bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion of cold magnetospheric ions
Authors: Birmingham T. J. , Northrop T. G.
Published: February 2008

We investigate conditions under which a diffusion equation is a valid description of the transport across magnetic field lines of low energy magnetospheric plasma. In this paper we consider the case where the guiding center drift , and in particular its fluctuating component , are comparable in size to the particle thermal speed. We conclude that a two dimensional diffusion equation is valid in the α, β space of the Euler potentials provided that the curl of the total electric field component parallel to
vanishes and provided the fluctuations have a short enough correlation time that guiding center drifts other than remain negligible. Ions in Jupiter's Io plasma torus are thus described by a diffusion equation if this correlation time is no more than a few rotation periods of the planet.
The Voyager 1 EUV spectrum of the Io plasma torus
Authors: Shemansky D. E. , Smith Gerald R.
Published: February 2008

The Voyager 1 EUV spectrum of the hot Io plasma torus has been analyzed by using a collisional model. The estimated effective electron temperature of the central dense region of the plasma is 8 × 104 K. The torus half width number densities (cm−3) obtained from the model calculation are O II (50), O III (340), O IV (<17), S II (44±20), S III (160), S IV (220), S V (≤11), and K III (≤80). The relative oxygen/sulfur number densities are ΣOn/ΣSn ≃0.9. Comparison of the model calculations with other spectroscopic observations that can be clearly identified as originating in the hot plasma torus shows satisfactory agreement. However, the EUV observations show strong morphological differences with recent ground‐based observations of S II emission, raising questions concerning excitation mechanisms and radial dependence of the observed characteristics. The ion densities indicated by the EUV data analysis show distinct differences with the in situ Voyager 1 plasma science estimates.
Some experimental tests of Perkins Spread F Theory
Authors: Imel G. , Klevans E. H. , Carpenter L. A.
Published: February 2008

Equilibrium predictions from the Perkins midlatitude spread F instability theory are tested by using nighttime incoherent scatter data obtained at the Arecibo Observatory. The field line integrated Pedersen conductivity is obtained by two different methods, one representing direct field line integration and the other using the equilibrium formula developed by Perkins. Of the four nights considered, agreement is good on three of the nights for times when an equilibrium is appropriate. During the post‐sunset rise and the midnight collapse, when equilibrium does not exist, agreement is poor. Calculation of the east‐west neutral winds required for instability growth times of 30 min indicate that east‐west wind velocities would need to be comparable to the measured north‐south winds. Shorter growth times would require higher east‐west wind velocities.
Field‐aligned currents and the structure of the auroral zone ionosphere
Authors: Hruška A.
Published: February 2008

A general formula expressing the density of the magnetic field‐aligned current in a partially ionized gas as a function of other physical parameters is derived, and its approximate form, suitable for ionospheric studies, is discussed. Changes of the field‐aligned currents in the ionosphere depend on the properties of the vector G representing the total mechanical force acting on a volume of a multicomponent ionospheric ‘fluid’; div j⊥, and consequently div j∥, is different from zero if and only if B · curl G≠0. Heating of the auroral ionosphere, and a high‐altitude enhancement of the atmospheric density associated with it, produces vorticity of the G field that is compatible with the pattern of the field‐aligned currents observed above the ionosphere. Variation of E⊥ in the auroral ionosphere is determined from the pattern of j⊥ and from the generalized Ohm law.
HEAO 3 measurements of the atmospheric positron annihilation line
Authors: Mahoney W. A. , Ling J. C. , Jacobson A. S.
Published: February 2008

All spectra measured with the High Energy Resolution Gamma‐Ray Spectroscopy Experiment (HEAO C‐1) on the third High Energy Astronomy Observatory (HEAO 3) contain a strong line at 511 keV resulting from positron annihilation. This line originates in the instrument itself, the earth's atmosphere, and cosmic sources, possibly including the diffuse cosmic background. In order to understand the emission from cosmic sources, the atmospheric positron annihilation line emission has been determined as a function of geomagnetic latitude and zenith angle. Although the intensity of the line increases with increasing latitude, it was found that variations with zenith angle can be satisfactorily explained only if the atmospheric emission exhibits significant limb darkening. The atmospheric line has an energy of 511.07±0.10 keV and a net width of 2.29±0.30 keV FWHM. Characteristics of the instrument background have allowed an upper limit of 9.4 × 10−3 photons/cm² ‐sec‐sr to be placed on any narrow (≲3 keV) diffuse cosmic emission at 511 keV.
Long‐term intensity decrease in the 8‐ to 25‐MeV proton fluxes at low L values
Authors: Parsignault Daniel R. , Holeman Ernest , Filz Robert C.
Published: February 2008

A five year continuous observation, 1963–1968, of the 8‐ to 25‐MeV proton population, at L < 2.0, had shown a monotonic decrease in this population. We have observed the same proton population from 1970 to 1976, using experiments flown on several USAF satellites (72‐1, S3‐2, S3‐3). These data, together with published data from the DIAL satellite, show that the decreases in the proton fluxes first observed from 1963 to 1968 have continued unabated, at least until August 1976, and with the same original mean lives. The proton flux at L=1.35 decayed over the 13‐year period (1963–1976) with a mean life τ of 5.7±0.5 years. At L=1.90, τ was 4.55±0.16 years. However, the proton flux at L=1.20, which had first been reported as constant, started decreasing ∼ 1970–1976 with τ=3.07±0.25 years. Possible explanations for this phenomenon can be divided into the two categories of natural and artificial effects. We reviewed these different effects and conclude that most likely we are seeing the decay of the high energy protons redistributed by the ‘Starfish’ high‐altitude nuclear explosion.
Electromagnetic effects in the analysis of prompt striations
Authors: Sperling J. L.
Published: February 2008

In a number of barium injection experiments in the ionosphere, field‐aligned structures have been observed to develop on the ion‐cyclotron time scale. These structures, called prompt striations, have been attributed to plasma jetting across the ambient magnetic field and have previously been analyzed in the electrostatic limit. The electrostatic analysis is reasonable for experiments in which the directed ion kinetic energy per unit volume is much smaller than the magnetic field pressure; however, for higher altitude experiments in which the ambient magnetic field strength is weaker, justification for the electrostatic treatment fails and the full electromagnetic dispersion relation must be examined. It is demonstrated that electromagnetic effects inhibit the growth of the linear instability considered to be the source of prompt striations in the earlier experiments. Consistent with the electrostatic analysis, cold background plasma and thermal spread in the ion loss cone distribution function tend to stabilize the instability in the full electromagnetic treatment. The theory suggests that prompt striations in the magnetosphere can form from ion jets only if the plasma density is sufficiently tenuous so that electromagnetic stabilization is not complete.
Short‐term EUV flux variations from AE‐E He+ abundances
Authors: Sternberg A. , Brinton H. C.
Published: February 2008

The ionization rate of helium in the thermosphere is inferred from AE‐E ion and neutral particle composition measurements made on 20 days between January 1979 and June 1980. The variations in the inferred rate are consistent with the variations in the ultraviolet flux measured during the same period by the EUV spectrometer on board the AE‐E satellite.
Short‐period fluctuations in F region ionization observed at Arecibo
Authors: Ganguly S. , Behnke R. A.
Published: February 2008

Small fluctuations in the critical frequency of the F region plasma have been measured at Arecibo with frequency resolution better than 1 kHz and time resolution of 1 s. For periods in the 10‐ to 20‐min range, f0F2 fluctuations fall off with fluctuation frequency (f) as f−k, with k ≥ 4.5. While no oscillation is observed in the period range 4–8 min, significant oscillations with amplitude of Δf0F2 ≈ 500 Hz are observed with a period of τ ≈ 3 min, corresponding to a fractional change in number density of 1–2 parts in 104. Several possible sources of these fluctuations are explored: acoustic waves in the F region, hydromagnetic or Alfven‐type oscillations, and small and large scale electric field fluctuations. Coordinated experiments employing incoherent scatter, magnetograms, and preferably an HF‐CW doppler sounder would be able to resolve the origin and nature of these intriguing waves observed for the first time in f0F2 fluctuations.
Mappings of energetic electron precipitation following substorms using the satellite Bremsstrahlung technique
Authors: Imhof W. L. , Stadsnes J. , Kilner J. R. , Datlowe D. W. , Nakano G. H. , Reagan J. B. , Stauning P.
Published: February 2008

With an array of collimated cadmium telluride spectrometers on a spinning polar‐orbiting satellite (P78‐1) a study has been made of the energetic bremsstrahlung X ray ( > 21‐keV) patterns following substorms. From an altitude of ∼600 km, X rays emanating from a wide range of magnetic local times can be observed and the local time profiles mapped on a given pass of the satellite across either polar cap. Pronounced longitude variations in the X ray intensities and hence in the precipitating electron fluxes were observed in the daytime sector at various delay times after the onset of substorms near local midnight. The longitude profile features were found to persist over time periods of at least a few minutes. Longitude variations in the energy spectra of the bremsstrahlung X rays were also obtained, and in several cases the spectra were found to be harder at later local times after midnight, although no consistent trends were evident. Coordinated measurements of electrons from the SCATHA satellite at near‐synchronous orbit revealed enhancements in the fluxes of trapped electrons on the dayside at the times of the X ray events, indicating a correlation between the trapped and precipitating electron fluxes. Additional information on the longitude profiles of electron precipitation was obtained from riometer measurements in the Danish chain, which also provided complete time histories at the station longitudes. The longitude distributions of energetic electron precipitation as inferred from satellite X ray intensity and from riometer absorption measurements show very good agreement. The riometer absorption at the Narssarssuaq station with an L value of 7.3, comparable to the SCATHA values, was found to be very similar in time profile to the trapped electron fluxes measured at SCATHA, showing a close association between the trapped and precipitating fluxes of electrons.
Coupling instability of the shear Alfvén wave in the magnetosphere with the ionospheric ion drift wave, 1. Energetic consideration
Authors: Tamao Tsutomu , Miura Akira
Published: February 2008

It is shown that the negative ohmic dissipation associated with the ion drift wave in the ionosphere under the presence of the large‐scale stationary electric field results in the shear Alfvén instability in the magnetosphere. A criterion of the instability is derived from a simple energetic consideration, which requires the reverse sign of the perturbed electric field in the ionosphere comparing with that at the equator. In fact, numerical solutions of the eigen‐mode oscillations in realistic ionosphere‐magnetosphere coupling system indicate such a change of sign between the two and also yield an upward field‐aligned Poynting flux from the ionosphere for the unstable oscillations, while for the damping oscillations we have the downward energy flow along a field line.
Harmonic structure of Pc 3–4 pulsations
Authors: Takahashi Kazue , McPherron Robert L.
Published: February 2008

Power spectra of magnetic pulsations observed at synchronous orbit by the ATS 6 satellite often show several spectral peaks simultaneously. Such pulsations, which we call harmonic events because of the nearly constant separation between successive peaks, are continuously observed in the dayside in the Pc 3–4 frequency range (6.6–100 mHz). The harmonic events are seen clearly only in the east‐west magnetic field component. The spectral peaks are regularly spaced with a typical minimum separation of 14 mHz in the morning gradually decreasing to 10 mHz in the afternoon. In the dynamic spectra of harmonic events, the fundamental mode is usually absent. In addition, the relative amplitudes of the higher harmonics depend on the magnetic latitude. These observed features can be explained by a standing Alfvén wave consisting of many discrete harmonic frequencies. A statistical analysis of power spectra demonstrates that at least 10–30% of Pc 3 pulsations can be classified as harmonic events. Using the harmonic events, we are able to estimate the plasma mass density. For a selected event on August 7, 1975, the plasma mass density at the synchronous orbit is estimated to be 3–8 hydrogen mass/cm³.
Enhanced scintillations associated with high speed streams in the solar winds
Authors: Basu Aparna , Das A. C.
Published: February 2008

The long wavelength (λ > ρi ion‐gyro radius) density homogeneities in the solar wind that raise the stellar radio scintillation index during the onset of a high‐velocity stream, may be generated by a low‐frequency compressional electromagnetic mode such as the magnetosonic (MS) wave. Our investigation shows that obliquely propagating MS waves are driven unstable by the double‐peaked proton distributions observed in the solar wind. We propose this as a reason for the correlation of high speed streams with enhanced scintillation. The stability at 1 AU of the observed nonequilibrium, double‐peaked particle distributions emerges as a natural consequence of the suggested mechanism.
The lower hybrid drift instability in nonantiparallel reversed field plasmas
Authors: Huba J. D. , Gladd N. T. , Drake J. F.
Published: February 2008

The lower hybrid drift instability is investigated in nonantiparallel reversed field plasmas, i.e., the magnetic fields on either side of a neutral line are not antiparallel. Such a magnetic field configuration contains magnetic shear, which has a stabilizing influence on the lower hybrid drift instability. It is found that magnetic shear has an inhibiting effect on the linear penetration of the lower hybrid drift mode toward the neutral line. The implications of this result to reconnection processes in the magnetosphere (i.e., the nose and the magnetotail) are discussed.
The ultraviolet spectrum of an aurora 530–1520 Å
Authors: Feldman P. D. , Gentieu E. P.
Published: February 2008

Ultraviolet spectra between 530 and 1520 Å of an active auroral arc were obtained at 6.5‐Å instrumental resolution. Several new emission features are identified, including several bands of the N2 Birge‐Hopfield (1,υ″) progression and numerous N I multiplets, the latter being preponderant at low altitudes. The improved instrumental resolution over previous experiments in the wavelength region below 1200 Å allows for a partial resolution of the complex structure between 900 and 1100 Å reported in earlier work. The ratio of O I λ1356 to N2 Lyman‐Birge‐Hopfield is smaller than in the dayglow at a similar altitude, and this is interpreted as evidence for a depletion of atomic oxygen in the auroral ionosphere relative to mid‐latitude composition.
Electric currents above Saint‐Santin: 2. Model
Authors: Mazaudier Christine , Blanc Michel
Published: February 2008

We use Ohm's law and a combination of various local models of the electrodynamic parameters of the ionsphere derived from previous incoherent scatter studies (electric fields, neutral winds, ion composition, and ion neutral collision frequencies) to generate an empirical model of the local time and seasonal variations of the horizontal electric current flow above Saint‐Santin (geographic latitude 44.1°N, geographic longitude 2.3°E). The various contributions to the total current (Hall and Pedersen contributions, neutral wind driven contributions, and electric field driven contributions) are explicitly obtained in this model. The local time variations of the two components of the total height‐integrated horizontal current are compared with the Sr magnetic variation at our location. For all seasons the zonal component is weak, mainly as the result of equal and opposite contributions of the electric field and neutral winds. This result, which is consistent with the weak observed Sr variation of H, is expected for a station such as ours close to the latitude of the Sq focus where the current flow is essentially meridional. In contrast to the usual picture of the Sq system, which suggests a southward current in the morning and a northward current in the afternoon, our model meridional current is found to be always northward during the daytime. This surprising feature of the model is supported by the direct calculation of the current from the ion drifts on a series of individual days. Examination of the SR variation of the D component of ground magnetic variations shows that a north‐south current asymmetry, though of smaller intensity, is also present in the magnetic variations. Both the net northward flow of charges revealed by the ionospheric data, and the observed discrepancy between calculated ionospheric currents and magnetic data, suggest that field‐aligned currents must be flowing from the northern to the southern hemisphere in our longitude sector during a least part of the day. This situation seems to be quite different from the American sector, where no similar asymmetry has been detected in the average current flow over Millstone Hill. Explanations of these features will have to involve the possible effects of the inclination of the magnetic dipole of the earth with respect to its rotation axis, as well as of antisymmetric tidal modes, which are likely to produce, interhemispheric asymmetries and longitude variations.
Energetic O+ precipitation
Authors: Kozyra J. U. , Cravens T. E. , Nagy A. F.
Published: February 2008

Fluxes of energetic O+ ions are often observed precipitating into the atmosphere and are possibly a significant energy source for the ionosphere and thermosphere. Models of these events indicate that most of the energy of such an O+ beam is deposited as neutral heat at F region heights and a significant escape flux of O atoms results. The distribution of this heating with altitude, however, has a major effect on the type and significance of the aeronomical consequences that it can initiate. The particulars of this distribution are very sensitive to the cross sections and scattering parameters used in the modeling. A comparison of hard sphere and classical elastic parameters indicates that using the latter, more realistic formulation not only results in a more penetrating beam but reduces the escape flux by as much as a factor of 2 over the hard sphere treatment.
VHF power scattered from the mesosphere at mid‐latitudes
Authors: Røyrvik O. , Gibbs K. P. , Bowhill S. A.
Published: February 2008

Scattered power profiles from the Urbana VHF radar have been analyzed. Coherent power returns from the mesosphere (60–90 km) show that a large portion of these returns occur in well‐defined stable layers lasting for more than 6 hours in some cases. It is concluded that some of these layers may be caused by standing diurnal tides. Short time variation in scattered power is attributed to internal gravity waves modifying the amplitude and altitude of maximum vertical shear in the horizontal wind. Correlation time of the scattered signal varies with altitude as well as with scattered power. Seasonal averages of the scattered power show a broad peak around 76 km. The decrease in scattered power below 76 km appears because of a decrease in the electron density gradient, while the decrease above 76 km is due to a decrease in the intensity of turbulence. The amplitude of short‐period gravity waves shows a decrease with altitude below 66 km, attributed to the Brunt‐Väisälä barrier, and a slight increase with altitude above 70 km. The dominant period of the vertical oscillations shows an increase above 63 km, giving further evidence that the high‐frequency oscillations present below 63 km cannot propagate to higher altitudes.
Mapping of auroral X‐rays from rocket overflights
Authors: Goldberg R. A. , Barcus J. R. , Treinish L. A. , Vondrak R. R.
Published: February 2008

In March 1978, two Nike Tomahawk payloads were launched from Poker Flat, Alaska, to observe the structure of bremsstrahlung x rays and precipitating particles during both nighttime and daytime aurorally disturbed conditions. Each flight carried an on axis nadir viewing NaI x ray scintillator to observe x rays in four spectral ranges (5–10 keV, 10–20 keV, 20–40 keV, and >40 keV). Particle contamination of the detectors was avoided with broom magnet shielding techniques. By virtue of the payloads' approximate 20° coning angle (about 10.5‐s period), the detectors scanned wide regions on either side of the trajectory paths. This has permitted construction (using computer color graphics) of the time averaged (∼4 min) x ray source regions near 100 km, a height consistent with Chatanika radar electron density maps obtained during each flight period. X ray image maps for both flights exhibit enhanced source regions well outside the rocket trajectory planes. For the nighttime overflight, Chatanika radar scan data and Fort Yukon riometer data were used to verify the presence of an x ray imaged enhancement of electron precipitation, approximately 30 km to the east of the rocket trajectory plane. The daytime x ray data also exhibited several regions of enhanced emission, but outside the region scanned by Chatanika radar. A comparison of the x ray emissions from the two events shows the daytime x ray spectral distributions to be significantly harder but less intense than the nighttime distributions. Furthermore, for both events, spectra compared within and nearby each enhanced emitting region exhibit characteristics of a two component spectrum, such that the bright regions show an increased flux primarily in the low‐energy component. Electron fluxes measured on each of the two flights with Geiger tubes are mainly isotropic over the downward hemisphere at night but show anisotropic pitch angle characteristics by day, consistent with the concept that the enhancement of the low‐energy x ray flux component is predominantly induced by electrons filling the loss cone.
Differential charging of high:Voltage spacecraft: The equilibrium potential of insulated surfaces
Authors: Katz I. , Mandell M. J.
Published: February 2008

A theory is presented for the steady‐state potential of insulated surfaces near exposed high voltages. The term ‘insulated surfaces’ is used to mean either dielectric surfaces or electrically isolated metallic surfaces. The potential is bounded below by the zero of the material's I‐V curve assuming total suppression of secondary electrons, and above by assuming total extraction of secondaries. Within these bounds, the material's surface potential is determined consistently with the solution to Poisson's equation external to the vehicle. The theory is compared with rocket experiments and with SCATHA satellite data. Also, an explanation is suggested for the observed ‘snapover’ of solar cell coverslips from near plasma ground potential to near the potential of positively biased interconnects with increasing bias voltage.
Energetic interplanetary nucleon flux anisotropies: The effect of Earth's bow shock and magnetosheath on sunward flow
Authors: Christon S. P.
Published: February 2008

Recent statistical surveys of interplanetary MeV energy nucleon flux anisotropies observed between prompt solar particle events during solar activity minimum have included time blocks of data obtained when the interplanetary magnetic field (IMF) connects the near earth spacecraft to earth's bow shock. The ensemble average nucleon flux anisotropy in the solar wind reference frame <ξD> obtained on these ‘connected’ field lines does not accurately represent the unperturbed <ξD> obtained on field lines free of this magnetic connection. Hourly average observations of interplanetary 0.5‐ to 1.8‐MeV proton fluxes, obtained near earth from 1972 to 1977, are correlated herein with simultaneous measurements of the IMF and solar wind plasma. At moderate flux levels during solar activity minimum, <ξD> indicates that nucleon flow in the solar wind frame is toward the sun and primarily along the IMF, although <ξD> is directed more sunward than strict field‐aligned propagation requires. Cross‐field transport is statistically significant and in the direction expected from the large‐scale MeV energy nucleon flux distributions throughout the heliosphere. The unperturbed nucleon flow direction relative to the IMF is used to demonstrate and characterize the interaction of MeV energy nuclei with the earth's bow shock and magnetosheath. The result of this interaction is that the mean value of <ξD> perpendicular to connected field lines is consistent with zero and therefore is not statistically significant. Obstruction of sunward nucleon flow on connected field lines is indicated by the variation of <ξD> with spacecraft position.
Observation of weak HF electrostatic turbulence in the auroral ionosphere
Authors: Pottelette R. , Illiano J. M.
Published: February 2008

Results are presented from the HF electrostatic wave detection experiment flown on the PORCUPINE F3 rocket. In this experiment, we measured the cross spectrum of natural random high‐frequency waves received on two small dipoles. We observed natural electrostatic emissions around the three‐halves harmonic of the electron gyrofrequency (fb) and also around the upper hybrid frequency (fuh). A linear calculation shows that the amplitudes of these emissions are above the thermal noise level for the plasma. To explain the observations, it is necessary to take into account, in addition to the cool isotropic plasma, the presence of low‐energy precipitating suprathermal electrons (1–20 eV). It appears that these electrons are highly anisotropic and enhance greatly the noise around 3/2 fb. However, the electron distribution function remains stable and the most intense emissions are observed around fuh.
Nonlinear resonance theory of Pc 3 magnetic pulsation
Authors: Yumoto Kiyohumi , Saito Takao
Published: February 2008

Compressional Pc 3 magnetic pulsations with large wave numbers normal to the static magnetic field in the magnetosphere and the beating type Pc 3 pulsations on the ground are hardly interpreted with respect to the linear resonance theory based on the idea of a resonance coupling between a monochromatic surface wave at the magnetopause and a shear Alfvén wave at a local field line in the inner magnetosphere. A parametric excitation of an Alfvén wave (kA, ωA) by a magnetosonic pump wave (k1fs, ω1fs), which propagates obliquely to the static magnetic field, has been analyzed. The resonance conditions are chosen such that k1fs = k2fs + kA and ω1fs ‐ ωA = δ ∼ ω2fs. For both standing and propagating pumps the growth rates of the excited HM waves depend not only on the pump power but also on β. It is found that large growth rates of parametric excitation of Alfvén waves by the fast magnetosonic pump waves arise if θ1f = ∠ (k1f, B0) ∼ 70°–80° and the regions of parametric excitation are localized at the resonance point in the magnetosphere where β ∼ me/mi. It is concluded that parametric excitation of Pc 3 range HM waves is a more attractive theory of the beating type geomagnetic pulsations than the linear resonance theory.
Interpretation of anisotropy in corotating events
Authors: Palmer I. D. , Jokipii J. R.
Published: February 2008

Measurements of anisotropy in ∼1 MeV corotating events at 1 AU indicate an average direction more or less perpendicular to the interplanetary magnetic field and outwards from the sun. In a general diffusion‐convection model the steady‐state anisotropy is determined by spectral index γ, diffusion coefficient κij, and particle velocity v (and possibly shock reflection coefficient β). If the anisotropy mimics that produced by the E × B drift it must be fortuitous (scatter‐free propagation does not predict the right behavior). Several models are examined, but when fitted to three comparable sets of anisotropy observations, there is a diversity of best‐fit λ∥ and κ⊥/κ∥ values. First, a discrepancy in κ⊥/κ∥ that may exist between 6‐hour and 1‐hour observations would be consistent with the concept of random walking of field lines. Second, anisotropies measured parallel to the field probably underestimate those pertinent to pure corotating events owing to (1) a solar‐injected component, (2) magnetospheric effects, and (3) spiral field geometry variations. The last seems particularly important. Thus the best fit value of λ∥ would be an underestimate too, and this may account for the discrepancy in λ∥ deduced from the different sets of data. After considering these effects, our best estimate of λ∥ is 0.05–0.13 AU and κ⊥/κ∥ < 0.25 at 1 AU. Our best fit estimate of λ∥ agrees with model independent values obtained independently from corotating events and is also consistent with the range λ∥ = 0.08–0.3 AU at 1 AU obtained from impulsive flare events.
Propagation of electrostatic upper‐hybrid emission and Z mode waves at the geomagnetic equatorial plasmapause
Authors: Lembege Bertrand , Jones Dyfrig
Published: February 2008

A theory proposed for the generation of terrestrial myriametric radiation (nonthermal continuum) invokes the linear conversion of electrostatic upper‐hybrid emissions to escaping left‐hand polarized ordinary (L‐O) waves by virtue of propagation primarily in a plasma density gradient. The electrostatic waves first become electromagnetic Z mode waves and these subsequently escape by propagating through the radio window where the wave frequency equals the electron plasma frequency. A realistic model of the plasmapause based on spacecraft data is adopted and the electrostatic wave ray paths are computed by using Poeverlein's construction. The electromagnetic Z and L‐O rays are obtained by using a full ray‐tracing program. The accessibility of the radio window to the waves is discussed and possible inferences concerning the portion of the wave dispersion branch on which the initial instability occurs are considered.
Helium, hydrogen, and oxygen velocities observed on ISEE 3
Authors: Ogilvie K. W. , Coplan M. A. , Zwickl R. D.
Published: February 2008

The velocities of helium, oxygen, and hydrogen ions have been recorded over a full range of solar wind conditions by the ion composition instrument (ICI) and Los Alamos National Laboratory plasma instrument (LANLPI), respectively, aboard the ISEE 3 spacecraft between August 1978 and December 1979. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s−1 the helium velocity exceeded the hydrogen velocity by 5 km s−1 on the average. For solar wind velocities between 400 and 500 km s−1 the average difference was 14 km s−1; however, no evidence was found for a systematic nonzero average velocity difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Helium‐hydrogen velocity differences are generally bounded by the Alfvén speed. Velocity differences show abrupt changes across interplanetary discontinuities, presumably tangential. Differences between the speeds of differently charged minor ions appear also to result from the electrostatic potential differences across the interplanetary shocks. The potential difference, calculated from the energy jump condition for a perpendicular hydromagnetic shock, is of the correct magnitude to produce the observed effects.
Charged particle motions in the distended magnetospheres of Jupiter and Saturn
Authors: Birmingham Thomas J.
Published: February 2008

Charged particle motion in the guiding center approximation is analyzed for models of the Jovian and Saturnian magnetospheric magnetic fields based on Voyager magnetometer observations. Field lines are traced and shown to exhibit the previously recognized (Connerney et al., 1981a, b) distention that arises from azimuthally circulating magnetospheric currents. The spatial dependencies of the guiding center bounce period and azimuthal drift rate are investigated for the model fields. The bounce period may be shorter or longer by a factor of 1–3 than in the field of the planetary dipole alone depending on whether a particle mirrors close to the magnetic equator and experiences predominantly an enhanced mirror force or at high latitude and is affected principally by the extended length of the field line. Nondipolar effects in the gradient‐curvature drift rate are most important at the equator and affect particles with all mirror latitudes. The effect is a factor of 10–15 for Jupiter with its strong magnetodisc current and 1–2 for Saturn with its more moderate ring current. Limits of adiabaticity are discussed and are shown to occur at quite modest kinetic energies for protons and heavier ions.
The dynamics of the Venus ionosphere: 1. A simulation of the solar wind compression of the upper dayside ionosphere
Authors: Wolff R. S. , Stein R. F. , Taylor H. A.
Published: February 2008

The effects of the solar wind compression of the dayside Venus ionosphere are simulated numerically. The initial ionosphere is assumed to be in pressure equilibrium with the (shocked) solar wind at the upper boundary of the ionosphere. Composition, densities, and temperatures of ions and electrons in the ionosphere are chosen in accordance with Pioneer Venus data. A spherically symmetric Lagrangian hydrodynamic code using a two‐fluid model of the ionosphere consisting of O+ and electrons is employed to simulate the effects on the ionosphere of rapid changes in solar wind pressure. Sudden increases in solar wind pressure are found to generate shock waves in the ions that propagate from the ionopause downward into the ionosphere with velocities as high as 5 km/s. The effect of shock waves on ionospheric density profiles is dramatic with distinct ‘ledges’ developing in the ionosphere at the shock front. Comparison of density profiles from our simulation with select Pioneer Venus ion mass spectrometer data suggest possible agreement between shock produced ionospheric ledges resulting from rapid solar wind compression and observed ionospheric ledges.
Pc 5 micropulsation resonance regions observed with the STARE radar
Authors: Poulter E. M.
Published: February 2008

Specific theoretical predictions of the spatial variation of resonant Pc 5 pulsations have recently been presented by Walker (1980). STARE radar observations of the pulsation electric fields in the ionosphere have been successfully described in terms of a toroidal mode resonance by Walker et al. (1979). In the present paper we consider a suitable method for extracting the smaller poloidal component from the STARE data and compare the resulting amplitude and phase information with the theoretical predictions. The observed toroidal and poloidal components are found to be in reasonable agreement with Walker's predictions, which are based on the idea that these pulsations are generated by the Kelvin‐Helmholz instability at the magnetopause.
High‐latitude F region irregularities observed simultaneously with ISIS 1 and the Chatanika radar
Authors: Muldrew D. B. , Vickrey J. F.
Published: February 2008

Simultaneous measurements of the high‐latitude ionosphere were made by the Chatanika radar and the ISIS 1 topside sounder and cylindrical electrostatic probe (CEP) when the satellite was at a height of about 700 km. The variation of enhancements and valleys of electron density with invariant latitude at the satellite, on the scale of a few hundred kilometers, agrees reasonably well with the radar results, even though the satellite displacement changed from almost coincident to about 500 km magnetic west of the radar scan path. These density enhancements comprise a collection of large‐scale (tens of kilometers) irregularities or ‘blobs.’ Evidence for the formation of these blobs was obtained from the sounder. Natural, intense radio noise (hiss) was observed on the sounder ionograms recorded on the poleward side of the auroral zone, indicating the presence of precipitating kiloelectron volt electrons. A few minutes after these ionograms were recorded the radar scanned the same invariant latitude region and a large‐scale ionization enhancement, or ‘blob,’ not present 13 minutes earlier, had developed in the bottomside F layer. ISIS 1 telemetry dropouts resulting from medium‐scale irregularities, and enhanced irregularities down to about 200 m, observed with the CEP, are observed in association with blobs. Scatter signatures observed on the ISIS ionograms may be associated with large‐scale irregularities that can be identified in the radar data. The scattering detected by the sounder is caused by 30‐ to 60‐m wavelength irregularities (small‐scale) that presumably are created by instabilities operating on the edges of the large‐scale irregularities. The small‐scale irregularities, however, are observed on both poleward and equatorward directed gradients. If the gradient‐drift instability is responsible for these irregularities, then they either convect to the point of observation, are due to zonal gradients, or are field‐aligned extensions of irregularities generated at lower heights.
The Schumann‐Runge continuum of oxygen at wavelengths greater than 175 NM
Authors: Gies H. P. F. , Gibson S. T. , Blake A. J. , McCoy D. G.
Published: February 2008

A highly temperature dependent continuum corresponding to absorption by thermally excited molecules underlies the higher bands of the Schumann‐Runge system of oxygen. This continuum has been experimentally determined at 18 wavelengths in the range 175 nm to 179 nm, and at temperatures of 90°K and 294°K. Calculations of the continuum cross‐section made by solving the Schrödinger equation for the molecular potentials provide good agreement with the measured values. The continuum cross‐section has been calculated at a range of temperatures for use in studies of the atmospheric absorption of solar radiation.
Some consequences of corotating magnetospheric convection
Authors: Hill T. W. , Goertz C. K. , Thomsen M. F.
Published: February 2008

We compare the expected signature of the inflow region of the proposed corotating convection pattern with relevant magnetic field and plasma flow observations made by Pioneers 10 and 11 and Voyagers 1 and 2 in the Jovian magnetosphere (r ≳ 10 RJ). A region of net plasma inflow would be characterized by superrotation and a negative radial current in the equatorial plane within a characteristic distance L*. We find that no value of L* exists that is consistent with both plasma and magnetic field observations. Hence we conclude that at the time of these flybys, such a simple large‐scale convection pattern did not dominate the plasma transport in the outer magnetosphere, although the existence of such a pattern in the inner magnetosphere is not ruled out. We propose a more detailed test to determine whether or not a supersposition of corotating convection and radial diffusion is consistent with the observations.
A cross spectral analysis of high‐latitude Pc 5 pulsations in the morning sector
Authors: Saka O. , Kim J. S. , Sugiura M.
Published: February 2008

The spatial phase and amplitude distributions of morning Pc 5 pulsations are studied by using the North American IMS magnetometer network data from the Alaska, East‐West, and Fort Churchill chains. The following results have been obtained: (1) Signals in all the X (magnetic north‐south), Y (magnetic east‐west), and Z (vertical) components propagate from noon to the night side. The apparent phase velocity is approximately 13 km/s. (2) The phase varies with latitude. The total latitudinal phase differences across the Pc 5 active region are 200° and 90° for the X and Y components, respectively. These phase changes are well explained by the ionospheric modifications of the waves generated by field line resonance. (3) The corresponding latitudinal phase differences in Z are different between the Alaska and Fort Churchill chains. The total change is 550° along the Alaska chain, while it is 360° along the Fort Churchill chain. A model calculation indicates that the phase variation for the Fort Churchill chain is explained by the ionospheric Hall current associated with the field line resonance and the earth induction current. For the Alaska chain, the earth induction current flowing in the shallower depths near Fort Yukon is essential to account for the observed large phase change in Z.
STARE and GEOS 2 observations of a storm time Pc 5 ULF pulsation
Authors: Walker A. D. M. , Greenwald R. A. , Korth A. , Kremser G.
Published: February 2008

A study is presented of a storm time Pc 5 pulsation, observed by GEOS 2 particle detectors and magnetometers at geocentric orbit and by the STARE auroral radar in the ionosphere. These measurements allow the comparison of phase relationships between the magnetic field components, energetic particle flux, and electric field in the ionosphere over a substantial region. They also permit measurements of the wavelength of the disturbance in the ionosphere. A theory of the coupling between a drift mirror wave and a standing Alfvén wave is developed. The results are compared with this theory and are found to support it. In particular, it is found that the disturbance is of wavelike nature, propagating westward in the equatorial plane at 6.6 RE with a wavelength of about 1 RE. Its period is initially 213 s, lengthening to 300 s later in the event. In the equatorial plane the disturbance in the particle flux and the compressional magnetic field are out of phase as is consistent with a drift mirror wave. There is a large transverse magnetic field oscillation in the meridian plane as is consistent with a guided poloidal oscillation. In the ionosphere the oscillation is consistent with the existence of a guided poloidal Alfvén wave and is entirely different from toroidal oscillations that have been observed at Pc 5 frequencies on other occasions. The observations are consistent with a particle driven drift mirror wave, couplied to a standing Alfvén wave. The azimuthal wavelength is consistent with a drift mirror wave whose Doppler shifted frequency matches the natural frequency of the standing Alfvén wave.
Evidence for interactions between Pc 1 hydromagnetic waves and energetic positive ions near the plasmapause
Authors: Cahill L. J. , Arnoldy R. L. , Mende S. B.
Published: February 2008

Two instruments at Siple Station, Antarctica have provided additional evidence of the generation of 1 Hz hydromagnetic waves in the magnetosphere. The waves result from ion cyclotron interaction with positive ions on L = 4 field lines near the equator. In a previous report we presented one event, August 1, 1977, where structured Pc 1 hydromagnetic pulsations, pearls, were accompanied by delayed optical pulsations with the same repetition rate. By using the observed wave frequency, pulsation repetition rate, optical pulsation delay time, and calculations employing model plasma parameters we were able to show the waves could be due to tens of keV energy O+ or He+ ions or to MeV protons. Two additional events, August 4, 1977 and May 29, 1978, have now been analyzed. These events, using the same model parameters, are consistent with tens of keV energy protons, more plentiful in the ring current than MeV protons, as well as tens of keV O+ and He+. The wave/particle interpretation has been compared with the availability of energetic positive ions, with expected generation close to the plasmapause, and with theoretical predictions of wave frequency and growth rate. The comparison is favorable in each case to our interpretation. A few inconsistencies are also examined, the location of all of the proton interaction regions north of the equator, for example, and a modification of our original model is proposed.
Unusual characteristics of the cosmic ray intensity increase of September 17–18, 1979
Authors: Agrawal S. P. , Venkatesan D.
Published: February 2008

The data from a number of neutron and meson monitors are examined for the cosmic ray event of September 17–18, 1979. The profiles of the observed cosmic ray intensity increase at various stations exhibit an apparent solar flare origin, if one were to look at a limited amount of data. It is clearly shown that the ‘flare‐type’ increase is unusual and is of nonsolar origin. A suggestion is made for explaining this in terms of interplanetary structures for which supportive evidence is provided by reference to in situ observations.
Cosmic ray north‐south anisotropy: The role of the interplanetary magnetic field
Authors: Pomerantz M. A. , Duggal S. P. , Owens A. J. , Tolba M. F. , Tsao C. H.
Published: February 2008

Nucleonic intensity data from the north and south polar stations Thule and McMurdo are analyzed to determine the nature of periodicities in the north‐south asymmetry of relativistic galactic cosmic rays. The 24‐hour average intensity differences on individual days range from 0 to ±1.5%, and the most prominent time variation is a recurrence tendency with a period consistent with the 27‐day solar rotation period. A recently developed procedure for evaluating the statistical significance of quasi‐persistent data has been utilized to establish the reality of the 27‐day signal disclosed by superposed epoch analysis of the north‐south asymmetry data. Analyses of various components of the interplanetary magnetic field reveal that the IMF component
(parallel to the nominal garden hose direction) also displays a 27‐day variation with maximum amplitude. Furthermore, a significant relationship between
and the north‐south asymmetry is established by Chree analysis. On the basis of this relationship, it is suggested that the 27‐day variation in the north‐south asymmetry arises from the
drift, where
represents the radial gradient of cosmic rays.