations in the magnetic polar cap occur near 0900 UT, when the dawn sector of the auroral oval passes over the south geographic pole. The overall pattern of the calculated temperature variation is similar to that observed except for the period between 1300 and 1500 UT. Better agreement with temperature in this time range is obtained with the inclusion of auroral particle precipitation within the magnetospheric cusp.
Large‐scale interplanetary magnetic fields: Voyager 1 and 2 observations between 1 AU and 9.5 AU
Authors: Burlaga L. F. , Klein L. W. , Lepping R. P. , Behannon K. W.
Published: February 2008

The strength B of the interplanetary magnetic field observed by the Voyager spacecraft between 1 AU and ∼9.5 AU was found to decrease with distance R from the sun as B = 4.75 (1 + R²)1/2/R², in agreement with the spiral field model. Between August 1977 and July 1979, when solar activity was increasing, corotating flows were observed at an average rate of at least 1 every 20 days, but the flows were evolving with time and seldom recurred from one solar rotation to the next without change. Many transient flows were also observed in this period. Large‐scale fluctuations in B with respect to the average spiral field were observed in association with interplanetary shocks and corotating stream interfaces, and these fluctuations varied with time in association with changes of the flows. The amplitude of the fluctuations in B relative to the mean field was large. There was a tendency for it to increase with distance to 5 AU, but the temporal variations were comparable to or larger than the radial variations. At large distances, B and the plasma density increased together, consistent with the idea that the structure of the outer heliosphere may be determined by stream interactions. The width of interaction regions increased with R owing to expansion, and closely spaced interaction regions often coalesced. A four‐sector pattern was observed from day 267, 1977, to approximately day 173, 1978, followed by a two‐sector pattern which lasted to at least day 179, 1979. In the interval with four sectors, there were usually several small‐amplitude peaks in B together with many transient streams and shocks on each solar rotation, whereas in the interval with two sectors there were one or two maxima in B together with interfaces and shock pairs on each solar rotation. Thus, the relatively abrupt change in sector pattern was accompanied by a change in the pattern of fluctuations in B and a change in the nature of the dominant flows.
A comparison of the observed mid‐latitude magnetic disturbance fields with those reproduced from the high‐latitude modeling current system
Authors: Sun W. , Ahn B.‐H. , Akasofu S.‐I. , Kamide Y.
Published: February 2008

Magnetic disturbance fields at six mid‐latitude stations are computed at 5‐min intervals for March 17, 18, and 19, 1978. The three‐dimensional current system responsible for the fields was determined on the basis of magnetic records from the six International Magnetospheric Study meridian chains of stations above invariant latitude 50° through a numerical modeling method developed by Kamide et al. (1981a). Then each ionospheric high‐latitude current segment is assumed to be connected to two (upward and downward) field‐aligned currents along the dipole field lines and a closure current in the equatorial plane of the magnetosphere. None of the magnetic records from the six mid‐latitude stations were used in determining the high‐latitude modeling current system. It is shown that the middle‐latitude magnetic disturbance fields thus constructed can reproduce fairly well the observed fields (both the H and D components), indicating that the method developed by Kamide et al. (1981a) is fairly reliable. Further, in agreement with earlier studies, the field‐aligned current segments have, in general, the largest contribution to both the H and D components in the middle latitude. The differences between the observed and computed magnetic fields are discussed in detail.
Cross‐tail ion drift in a realistic model magnetotail
Authors: Propp Keith , Beard D. B.
Published: February 2008

Integrating the exact equations of motion, we have followed particle orbits in a good model magnetospheric field consisting of a planetary dipole, forward magnetosphere, and magnetotail current system. Proton energies from 2 eV to 20 keV were used for the full range of equatorial pitch angles and phase. Despite considerable pitch angle scattering in the equatorial plane crossings, we find, first, that the bounce‐averaged cross‐tail drift velocity is approximately independent of pitch angle. Second, we find that, averaged over initial gyrophase, the drift velocity (due to field curvature and gradient) is proportional to proton energy and is given to good approximation by adiabatic approximations, even up to 20 keV, despite the extreme lack of meeting the adiabatic criteria.
Drift waves in high‐β two‐temperature plasmas
Authors: Migliuolo Stefano
Published: February 2008

The linear stability of low‐frequency drift‐compressional and drift‐mirror modes is examined in two‐component (hot and cold) plasmas. A full‐β dispersion relation is derived that retains finite temperature effects for the cold component. The effect of a nonzero ratio Tc/Th is examined, and the critical value of this parameter (that produces stabilization of the modes) is determined. The main result of this work shows that very small temperature ratios (Tc/Th less than 1%, in some cases) are sufficient to completely stabilize these modes at certain wave numbers.
EUV airglow during active solar conditions: 2. Emission between 530 and 930 Å
Authors: Gentieu E. P. , Feldman P. D. , Eastes R. W. , Christensen A. B.
Published: February 2008

Daytime airglow spectra between 530 and 930 Å were obtained at ∼4 Å resolution from a rocket launch at White Sands, New Mexico, June 27, 1980. Portions of the spectrum were observed in second order at ∼2Å resolution. The higher resolution of the present data confirms our previous identification of O II transitions and resolves the identification of O II emission at 537–539 Å as due to both a doublet and a quartet component. For the case of viewing at 90° to the zenith between 196 and 242 km ∼1/3 of the 537‐539 Å emission originates from the O II 2s 2p4 ²P state. We infer a 538/581 Å branching ratio of ∼ 3 in agreement with laboratory and calculated values of 1.6 to 3.3. Other O II branching ratios are in agreement with laboratory data. A somewhat low value for the 718/796 ratio in the flight data is interpreted as due to blended N2 emission at 796 Å. The observed emission rate from the 2s 2p4 ²P state is more adequately modeled using partial photoionization cross sections calculated using the dipole velocity rather than the dipole length approximation. This fact must be considered when computing the 834 Å emission rate from direct photoionization. N II is seen to be a very minor source of emission below 916 Å in the dayglow. The identification of O II 581 Å emission confirms a prediction made in 1977 by Delaboudinière. The O II emission at 581 Å complicates interpretation of low resolution spectral observations near 584 Å in the airglow and also for the case of comets and planets where O atoms and O bearing molecules are present.
Characteristics of energetic particle events associated with interplanetary shocks
Authors: Wenzel K.‐P. , Reinhard R. , Sanderson T. R. , Sarris E. T.
Published: February 2008

We present observations of the 35‐ to 1600‐keV proton intensity‐time profiles and the three‐dimensional 35‐ to 56‐keV anisotropy distributions recorded during two interplanetary shock events on ISEE 3, and discuss these in the light of current particle acceleration models. The large April 5, 1979, event associated with a quasi‐parallel shock shows an extended foreshock region with a strong increase of the upstream proton flux, a downstream plateaulike profile, upstream flow from the shock, and downstream isotropy in the solar wind frame of reference. The small March 9, 1979, event has a structured intensity‐time profile, a narrow shock spike, and anisotropic angular distributions both upstream and downstream, the anisotropies immediately behind the shock exhibiting an intensity peak at pitch angles around 90°. The April event, representative for a class of large energetic storm particle events, shows many observational features which are in agreement with predictions made by diffusive shock acceleration models. The March event, representative for a class of events with irregular profiles and mainly associated with quasi‐perpendicular shocks, exhibits features which are characteristic of shock drift acceleration. We conclude that both acceleration models are operative in association with interplanetary shocks.
Whistler damping at oblique propagation: Laminar shock precursors
Authors: Gary S. Peter , Mellott M. M.
Published: February 2008

This paper addresses the collisionless damping of whistlers observed as precursors standing upstream of oblique, low‐Mach number terrestrial bow shocks. The linear theory of electromagnetic waves in a homogeneous Vlasov plasma with Maxwellian distribution functions and a magnetic field is considered. Numerical solutions of the full dispersion equation are presented for whistlers propagating at an arbitrary angle with respect to the magnetic field. It is demonstrated that electron Landau damping attenuates oblique whistlers and that the parameter which determines this damping is βe. In a well‐defined range of parameters, this theory provides damping lengths which are the same order of magnitude as those observed. Thus electron Landau damping is a plausible process in the dissipation of upstream whistlers. Nonlinear plasma processes which may contribute to precursor damping are also discussed, and criteria for distinguishing among these are described.
High time resolution characteristics of intermediate ion distributions upstream of the Earth's bow shock
Authors: Potter Douglas W.
Published: February 2008

High time resolution particle data upstream of the bow shock during time intervals that have been identified as having intermediate ion distributions often show high amplitude oscillations in the ion fluxes of energy 2 and 6 keV. These ion oscillations, observed with the particle instruments of the University of California, Berkeley, on the ISEE 1 and 2 spacecraft, are at the same frequency (∼0.04 Hz) as the magnetic field oscillations. Typically, the 6‐keV ion flux increases then the 2‐keV flux increases followed by a decrease in the 2‐keV flux and then the 6‐keV flux decreases. This process repeats many times. Although there is no entirely satisfactory explanation, the presence of these ion flux oscillations suggests that distributions often are misidentified as intermediate ion distributions.
Solar wind variations and geomagnetic storms: A study of individual storms based on high time resolution ISEE 3 data
Authors: Akasofu S.‐I. , Olmsted C. , Smith E. J. , Tsurutani B. , Okida R. , Baker D. N.
Published: February 2008

We employ two independent methods to determine the relationship between the ε parameter and the total energy dissipation rate of the magnetosphere by selecting disturbed periods from the same data set used by Baker et al. (1983). Specifically, four storms are examined in detail, since the accuracy of estimating UT is significantly improved during disturbed periods. The first method assumes UT = MA2α ε, where MA is the Alfvén Mach number and α varies with time. The second method considers a linear, time‐invariant dynamic system with ε as input and UT as output. This means UT = W*ε, where * is convolution and W is a transfer function characteristic of the system. It is found that α values fluctuate mainly between 0 and −0.25. The transfer function analysis indicates that W often resembles a δ‐function or a narrow rectangular impulse. Both results give the same implication (namely, UT ∼ ε) and thus are consistent with the view that the magnetosphere is primarily a directly driven system during disturbed periods.
Magnetopause merging site asymmetries
Authors: Crooker N. U. , Luhmann J. G. , Spreiter J. R. , Stahara S. S.
Published: February 2008

Regions where a draped model magnetosheath magnetic field is nearly antiparallel to a model geomagnetic field are shown to be asymmetric for an interplanetary magnetic field (IMF) at the garden hose angle, as suggested by Heelis. When the IMF has a southward component, the asymmetry favors the dawn region for both IMF polarities. The dusk region is favored when the IMF has a northward component. If the regions of antiparallel fields are assumed to be sites of maximum magnetic merging, then the asymmetry is consistent with observed seasonal variations of geomagnetic activity and with dawn‐displaced magnetospheric phenomena. In the alternate merging geometry of a merging line passing through the subsolar region, the asymmetry is predominantly north‐south rather than dawn‐dusk. The subsolar merging‐line geometry is consistent with the seasonal variations but not with the dawn‐displaced phenomena.
Theory of spectral asymmetries and nonlinear currents in the equatorial electrojet
Authors: Kudeki Erhan , Farley Donald T. , Fejer Bela G.
Published: February 2008

The spectral up‐down asymmetry of type 1 echoes returned from the equatorial electrojet irregularities is shown to be a consequence of the nonlinear development of the horizontally propagating large scale primary waves which dominate the k spectrum of the electrojet turbulence. The waves reduce the vertical electric polarization field of the electrojet and suffer second harmonic distortion as they grow. These effects together could cause an asymmetry exceeding 20% between the upward and downward components of the relative (to the ions) electron velocity associated with the primary waves. This asymmetry, which changes its direction from day to night as does the horizontal electrojet current, could easily account for the radar observations. The modification of the vertical polarization field also limits the perturbed vertical electron velocity to a value about the same as the mean horizontal electron velocity, which should explain why type 1 echoes are observed in all directions only when the mean electron velocity is supersonic. Finally, this modification of the polarization field amounts to a significant reduction in the electrojet conductivity, an effect which should be included in electrojet models.