bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution topside in situ data of electron densities and VHF/GHz scintillations in the equatorial region
Authors: Basu Sunanda , Basu Santimay , McClure J. P. , Hanson W. B , Whitney H. E.
Published: February 2008

Coordinated in situ measurements of high‐resolution (spatial resolution 35 m) irregularity structures in the topside ionosphere using the retarding potential analyzer (RPA) on the AE‐E satellite and scintillation measurements using the geostationary satellite Marisat transmissions at 257 MHz and 1.54 GHz from Ascension Island were made in December, 1979 during the recent solar maximum period. The in situ irregularity spectra could be classified into two categories: those having or not having spectral breaks. The first category of spectra is characterized by two spectral indices: one above and the other below a scale‐length that lies typically between 500 m and 1 km. The spectral index in the long scale‐length end (10 km to ∼1 km) varies between −1 to −1.5, whereas the index in the short scale‐length end (∼1 km to 70 m) is between −3 to −3.5. In the second category, the power law spectral index of the irregularities ranges between −2 to −2.5 over the entire scale‐length range of 70 m to 10 km. The in situ measurements reveal that in the early evening hours, the E‐W gradient scale‐lengths can be as small as 35 m, the sampling interval of the RPA instrument. In the pre‐midnight and post‐midnight hours, the gradient scale length becomes larger, but scale lengths of several hundred meters are frequently encountered. The temporal variation of 1.54‐GHz scintillation magnitudes are found to track the E‐W bubble structure, scintillations being minimum when the ray traverses the center and large when it crosses the eastern and western walls of the bubble. On the other hand, scintillations at 257 MHz remain saturated during an encounter with a bubble and focussing is often observed, but the autocorrelation interval tracks the bubble structure, being large when the ray path is deep within the bubble where the perturbation is weaker. The power spectra of weak 1.54‐GHz scintillations are found to be consistent with the predictions of weak scatter theory based on irregularities having the observed in situ spectra. Significant differences are noted in the spectra of strongly scattered 257‐MHz scintillations. In this case the decorrelation bandwidth extends beyond 1 Hz, and the spectral slope of the transitional portion of the spectrum becomes as steep as −6. The moderate to strong GHz scintillations sometimes show a dual slope power spectrum with the lower frequencies exhibiting a slope of −1.5 and the higher frequencies showing a slope of −5.5. The observations of steep structures in irregularities with scale‐length of a few hundred meters near midnight, implying relatively slow erosion of sharp gradients are discussed in terms of plasma processes in the topside ionosphere.
High‐energy tail distributions and resonant wave particle interaction
Authors: Leubner M. P.
Published: February 2008

High‐energy tail distributions (κ distributions) are used as an alternative to a bi‐Lorentzian distribution to study the influence of energetic protons on the right‐ and left‐hand cyclotron modes in a hot two‐temperature plasma. Although the parameters are chosen to be in a range appropriate to solar wind or magnetospheric configurations, the results apply not only to specific space plasmas. The presence of energetic particles significantly alters the behavior of the electromagnetic ion cyclotron modes, leading to a wide range of unstable frequencies and increased growth rates. From the strongly enhanced growth rates it can be concluded that high‐energy tail distributions should not show major temperature anisotropies, which is consistent with observations.
Quantitative study of substorm‐associated VLF phase anomalies and precipitating energetic electrons on November 13, 1979
Authors: Kikuchi Takashi , Evans David S.
Published: February 2008

The phase anomalies associated with substorms are observed on VLF signals propagating on transauroral paths (transmitters at OMEGA‐ALDRA (13.6 kHz), GBR (16.0 kHz), and OMEGA‐NORTH DAKOTA (13.6 kHz)) which were continually received at Inubo, Japan, during the events on November 13, 1979. Detailed comparisons are made between these phase anomalies and geomagnetic bays, and quantitative relations are obtained with precipitating energetic electrons (E > 30, E > 100, and E > 300 keV) detected on board the TIROS‐N and NOAA 6 satellites. It is concluded that two types of VLF phase anomalies exist which, in turn, are associated with two phases in the history of energetic electron precipitation into the atmosphere. The first type of phase anomaly is associated with direct injection of energetic electrons into the outer magnetosphere and atmosphere which, in turn, is completely correlated in time with development of the auroral electrojet current system. The second type arises from energetic electrons which subsequently precipitate from a trapped electron population and has a delayed onset and prolonged duration. An excellent quantitative correlation is obtained between the logarithm of the electron flux and the magnitude of the phase anomaly on the OMEGA‐ALDRA signal. From the local time characteristics of this quantitative relation it is deduced that the electrons with E > 300 keV are the main source of D region ionization responsible for the VLF phase anomaly.
A sounding rocket observation of an apparent wake generated parallel electric field
Authors: Bering Edgar A.
Published: February 2008

Sounding rocket Terrier‐Malemute 29.007 was launched over a 40 kR quiet auroral arc at 0813 UT on March 9, 1978. Payload instrumentation included a single‐axis double probe electric field detector. The reduced data from this detector are modulated by a square wave which is coherent with the diagnostic float‐bias cycle of the detector for the last ∼80 s of the flight when the analysis is carried out under the assumption that E · B = 0. This modulation may be removed by assuming that a time‐varying, vehicle‐generated apparent parallel field was present during the periods when the probes were floating. Three possible models for the effect were considered: a gradient in the nonthermal probe current, a gradient in plasma temperature near the rocket, and a variable dipole moment of the wake. There are significant problems with all these models. On balance, the third one appears to be the most likely. The observed effect may account for some previously reported measurements of low altitude parallel fields. It must be stressed that it cannot account for all such reports.
Solar wind deceleration and MHD turbulence in the Earth's foreshock region: ISEE 1 and 2 and IMP 8 observations
Authors: Bonifazi C. , Moreno G. , Russell C. T. , Lazarus A. J. , Sullivan J. D.
Published: February 2008

The interaction of the solar wind with ions backstreaming from the earth's bow shock is investigated using plasma and magnetic field measurements on ISEE 1 and 2 and IMP 8 at widely separated positions in the earth's foreshock. This technique separates temporal and spatial variations within the foreshock. It is found that the solar wind acceleration associated with backstreaming ions is correlated with the amplitude of the MHD turbulence and that the largest decelerations are seen close to the bow shock. The density of the backstreaming ion beam is strongly correlated with distance from the shock and decreases by about a factor of 3 in a distance of about 3 RE.
Mass composition of substorm‐related energetic ion dispersion events
Authors: Strangeway R. J. , Johnson R. G.
Published: February 2008

The Lockheed ion mass spectrometer flown onboard the SCATHA (P78‐2) spacecraft is used to study the mass composition of two ion dispersion events. The energy‐dispersed ions are observed over the full energy range of the instrument (0.1–32 keV/q) in the noon‐dusk local time sector. On one of the days, March 22 (day 81) 1979, the dispersing ions are first observed following an isolated substorm. A long period of low magnetic activity is present prior to the substorm on this day, and a decrease in Dst is observed following the first observation of the dispersing ions. On the second day studied, June 7 (day 158), 1979, the correlation between ground magnetic activity and initial observation of dispersing ions is not so clear, since the dispersion follows a period of high magnetic activity. Both dispersion events follow a marked reduction in the preexisting near‐geosynchronous plasma near the noon sector. The mass composition shows that although there are similarities in the dispersion for both protons and oxygen, there are also distinct differences. Both species show a definite dispersion ridge, but the protons also have additional fluxes at energies greater than the dispersion ridge energy. It is proposed that the composition changes are attributed to localized injection of ionospheric plasma in the dusk‐midnight sector, with proton‐rich plasma sheet ions convecting past the spacecraft from larger radial distances. By using the ability to scan in pitch angle, it is noted that there are both pitch angle and mass dependences to the arrival times of the dispersing ions. Protons at 30° pitch angles arrive at the spacecraft before oxygen ions at the same pitch angle.
Atomic nitrogen emissions from photodissociation of N2
Authors: Wu C. Y. Robert , Chen J. K. , Judge D. L.
Published: February 2008

Cross sections for the production of N I emissions at 1412, 1493, and 1743 Å and the undisperesed fluorescence in the range 1050–1800 Å produced through photodissociative excitation of N2 have been determined at selected intense atomic emission lines and throughout the synchrotron radiation continuum from 400 to 620 Å. The neutral excited atomic nitrogen fragments are produced through direct dissociation processes as well as predissociation from the well‐known two‐electron excited Rydberg states. The yield for photodissociative excitation processes is found to have the same magnitude as that for photodissociative ionization processes reported by other investigators. The Doppler shifts of the excited atomic fragments have been calculated, and the relevance to atmospheric observations is discussed.
Alfvén wave propagation in the Io plasma torus
Authors: Bagenal Fran
Published: February 2008

Gurnett and Goertz (1981) proposed that the large number of discrete arcs observed in the Jovian decametric radio emission is caused by multiple reflections of Alfvén waves excited by Io. In this paper the plasma measurements that were made by the Voyager 1 plasma science experiment have been combined with a model of Jupiter's magnetic field to calculate the time an Alfvén wave takes to travel between Io and Jupiter's ionosphere and the period of subsequent bounces between the northern and southern hemispheres. The result is a wave pattern extending around Jupiter as the multiply reflected Alfvén waves are carried away from Io by the corotating magnetospheric plasma. Although the whole pattern continually changes over the 13 hours Io takes to move through 360° of Jovigraphic longitude, a general longitudinal structure is exhibited independent of the position of Io, due to the geometry of the magentic field and the distribution of plasma in the Io torus. If the Alfvén waves stimulate the decametric radio emission, then the wave pattern predicts specific properties of the decametric emission which can be compared with radio observations.
The dynamic response of the high‐latitude thermosphere and geostrophic adjustment
Authors: Larsen M. F. , Mikkelsen I. S.
Published: February 2008

We find that certain features of the response of the high‐latitude thermosphere to inputs of energy and momentum can be explained qualitatively in terms of the theory of geostrophic adjustment. The theory is well known in the fields of oceanography and meteorology. The adjustment process is critically dependent on the ratio of the scale size of the forcing to the Rossby radius of deformation, a natural parameter of the mean atmospheric state. When the ratio is small, large wind speeds are efficiently generated by a momentum source. When the ratio is large, changes in the mass field associated with a heat source are more effectively produced. The variation of the Rossby radius with height explains the qualitatively different responses of the high‐latitude E and F regions during disturbed geomagnetic conditions as shown by both observations and numerical models. The E region is a more efficient generator of large winds, whereas the F region creates perturbations equally well in the mass field and the wind field. Earlier results by Dickinson et al. (1971) and Volland and Mayr (1971) are explained in terms of geostrophic adjustment, and the analytic solutions are also compared to the results of the integration of the spectral numerical model of Mayr and Harris (1978). We find that the analytic solutions are in good agreement with the model results regarding the apportionment of energy between the divergent and rotational components of the wind field as a function of wavenumber.
Thermospheric odd nitrogen: 2. Comparison of rocket observations with a diffusive transport chemical model
Authors: McCoy Robert P.
Published: February 2008

A one‐dimensional model of thermospheric odd nitrogen chemistry is used to simulate simultaneous rocket measurements of NO, N(4S) and O(³P) at twilight. Good agreement between the observations and the model is obtained for the N(4S) densities above 100 km and for the NO densities above 130 km. Differences between the N(4S) profiles from the upleg nightglow and downleg twilight airglow measurements are consistent with the diurnal variation of N(4S) predicted by the theory. The model shows that with high thermospheric temperatures the diurnal variation of NO decreases, while the N(4S) diurnal variation increases. This behavior is attributed to the temperature sensitivity of the rate for the production of NO from N(4S) and O2. The model is used to predict the solar cycle dependence of the NO chemiluminescence.
Sounder‐accelerated particles observed on ISIS
Authors: James H. G.
Published: February 2008

The soft‐particle spectrometers aboard the spacecrafts ISIS I and ISIS II detect sounder‐accelerated particles, i.e., fluxes of electrons and ions energized by the 100‐μs transmitter pulse (nominal peak power: 400 W). Fluxes of up to 108 st−1 eV−1 cm−2 s−1 are observed. Typical highest electron and ion energies are several hundred electronvolts and 100–200 eV, respectively. Sounder‐accelerated electron fluxes detected on ISIS II are energized near the major electron resonant frequencies: ƒpe (plasma frequency), ƒce (gyrofrequency), 2ƒce and the oblique resonance frequency domains. Ion fluxes are present from the lowest sounder frequency (0.1 MHz) up to the greater of ƒpe and ƒce. Electrons are observed at pitch angles near 90° while ions are present at all pitch angles. The observations can be interpreted using a model of particle motion and spacecraft dc potential both induced by the intense rf field (∼100 V/m). The ion results indicate that at ƒ < ƒpe, ƒce, a negative potential of about 100 V is on the spacecraft, whereas at ƒ > ƒpe, ƒce, the potential is much smaller. ISIS I data from equatorial perigee conditions show that electrons remain energized for a few milliseconds after the end of the rf pulse.
Parallel electric fields and shear instabilities
Authors: Thompson W. B.
Published: February 2008

A preliminary kinetic analysis is presented of the effects of variation along the magnetic field lines on Kelvin Helmholtz instabilities driven by transverse velocity shear. These develop provided the parallel variation is much less than the transverse, k∥ls < (m/M)1/2k⊥rL, where rL is the ion gyroradius and ls the shear length. They produce small parallel electric fields, but substantial potential drops along field lines.
Unified theory of Type I and Type II irregularities in the equatorial electrojet
Authors: Sudan R. N.
Published: February 2008

A nonlinear unified theory of type I and II irregularities is presented that explains their principal observed characteristics. The power spectrum is predicted by using Kolmogoroff‐type conservation law for the power flow in cascading eddies.
Joule heating at high latitudes
Authors: Foster J. C. , St.‐Maurice J.‐P. , Abreu V. J.
Published: February 2008

High latitude Joule heating has been calculated from simultaneous observations of the electric field magnitude and the Pedersen conductivity calculated from individual measurements of the ion drift velocity and particle precipitation observed over the lifetime of the AE‐C satellite. The data were sorted by latitude, local time, hemisphere, season, and Kp index and separate averages of the electric field magnitude, Pedersen conductivity and Joule heating were prepared. Conductivities produced by an averaged seasonal solar illumination were included with those calculated from the particle precipitation. We found that high‐latitude Joule heating occurs in a roughly oval pattern and consists of three distinct heating regions: the dayside cleft, the region of sunward convection at dawn and dusk, and the midnight sector. On the average, heating in the cleft and dawn‐dusk regions contributes the largest heat input. There is no apparent difference between hemispheres for similar seasons. Hemisphere averaged Joule heating at equinox amounts to approximately 25 GW for Kp = 1 conditions, 85 GW for Kp = 4, and varies linearly as a function of Kp. The Joule heat input is 50% greater during the summer than during winter primarily due to the increased conductivity caused by solar production.
The extreme ultraviolet spectrum of dayside and nightside aurorae: 800–1400 Å
Authors: Paresce Francesco , Chakrabarti Supriya , Bowyer Stuart , Kimble Randy
Published: February 2008

Satellite observations of the auroral emission spectrum between 800 and 1400 Å at 8 Å resolution are presented. The spectrum is dominated by lines of neutral and ionized oxygen and nitrogen and by N2 Birge‐Hopfield and Lyman‐Birge‐Hopfield band emission. A number of bright lines, most notably the O II, 834 and the O I, 989 and 1304 Å features, are detectable at all zenith angles sampled by the spectrometer (30–150°). The day auroral spectrum is dominated by atomic oxygen and nitrogen line emissions. The H I, 1216 Å Lyman alpha line is a prominent feature of many of the night and day auroral events.
Some results of ionospheric slab thickness observations at Lunping
Authors: Huang Yinn‐Nien
Published: February 2008

The subject of the present study is to analyze the characteristic variations of the ionospheric slab thickness observed at Lunping Observatory. The slab thickness data obtained from March 1977 to February 1982 were used to analyze the diurnal, seasonal, and solar cycle variations. The diurnal variation showed an unusually large peak that appeared in pre‐sunrise hours, especially during winter time. Lunar variations of slab thickness were obtained by Chapman‐Miller method and discussed. The storm time variation and disturbance daily variation of slab thickness were obtained by selecting 138 strong and weak geomagnetic storms. Superposed epoch method was also used to analyze the geomagnetic activity effect on the variation of slab thickness.
Lorentz forces on the dust in Jupiter's ring
Authors: Consolmagno Guy J.
Published: February 2008

A numerical integration program was developed to follow the paths of dust particles in the Jovian ring, including the acceleration due to gravity and the Lorentz and drag accelerations arising from the motions of the charged dust through the Jovian plasma. Particles were assumed to start from circular, noninclined Keplerian orbits. The orbit of a 2.5‐μ‐radius spherical dust particle of density 2 g/cm³ − 10 V will become significantly perturbed. The ring will tend to warp northwards near 130–160° longitude (where the longitudinal component of the Jovian magnetic field is strongest); the maximum excursion of these Jupiter ring grains is about 0.1°, consistent with a distance of 220 km above the equatorial plane. This distance is more than an order of magnitude larger than the observed upper limit to the half‐thickness of the ring. Either the particles are larger or the voltages on them less than what has been inferred by previous workers. The plasma near the ring may be considerably cooler than was estimated. Particles of 0.3 μ with −10 V potentials, starting as before in circular orbits near the outer edge of the ring (1.78 RJ), are spread from 1.68 to 1.98 RJ and inclined up to 7° out of the equatorial plane. Their paths do not follow Keplerian orbits, and particle positions are not symmetric about the equatorial plane. Particles of 0.4‐μ radius show much less asymmetry in their orbits than the 0.3‐μ particles, while particles of 0.2 μ or less are perturbed into the Jupiter cloudtops within a few tens of hours.
Dependence of 50‐keV upstream ion events at IMP 7&8 upon magnetic field bow shock geometry
Authors: Mitchell D. G. , Roelof E. C.
Published: February 2008

We present the results of a statistical study of 4 years (1972–1976) of IMP 7 and 8 observations at ∼40 RE of 50‐ to 200‐keV upstream ion events measured with the JHU/APL Energetic Particle Experiment (EPE). We find a monotonic increase in the probability of observing upstream particle events with a decrease in the angle (θBn) between the interplanetary magnetic field (IMF) and the local shock normal at the point where the IMF intersects the bow shock, independent of the length of time of bow shock connection (if it exceeds ∼10 min). We find roughly equal probability of observing an event above a given flux from any portion of the bow shock with the same value of θBn, a growth time of the 50‐ to 200‐keV events of ∼10 min, a maximum attainable flux of ∼2.5×104 (cm²s sr)−1, and a positive correlation between the probability of exceeding a given flux and the 3‐hour Kp index. The results imply that the local structure of the bow shock in the immediate vicinity of the field line connection is the dominant influence in the generation process of energetic upstream particle events and that wave‐particle interactions produce a self‐throttling mechanism that limits the maximum flux of ions escaping the upstream foreshock.
Coupled hydromagnetic wave excitation and ion acceleration at interplanetary traveling shocks
Authors: Lee Martin A.
Published: February 2008

A self‐consistent theory is presented for the excitation of hydromagnetic waves and the acceleration of ions upstream of interplanetary traveling shocks. The waves are excited by the ions by virtue of ion streaming relative to the solar wind; the ions are accelerated by being coupled to the compression of the shock via pitch angle scattering on the upstream waves and the downstream turbulence. Diffusion equations describing the ion transport and wave kinetic equations describing the hydromagnetic wave transport are solved self‐consistently to yield analytical expressions for the differential wave intensity spectrum as a function of wave number k and distance z upstream of the shock and for the ion omnidirectional distribution functions and anisotropies as functions of energy E and z. In quantitative agreement with observations the theory predicts, for example, (1) power law ion spectra at the shock αE−r with 2 ≲ Γ ≲ 3, (2) a decrease in intensity and hardening of the ion spectra with increasing z, (3) upstream ion anisotropies (∼0.3 fo 30‐keV protons) away from the shock front in the frame of the solar wind, (4) an unpolarized enhanced wave intensity spectrum in the wave number range corresponding to 0.4–3×10−2 Hz in the spacecraft frame, and (5) a decrease in the wave intensity spectrum with increasing z.
The source location of certain Jovian decametric radio emissions
Authors: Calvert W.
Published: February 2008

New evidence supporting the widely accepted concept that certain of the Jovian decametric radio waves originate as northern hemisphere extraordinary mode cyclotron emissions (possibly from the Io flux tube) has been found in the Voyager radio observations. Shortly after the closest approach to Jupiter, the wave signals received by Voyager 1 near 10 MHz exhibited cusps in the fringe pattern which is attributed to Faraday rotation in the Io plasma torus. The diminished Faraday rotation indicated by these cusps implies that the wave path had become perpendicular to the magnetic field in the torus. At nearly the same time, the wave polarization near 1 MHz (where Faraday rotation is absent) exhibited a sudden reversal of its rotation sense, indicating that the wave path for those frequencies had also become perpendicular to the magnetic field at the spacecraft. For these two events it was possible to project the wave paths back toward Jupiter and determine to some extent where the waves originated. It was found that the waves came from the northern hemisphere, at progressively lower altitudes with increasing frequency, and if the source is assumed to be associated with an L = 6 field line, the emission seems to have occurred near the source cyclotron frequency somewhere in the local midnight sector. This suggests that the source could be at the Io flux tube, since Io was then also near local midnight. Since the polarization rotation sense was apparently right handed with respect to the source magnetic field, the emitted wave mode must have been extraordinary. Furthermore, in order for the torus to produce a detectable Faraday rotation, the emitted wave polarization must have been substantially noncircular, and that would require a low plasma density near the source, much like that which occurs with auroral kilometric radiation at the earth.
A comparative study of VHF scintillation and spread F events over Natal and Fortaleza in Brazil
Authors: de Medeiros R. T. , Abdu M. A. , Kantor I. J.
Published: February 2008

A comparative study is carried out of the equatorial ionospheric irregularity occurrences, as observed by range spread F events over Fortaleza (4°S, 38°W, dip latitude 1.8°) and satellite VHF signal scintillation event over Natal (5.8°S, 33.23°W, dip latitude 4.8°S) for a one‐year period 1978. Close association is observed in the occurrences and the durations of the irregularities at the two stations. Marked differences in the seasonal behavior of the occurrences of the irregularity events over these two stations are noted with respect to that over Huancayo, most important of them being that while the latter station presents equinoctial maxima in the occurrence rates (as over some African stations), the Brazilian stations show an additional and pronounced peak in December. This result is explained as possible evidence of magnetic declination control of the spread F irregularity generation and its seasonal dependence. The present results have important implications also on the coexistence of different irregularity scale sizes during equatorial plasma bubble irregularity events.
Parametric excitation and suppression of convective plasma instabilities in the high‐latitude F region ionosphere
Authors: Keskinen M. J. , Chaturvedi P. K. , Ossakow S. L.
Published: February 2008

Parametric coupling processes of a large‐amplitude electromagnetic pump wave with convective plasma fluid instabilities (E×B gradient drift and current convective) in the high‐latitude F region ionosphere have been studied. We find that a pump wave, with frequency near the upper hybrid frequency and with electric field component perpendicular to the ambient magnetic field, can stabilize or destabilize the E×B gradient drift and/or current convective instability. For parameters typical of the nighttime high‐latitude F region ionosphere we find stabilization or destabilization with a vertically incident O mode carrying a free space incident power density of the order of 10−4 W/m².
Reflection of the solar wind ions at the Earth's bow shock: Energization
Authors: Bonifazi C. , Moreno G. , Russell C. T.
Published: February 2008

The energies of the field‐aligned proton beams observed upstream of the earth's bow shock are tested, on a statistical basis, against a simple reflection model. The comparison is carried out using both plasma and magnetic field data collected by the ISEE 2 spacecraft. The observations refer to the period from November 5 to December 20, 1977. According to this model, some of the solar wind protons incident upon the earth's shock front when reflected upstream gain energy by displacement parallel to the interplanetary electric field. The energy gained in the reflection can be described as a function of the angles between the interplanetary magnetic field, the solar wind bulk velocity, and the local shock normal. The task of finding these angles, i.e., the expected source point of the reflected ions at the earth's shock front, has been resolved using both the measured magnetic field direction and the actual beam trajectory. The latter method, which takes into account the ion drift velocity, leads to a better agreement between theory and observations when far from the shock. In particular, it allows us to check the energies of the field‐aligned beams even when they are observed far from the earth's bow shock (at distances up to 10–15 RE). We confirm, on a statistical basis, the test of the model recently carried out using the Los Alamos National Laboratory/Max‐Planck‐extraterrestrische observations on ISEE 1 and 2. We infer that reflected beams can sometimes propagate far upstream of the earth's bow shock without changing their energy properties.
Evidence for the E×B drift of pulsating auroras
Authors: Scourfield M. W. J. , Keys J. G. , Nielsen E. , Goertz C. K. , Collin H.
Published: February 2008

Simultaneous measurements of ionospheric electric fields by STARE and TV imaging of pulsating auroral forms strongly suggest that the latter undergo E×B drift. A display of pulsating auroras is considered as the projection on the ionosphere of an assembly of ducts of enhanced plasma density convecting with the background plasma. Energetic electrons, convecting and with additional gradient and curvature drift, sweep through these ducts which are ‘illuminated’ by pulsating precipitation of these energetic electrons. Both the self‐sustained pulsation model of Davidson (1979) and the driven pulsation model of Coroniti and Kennel (1970) are compatible with our observations.
Distribution of molecular hydrogen in the atmosphere of Titan
Authors: Bertaux J. L. , Kockarts G.
Published: February 2008

The diffusion problem of light gases in the atmosphere of Titan is reassessed after Voyager encounter. The pre‐Voyager theoretical work of Hunten (1973a) is completed by the use of parameters derived from Voyager encounter: the radial distances of turbopause level (3500 km) and critical level (4100 km), the exospheric temperature (186 K) and the volume mixing ratio of 2×10−3 for H2. An analytical expression of the solution of the diffusion equation is given for a spherical geometry and an isothermal atmosphere. It is used to predict an altitude profile of H2 in the upper atmosphere of Titan. The modification of this profile by a possible return flow of H2 from a torus to the atmosphere of Titan is addressed, and is found negligible since there is observational evidence from Voyager that the H2 density is less than 100 cm−3 in the torus, at large distance from Titan. The H2 concentration at the exobase level is 3.1×105 cm−3, and the thermal escape of H2 is nearly equal to the diffusion limiting flux of 3.4×109 molecules cm−2 s−1 at the turbopause level. Photodissociation of CH4 has to provide for an equal constant supply of H2.
The control networks of Tethys and Dione
Authors: Davies Merton E. , Katayama Frank Y.
Published: February 2008

Control networks of Saturnian satellites of Tethys and Dione have been established photogrammetrically from pictures taken by the two Voyager spacecraft during their flybys. Coordinates of 110 points on Tethys and 126 points on Dione are listed; selected points are identified on U.S. Geological Survey maps of the satellites, and many are identified by name. Measurements of these points were made on six pictures from Voyager 1 and 21 from Voyager 2 for Tethys and on 27 pictures from Voyager 1 and 1 from Voyager 2 for Dione. The longitude systems on the satellites have been defined by craters on their surfaces. The mean radii have been determined as 524±5 km for Tethys and 559±5 km for Dione.
The Mimas Ghost revisited: An analysis of the electron flux and electron microsignatures observed in the vicinity of Mimas at Saturn
Authors: Chenette D. L. , Stone E. C.
Published: February 2008

An analysis of the electron absorption signature observed by the Cosmic Ray System on Voyager 2 near the orbit of Mimas is presented. We find that these observations cannot be explained as the absorption signature of Mimas. Combining Pioneer 11 and Voyager 2 measurements of the electron flux at Mimas's orbit (L = 3.1), we find an electron spectrum where most of the flux above ∼100 keV is concentrated near 1 to 3 MeV. This spectral form is qualitatively consistent with the band‐pass filter model of Van Allen et al. (1980b). The expected Mimas absorption signature is calculated from this spectrum neglecting radial diffusion. Since no Mimas absorption signature was observed in the inbound Voyager 2 data, a lower limit on the diffusion coefficient for MeV electrons at L = 3.1 of D > 10−8 Rs² s−1 is obtained. With a diffusion coefficient this large, both the Voyager 2 and the Pioneer 11 small‐scale electron absorption signature observations in Mimas's orbit are enigmatic. Thus we refer to the mechanism for producing these signatures as the Mimas ghost. A cloud of material in orbit with Mimas may account for the observed electron signature if the cloud is at least 1% opaque to electrons across a region extending over a few hundred kilometers.
Solar wind iron abundance variations at speeds >600 km s−1, 1972–1976
Authors: Mitchell D. G. , Roelof E. C. , Bame S. J.
Published: February 2008

We have analyzed the Fe/H ratios in the peaks of high‐speed streams during the decline of solar cycle 20 and the following minimum (October 1972–December 1976). We utilized the response of the 50‐ to 200‐keV ion channel of The Johns Hopkins University Applied Physics Laboratory energetic particle experiments (EPE) on IMP 7 and 8, which is (in the absence of energetic ions) dominated by solar wind iron ions at high solar wind speeds (V ≳ 600 km s−1) as inferred from calibrations of flight spare detectors. We have compared our Fe measurements with solar wind H and He parameters from the Los Alamos National Laboratory instruments on the same spacecraft. In general, the Fe distribution parameters (bulk velocity, flow direction, temperature) are found to be similar to the He parameters. Although the average Fe/H ratios found in the peaks of many steady high‐speed streams agree within observational uncertainties with the nominal coronal ratio of 4.7×10−5, abundance variations of a factor of up to 6 are obtained across a given coronal‐hole associated high‐speed stream. There are, as well, a factor of 2 variations between stream‐averaged abundances for recurrent high‐speed streams emanating from different coronal holes occurring on the sun on the same solar rotation. Flare‐related solar wind flows sometimes show Fe/H ratios enhanced by factors of 4–5 more than in coronal‐hole associated, quiet‐time streams, while in one case the Fe/H enhancement was still observable one rotation after the flare activity. Over the period 1973–1976, a steady decrease in the average quiet time Fe/H ratio by a factor ∼4 is measured on both IMP 7 and 8.
Self‐consistent magnetotail theory: Equilibrium structures including arbitrary variation along the tail axis
Authors: Zwingmann Wolfgang
Published: February 2008

The self‐consistent theory of the quiet magnetotail is extended to two‐dimensional static equilibrium configurations with arbitrary variations in two cartesian space dimensions. For the case of negligible pressure anisotropy and small plasma flow velocities, self‐consistent theory leads to a nonlinear equation which is solved numerically and analytically for several special cases. To define boundary conditions we use the weakly two‐dimensional magnetotail theory by Birn et al. [1975] to fit the tail region to the entire magnetosphere. We investigate the influence of boundary conditions and find that small changes of boundary values cause the equilibrium to form oscillatory structures with magnetic islands in the plasma sheet. This model is able to explain structures observed in the quiet magnetotail as equilibrium phenomena. Besides these taillike solutions, there exists another class of equilibria which is stable against all two‐dimensional perturbations. These solutions have one neutral point; they contain less energy than the taillike solution, the difference of energy being of the same order as the energy release in a magnetospheric substorm.
On the latitudinal variations of the ionospheric electric field during magnetospheric disturbances
Authors: Gonzales C. A. , Kelley M. C. , Behnke R. A. , Vickrey J. F. , Wand R. , Holt J.
Published: February 2008

A joint alert campaign was organized during the month of October 1980 by the incoherent scatter radars in the American sector: namely, Jicamarca, Arecibo, Millstone Hill, and Chatanika. The campaign, which met with success, was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions. The Arecibo data in this campaign support present and previous observations at Jicamarca that suggest that when the convection E field suddenly decreases, the Alfvén layer shielding field becomes unbalanced and penetrates the plasmasphere. While this type of observation is reasonably convincing, others are more difficult to categorize. We suggest that, beside the high‐latitude electric fields, time‐varying auroral conductivity models will have to be considered in order to understand the morphology of the low‐latitude E field disturbances. We present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30° geometric latitude (Arecibo) to the field at 0° (Jicamarca). Other highlights of the paper are a discussion of DP2, which may help clarify the controversy surrounding it, and a discussion of the sensitivity of low‐ and mid‐latitude radars to disturbances of magnetospheric origin. We show that this sensitivity maximizes at the magnetic equator.
Magnetospheric plasma drifts during a sudden impulse
Authors: Baumjohann W. , Bauer O. H. , Haerendel G. , Junginger H. , Amata E.
Published: February 2008

An interplanetary shock front (monitored by the ISEE 1/2 satellite pair) hit the earth's magnetosphere on October 17, 1978, around 0430 UT. The changes in magnetospheric plasma drift and magnetic field associated with this sudden impulse (SI) were measured by GEOS 2 in the equatorial plane near the dawn meridian. After the SI the plasma drift first increased (in an inward direction), followed by an exponential decay. The magnetic field changes were purely compressional with an amplitude increase which also exponentially decayed. These features can be explained by adiabatic (quasi‐static) compression of the magnetopause due to the increased solar wind pressure behind the shock front. In addition, both data sets exhibit also the excitation of a highly damped compressional hydromagnetic oscillation by the SI, thus hinting of a second, wavelike component in the compression of the magnetosphere.
Temporal development of diffuse ion events upstream of the Earth's bow shock: The October 31, 1977, event
Authors: Skadron George , Lee Martin A.
Published: February 2008

We examine the origin of the intensity‐time profile characteristic of diffuse ion events upstream of the earth's bow shock. This profile is believed to result from a rotation of the interplanetary magnetic field which produces a systematic variation in the connection time of field lines with the bow shock. A plateau in the ion intensity is formed if the connection time exceeds the time needed to reach equilibrium between the shock acceleration and ion loss processes. This scenario is tested using the October 31, 1977, upstream diffuse ion event for which simultaneous magnetic field and ion intensity data have been published. We analyze this event using a two‐dimensional Gleeson‐Axford equation to describe the shock acceleration process and a model bow shock whose nose serves as a uniform source of ions injected into the acceleration process. Intensity‐time profiles are calculated for 30‐keV and 120‐keV protons for a range of diffusion coefficients, K∥ and K⊥, using connection times based upon the shock geometry and the magnetic field data. It is found that the calculated and observed profiles are in good general agreement during the growth phase but diverge during the decay. The best overall fit is achieved with diffusion coefficients, K∥(30 keV) ∼ 4×1017 cm² s−1, K∥(120 keV) ∼ 1.2×1018 cm² s−1, and K⊥(120 keV) ∼ 1016 cm² s−1. These values also produce cross‐field anisotropies at 0430 UT which are in satisfactory agreement with the observed anisotropies.
Characteristics of storm sudden commencement at geostationary orbit
Authors: Kokubun Susumu
Published: February 2008

Eighty‐one storm sudden commencements (ssc) observed on board GOES satellites at geostationary orbit are used to examine the local time variation of ssc amplitude. It is found that ssc amplitudes at synchronous altitude have a strong local time dependence in contrast to previous observations in the magnetosphere. Amplitude ratios (satellite amplitude/ground amplitude) are larger than unity in most cases observed in the daytime during 0600–1500 LT. The ssc amplitude tends to become very small near midnight as compared with that on the ground. Even a decrease in total force sometimes occurs in the midnight region. This means that magnetic compression does not always occur in the magnetic equator near synchronous orbit. The implication of these ssc characteristics are discussed in relation to ssc‐associated phenomena.
The 300‐ to 900‐Å spectrum of a nightside aurora
Authors: Paresce Francesco , Chakrabarti Supriya , Kimble Randy , Bowyer Stuart
Published: February 2008

Results of a satellite observation of the nighttime auroral emission spectrum between 300 and 900 Å at 8‐Å resolution are presented. The spectrum was taken from a 600‐km altitude looking down on a bright, well‐defined auroral arc located near the midnight meridian in the north polar region on March 10, 1979, when AE = −500γ (Kp = 4). The most prominent features in this wavelength range are identified as the O II 538‐, 617‐, 718‐, and 834‐Å emission lines, which have intensities exceeding 50 R. A number of weaker O II (and possibly N II and O III) lines are found widely scattered from 430 to 800 Å at intensity levels of ≃ 10–40 R. As in the dayglow, the measured intensity ratio of the 540 to 585 Å features r ⩾ 4.1 is discrepant with laboratory measurements of the O II 538/581‐Å line ratio. Since He I, 537‐Å contamination is probably negligible, this result indicates that at least 70% of the observed 540‐Å feature is due to the O II 2p³ 4S0‐3s 4P transition multiplets at 539 Å.
Dynamic variation of the auroral oval during intense magnetic storms
Authors: Meng C.‐I.
Published: February 2008

The latitudinal variations of the noon sector polar‐cusp region and the nightside auroral oval were examined to investigate the auroral oval dynamics during three intense geomagnetic storms. The variations were compared with the variation in ring‐current intensity (i.e., Dst) and with changes of the interplanetary magnetic field Bz component to determine the dominant parameter of the large‐scale polar‐region configuration changes during magnetic storms. Deviations of the polar cusp and the midnight auroral oval from their normal quiet time position are also compared to determine the occurrence of the large‐scale reconfiguration of the polar‐region geometry. It is found that (a) the large (>10° geomagnetic latitude) equatorial shift of the auroral oval occurs in coordination with the equatorward motion of the polar‐cusp region; (b) the polar cusp is displaced by a few degrees more than the nightside auroral oval near the peak of a magnetic storm; (c) the midnight auroral oval recovers more slowly than the polar‐cusp region during the storm recovery phase; and (d) the midnight oval and the noon sector polar‐cusp region move coherently with the southward variation of the interplanentary magnetic field Bz, but not necessarily with the Dst intensity variations.
Latitudinal profile of the magnetospheric convection electric field at ionospheric altitudes from a chain of magnetic and radar data
Authors: Mazaudier C. , Blanc M. , Nielsen E. , Zi Min‐Yun
Published: February 2008

In this paper a combination of magnetic records with coherent and incoherent radar data at auroral and middle latitudes (STARE and Saint‐Santin) allows a quantitative analysis of the latitudinal profile of the convection electric field. This latitudinal profile is compared with the predictions of the semi‐analytical convection model of Senior and Blanc. The auroral conductivities used in this model are deduced from comparison of the STARE electric field and the magnetic disturbance. Once this normalization is performed, a good agreement is found between the experimental and theoretical electric field profiles.
Aurora and electrojet configuration in the early morning sector
Authors: Kamide Y. , Robinson R. M. , Akasofu S.‐I. , Potemra T. A.
Published: February 2008

Nearly simultaneous data from the Chatanika radar, the TRIAD satellite, and the IMS Alaska meridian chain of magnetic and auroral observatories are utilized to examine the spatial relationship among auroras, field‐aligned currents, ionospheric electric fields, and conductivities in the westward electrojet in early morning hours. The westward electrojet is found to be dominated by one of two different quantities, depending on latitudinal locations in this local time sector. The poleward half of the electrojet is governed by a relatively intense southward electric field. On the other hand the Hall conductivity is the dominant factor in controlling the electrojet current in the equatorward half. The electrojet center appears to be located within the region of the upward field‐aligned current. Major auroral activity is present only in the equatorward half of the electrojet in which the upward field‐aligned current prevails, although it appears that the latitudinal variations of the conductivity and current intensity are not well related within that region.
Fourier analysis of polar cap electric field and current distributions
Authors: Barbosa D. D.
Published: February 2008

A theoretical study of high‐latitude electric fields and currents, using analytic Fourier analysis methods, is conducted. A two‐dimensional planar model of the ionosphere with an enhanced conductivity auroral belt and field‐aligned currents at the edges is employed. Two separate topics are treated. A field‐aligned current element near the cusp region of the polar cap is included to investigate the modifications to the convection pattern by the east‐west component of the interplanetary magnetic field. It is shown that a sizable one‐cell structure is induced near the cusp which diverts equipotential contours to the dawnside or duskside, depending on the sign of the cusp current. This produces characteristic dawn‐dusk asymmetries to the electric field that have been previously observed over the polar cap. The second topic is concerned with the electric field configuration obtained in the limit of perfect shielding, where the field is totally excluded equatorward of the auroral oval. When realistic field‐aligned current distributions are used, the result is to produce severely distorted, crescent‐shaped equipotential contours over the cap. Exact, analytic formulae applicable to this case are also provided.