bluuebunny/crossref_metadata_2025 huggingface dataset:
Coronal mass ejections and interplanetary shocks
Authors: Sheeley N. R. , Howard R. A. , Koomen M. J. , Michels D. J. , Schwenn R. , Mühlhäuser K. H. , Rosenbauer H.
Published: February 2008

A comparison between Solwind observations of coronal mass ejections (CME's) and Helios 1 observations of interplanetary shocks during 1979–1982 indicates that 72% of the shocks were associated with large, low‐latitude mass ejections on the nearby limb. Most of the associated CME's had speeds in excess of 500 km/s, but some of them had speeds in the range 200–400 km/s. An additional 26% of the shocks may have been associated with CME's, but we were less confident of these associations because the sizes and locations of the CME's did not seem appreciably different from those of the numerous CME's without Helios shocks. Only 2% of the shocks clearly lacked CME's. As the average level of sunspot activity declined during 1982, the shock frequency also declined, but the observed shocks and some of their associated CME's had unusually high speeds well in excess of 1000 km/s.
A study of the formation, evolution, and decay of shocks in the heliosphere between 0.5 and 30.0 AU
Authors: Smith Z. K. , Dryer M. , Steinolfson R. S.
Published: February 2008

The spatial and temporal evolution of corotating interaction regions is examined between 0.5 and 30 AU using a solar wind simulation with a continuous sinusoidally varying velocity, density, and temperature input pulse train. We show (1) the well‐known formation of forward‐reverse MHD shock ensembles, followed by (2) their interaction that results in a highly nonlinear “pressure” wave that eventually reforms into a new but more irregular set of forward‐reverse shock pairs. As a result of these compound interactions, the overall temperature decays much more slowly than the classical steady state adiabatic radial dependency of R−4/3.
Nonlinear evolution of slow waves in the solar wind
Authors: Hada T. , Kennel C. F.
Published: February 2008

We show by numerical simulation using a hybrid code that comparison of the nonlinear steepening rate, calculated from fluid theory, with the linear collisionless damping rate, defines reasonably well the parameters for which fast and slow MHD waves should steepen. Our results indicate that, whereas fast modes should ordinarly steepen, steepened slow waves should occur rarely in the solar wind near 1 AU.
GEOS 2 electric field observations during a sudden commencement and subsequent substorms
Authors: Knott K. , Pedersen A. , Wedeken U.
Published: February 2008

This paper presents and discusses electric field and plasma density data obtained by the GEOS 2 double probe experiment on March 22, 1979. The observation period encompasses a sudden storm commencement and two consecutive substorms. The E field data are compared with magnetic field recordings both at GEOS and on the ground. The influence of the solar wind on magnetospheric dynamics is studied with the help of additional data from IMP 8 and ISEE 3. The E field data, which were obtained when GEOS was in the dayside (front) of the magnetosphere, are grouped in transients, pulsations and underlying dc electric fields. We find that solar wind discontinuities cause strong electric field transients in the dayside magnetosphere. These transients are followed by Pc 4 oscillations of considerable amplitude. The data also show the existence of dc electric fields during buildup, onset and expansion phase of the two substorms. The combined observations by GEOS 2, ISEE 3, IMP 8 and ground‐based magnetometers provide information on propagation of transients in the magnetosphere, on the nature of large scale oscillations and on the overall convection pattern during periods when the interplanetary magnetic field has a negative Bz component.
Observations of magnetic field perturbations at GOES 2 and GOES 3 during the March 22, 1979, Substorms: CDAW 6 analysis
Authors: Barfield J. N. , Lin C. S. , McPherron R. L.
Published: February 2008

The GOES 2 and GOES 3 satellite high resolution magnetometer data are examined for the March 22, 1979, substorm interval selected by the Coordinated Data Analysis Workshop 6 analysis. Both GOES satellites were on the geographic equator with GOES 2 at 104° west geographic longitude and GOES 3 at 135° west geographic longitude. From the comparison of the two GOES magnetometer data sets, the spatial and temporal characteristics of the substorm‐associated variations in the geomagnetic field near synchronous orbit are studied. The onset of the first substorm (expansion phase) was observed at GOES 3 at 1053 UT, and at GOES 2 at 1110 UT about 17 min later. At this time, GOES 3 was at 0200 LT and GOES 3 was at 0400 LT. Prior to the expansion phase, both GOES satellites detected a growth phase during which the field was distended tailward, and the azimuthal component underwent a negative (westward) excursion. The growth phase began almost simultaneously at the two satellites. During the second substorm, the two satellites did not observe clear substorm signatures because they were at dawn. The magnetic field observations for the first substorm are characterized by the current wedge model proposed by McPherron et al. (1973).
Plasma measurements of the Pioneer Venus Orbiter in the Venus ionosheath: Evidence for plasma heating near the ionopause
Authors: Pérez‐de‐Tejada H. , Intriligator D. S. , Scarf F. L.
Published: February 2008

A study of the angular spread of plasma fluxes detected in the Venus ionosheath is presented. It is shown that in the inner regions of the ionosheath, where the flux intensity is severely decreased with respect to solar wind values, the width of the azimuthal distribution of the local plasma is comparable to, or even larger than, that of the stronger fluxes measured in the outer ionosheath. The observed variation of the angular width suggests the existence of a source of heating near the ionopause but is not consistent with the overall cooling that would be expected if mass loading and charge exchange collisions were solely responsible for the interaction process at that boundary. Dissipative phenomena associated with local plasma turbulent processes seem to be required to account for the broad angular distributions seen near the ionopause.
Coherent generation mechanism for auroral kilometric radiation
Authors: Buti B. , Lakhina G. S.
Published: February 2008

Generation of electromagnetic radiations from the nonlinear interaction of whistler solitons with the upper hybrid waves is investigated. The power emitted from the right‐hand polarized fundamental whistler sideband of upper hybrid frequency is obtained. The results are applied to the generation of auroral kilometric radiations (AKR) on the auroral field lines in the earth's magnetosphere. The power is found to be larger in the plasma depletion region as compared to high‐density region. It is found that about 10³–104 whistler solitons filling a volume of ≲4×108 km³ in a region of field‐aligned auroral cavity can generate the observed AKR power of 109 W. Theoretical predictions agree very well with the observed properties of AKR, e.g., frequency range, polarization, peak power and its tendency to occur in the density depletion regions.
The secondary radiation under Saturn's A‐B‐C rings produced by cosmic ray interactions
Authors: Cooper J. F. , Eraker J. H. , Simpson J. A.
Published: February 2008

From measurements on the Pioneer 11 spacecraft, electrons and protons under Saturn's A‐B‐C rings were reported by Simpson et al. (1980) and Chenette et al. (1980) and identified as the secondary products of cosmic ray nucleons with energies ≫10 GeV interacting with ring matter. We have extended their analysis and have also found both secondary gamma ray fluxes with energies ≫15 MeV and fragmentation nuclei (H and heavier nuclei) with energies <10 MeV/nucleon, which are consistent with this interpretation. From a comparison of the measured low‐energy proton and gamma ray fluxes with fluxes from numerical simulations of the secondary particle production and propagation in material slabs (protons) and the Earth's atmosphere (gamma rays) we find that the A‐B‐C ring mean surface density 〈σ〉 (g/cm²) sampled along the trajectory of Pioneer 11 is
. Direct measurement of the A‐B‐C ring surface density 〈σ〉 in radial intervals of ∼300‐1000 km is obtained from the measured higher‐energy secondary particles (electrons ≫25 MeV and protons ≫67 MeV). The surface density of the optically thick B ring is measured for the first time. Two analyses with separate data sets yield surface densities for the B ring of
and 62 ± 25 g/cm². The latter value yields a B ring mass of 1.0 ± 0.4 × 1022 g; we obtain a value for the A‐B‐C ring mass of
, where Ms (Saturn';s mass) = 5.7 × 1029 g. Our surface density measurements are shown to be consistent with results derived from Voyager ring radio/optical opacity measurements and the observed damping of density waves in the ring.
Effects of chemical releases by the STS 3 Orbiter on the ionosphere
Authors: Pickett Jolene S. , Murphy Gerald B. , Kurth William S. , Goertz Christoph K. , Shawhan Stanley D.
Published: February 2008

The Plasma Diagnostics Package, which was flown aboard STS 3 as part of the Office of Space Science first shuttle payload (OSS 1), recorded the effects of various chemical releases from the orbiter. Changes in the plasma environment were observed to occur during flash evaporator system releases, water dumps, and maneuvering thruster operations. During flash evaporator operations, broadband orbiter‐generated electrostatic noise was enhanced, and plasma density irregularities (ΔN/N) were observed to increase by 3–30 times with a spectrum which rose steeply and peaked below 6 Hz. Ions with energies up to several hundred eV were also observed during one flash evaporator operation. In the case of water dumps, background electrostatic noise was enhanced at frequencies below about 3 kHz and suppressed at frequencies above 3 kHz during the dump, and ΔN/N was also seen to increase by 5–6 times. Various changes in the plasma environment were effected by primary and vernier thruster operations, including increases in electron density by as much as 3 orders of magnitude, neutral pressure increases to as high as 10−4 torr from the nominal 10−7 torr, and perturbations in the spacecraft potential by several volts, particularly when measured in relation to the plasma potential in the wake. Thruster activity also stimulated electrostatic noise with a spectrum which peaked at approximately 0.5 kHz. In addition, ions with energies up to 1 keV were seen during some thruster events.
Ionospheric electron content depletion associated with amplitude scintillation at the equatorial anomaly crest region
Authors: Huang Yinn‐Nien
Published: February 2008

The diurnal and seasonal behaviors of the ionospheric total electron content (TEC) depletion associated with VHF amplitude scintillation observed at Lunping, Taiwan (25.00°N, 121.17°E geographic), during the period March 1977 to February 1980 were presented. Diurnally, the maximum occurrence of TEC depletion appears during the late evening hours for all seasons except winter. Seasonally, the maximum occurrence of TEC depletion is not fixed at a certain season but varies with sunspot number because of the different sunspot number dependence of the occurrence of TEC depletion in different seasons. The most probable maximum TEC depletion ranges from 0.8 to 3.6×1016el/m², and the duration ranges from 10 to 33 min. No correlation was found between the maximum TEC depletion and the duration or between the maximum TEC depletion and the associated ionospheric scintillation index. The association between TEC depletion and range spreadFis much better than that between TEC depletion and frequency spreadF.
Observations of He+ ions in the solar wind
Authors: Pissarenko N. F. , Dubinin E. M. , Zakharov A. V. , Budnik E. Yu. , Lundin R.
Published: February 2008

This paper describes results obtained from the Prognoz 8 ion composition experiment which indicates that He+ ions may be more abundant in the solar wind than previous measurements have indicated. The experiment has a sufficiently high mass resolution to accurately discriminate between H+, He++, He+, and O+ ions over the energy range 0.35–5.2 keV/el. Furthermore, the fact that the experiment is continuously monitoring in the solar direction means that fairly good statistics can be aquired as well. In a few cases, He+/He++ ratios up to ≈0.05 have been found, but in most cases when He+ was observed it was generally of the order 0.3–3% of the He++ content. We compare our results with previous measurements of He+ ions in the solar wind and discuss also other constituents with M/q = 4 as alternative candidates. Finally, a possible explanation for the high He+ abundance in the disturbed solar wind is given.
Dynamics of the Arecibo ionosphere: A case study approach
Authors: Behnke R. , Kelley M. , Gonzales C. , Larsen M.
Published: February 2008

A number of different processes have been suggested to explain the F layer plasma drifts measured over the Arecibo Observatory. A series of experiments are described here which take advantage of neutral wind measurements now available at Arecibo as well as an unusual event during which large high‐latitude electric fields penetrated to the low‐latitude ionosphere. With this added information we are able to differentiate between the competing processes controlling the F layer. We show that depending on various conditions, both the F layer dynamo mechanism and the external electric field‐diffusion velocity mechanism can control the dynamics of the F layer. We also present a case in which neither of these mechanisms is sufficient to explain the observed behavior of the nighttime F layer plasma. In addition, we have carried out calculations that demonstrate that during magnetically active times, the penetration electric fields can set the low‐latitude thermosphere in motion via ion drag. Finally we show that at times, conjugate point electric fields appear to be present and that the conductivity at the conjugate point can dominate the local value with observable consequences.
The spatial evolution of energetic electrons and plasma waves during the steady state beam plasma discharge
Authors: Llobet X. , Bernstein W. , Konradi A.
Published: February 2008

Changes in the characteristics of the electron beam and the associated wave spectrum as a function of axial distance from the electron gun have been studied in a steady state laboratory beam plasma discharge. The beam energy distribution evolves from a monoenergetic beam to a heated beam (characteristic of trapping) and then to an almost flat (plateau) distribution with increasing distance from the gun. The wave spectrum evolves similarly from a small amplitude single band at the upper hybrid frequency fUHF = (fp² + fc²)1/2 to a much larger amplitude, harmonic rich spectrum with increasing distance. Accompanying the degraded energy spectrum, the valleys between the harmonic peaks disappear to produce a continuous spectrum greater than fUHF with reduced amplitude. Very little spatial diffusion or pitch angle scattering of the beam is observed, indicating that the interaction is predominantly one‐dimensional. The axial positions, where these different wave‐beam electron configurations appear, depend upon the experiment parameters, beam current Ib, beam energy Eb, and neutral density. The described results clearly indicate the occurrence of the absolute rather than the convective instability and confirm that the beam plasma discharge (avalanche ionization) is a particular manifestation of the well‐studied strong beam‐plasma interaction (avalanche ionization absent).
Ionospheric evidence for irregular reconnection and turbulent plasma flows in the magnetotail during periods of northward interplanetary magnetic field
Authors: Bythrow P. F. , Burke W. J. , Potemra T. A. , Zanetti L. J. , Lui A. T. Y.
Published: February 2008

Measurements of magnetic and electric fields in the summer polar cap during periods when Bz > 0 have revealed a stable well‐developed “W” pattern in the transverse component of
and in the orbit parallel component of Ē (Iijima et al., 1984; Burke et al., 1979). This W pattern found in
and Ē characterizes a four‐celled ion drift pattern having sunward flow in the central polar cap flanked by regions of antisunward flow that reverses to sunward once again at lower latitudes. Subsequent investigation of electric and magnetic fields from the S3‐2 and Magsat data sets shows that in the summer hemisphere a transition from this W shape into a more structured pattern occurs near the magentic dawn‐dusk meridian. Since, on a seasonal basis, Magsat's orbit remained fixed with respect to the terminator, the conductivity distribution beneath the orbit track was essentially constant from one orbit to the next. Thus, this effect is not due to conductivity variations. In the winter polar cap the W pattern is difficult to identify in the measurements of the transverse component of
or Ē made on either side of magnetic dawn‐dusk; however, analysis of the radial component of
measured in both polar caps at, or tailward of, the dawn‐dusk meridian shows the presence of a weak ionospheric Hall current system with a W‐shaped distribution for scale sizes >600 km. From these observations we conclude that a basic two‐cell reverse convection pattern persists in the polar caps of both hemispheres and on both sides of the dawn‐dusk meridian (in addition to the auroral viscous cells). These polar cells are distorted in the tail side of the sunlit hemisphere and in the entire dark hemisphere, with major perturbations in the sunward‐antisunward direction. This is related to an irregular reconnection process in the plasma sheet driven by opposing dawn‐dusk and dusk‐dawn electric fields that have their sources in the boundary layer and solar wind, respectively. This process gives rise to the ionospheric turbulence observed in the electric field and Birkeland current signature and may be associated with sun‐aligned arcs.
“Electron conic” signatures observed in the nightside auroral zone and over the polar cap
Authors: Menietti J. D. , Burch J. L.
Published: February 2008

A preliminary search of the Dynamics Explorer 1 high‐altitude plasma instrument data base has yielded examples of “electron conic” signatures. The three example passes show an association with regions of downward electron acceleration and upward ion beams, but this is not true of all the electron conic events. The electron conic signatures are clearly discernible on energy‐flux‐versus‐time color spectrograms as pairs of discrete vertical bands which are symmetric about a pitch angle of approximately 180°. One of the examples is a polar cap pass with electron conic signatures observed at invariant latitudes from 84° to 75°. The other two cases are nightside auroral zone passes in which the regions of detectable electron conies are spatially more confined, covering only about 1° in invariant latitude. The conic signatures have been found at energies that range from 50 eV < E < 2 keV, with the lowest‐energy examples found in the polar cap. The distribution of the electrons about a pitch angle of 180° is larger than expected for a loss cone feature. If the electrons conserve the first adiabatic invariant in a dipole magnetic field, and in some cases a parallel electric field, the mirroring altitude varies between about 500 km and 8000 km, which is above the atmospheric loss region. For this reason, and in analogy with the formation of ion conics, we suggest that the conic signatures are produced by heating of the electrons perpendicular to the magnetic field.
Temporal characteristics of the solar UV flux and He I line at 1083 nm
Authors: Donnelly R. F. , Harvey J. W. , Heath D. F. , Repoff T. P.
Published: February 2008

Temporal variations of the Nimbus 7 measurements of solar UV flux, important for their stratospheric effects, are compared with ground‐based measurements of the solar infrared He I absorption line at 1083 nm. The close similarity of their temporal characteristics shows that the 1083‐nm line is a better estimator of the UV flux than the classical indices of solar activity, the 10.7‐cm radio flux and the sunspot number, for short time scales (days, weeks). The power spectrum of the He I line intensity matches that of the Nimbus 7 205‐nm flux at the 27‐day period peak but is weaker at the peak near 13 to 14 days period. The 27‐day peak is caused by the combination of solar rotation of active regions with one major concentration in their solar longitude distribution, and the 13‐day case involves two concentrations with solar longitude roughly 180° apart. The 13‐day periodicity is not simply a second harmonic of the 27‐day periodicity, because some episodes of activity are dominated by the 13‐day periodicity with very weak 27‐day periodicity while other episodes are dominated by 27‐day periodicity with weak 13‐day periods. These episodes of activity, which last typically 4 to 8 months, are caused mainly by groups of strong active regions that dominate the solar‐rotational variations for several months. In addition to the enhanced short‐term modulation during these episodes, the valleys in the solar‐rotational modulation also slowly rise and decay. F10 and R tend to rise more steeply and peak earlier during these episodes than the UV flux and the He I line.
Plasma‐dominated magnetic field configurations for the magnetosphere of Uranus
Authors: Ip A. K. , Voigt G.‐H.
Published: February 2008

We present hydromagnetic equilibrium configurations for the nonrotating “pole‐on” magnetosphere of Uranus. According to a plasma supply mechanism proposed by Cheng (1984) we assume that charged particle sputtering of the water‐ice covered moons of Uranus provides a continuous internal plasma source to the Uranian magnetosphere. We assume further that (1) dynamical changes of the magnetosphere are quasi‐static, (2) the internal plasma source fills the Uranian magnetosphere in a homologous manner, and (3) the plasma residence time within the magnetospheric cavity is long enough to allow the Uranian magnetosphere to evolve from a vacuum configuration toward a plasma‐dominated equilibrium. With these assumptions, we calculated configurational changes of Uranus's magnetosphere, given the amount of the thermal plasma pressure as a free parameter. In order to include Uranus's dipole in the equilibrium calculations the homogeneous Grad‐Shafranov equation for cylindrically symmetric magnetospheres has been complemented by an inhomogeneous source term. We derived linear analytic solutions to the inhomogeneous problem. We found that a plasma ring forms near the equatorial plane of the planet when the thermal pressure reaches about 75% of the maximum amount that would lead to a Harris sheet magnetotail configuration. The appearance of a plasma ring is due to the particular pole‐on orientation of Uranus's dipole; such a ring would not exist in an earth‐type equilibrium magnetosphere.
Refilling of geosynchronous flux tubes as observed at the equator by GEOS 2
Authors: Sojka J. J. , Wrenn G. L.
Published: February 2008

During periods of extended quiet geomagnetic activity the geosynchronous satellite orbit lies inside the plasmasphere. Five such periods were observed by the GEOS 2 satellite. During the initial 48 hours of such periods the equatorial plasma flux tube density increases at 30 to 50 cm−3/day. However, on reaching ∼100 cm−3 the refilling rate decreases, and refilling is limited. Only when the density reaches ∼100 cm−3 do the plasma characteristics and fluctuations appear to be plasmaspheric and the flow predominantly corotational. The “hot outer zone” of the plasmasphere is highly structured in density and temperature when viewed from a corotating satellite. This region also has a relatively dense population of warm subkilovolt electrons. These warm electrons whose density is ∼1% to 50% of the cold plasma may be the heat source for the hot outer zone ions.
Optimization of energetic electron energy degradation calculations
Authors: Swartz Wesley E.
Published: February 2008

The optimization of the energy degradation and reapportionment computer algorithms within theoretical computations of the effects and behavior of photoelectrons and other energetic electrons is established within a framework of discrete losses resulting from inelastic collisions with a neutral gas and interactions with the ambient electron gas. The basic method described guarantees energy conservation, while allowing large increases in the energy cell sizes with increasing energy with minimal distortion of the total excitation rates of neutrals and heating of the ambient electrons over what would otherwise be possible. When energy resolution of the spectra can be sacrified, extensions to very large energies are economically feasible using approximately seven cells per decade of energy without significant distortions in the energy reapportionment to other species. The emphasis is not on what particular set of cross sections should be used but rather on how to adapt the energy degradation procedure and the energy grid to the characteristics of the cross sections over the energy range of interest. For example, accurate determination of the ambient electron heating rate in terrestrial applications requires fairly small energy cells at low energies (usually less than 0.2 eV wide below 10 eV), while secondary ionization rates and most neutral excitation rates place no severe limitations on the energy cell sizes. Cell widths much larger than the excitation thresholds are possible and can be large fractions of the mean cell energy. At energies above 30 eV, cell widths that are up to 40% of the mean cell energy appear adequate for some applications not requiring high spectral resolution.
A theory for the 2fp radiation upstream of the Earth's bow shock
Authors: Cairns I. H. , Melrose D. B.
Published: February 2008

A theory for the radiation at the second harmonic of the plasma frequency fp observed near the earth's bow shock is advanced in which the dominant plasma emission mechanisms are the processes L + L ± S→t, proceeding in two three‐wave steps, L ± S→L′ and L + L′→t, where L, S, and t denote Langmuir, ion sound, and electromagnetic waves, respectively. This theory receives strong observational support from the correct prediction of the existence and frequencies of a class of low‐frequency ion‐sound‐like waves associated with Langmuir waves in the earth's foreshock. Three predictions of the theory which may be suitable for observational testing are stated. The observed brightness temperature of the 2fp source is calculated to be of the order of 1011 K. It is shown that Fung et al.'s (1982) theory cannot explain either the 2fp radiation due to an intrinsic brightness temperature limit of 3×109 K for their model or the observed levels of Langmuir waves in the foreshock region.
Ionization frequencies for solar cycle 21: Revised
Authors: Torr Marsha R. , Torr D. G.
Published: February 2008

Detailed spectra of the extreme ultraviolet solar flux at the earth were provided by instruments on the Atmosphere Explorer satellites. These data have been used for aeronomical purposes in a large number of studies. An important parameter for such studies is the rate of production of various ions through the photoionization process. This parameter, known as an ionization frequency, is the integral over wavelength of the product of the solar flux and the cross section for the ionization of the particular constituent. Thus the determination of the ionization rate is dependent on a good knowledge of the solar EUV intensities for the solar period in question. Over the past few years the EUV solar spectra that have been developed for use by aeronomers as reference spectra for such photochemical and ionospheric studies have been improved. In this paper we report the results of a redetermination of the most important ionization frequencies using the revised solar fluxes. The impact is found to be more significant at solar maximum, amounting to a reduction of 12–21% in the ionization frequencies of the major terrestrial thermospheric constituents for solar minimum conditions and 21–33% for solar maximum conditions. The corrections are apart from the ongoing debate concerning the absolute intensity of EUV solar flux measurements for the solar cycle 21 maximum period.
The electrostatics of a dusty plasma
Authors: Whipple E. C. , Northrop T. G. , Mendis D. A.
Published: February 2008

We derive the potential distribution in a plasma containing dust grains where the Debye length can be larger or smaller than the average intergrain spacing. We treat three models for the grain‐plasma system, with the assumption that the system of dust and plasma is charge‐neutral: the permeable grain model of Goertz and Ip (1984), an impermeable grain model, and a capacitor model that does not require the nearest neighbor approximation of the other two models. We use a gauge‐invariant form of Poisson's equation which is linearized about the average potential in the system. The charging currents to a grain are functions of the difference between the grain potential and this average potential. We obtain expressions for the equilibrium potential of the grain and for the gauge‐invariant capacitance between the grain and the plasma. The charge on a grain is determined by the product of this capacitance and the grain‐plasma potential difference. The three models give similar but not identical results. The results depend primarily on the parameter Z = 4πλ²NC, where λ is the Debye length, N is the grain concentration, and C is the grain to plasma capacitance. When Z ≫ 1, the number of charges on a grain that is only charged by plasma currents is given by
where µ is the square root of the ion to electron mass ratio, and
and
are the average ion and electron densities. We confirm the result of Goertz and Ip (1984) that the charge on a grain in regions such as Saturn's F ring and spokes can be severely decreased from its free space value. The charge reduction occurs because the plasma electrons are depleted so that the grain does not need to be as negatively charged to equalize the ion and electron fluxes to its surface, despite the increased grain to plasma capacitance.
Energetic particle precipitation into the high‐latitude ionosphere and the auroral electrojets: 3. Characteristics of electron precipitation into the morning sector auroral oval
Authors: Rostoker G. , Kamide Y. , Winningham J. D.
Published: February 2008

Data from the University of Alberta meridian line of magnetometers are utilized to define the poleward and equatorward borders of the westward electrojet in the morning sector. Soft particle spectrometer data from the Isis 2 polar orbiting satellite are organized in the framework of the westward electrojet for cases where the satellite orbital path took it close to the meridian line of magnetometers. It is found that, in the morning sector, the energetic electron data are organized into four distinct regions as a function of latitude. The southernmost region (D) features trapped electrons across a broad energy range. Region C, just poleward of Region D, contains fluxes of hot (several keV) electrons with a Maxwellian spectrum which are precipitating into the southern portion of the westward electrojet. These Region B fluxes are colocated with the poleward portion of the westward electrojet and are less capable of creating ionospheric Hall conductivity than are their more energetic Region C counterparts. Finally, Region A, poleward of the northern border of the westward electrojet, contains irregular latitudinally localized regions of precipitating electrons whose spectrum contains drifting Maxwellians and which are evidently being accelerated along the field lines on which they are being observed. The energies of electrons in Region A are of the order of a few hundred electron volts and rarely exceed ∼1–2 keV. The phenomenology of Region A is remarkably similar to the acceleration region in the poleward portion of the auroral oval in the evening sector although the peak energies of the electrons are smaller in the morning sector compared to the evening sector. Our results suggest that the Harang discontinuity does not signify any significant asymmetry in convection drift paths in the magnetosphere and that asymmetries noted in ionospheric current flow and auroral luminosity are due solely to asymmetries in the energies to which electrons may be accelerated in the morning compared to the evening sector. We present a model of plasma convective flow in the magnetosphere which is consistent with the observations reported in this paper.
Electrostatic instabilities in plasmas with two electron components
Authors: Peter Gary S.
Published: February 2008

This paper considers the linear theory of electrostatic Vlasov instabilities driven by the relative drift between two Maxwellian electron components in an unmagnetized, homogeneous plasma bearing zero current. The dispersion properties, threshold drift speeds, and growth rates of the electron beam instability, the conventional ion acoustic instability, and the ion acoustic beam instability are compared in detailed parametric studies. A new way of illustrating the parameter regimes in which each of these three instabilities has the lowest threshold drift speed is demonstrated. This leads to clearly illustrated criteria for determining when enhanced electrostatic fluctuations between the ion and electron plasma frequencies may be observed in plasmas with two electron components. In the case of a hot beam this criterion is a beam density nb which satisfies 0.05 ≲ nb/ne ≲ 0.30 where ne is the total electron density.
“Alfvén wing” models of the induced electrical current system at Io: A probe of the ionosphere of Io
Authors: Herbert Floyd
Published: February 2008

Models are presented of the electrodynamic interaction between corotating Jovian magnetospheric plasma and the ionosphere of Io. The interaction is treated as a purely transverse Alfvén wave which is controlled by the electrical conductivity distribution of Io's ionosphere. By quantifying the connection between the ionospheric conductivity and the magnetic field and velocity perturbations observed during the Voyager 1 flyby, the observations serve as a probe of the ionosphere, under the assumption that the ionosphere constitutes the principal cross‐field conductance near Io. If the electron density is assumed to be that measured earlier by Pioneer 10, the ionospheric resistivity is controlled by the electron‐neutral collision rate. Parameterized approximations for the neutral density distribution are varied to produce a fit between the calculated magnetic field and observations made by Voyager 1. The best‐fitting ionospheric models assume a neutral density distribution containing a significant global component (of the order of 109 to 1010 cm−3). However, the cold‐trap model (according to which Io has a very low‐density atmosphere) can be accommodated with the assumption of a significant SO2 coverage of the trailing hemisphere resulting from outgassing of the major plumes there. After taking account of field line curvature and Alfvén speed variation over the distance between Io and Voyager 1, the Io plasma torus charged‐mass density required for a proper match to the data is larger than earlier estimates based on the width of the Alfvén wing signature.
Multiple peaks in the spectrum of inner belt electrons
Authors: Datlowe D. W. , Imhof W. L. , Gaines E. E. , Voss H. D.
Published: February 2008

We report on a systematic study of energetic electron spectra in the inner magnetosphere. The observations were made from the low‐altitude satellite S81‐1 during the period June–November 1982. The electron spectrometers covered the energy range 6 keV to 1 MeV. In most geographic areas the electron energy spectra are smooth, but in the region of the South Atlantic Anomaly the spectra often consist of a series of broad peaks. The number of peaks is typically three, but may be as many as eight, or in some cases there may be none. The peak‐to‐valley ratios are often an order of magnitude or more. Peaks in the spectra of electrons from 100 keV to above 1 MeV at higher altitudes have been reported earlier in conjunction with geomagnetic storms. At the 250‐km nominal altitude of the S81‐1 observations, peaks in the energetic electron spectra are observed on most days and at all levels of geomagnetic activity.
Energy partitioning in the Io plasma torus
Authors: Smith Robert A. , Strobel Darrell F.
Published: February 2008

The plasma state of the hot torus is studied with a local, homogeneous, steady state model described by a set of coupled quasi‐linear equations for the distribution functions of S+, S++, S+++, O+, and O++. The equations contain model Fokker‐Planck operators for ion‐ion and ion‐electron collisions, a species‐ and energy‐independent loss rate τ−1, impact ionization of S, S+, S++, O, and O+, recombination of S+++, and 11 charge exchange reactions. The only free parameters, which are not governed by physical processes contained in the model, are the ion confinement or residence lifetime τ and the neutral densities of sulfur, nS, and oxygen, nO. Equivalently, if nS, nO, and the electron density ne are adopted as parameters, then τ is determined by imposing charge neutrality. Under the constraints that the pickup mechanism for newly created ions is the dominant energy source and that the torus is in equilibrium between collisional energy loss from ions to electrons and radiative UV loss from ions excited by ion‐electron collisions, the densities, average energies, and distribution functions of all ion species and the temperature of the electrons, which are assumed to be Maxwellian, are calculated as functions of the input parameters. Among the results are the following: (1) The ion velocity distributions are significantly non‐Maxwellian for the major species, with high‐energy tails extending to the pickup energy. A quasi‐thermal core exists for the O+ and/or S+ ion velocity distribution functions only if the EUV luminosity of the torus is less than 0.2 eV cm−3 s−1. The core “temperature” is at most Ti ∼ 100 eV; the average energy of the total distribution is generally less than 0.5 of the pickup energy. The ion velocity distributions do not drive the ion loss cone instability for parameters generally typical of the torus. (2) The EUV luminosity of the torus during the Voyager 1 encounter was ∼0.15 eV cm−3 S−1, a factor of ∼1.8 less than that reported by Shemansky and Smith (1981). This downward revision in the EUV intensities is in agreement with calibration adjustments adopted by Holberg et al. (1982) at longer wavelengths (912–1050 Å). (3) During the Voyager 1 encounter the approximate average torus ion densities were S+: <350, S++: 420, S+++: 10–20; O+: 660, O++: 40–80 cm−33 with Te ∼ 4.8 eV, τ ∼ 60 days, and ne ∼ 2000 cm−3. The average neutral torus densities were nS ∼ 6 and nO ∼ 30 cm−3 and consistent with an SO2 source. (4) The upper limit obtained by Brown et al. (1983b) on O++ concentrations is only applicable to short duration periods when transient, large eruptions of sulfur‐driven volcanoes occur on the surface of Io (McEwen and Soderblom, 1983) and mass loading of the neutral torus is preferentially by sulfur. The resultant plasma torus contains S+ and S++ densities of ∼600, O+ ∼120, O++ < 10, and S+++ < 40 cm−3. The increased mass loading reduces τ to ∼1 week.
Three‐dimensional plasma observations near the outer magnetospheric boundary
Authors: Eastman T. E. , Popielawska B. , Frank L. A.
Published: February 2008

Detailed analyses of 18 ISEE 1 magnetopause crossings have been made using three‐dimensional plasma data obtained by the University of Iowa LEPEDEA's which detect ions and electrons from 1 eV to 45 keV. Crossings were examined that occurred on both the dawn and dusk flanks near the sunward, outer magnetospheric boundary. Nearly all cases show a de‐energization of magnetosheath plasma after this plasma crosses the magnetopause to produce the magnetospheric boundary layer. The bulk plasma flow frequently changes direction as it crosses the magnetopause, resulting in boundary layer flow that has an enhanced cross‐field flow component without, typically, any increase in speed. These observed flow directions are consistent with Ep × B drifts imposed by polarization fields Ep established near the forward extent of penetrating magnetosheath irregularities which are producing the boundary layer. Our three‐dimensional observations of plasma flow demonstrate that these polarization fields are present and significant. In addition, we directly observe the field‐aligned depolarizing currents linked to this dynamo region, which is likely a primary generator for the cusp region and system 1 field‐aligned currents. A few exceptional crossings do show plasma energization in the boundary layer, a condition that occasionally results from Maxwell stresses on impulsively injected magnetosheath plasma. However, some principal cases of such energized plasma appear to occur on closed field lines, so that the reconnection mechanism is not necessarily involved in these exceptional crossings. The reconnection hypothesis also predicts that plasma is energized at the expense of field energy density. However, our study demonstrates that the dominant process in the solar wind‐magnetosphere interaction results in plasma de‐energization as magnetosheath plasma crosses the magnetopause to supply the magnetospheric boundary layer.
The detailed intensity distribution of the AKR emission cone
Authors: Green James Lauer , Gallagher Dennis L.
Published: February 2008

Auroral kilometric radiation (AKR) observations in the northern hemisphere from 3.5 years of IMP 6 data and 4 years of Hawkeye data, at large radial distances, are combined to produce detailed intensity distributions of the AKR emission pattern below 200 kHz. All Hawkeye and IMP 6 AKR observations are normalized to a radial distance of 7 earth radii (RE) from the average source region reported by Gallagher and Gurnett (1979). The normalization is done to compensate for the expected radial variations in the intensity. Unlike previous emission pattern studies which showed the AKR frequency of occurrence above a preset power flux threshold, intensity contours of spectral power flux are presented. The AKR observations are well ordered in the source‐centered coordinates which provides further support for auroral zone generation of this emission at those altitudes. AKR is found to be emitted into a large emission cone pattern whose size decreases with frequency from the AKR spectral peak to low frequencies, consistent with previous studies. The emission cones have solid angles of 4.6, 3.3, and 2.7 steradians at 178, 100, and 56.2 kHz, respectively. Unexpected in these results is that there is less than a 10 dB variation in the illumination intensity across nearly the entire time‐averaged AKR emission patterns, at 178 and 100 kHz. In addition, simultaneous observations by Hawkeye and IMP 6 reveal that individual bursts of AKR can easily illuminate the northern emission cone uniformly. No systematic AKR intensity difference in longitude or latitude, within the cone at 178 kHz, is found during the simultaneous two spacecraft observations. This is not consistent with the hollow emission cone pattern reported by AKR at low frequencies (see Calvert, 1981c) near the source region.
Polar convection patterns under quiet conditions
Authors: Barbosa D. D.
Published: February 2008

Convection electric field patterns at high latitudes appropriate to periods of low geomagnetic activity are presented. The postulate that the global Joule dissipation rate is a minimum is employed to derive characteristic field distributions for the situation when ring current ohmic losses are negligible and the auroral oval enhancement of height‐integrated Hall conductivity is small. The fast Fourier transform is introduced to compute Fourier coefficients of discrete field‐aligned current data, and the method is shown to be quite useful in this context as a least squares fitting routine. The model calculations demonstrate the approach of the high‐latitude ionosphere toward the perfect shielding configuration predicted by the theory for quiet times.
Observations of limb radiance with Cryogenic Spectral Infrared Rocket Experiment
Authors: Stair A. T. , Sharma R. D. , Nadile R. M. , Baker D. J. , Grieder W. F.
Published: February 2008

A Spectral Infrared Rocket Experiment was launched from Poker Flat, Alaska, on September 28, 1977, to measure infrared emission spectra from the earth limb atmosphere. Spectrometers measured emission spectra from 1.40 to 16.5 µm during 12 vertical scans of the limb region (tangent heights 0 to 250 km) traversing the night, terminator, and day sectors of the limb atmosphere. The spectrometers were cryogenically cooled and telescoped for out‐of‐field rejection of the more intense radiation from lower altitudes. High‐quality spectra were obtained with clearly identifiable features of CO2, O3, NO, OH, H2O, NO2, HNO3, and O2, as well as Rayleigh scattering. Spectra and tangent height emission profiles of selected species are presented and compared with theoretical emission models including those of Degges and Smith (Limb Model) and LOWTRAN 4. The salient findings are as follows: At a height of 80 km, CO2 daytime emission from fluorescence around 4.3 µm was almost 2 orders of magnitude greater than the nighttime emission. At 15 µm the CO2 radiance profiles showed little day‐night differences but exhibited an unexpected radiance plateau between 95 and 110 km. The ozone peak radiance at 9.6 µm (ν3) showed order of magnitude day‐night differences above 70 km tangent height showing a decrease in concentration of O3 during daytime due to photodissociation. The observed radiance in the 9‐ to 12‐µm wavelength region exhibited evidence of chemiluminescent emission from hot bands of O3. NO (Δυ = 1) peak radiance at 5.3 µm, due to O atom excitation, is a broad maximum at 120 km tangent height. The nighttime OH fundamental (Δυ = 1) and overtone (Δυ = 2) emissions showed extensive radiation from higher vibrational levels. The daytime 2.7‐µm fluorescent radiation was composed of emission from both H2O and CO2. Emission from NO2 at 6.15 µm (ν3) was observed at night only but was clearly identifiable amid the H2O (ν2) spectrum. Measured radiation in the 6.3‐µm vibrational band of water vapor at 60 and 70 km agrees with the Air Force Geophysics Laboratory non‐local thermodynamic equilibrium Limb Model using mixing ratios of 5 and 1.5 parts per million by volume, respectively. The radiance from O2 (a¹Δg) at 1.58 µm was observable from tangent heights of 30 to 80 km in the daytime only and shows a critical dependence upon the solar elevation angle. As expected, Rayleigh scattering was the dominant daytime source of radiation between 1 and 3 µm in the limb atmosphere for tangent heights of up to 40 km.