bluuebunny/crossref_metadata_2025 huggingface dataset:
An analytic study of the energy and pitch angle distribution of inner‐zone protons
Authors: Jentsch V. , Wibberenz G.
Published: February 2008

We present analytic solutions for near equatorially mirroring protons of energies E ≈ 5–100 MeV at the lower edge of the radiation belt (L ≤ 1.25), based upon Crand‐injection and time‐varying energy losses. The proton spectral shape is essentially determined by Crand, whereas the ambient atmosphere controls the anisotropy and the spatial and temporal variations of the flux. The experimental data of Fischer et al. (1977) are used to check the results. Above L=1.25, radial diffusion gives rise to an enhancement of the flux, an increase of the anisotropy and a change of the energy spectrum. By means of perturbation methods, we show that the observed modifications of the energy spectrum require diffusion coefficients of the form DLL α μ−r with r >1.
Dependence of coherent nonlinear whistler interaction on wave amplitude
Authors: Matsumoto H. , Hashimoto K. , Kimura I.
Published: February 2008

Dependence of coherent nonlinear whistler interaction on wave amplitudes is investigated by both computer simulations and accompanied theoretical consideration. Six self‐consistent computer simulations have been carried out for six different intitial amplitudes of whistler waves. The computer code follows Newtonian dynamics of 3072 superparticles in a self‐consistent wave field. In four cases, a monochromatic whistler wave grows up exponentially and subsequently shows an amplitude oscillation around a saturation level. The saturation levels in these four cases are, however, almost the same regardless of the initial wave amplitudes. In the other two cases in which the initial wave amplitudes are larger than the saturation level of the previous four cases, the whistler wave shows neither growth nor damping but merely shows gradually decaying amplitude oscillations. The difference in nonlinear behaviors of resonant electrons in these six computer runs such as phase trapping, phase bunching, and pitch angle diffusion is also considered and discussed. A theoretical interpretation of the simulation results is given based on a rather simple model. An analytical expression for the saturation level is derived based on the model, which shows a good agreement with our simulation results.
On the origin of corotating energetic particle events
Authors: Scholer M. , Morfill G. , Van Hollebeke M. A. I.
Published: February 2008

Energetic corotating particle events could be produced by acceleration at the forward and reverse shock pair, which bounds a corotating interaction region, via the process of successive multiple reflections. In the steady state, which should be the situation applicable to corotating events, the energetic particle intensity at the shock depends only on the acceleration strength of the shock and on the intensity of the source particles. Measurements of energetic particles show systematic variations: intensities at the forward shock are typically smaller than those at the reverse shock and increase with heliocentric distance (between ∼1 and 5 AU), whereas intensities at the reverse shock tend to decrease with heliocentric distance. Since there is no obvious difference between forward and reverse shock strengths, the origin for this behavior could lie in the particle source. Assuming that this source is part of the solar wind plasma and that the solar wind temperature is the best available indicator for the intensity of these particles, it is argued that a correlation between energetic particle intensities and plasma temperature should exist. Detailed analysis of individual events, as well as a statistical analysis, yields such a correlation. This suggests that the solar wind is the original particle population that is accelerated in the stationary shocks up to several MeV.
Nonlinear equatorial spread F: Spatially large bubbles resulting from large horizontal scale initial perturbations
Authors: Zalesak S.T. , Ossakow S.L.
Published: February 2008

Motivated by the observations of large horizontal scale length equatorial spread F ‘bubbles,’ we have performed numerical simulations of the nonlinear evolution of the collisional Rayleigh‐Taylor instability in the nighttime equatorial ionosphere, using large horizontal scale length initial perturbations. The calculations were performed using a new, improved numerical code which utilizes the recently developed, fully multidimensional flux‐corrected transport (FCT) techniques. We find that large horizontal scale initial perturbations evolve nonlinearly into equally large horizontal scale spread F bubbles, on a time scale as fast as that of the corresponding small horizontal scale length perturbations previously used. Further, we find the level of plasma depletion inside the large‐scale bubbles to be appreciably higher than that of the smaller‐scale bubbles, approaching 100%, in substantial agreement with the observations. This level of depletion is due to the fact that the plasma comprising the large‐scale bubbles has its origin at much lower altitudes than that comprising the smaller scale bubbles. Analysis of the polarization electric fields produced by the vertically aligned ionospheric irregularities show this effect to be due to fringe fields similar in structure to those produced at the edge of a parallel plate capacitor.
Io's interaction with the plasma torus
Authors: Goertz C.K.
Published: February 2008

A new model for the interaction of Io with the dense corotating plasma of the Io torus is described which involves pickup and Alfvén waves carrying a field‐aligned current. Pickup refers to the process whereby ions freshly created near Io are accelerated by the corotational electric field. It is shown that the pickup current is connected to a field‐aligned current carried by an Alfvén wave. The combination of currents allows for a self‐consistent determination of the electric field in Io's vicinity. Using a simplified solution for the electric field, we calculate the total pickup rate, field‐aligned current, enhancement of plasma density in Io's vicinity, thermal energy injected into the torus, UV radiation power, and inertial drag on the magnetosphere. All observations made by Voyager are compatible with an electron impact ionization mechanism and a neutral SO2 Io atmosphere with a density of 109 cm−3.
An electrostatic flow shear instability
Authors: Gary S. Peter , Schwartz Steven J.
Published: February 2008

This paper considers a plasma microinstability driven by a macroscopic shear in the flow velocity parallel to a uniform magnetic field. The linear electrostatic dispersion relation for a Vlasov plasma is used. The flow shear instability which results has zero frequency. The wave number at maximum growth rate is of the order of the reciprocal ion gyroradius, but there is appreciable growth at the reciprocal of the electron gyroradius. This instability may provide wave‐particle viscous effects at the magnetopause or stream‐stream interfaces in the solar wind.
Modeling Jupiter's current disc: Pioneer 10 outbound
Authors: Jones D.E. , Melville II J.G. , Blake M.L.
Published: February 2008

The magnetic field of the Jovian current disc has been modeled by using Euler functions and the Biot‐Savart law applied to a series of concentric, but not necessarily coplanar, current rings. We find that a best fit to the Pioneer 10 outbound perturbation magnetic field data (Btotal ‐ Bdipole) is obtained if the current disc is twisted (outer edges increasingly lag behind inner edges with radial distance) and also bent so as to tend toward parallelism with the Jovigraphic equator. The inner and outer radii of the disc appear to be about 7 RJ and 150 RJ, respectively, although some indication of a changing magnetopause location is apparent in the data. Because of the observed current disc penetrations, the bent disc also requires a deformation in the form of a bump or wrinkle whose axis tends also to exhibit spiraling. The radial dependence of the azimuthal current in the disc is not described by a simple power law, the outer region showing a smaller power law dependence. Modeling of the azimuthal field shows it to be due to a thin radial current sheet, but there is some evidence that this may, in fact, be due in large part to penetration of a tail current sheet as suggested by the Voyager observations.
Magnetopause characteristics at 0840–1040 hours local time
Authors: Williams D.J.
Published: February 2008

We have analyzed three‐dimensional energetic (≳24 keV) particle distributions for 14 consecutive inbound ISEE orbits during times of magnetopause crossings and close approaches. The data are from the November 10 through December 11, 1977, time period and cover local times of ∼0840–1040 hours. We find that in this period the magnetopause as defined by energetic particles can be represented as a sharp (very much less than the ion gyroradius) and very well defined boundary for magnetospherically trapped particles for a wide range of magnetospheric activity and magnetosheath field conditions. Using the technique described by Williams (1979) we have determined the magnetopause position, orientation, and velocity for all identified magnetopause crossings and close approaches. We find that the magnetopause is nearly always in motion with velocities ranging from near zero to ≳±25 km/s. Large‐amplitude (>1000 km) radial motions often are present and at times are quasi‐periodic. Superimposed on these large‐scale motions is the nearly continuous presence of orientation angle variations consistent with boundary waves having periods of ∼100–450 s and amplitudes of a few hundred kilometers. During a rare interval when the boundary orientation was steady, large magnetopause radial motion was observed. Conversely, during an interval of near‐zero magnetopause velocity, orientation angle variations were observed. Correlations with published plasma, magnetic field, and plasma wave magnetopause identifications show the energetic (≳24 keV) particle results to be accurate and an important factor in determining magnetopause characteristics and behavior. Comparison of our results with published plasma data for the November 10, 1977, inbound magnetopause encounters yields a scale length (e‐folding distance) for magnetosheath plasma penetration into the magnetosphere of ∼60–90 km for electrons and ∼90–110 km for protons.
Amplified Cerenkov emission of auroral hiss: Limitations implied by quasi‐linear theory
Authors: Melrose D.B. , White S.M.
Published: February 2008

Auroral hiss is attributed to amplified Cerenkov emission of nearly resonant whistlers. Such emission occurs only when the precipitating electron flux corresponds to a one‐dimensional distribution with a peak in parallel energy. Only particles below this peak contribute to the amplified emission. The back reaction of the hiss on the electrons is treated by using quasi‐linear theory. The primary effect is to reduce the positive gradient in energy below the peak. This tends to suppress the generation of the waves. A relation between the expected intensity of the hiss and the properties of the stream is derived. The observational data are consistent with limitation of the intensity by quasi‐linear relaxation.
Preliminary report of numerical simulations of intermediate wavelength E × B gradient drift instability in ionospheric plasma clouds
Authors: Keskinen M.J. , Ossakow S.L. , Chaturvedi P.K.
Published: February 2008

Two‐dimensional numerical simulations of intermediate wavelength (100–1000 m) E × B gradient drift instability in local unstable regions of large F region ionospheric plasma clouds have been performed, using an initial one‐dimensional cloud geometry, for plasma cloud density gradient scale lengths L=3, 6, 10 km. For conditions typical of 200‐km barium releases we find that linearly unstable modes saturate by nonlinear generation of linearly damped modes along the y direction (parallel to E × B drift). In the nonlinear regime, power laws are observed in the one‐dimensional parallel P(ky) ∝ ky−n and perpendicular P(kx) ∝ kx−n power spectra with n ≃2–3. These results are compared with in situ experimental measurements and theoretical predictions.
Energy addition in the solar wind
Authors: Leer Egil , Holzer Thomas E.
Published: February 2008

A general study of energy addition, energy loss, and energy redistribution in the solar wind, for both spherically symmetric and rapidly diverging flow geometries, is presented. It is found that energy addition in the region of subsonic flow increases the solar wind mass flux but either has little effect on (for heat addition) or significantly reduces (for momentum addition) the solar wind flow speed at 1 AU. In contrast, energy addition in the region of supersonic flow has no effect on the solar wind mass flux but significantly increases the flow speed at 1 AU. It is also found that both momentum loss in the subsonic region and energy exchange (involving loss in the subsonic region and gain in the supersonic region) can lead to an increase in the asymptotic flow speed. This general study thus places certain constraints on viable mechanisms for driving high‐speed solar wind streams and points to a number of specific, self‐consistent studies of such mechanisms that need to be carried out in the future.
Energization of solar wind ions by reflection from the Earth's bow shock
Authors: Paschmann G. , Sckopke N. , Asbridge J.R. , Bame S.J. , Gosling J.T.
Published: February 2008

The existence of ion beams with energies a few times the solar wind energy and streaming outward from the earth's bow shock has been known for some time. To explain the observed ion energies, a simple reflection model has been proposed in which the particles gain energy by displacement parallel to the interplanetary electric field. In this model the energy gained in the reflection can be described as a function of the angles between the interplanetary magnetic field, the solar wind velocity, and the local shock normal. Ion beams under widely varying conditions have been observed with Los Alamos Scientific Laboratory/Max‐Planck‐Institut instrumentation on Isee 1 and 2. For 18 cases, with beam energies ranging from ∼1.4 to ∼30 times the solar wind energy, a comparison between the observed and the predicted beam energies has been made. Good agreement between the reflection theory and the observations has been found. Thus simple reflection can account for the several keV ion beams observed upstream from the earth's bow shock.
Structure of the ionosphere and atmosphere of Saturn From Pioneer 11 Saturn radio occultation
Authors: Kliore Arvydas J. , Patel Indu R. , Lindal Gunnar F. , Sweetnam Donald N. , Hotz Henry B. , Waite J. Hunter , McDonough Thomas R.
Published: February 2008

During the flyby of Saturn by Pioneer 11 on September 1, 1979, radio occultation measurements of the ionosphere and upper neutral atmosphere were made near the terminator at latitudes 9.7° south and 11.6° south. The principal electron density peak of the ionosphere occurs at an altitude of about 1,800 km and has a magnitude of 11,400 cm−3, with a sharp lower peak of about 9,000 cm−3 at about 1,200 km. The scale height above the main peak corresponds to an exosphere temperature of about 1150 K for an H+ ionosphere. Ionization appears to extend to 30,000 km, with a broad peak of magnitude 7,000 cm−3 at an altitude of about 14,500 km, corresponding to the inner edge of the C ring. The low density of the lower portion of the ionosphere can probably be explained by ring shadowing and equatorial anomaly, and the relatively high densities about 30,000 km, if real, could be explained if densities of ∼105 exist at higher latitudes that are connected to the site of measurement by field lines and by plasmaspheric heating by the rings. In the neutral atmosphere, measurements were made to a pressure level of about 180 mbar, showing a temperature inversion region with a triple minimum. The temperature at the principal minimum at 60,344 km is 88±4 K at a pressure of 74 mbar, and there is a prominent minimum about 80 km above the principal one. Comparisons with the temperature structure derived from the infrared radiometer data (Ingersoll et al., this issue) suggest that the helium fraction in the Saturnian atmosphere is 10±4%.
A new predictive model for determining solar wind‐terrestrial planet interactions
Authors: Spreiter John R. , Stahara Stephen S.
Published: February 2008

A computational model has been developed for the determination of the gasdynamic and magnetic field properties of the solar wind flow around a magnetic planet, such as the earth, or a nonmagnetic planet, such as Venus. The procedures are based on an established single‐fluid, steady, dissipationless, magnetogasdynamic model and are appropriate for the calculation of axisymmetric, supersonic, super‐Alfvénic solar wind flow past a planetary magneto/ionosphere. Sample results are reported for a variety of solar wind and planetary conditions. Some of these are new applications; others are included to show that the new procedures produce the same results as previous procedures when applied to the same conditions. The new methods are completely automated and much more efficient and versatile than those employed heretofore.
The morphology of metallic ions in the upper atmosphere
Authors: Kumar Shiv , Hanson W. B.
Published: February 2008

The metallic ion data from a day‐night pair of rockets, from Ogo 6, and from the elliptic phases of AE‐C and AE‐D have been examined for their morphological implications. The high altitude (>400 km) nighttime data from Ogo 6 show Fe+ ions only at low (<30°) magnetic latitudes. The detection probability of Fe+ decreases with altitude, is maximum over the Atlantic and minimum over India, and appears to be influenced by zonal winds. The rocket data show ions in the E region during the day and on the bottom of the F layer at night, as might be expected from the influence of global winds. Metal ions are observed below 250 km at all latitudes and local times by the Atmosphere Explorer satellites. There is a high spatial correlation in the appearance of the different metallic ions. Mg+ and Fe+ are the dominant ions, but Al+, Na+, Si+, and Ca+ are very often detectable. The Atmosphere Explorer data also reveal the presence of these ions in the topside ionosphere near the daytime equator and at midlatitudes during summer mornings. At high latitudes metal ions show a preference for afternoon over morning that is probably caused by global winds and large scale ion convection. There appears to be a strong positive correlation between solar activity and the metallic ion detection probability at low latitudes and high altitudes at night.
The Parker spiral configuration of the interplanetary magnetic field between 1 and 8.5 AU
Authors: Thomas Barry T. , Smith Edward J.
Published: February 2008

An analysis is presented of the magnetic field data obtained by the Pioneer 10 and 11 spacecraft. The purpose is to provide a quantitative picture of the overall configuration of the interplanetary magnetic field in the outer heliosphere. The field directions observed between 1 and 8.5 AU are found, on average, to conform to the Parker spiral directions within both quiet regions and interaction regions to an overall accuracy of 1.1°. The average latitude angle of the field is shown to be zero within a similar accuracy. The included angle between the inward and outward sectored field directions is found to be very close to 180° and displays no solar cycle dependent trends, such as have been previously reported. The field direction is shown to display greater variability in quiet regions than in interaction regions, a fact which is important in terms of the effect of interaction regions on the propagation of energetic particles. The fractional polarities for observations below 10° heliographic latitude are shown to be dominated by temporal variations; however, dual‐spacecraft studies have allowed a significant latitudinal gradient to be extracted. This result is qualitatively consistent with the almost complete disappearance of the inward sector at 16° heliographic latitude, although it is suggested that the latter effect may be due to a lower than average current sheet inclination in 1976. The sector structure is shown to extend occasionally to these high latitudes during this time, implying a deflection of the equatorial current sheet, in association with individual interaction regions. It is suggested that the fast streams associated with interaction regions may move the current sheet to higher heliographic latitudes when the source of the fast plasma is in the southern solar hemisphere.
Introduction to Pioneer Venus Special Issue
Authors: Mutch Thomas A.
Published: February 2008

The arrival of the Pioneer Venus spacecraft in December of 1978 marked the initiation of a new phase of planetary exploration. For the first time a mission had been designed to investigate the global scale properties of another planet's atmosphere. The four entry probes and their bus spacecraft were largely new innovations. The orbiter instruments drew heavily upon the successful Atmosphere Explorer satellites which had been used for studies of earth's atmosphere since 1973.
Solar wind flow past Venus: Theory and comparisons
Authors: Spreiter John R. , Stahara Stephen S.
Published: February 2008

Advanced computational procedures are applied to an improved model of solar wind flow past Venus to calculate the locations of the ionopause and bow wave and the properties of the flowing ionosheath plasma in the intervening region. The theoretical method is based on a single‐fluid, steady, dissipationless, magnetohydrodynamic continuum model and is appropriate for the calculation of axisymmetric supersonic, super‐Alfvénic solar wind flow past a nonmagnetic planet possessing a sufficiently dense ionosphere to stand off the flowing plasma above the subsolar point and elsewhere. Determination of time histories of plasma and magnetic field properties along an arbitrary spacecraft trajectory and provision for an arbitrary oncoming direction of the interplanetary solar wind have been incorporated in the model. An outline is provided of the underlying theory and computational procedures, and sample comparisons of the results are presented with observations from the Pioneer Venus orbiter.
Zonal and meridional circulation of the lower atmosphere of Venus determined by radio interferometry
Authors: Counselman C. C. , Gourevitch S. A. , King R. W. , Loriot G. B. , Ginsberg E. S.
Published: February 2008

From earth‐based Doppler and interferometric radio observations we determined the paths, in three dimensions and as functions of time, taken by the Pioneer probes as they fell to the surface of Venus. From the motion of each probe below about 65‐km altitude we were able to infer the ambient wind velocity with an estimated uncertainty of about 1 m s−1 in each vector component. The magnitude of the velocity was about 1 m s−1 or less near the surface of the planet and about 100 m s−1 near 65‐km altitude at all four probe locations. Distinct strata of high wind shear were centered at altitudes of 15, 45, and 60 km, where the atmosphere is most stable against verticle motion. Except within a few kilometers of the surface, the wind velocity was always directed within a few degrees of due west. At the day and the night probe sites, which were separated by 100° in longitude and 3° in latitude, the altitude profiles of the westward velocity were virtually identical. Thus the dominant motion of the lower atmosphere seems to be a retrograde zonal rotation. Eddies appear to account for most of the instantaneous meridional velocity. However, in the radiatively heated middle cloud layer, between 50‐ and 55‐km altitude, equatorward flow of 1–7 m s−1 was observed for all four probes. These observations, coupled with other observations of ∼10 m s−1 poleward average meridional velocity for cloud top features at about 65‐km altitude, suggest that within the clouds a thermally driven mean meridional circulation is superimposed on the much more rapid zonal rotation.
Gravity anomalies on Venus
Authors: Sjogren W. L. , Phillips R. J. , Birkeland P. W. , Wimberly R. N.
Published: February 2008

Doppler radio tracking of the Pioneer Venus orbiter has provided gravity measures over a significant portion of Venus. Feature resolution is approximately 300–1000 km within an area extending from 10°S to 40°N latitude and from 70°W to 130°E longitude (≈200°). Many anomalies were detected, and there is considerable correlation with radar altimetry topography (Pettengill et al., this issue). The amplitudes of the anomalies are relatively mild and similar to those on the earth at this resolution. Calculations for isostatic adjustment reveal that significant compensation has occurred.
The diurnal and latitudinal variation of auroral zone ionospheric conductivity
Authors: Vickrey James F. , Vondrak Richard R. , Matthews Stephen J.
Published: February 2008

The great spatial and temporal variability of auroral ionospheric conductivity significantly influences the ionospheric closure path for high‐latitude, field‐aligned currents. Because these closure paths can extend to low latitudes, changes in auroral zone conductivity can influence the global electric field distribution. In this paper, synoptic Chatanika radar observations of auroral zone conductivity that cover ∼62° to 68° geomagnetic latitude are presented. They are representative of quiet winter, active winter, and equinoctial conditions. During the daytime the solar contribution to the height‐integrated conductivity is well represented by ΣP,H ≃ (5, 10) cos1/2(χ), where χ is the solar zenith angle. The nighttime, height‐integrated Pedersen and Hall conductivities (ΣP and ΣH) in the electron density trough are, at times, below our detection threshold of ∼0.5 mho. Following magnetic substorm onset, enhanced conductivity regions move southward and intensify. As the recovery phase begins, the conductivity pattern recedes northward and diminishes. The onset and cessation of precipitation associated with these events can be as abrupt as a few minutes. In one example the behavior of ΣP and ΣH are examined in the vicinity of the Harang discontinuity, which was quite sharp (≲30 min) in local time. At the Harang discontinuity on that day, the ratio of ΣH to ΣP decreased, indicating a softening of the precipitating energy distribution.
Auroral plasma lines: A first comparison of theory and experiment
Authors: Oran Elaine S. , Wickwar Vincent B. , Kofman Wlodek , Newman Alice
Published: February 2008

In this preliminary report on low‐energy (0.3 to 3 eV) secondary electrons in the auroral E layer (90 to 150 km), we compare intensities of plasma lines observed with the Chatanika radar to theoretical predictions obtained from a detailed numerical model. The model calculations are initiated with a flux of energetic auroral primary electrons which enter the atmosphere and lose energy to electrons, ions, and neutrals through a combination of elastic and inelastic collisions. This flux is chosen in order that the total calculated ionization rate matches one that is deduced from the radar measurements. From these same calculations the steady state secondary electron flux is deduced as a function of altitude, energy, and pitch angle. This flux is used to calculate plasma line intensities which are then compared with observed intensities. Initial comparisons suggest that the plasma line theory, when applied to low altitudes, must include the effect of electron‐neutral collisions. When this is done, the good agreement obtained between theory and experiment indicates the promise of this approach for the study of low‐energy auroral electrons.
Displaced isorigidity contours in the North Atlantic for 1975
Authors: König P. J. , Stoker P. H.
Published: February 2008

The results obtained from a neutron‐moderated detector aboard a commercial airline flight between Johannesburg and New York in 1976 revealed a mismatch between the counting rates in the two hemispheres when they were plotted against vertical cutoff rigidity values interpolated from the 1975 values of the 5° × 15° world grid. Cutoff rigidities in the North Atlantic had to be increased by approximately 0.5 GV for a good fit. Detailed vertical cutoff rigidity calculations by the trajectory‐tracing method along the flight path in the North Atlantic revealed deviations of up to 0.3 GV at ∼8 GV between these values and those calculated by interpolation of the 5° × 15° grid. These values resulted in a better, though by no means satisfactory, fit for the data in the two hemispheres. In order to investigate the extent of these deviations, vertical cutoff rigidities were calculated by trajectory tracing for a 1° × 1° grid in the area between 20° and 36° and 308° and 325°E. The isorigidity contours obtained for this area indicated that the size of the deviations could be ≳0.25 GV for a longitudinal extent of perhaps more than 12°. Furthermore, these deviations were found to extend for more than 1 GV in directions perpendicular to the isorigidity contours obtained by interpolation. This result is an indication that a 5° × 15° grid of calculated cutoff rigidities is not sensitive enough, at least for the North Atlantic. When the flight data were plotted against vertical cutoff rigidities calculated for 1980, a better fit was found between data for the two hemispheres at mid‐latitudes, thus casting doubt on the 1975 extrapolation from the 1965 international geomagnetic reference field model.
Spatial structure of flare‐associated perturbations in the solar wind simulated by a two‐dimensional numerical MHD model
Authors: D'Uston C. , Dryer M. , Han S. M. , Wu S. T.
Published: February 2008

The dynamic behavior of flare‐associated disturbances has been investigated using a time‐dependent two‐dimensional MHD numerical model for a one‐fluid solar wind with adiabatic expansion. Simulations of the development and propagation of perturbations have been performed between 18 Rs and 226 Rs (where Rs= solar radius) in an angular sector of the equatorial plane of the sun 90° wide. Several test computations have been carried out with different initial pulse characteristics. These pulses are set arbitrarily at the inner boundary assuming that a shock wave is already formed. The parameters are the velocity of the shock front, the angular width of the perturbation, and its time duration at 18 Rs. It is shown that in every case the time delay between 18 Rs and 226 Rs depends on the total amount of energy released by the prototype flare (hence in the pulse). This dependence is stronger with the initial velocity than with the angular width. Also it appears that the shock wave propagates according to a power law of time: R=atb. After a relatively short time the expansion of the wave is dominated by the internal energy so that the longitudinal extent of the perturbation at 1 AU seems to be only a function of the time elapsed after the arrival of the front shock at this distance. The existence of a reverse shock which is formed after a few hours is shown to last a time long enough to reach 1 AU. Its longitudinal extension is limited to the area around the flare central meridian where the pressure gradient induced by the initial condition is strong enough.
Magnetic field line reconnection experiments 1. Field topologies
Authors: Stenzel R. L. , Gekelman W.
Published: February 2008

A laboratory experiment on the reconnection of magnetic field lines in plasmas has been performed. A large‐volume stationary plasma is produced and a time‐varying magnetic field is applied to it. In vacuum the field exhibits an X‐type neutral point on axis. Because of the time variation, plasma flows across the separatrix and currents along the separator are induced. The plasma currents modify the magnetic field topology. Flat neutral sheets are observed when flux is transferred across the separatrix into regions of common flux. Forced tearing and magnetic island formation occur in the return phase of the flux. An axial magnetic field is applied along the neutral line. This first part of the report mainly deals with the magnetic field topologies, but subsequent reports will present observations of plasma properties, anomalous resistivity, particle heating, and acceleration.
Magnetospherically trapped ions as a source of magnetosheath energetic ions
Authors: Speiser T. W. , Williams D. J. , Garcia H. A.
Published: February 2008

It has been suggested that energetic ions observed in the magnetosheath may be due to direct leakage of trapped magnetospheric ions. To test this hypothesis, we utilize three‐dimensional ion spectra from the energetic particle experiment on Isee 1 for a magnetopause crossing on November 10, 1977. Three‐dimensional distribution functions in the magnetosphere and in the sheath are constructed from the observed data. Using the observed magnetic field, a simple one‐dimensional model of the magnetopause is developed. Ions are then followed in the model, starting in the magnetosphere, through the magnetopause and ending up in the sheath. Using Liouville's Theorem a model sheath distribution function is then built up by following the magnetospheric distribution function through the model fields. The model distribution is then compared with the observed sheath distribution. For this case we find that the main features of the observed ions in the sheath are consistent with direct leakage and with no energization or de‐energization processes, and an inward pointing normal component is required. The model results are sensitive to the direction of the normal component, but not to its magnitude. The energetic particles we map in this case apparently follow a flux tube which does not penetrate the magnetopause where local tangential electric fields have been reported.
Further determination of the characteristics of magnetospheric plasma vortices with Isee 1 and 2
Authors: Hones E. W. , Birn J. , Bame S. J. , Asbridge J. R. , Paschmann G. , Sckopke N. , Haerendel G.
Published: February 2008

Further studies of the vortices in magnetospheric plasma flow with the Los Alamos Scientific Laboratory/Max‐Planck‐Institut (LASL/MPI) fast plasma experiment on Isee 1 and 2 have revealed that the pattern of vortical flow has a wavelength of ∼20–40 RE and moves tailward through the magnetosphere at speeds of several hundred kilometers per second. The tendency toward vorticity pervades the total breadth of the plasma sheet tailward of the dawn‐dusk meridian. The sense of rotation of the plasma flow (as viewed from above the ecliptic plane) is clockwise in the morningside of the plasma sheet and counterclockwise in the eveningside. The sense of rotation in the morning and evening boundary layers is reversed from that in the contiguous regions of the plasma sheet. The occurrence of vortical flow is independent of the level of geomagnetic activity but is associated with long‐period geomagnetic pulsations. We believe that the source of the vortical motion is a Kelvin‐Helmholtz instability of the plasma boundary layer's inner surface (i.e., the interface between the plasma sheet and the boundary layer) that has recently been proposed by Sonnerup (1980).
Pulsations in total columnar electron content
Authors: Okuzawa T. , Davies K.
Published: February 2008

Radio signals from the ATS 6 beacon received at Boulder reveal small‐amplitude, quasi‐sinusoidal fluctuations with periods in the range of 10 to 50 s. Visual comparison of these data (116 events for October 1974 to April 1975) shows a good correspondence with simultaneous geomagnetic pulsations at Boulder in two thirds of the cases for which Boulder magnetograms were available, but they do not necessarily correspond with magnetic pulsations on ATS 6. Spectral analyses, by the method of maximum entropy, were made on sample records. The principal results are the following: (1) The occurrence of the pulsations is higher on magnetically disturbed days. (2) The maximum likelihood of occurrence is around 2100 UT (1400 LT). (3) The dominant spectrum peaks of the radio fluctuations and geomagnetic field on the ground generally coincide. Cases are found also in which temporal characteristics of the spectra are similar. These results indicate a close association of the radio fluctuations with the Pc 3–4 type pulsations of the geomagnetic field on the ground. It is suggested that the radio fluctuations originate mainly in the F region of the ionosphere, while some of them could be due to plasmapause effects.
Structure of the low‐latitude boundary layer
Authors: Sckopke N. , Paschmann G. , Haerendel G. , Sonnerup B. U. Ö , Bame S. J. , Forbes T. G. , Hones E. W. , Russell C. T.
Published: February 2008

Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the Los Alamos Scientific Laboratory/Max‐Planck‐Institut, Institut für Extraterrestrische Physik, fast plasma analyzer on board the Isee 1 and 2 spacecraft, have revealed a complex quasi‐periodic structure of some of the observed boundary layers: cool tailward streaming boundary layer plasma is seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over 1 hour or more. One such crossing, at 0800 hours local time and 40° northern GSM latitude, is examined in detail, including a quantitative comparison of the boundary layer entry and exit times of the two spacecraft. The data are found to be compatible with a boundary layer that is always attached to the manetopause but where the layer thickness has a large‐scale spatial modulation pattern which travels tailward past the spacecraft. Included are periods when the thickness is essentially zero and others when it is of the order of 1 RE. The duration of these periods is highly variable but is typically in the range of 2–5 min, corresponding to a distance along the magnetopause of the order of 3–8 RE. The observed boundary layer features include a steep density gradient at the magnetopause, with an approximately constant boundary layer plasma density amounting to about 25% of the magnetosheath density, and a second abrupt density decrease at the inner edge of the layer. It also appears that the purely magnetospheric plasma is occasionally separated from the boundary layer by a halo region in which the plasma density is somewhat higher, and the temperature somewhat lower, than in the magnetosphere. A tentative model is proposed in which the variable boundary layer thickness is produced by the Kelvin‐Helmholtz instability of the inner edge of the layer and in which eddy motion provides effective mixing within the layer.
Measurement of metastable N+(¹S) 5755‐Å emission in the twilight thermosphere
Authors: Torr D. G. , Torr M. R. , Meriwether J. W. , Burnside R.
Published: February 2008

Measurements are reported of the 5755‐Å emission arising from the transition N+(¹D‐¹S) made at Sutherland, South Africa (32.4°S, 20.8°E). The surface brightness of the emission in mid‐November 1977 decayed from ∼5 R at 10° solar depression angle (SDA) to ∼1 R at 15° SDA. Using these data we have determined that less than 5% of all N2 ionizations result in the production of N+ ions in the ¹S state. We find quenching of N+(¹S) by neutral constituents and electrons to be negligible above 220 km in the twilight thermosphere in November and December 1977. Measurements of the 5755‐Å emission therefore potentially provide a ground based means of measuring the N2 density in the twilight thermosphere.
Observations of energetic helium ions in the Earth's radiation belts during a sequence of geomagnetic storms
Authors: Spjeldvik Walther N. , Fritz Theodore A.
Published: February 2008

Every year a significant number of magnetic storms disturb the earth's magnetosphere and the trapped particle populations. In this paper, we present observations of energetic (MeV) helium ions made with Explorer 45 during a sequence of magnetic storms during June through December of 1972. The first of these storms started on June 17 and had a Dst index excursion to ‐190 gamma, and the MeV helium ions were perturbed primarily beyond 3 earth radii in the equatorial radiation belts with a typical flux increase of an order of magnitude at L= . The second storm period took place during August and was associated with very major solar flare activity. Although the Dst extremum was at best 35 gamma less than the June storm, this period can be characterized as irregular (or multi‐storm) with strong compression of the magnetosphere and very large (order of magnitude) MeV helium ion flux enhancements down to L ∼ . Following this injection the trapped helium ion fluxes showed positive spectral slope with the peak beyond 3.15 MeV at L=2.5; and at the lowest observable L shells (L ∼2–3) little flux decay (τ >100 days) was seen during the rest of the year. Any effects of two subsequent major magnetic storms in September and November were essentially undetectable in the prolonged after‐effect of the August solar flare associated MeV helium ion injection. The helium ion radial profile of the phase space density showed a significant negative slope during this period, and we infer that radial diffusion constitutes a significant loss of helium ions on L shells above L ≃4 during the aftermath of the August 1972 magnetic storm(s).
Simultaneous rocket‐borne beacon and in situ measurements of equatorial spread F—Intermediate wavelength results
Authors: Rino C. L. , Tsunoda R. T. , Petriceks J. , Livingston R. C. , Kelley M. C. , Baker K. D.
Published: February 2008

A high‐performance rocket carrying a four‐frequency, phase‐coherent beacon and full complement of in situ diagnostic instrumentation was launched into active equatorial spread F on July 17, 1979. In this paper we report the results of spectrally analyzing the beacon phase‐scintillation and Langmuir probe data. By using simultaneous backscatter data from the Altair radar we were able to establish that the scintillation develops in high‐density regions adjacent to the prominent plume structures and associated depletions. In these high‐density regions the in situ spectra show a pronounced change in the power law slope near a spatial wavelength of 500 m. Larger scale structures admit a systematically varying power law index that is generally less than 2, in good agreement with a large body of Wideband satellite data and recently analyzed Atmospheric Explorer E data. Smaller‐scale structures admit a spectral index much larger than 2. A single, overall power law near k−2 was found only in low‐density regions that did not contribute significantly to the scintillation. The results presented here and in a companion paper suggest that refinements in the current theories of equatorial spread F near and above the F region peak are needed.
A theoretical comparison between apparent and real vertical ionization drift velocities in the equatorial F region
Authors: Bittencourt J. A. , Abdu M. A.
Published: February 2008

A theoretical analysis of the time dependent distribution of ionization in the low‐latitude ionosphere is performed by using a realistic dynamic computer model of the equatorial F region, with special interest in the vertical motions of the electron density profile at the magnetic equator. The time dependence of the F2 peak height, at the magnetic equator, is governed primarily by the electromagnetic
plasma drift velocity. It is shown that, for special time periods during sunset and evening hours, when the height of the F layer is above a threshold of 300 km, the apparent vertical displacement velocity of the F layer, inferred from ionosonde measurements, is the same as the vertical
plasma drift velocity, as determined from incoherent backscatter radar measurements in the F region.
Charge exchange and wave‐particle interaction in the proton ring current
Authors: Solomon J. , Picon O.
Published: February 2008

We study, in a steady state situation, the relationships that can exist between charge exchange (CE) and the emission of electromagnetic ion cyclotron waves resonating with energetic ring current protons. The CE process between an energetic proton and a cold hydrogen atom is considered in both its aspects: as a loss of particles and as a source of anisotropy in velocity space. This anisotropy, which is required in order that the waves be amplified, can be generated by the CE process itself because of its dependance on the proton pitch angle. By an iterative procedure we establish a formula for the wave field which includes the possible CE effect. This last effect depends in particular on the intensity of the proton source (dn/dt). One deduces from it that there exists a critical value of the source intensity (dn/dt)c which requires discriminating between three different equilibrium situations. When (dn/dt)<(dn/dt)c, the CE process alone dominates the dynamic of the proton ring current, and there is no possible wave emission. When (dn/dt)>(dn/dt)c, a strong coupling can exist between wave‐particle interaction and CE, in a weak diffusion regime. In this last case one establishes a formula for the integrated wave field that only depends on three easily accessible parameters: the McIlwain parameter L, the cold plasma density n0, and the wave peak frequency fM. A preliminary study of some GEOS 1 data seems to indicate this effective coupling. Also we discuss, from this point of view, some aspects of the emission of the stable auroral red arcs. Finally, when (dn/dt)≫(dn/dt)c, protons undergo strong diffusion, and the CE effect has negligible effect on the wave emission.
Low‐energy ion pitch angle distributions in the outer magnetosphere: Ion zipper distributions
Authors: Fennell J. F. , Croley D. R. , Kaye S. M.
Published: February 2008

Ion pitch angle distributions, measured in a near‐synchronous orbit, are predominantly field aligned at low energies and predominantly peaked perpendicular to the magnetic field at higher energies. The transition from field‐aligned fluxes to fluxes peaked predominantly perpendicular to the magnetic field occurs over a very narrow energy range. These ion distributions have been observed at all local times between 5.3 and 7.8 RE. This transition energy correlates with the deep minimum observed in the ion spectra. There is no apparent correlation between the ion transition energy and magnetic local time, L, Kp, or Dst. However, the transition energy does respond to observed particle injections. The transition energy decreases prior to injection, increases abruptly at injection by as much as 10–20 keV, and then decreases slowly after injection. Fresh low‐energy ions are supplied at injection and decrease in intensity over several hours to instrument threshold level. Ion drift trajectory calculations indicate that the low‐energy component below the transition energy drifts in from the nightside plasma sheet via local morning to the dayside. The high‐energy component, above the transition energy, arrives on the dayside via local evening.
On the generation and growth of equatorial backscatter plumes 1. Wave structure in the bottomside F layer
Authors: Tsunoda Roland T. , White Barbara R.
Published: February 2008

We examine the initial conditions that lead to backscatter plume development in the equatorial F region ionosphere. By analyzing ALTAIR radar data we obtained the following principal results: (1) Prior to plume development, an altitude modulation of electron density contours exists in the bottomside F layer. These quasi‐periodic variations were mapped spatially over a 1200‐km east‐west distance by using incoherent scatter measurements and found to consist of three cycles with an average spatial wavelength of 400 km. (2) The wave structure observed in the bottomside electron density contours grew in amplitude at a rate consistent with that predicted by the generalized gradient drift instability. (3) Bottomside backscatter developed on the west walls of all three altitude‐modulated regions followed by plume development from near the crests of these regions.