bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation of beam‐driven VLF waves from the ionosphere toward the ground
Authors: Schriver David , Sotnikov Vladimir I. , Ashour‐Abdalla Maha , Ernstmeyer James
Published: February 2004

As part of the Cooperative High Altitude Rocket Gun Experiment (CHARGE‐2B) rocket mission, an electron beam was injected into the ionosphere with a modulated beam current in an effort to generate very low frequency (VLF) waves. The propagation of the beam‐driven VLF waves through the ionosphere is examined here to determine whether it is possible to detect these wave emissions with ground receivers. The paths of the VLF waves from where they were generated near the rocket were followed to the bottom of the ionosphere and the decrease in wave amplitude due to wave‐particle resonance and collisional damping was calculated. It was found that due to collisional damping, which for these VLF waves becomes large at altitudes below about 150 km, wave amplitudes were decreased below the background atmospheric noise level. A number of different beam injection events have been examined and in all of the cases studied the waves were sufficiently damped such that detection on the ground would not be possible. This is in agreement with observations on the ground in which no wave emissions were observed during the CHARGE‐2B mission. Control parameters that would be more favorable for beam‐generated VLF propagation to the ground are discussed for future experiments of this type.
Pioneer 10 ultraviolet photometer observations of Jovian UV emission in 1973
Authors: Wu F. M. , Gangopadhyay P. , Judge D. L.
Published: February 2004

The Pioneer 10 ultraviolet measurements obtained during the Jupiter encounter in 1973 have been further examined by using improved data handling and analysis techniques. The Pioneer 10 observations of Jupiter and its satellites during the encounter have been carefully reviewed in order to improve our understanding of the morphology of the Io plasma torus and Jupiter's upper atmosphere and to investigate the possible existence of other emission source such as Europa. In addition, the morphology of Io's bimodal torus observed during the Pioneer 10 encounter has been compared with the Voyager observations obtained approximately 6 years after the Pioneer 10 flyby and significant differences in the torus characteristics are found. The Io torus in 1973 was more similar to the 1992 Ulysses observations of a longitudinally asymmetric ring than to the complete ring observed by Voyager. Pioneer 10 observed a significantly dimmer Io torus and Jupiter upper atmosphere in the EUV compared to the Voyager observations. Apart from the torus and Jupiter, Pioneer 10 observed additional emissions which have been attributed to Io itself. Three distinct possibilities have been discussed to explain these additional emissions. The most likely is that Pioneer 10 observed volcanism on Io. There is also evidence of Pioneer 10 observing emissions from Europa. The present analysis clearly shows that the Jovian system in 1973 was significantly different from that observed in 1979.
Interactions between a solar wind filament and an open magnetosphere
Authors: Dai Wenlong , Woodward Paul R.
Published: February 2004

In order to understand the interaction between a solar wind filament and an open magnetopause, a set of one‐ and two‐dimensional simulations for the interaction are implemented. The magnetopause is assumed to have a dynamical structure which consists of a set of MHD waves, each of which evolves with time. The filament initially moves toward the magnetosphere. A fairly detailed picture for the interaction has been provided in this paper. The results of the simulations show that the filament may penetrate the compound structure of the magnetopause, across which the component of a magnetic field along the filament changes its direction, and may penetrate the contact discontinuity of the magnetopause. The normal component of the magnetic field is substantially increased behind the filament and decreased around the filament when the filament moves toward the magnetosphere.
An interpretation of a mysterious 3.0‐ to 4.6‐kHz emission band observed on Voyager 2 near Neptune
Authors: Sonwalkar Vikas S. , Inan Umran S. , Bell Timothy F.
Published: February 2004

A whistler mode interpretation is provided for the narrowband signal (fnof; ∼ 3 – 4.6 kHz, Δfnof; ∼ 200 – 800 Hz) detected by the plasma wave instrument on Voyager 2 during its encounter with Neptune. Our analysis indicates that this signal may have been generated in a limited spatial region and that it propagated to other regions of the Neptunian magnetosphere in the nonducted whistler mode with wave normal vectors lying close to the whistler mode resonance cone. The observed frequency variation of the emission along the Voyager 2 trajectory is consistent with this interpretation. The source location is estimated to be near the magnetic equator at L ∼ 4 and dipole longitude of 111°W (260° W longitude in Neptune coordinate system). The source frequency and bandwidth are estimated to be 3.6 kHz and 300 Hz, respectively. The waves most likely would have been generated by energetic electrons with 2‐ to 20‐keV parallel energy via a gyroresonance mechanism. Our interpretation of the narrowband emissions places the following limits on the Neptunian thermal plasma density and temperature: (1) Ne,min > 0.16 el/cm3 for 1.2 RN < R < 5RN, (2) Ne,max=597.5 cm−3 at R = 1.3RN, (3) Te,max < 500–1000° K at R ∼ 5 RN. It is also possible that the weak UV aurora observed near Neptune could have been caused by the precipitation of energetic particles by the narrowband emission as a result of wave particle interactions.
Interpretation of Dynamics Explorer far UV images of the quiet time thermosphere
Authors: Meier R. R. , Cox R. , Strickland D. J. , Craven J. D. , Frank L. A.
Published: February 2004

A selected set of far ultraviolet images of the Earth have been analyzed quantitatively to establish their validity for studying thermospheric “weather.” The set of images chosen for study was restricted to mostly geomagnetically quiet conditions in order to obtain a baseline understanding of the relationship between the observations and thermospheric phenomenology. The images included low to moderate solar activity levels. A new model was developed to generate global dayglow images using first principles methods. The mass spectrometer/incoherent scatter (MSIS‐86) model was used to predict the thermospheric concentrations. The analyses of thermospheric images observed in the 123 to 160‐nm nominal passband show that the spectral composition for observations on the projected Earth disk is dominated by O I 130.4‐nm radiation (85‐90%), with contributions from O I 135.6‐nm and N2 Lyman‐Birge‐Hopfield (LBH) bands of about 5‐8% each. The synthetic images reproduce the global features of the observed images rather well. Differences between the model and the data are attributed to real atmospheric effects, such as atomic oxygen depletions which are not well reproduced by the MSIS model when geomagnetic activity is elevated. The absolute values recorded were 38‐54% higher than predicted. We attribute this discrepancy to low values of the solar extreme ultraviolet irradiances used in the model. Images obtained in the 136 to 165‐nm nominal passband are a factor of 2.7 greater than the model. The excess signal observed is most likely due to a long wavelength tail in the instrument sensitivity which allowed Rayleigh scattered sunlight between 180 and 250 nm to be detected. The understanding of the DE 1 images gained by this study provides the basis for future work on the global response of the thermosphere to geomagnetic forcing.
Low‐altitude observations and modeling of quasi‐steady magnetopause reconnection
Authors: Onsager T. G. , Chang Shen‐Wu , Perez J. D. , Austin J. B. , Janoo L. X.
Published: February 2004

Data from two near‐conjugate passes of DE 1 and DE 2 through the cusp/cleft region of the Earth's magnetosphere are presented and compared with model calculations of particle transport from the solar wind to spacecraft locations in the magnetosphere. Comparison of the observed and calculated particle spectra shows that the model can successfully match the spectra at both spacecraft using the same model parameters. This demonstrates that the modeling technique is applicable at both high and low altitudes. We are also able to conclude that the particles originate from a fairly narrow spatial region on the magnetopause even though magnetosheath plasma has access to the magnetosphere over the entire magnetopause in the model. The success of the model in reproducing key features of the observed spectra and the fact that the two satellites in near magnetic conjunction but at different altitudes observed similar, distinctive features at times separated by 10–20 min demonstrates that there are quasi‐stationary, spatial features in the cusp/cleft region of the Earth's magnetosphere.
Observations of mirror waves and plasma depletion layer upstream of Saturn's magnetopause
Authors: Violante L. , Cattaneo M. B. Bavassano , Moreno G. , Richardson J. D.
Published: February 2004

The two inbound traversals of the Saturn's magnetosheath by Voyagers 1 and 2 have been studied using plasma and magnetic field data. In a great portion of the subsolar magnetosheath, large‐amplitude compressional waves are observed at low frequency (∼0.1 fp) in a high‐β plasma regime. The fluctuations of the magnetic field magnitude and ion density are anticorrelated, as are those of the magnetic and thermal pressures. The normals to the structures are almost orthogonal to the background field, and the Doppler ratio is on the average small. Even though the data do not allow the determination of the ion thermal anisotropy, the observations are consistent with values of T⊥/T∥ > 1, producing the onset of the mirror instability. All the above features indicate that the waves should be most probably identified with mirror modes. One of the two magnetopause crossings is of the high‐shear type and the above described waves are seen until the magnetopause. The other crossing is of the low‐shear type and, similarly to what has been observed at Earth, a plasma depletion occurs close to the magnetopause. In this layer, waves with smaller amplitude, presumably of the mirror mode, are present together with higher‐frequency waves showing a transverse component.
Estimating gravity wave parameters from oblique high‐frequency backscatter: Modeling and analysis
Authors: Bristow W. A. , Greenwald R. A.
Published: February 2004

A new technique for estimating electron density perturbation amplitudes of traveling ionospheric disturbances (TIDs), using HF radar data, is presented. TIDs are observed in HF radar data as enhancements of the ground‐scattered power which propagate through the radar's field of view. These TIDs are the ionospheric manifestation of atmospheric acoustic‐gravity waves. TID electron density perturbation amplitudes were estimated by simulating the radar returns, using HF ray tracing through a model ionosphere perturbed by a model gravity wave. The simulation determined the return power in the ground‐scattered portion of the signal as a function of range, and this was compared to HF radar data from the Goose Bay HF radar at a time when evidence of gravity waves was present in the data. By varying the amplitude of the electron density perturbation in the model it was possible to estimate the perturbation of the actual wave. It was found that the perturbations that are observed by the Goose Bay HF radar are of the order of 20% to 35%. It was also found that the number of observable power enhancements, and the relative amplitudes of these enhancements, depended on the vertical thickness of the gravity wave's source region. From the simulations and observations it was estimated that the source region for the case presented here was approximately 20 km thick. In addition, the energy in the wave packet was calculated and compared to an estimate of the available energy in the source region. It was found that the wave energy was about 0.2% of the estimated available source region energy.
The temporal variation of the frequency of high latitude field line resonances
Authors: Waters C. L. , Samson J. C. , Donovan E. F.
Published: February 2004

The diurnal variation in the frequencies of the continuum of ULF field line resonances has been calculated by using the cross‐spectral phase of the north‐south components of data from latitudinally spaced ground magnetometers in the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) array. On most days the continuum is seen only during the local daytime, and only a single harmonic with an inverted U‐shaped temporal variation in frequency is seen. At 67° geomagnetic latitude (L = 6.6) the general trend is a resonant frequency around 2 mHz near local dawn, increasing up to ∼5 mHz by 0600‐0700 local time, followed by a decrease in frequency to 2 mHz by 1500–1600 local time. Near local noon, the fundamental resonant frequency is ∼3 mHz at 71° (L = 11.3), increasing monotonically to 7 mHz at 65° (L = 6.1). The waves appear to be a part of the resonant Alfvén mode continuum as opposed to the single‐frequency, driven magnetic field line resonances often seen at high latitudes. The cross‐phase spectra show evidence of impulsively driven resonances that energize the continuum over the latitudinal range of the CANOPUS magnetometers. The temporal variation in the resonant frequency is modeled by using the Tsyganenko (1987) magnetic field model and cold plasma MHD theory. With the use of the observed resonant frequencies, the plasma density for June 1, 1990, was 4.2 × 106 H+/m³ at L = 6.6 while the data for June 7, 1990, showed densities up to 100×106 H+/m³. These results suggest that observations of the magnetohydrodynamic continuum in the magnetometer data may give a very effective method for ground‐based time‐dependent mapping of the equatorial plasma density.
Simulation study of the role of ion kinetics in low‐ frequency wave train evolution
Authors: Vasquez Bernard J.
Published: February 2004

The evolution of uniform, parallel propagating, low‐frequency (≲ion cyclotron) wave trains is followed with a one‐dimensional hybrid numerical code with fluid electrons and particle ions. We show that moderate amplitude (δB/B < 1/2) wave trains give instabilities and saturated states which differ completely from pure fluid evolution. This is most clearly seen when β > 1 and instability exists for wavenumbers both below and above the wavenumber of an initial, left‐handed wave train or pump wave. For corresponding parameters a fluid theory gives only a narrow range of instability above the pump wavenumber where decay and beat instabilities can occur. In simulations wave energy inverse cascades to smaller wavenumbers and into a greater number of forward than backward going waves. In fluids energy by decay goes mostly to backward ones of smaller wavenumber, and energy by beat goes mostly to forward ones of larger wavenumber. Neither fluid instability explains simulation results. The instability is saturated by thermalizing ions and sometimes exciting small wavenumber electrostatic or acoustic modes. In contrast, saturation in fluids first occurs by generating the harmonics of the growing linear modes. Harmonic generation is mostly absent in simulations. Simulations are carried out to long times and mostly reach a limit beyond which no further significant evolution can occur. Application to Alfvénic fluctuations in the solar wind is discussed.
A description of the solar wind‐magnetosphere coupling based on nonlinear filters
Authors: Vassiliadis D. , Klimas A. J. , Baker D. N. , Roberts D. A.
Published: February 2004

A nonlinear filtering method is introduced for the study of the solar wind — magnetosphere coupling and related to earlier linear techniques. The filters are derived from the magnetospheric state, a representation of the magnetospheric conditions in terms of a few global variables, here the auroral electrojet indices. The filters also couple to the input, a representation of the solar wind variables, here the rectified electric field. Filter‐based iterative prediction of the indices has been obtained for up to 20 hours. The prediction is stable with respect to perturbations in the initial magnetospheric state; these decrease exponentially at the rate of 30 min−1. The performance of the method is examined for a wide range of parameters and is superior to that of other linear and nonlinear techniques. In the magnetospheric state representation the coupling is modeled as a small number of nonlinear equations under a time‐dependent input.
Probing the properties of planetary ring dust by the observation of Mach cones
Authors: Havnes O. , Aslaksen T. , Hartquist T. W. , Li F. , Melandsø F. , Morfill G. E. , Nitter T.
Published: February 2004

Compressive dust acoustic waves can be excited in dusty plasmas. Big boulders in planetary rings move at the Keplerian velocity, while smaller dust particles move at a slightly different velocity due to the action of the Lorentz force. If the difference in velocity Δυ is larger than the dust acoustic wave velocity, αd, a wake will be formed with an opening angle of 2θ where sin θ = |αd/Δυ|. The discovery of wakes and the measurement of their opening angles by the space experiment Cassini to Saturn will yield added information on the dusty plasma conditions in regions through which Cassini will not pass. We find that in some regions the waves that are excited by the boulders may be weak because a large fraction of the interacting dust is absorbed rather than deflected by the boulder. For a given dust size the most favourable conditions for the observations of wakes exist in two fairly narrow regions, one inside and one outside the corotation radius. The favorable regions are closest to the corotation radius for the smallest dust particles and progressively further away for larger dust particles.
Particle signatures of magnetic topology at the magnetopause: AMPTE/CCE observations
Authors: Fuselier S. A. , Anderson B. J. , Onsager T. G.
Published: February 2004

Electron distributions at energies above 50 eV have been found to be a sensitive indicator of magnetic topology for magnetopause crossings of the AMPTE/CCE spacecraft. Progressing from the magnetosheath to the magnetosphere two abrupt transitions occur. First, the magnetosheath electron population directed either parallel or antiparallel to the magnetic field is replaced by a streaming, heated magnetosheath electron population. The other half of the distribution is unchanged. The region with unidirectional, heated magnetosheath electrons is identified as the magnetosheath boundary layer (MSBL). Second, the unheated magnetosheath electron population is replaced by a heated population nearly identical to the population encountered in the MSBL, resulting in a symmetric counterstreaming distribution. The region populated by the bidirectional heated magnetosheath electrons is identified as the low‐latitude boundary layer (LLBL). The MSBL and LLBL identified by the electron transitions are the same as the regions identified using ion composition measurements. The magnetosheath‐MSBL transition reflects a change in magnetic topology from a solar wind field line to one that threads the magnetopause, and the existence of a magnetosheath‐MSBL transition implies that the magnetopause is open. When the current layer is easily identified, the MSBL‐LLBL transition coincides with the magnetopause current layer, indicating that the magnetosheath electrons are heated in the current layer. Both magnetosheath‐MSBL and MSBL‐LLBL transitions are observed for low as well as high magnetic shears. Moreover, the transitions are particularly clear for low shear implying that magnetic topology boundaries are sharp even when abrupt changes in the field and other plasma parameters are absent. Furthermore, for low magnetic shear, solar wind ions with low parallel drift speeds make up the majority of the LLBL population indicating that the magnetosheath plasma has convected directly across the magnetopause. These observations are consistent with quasi‐steady, high‐latitude reconnection and indicate that the signatures of this reconnection geometry are commonly present in the subsolar region.
Bounce‐averaged Hamiltonian for charged particles in an axisymmetric but nondipolar model magnetosphere
Authors: Schulz Michael , Chen Margaret W.
Published: February 2004

In order to facilitate bounce‐averaged guiding center simulations of geomagnetically trapped particles, we express the kinetic energy of a particle with magnetic coordinates (L,ϕ) as an analytic function of the first two adiabatic invariants (M, J) and the L value of the field line. The magnetic field model is axisymmetric, consisting of a dipolar B field plus a uniform southward magnetic field parallel to the dipole moment μE. This model magnetosphere is surrounded by a circular equatorial neutral line whose radius b is an adjustable parameter. The L value of a field line is (by definition) inversely proportional to the flux enclosed by the corresponding magnetic shell of equatorial radius r0, and the L value at the neutral line (r0 = b) is denoted L*. The azimuthal coordinate ϕ measures magnetic local time. The best functional representation found for the normalized difference (L³a³/μE)(Bm ‐ B0) between mirror‐point field Bm and equatorial field B0 along any field line is a 5‐term expansion in powers (2/3 through 6/3) of the quantity X ≡ (La/μE)1/2K, where K ≡ (J²/8m0M)1/2 is an adiabatically conserved quantity independent of particle energy, m0 is the rest mass of the particle, and a is the radius of the Earth. This functional form is motivated by results for limiting cases in which particles mirror very near and very far from the magnetic equator. Expansion coefficients corresponding to various powers of X are obtained from least squares fits to numerically computed results for X as a function of L and Bm. These are accurately expressible as fourth‐order polynomials in (r0/b)³, hence indirectly as functions of L/L* = 3La/2b. This representation, which leads (except for a manageably small region of parameter space) to better than 1% accuracy in the specification of Bm as a function of K and L, allows bounce‐averaged guiding center simulations to be performed without actually tracing the bounce motions of individual particles. Bounce‐averaged drifts L (meridional) and ϕ (azimuthal) are proportional to derivatives of the Hamiltonian H (sum of kinetic and potential energies) with respect to ϕ and L, respectively. Our formulation thus provides a computationally efficient method for tracing the bounce‐averaged adiabatic motion (conserving all three invariants) and nonadiabatic transport (violating the third invariant while conserving the first two invariants) of geomagnetically trapped particles in the model magnetosphere.
The radiation impedance of orbiting conductors
Authors: Sanmartín J. R. , Martínez‐Sánchez M.
Published: February 2004

The dispersion relation for waves in a cold, magnetized plasma is discussed using the potential for the longitudinal part of the electric field. This clarifies wave emission from a conductor in low Earth orbit and should be useful in considering the far field and both hot plasma and nonlinear, near‐field effects. General formulas for radiation impedance are directly obtained. For tethers a fundamental dependence on contactor size is discussed. Spherical and ellipsoidal contactors and an (anodeless) bare tether are considered. Simple arguments on nonlinear contactor effects lead to a surprisingly simple result for impedances off the Alfvén branch.
Geoeffectiveness of the heliospheric current sheet
Authors: Mendoza Blanca , Enríquez Román Pérez
Published: February 2004

In the present paper we study the distribution of storm sudden commencements (ssc's) and their associated geomagnetic activity with respect to the Earth's crossing of the heliospheric current sheet. We found that most ssc events occur when the Earth is close to the current sheet. Also, we found that the geoeffectiveness of ssc's seems to be independent of their position with respect to the current sheet. Our results seem to suggest that coronal mass ejections, assumed as the sources of most ssc's, should follow the behavior of ssc's along the solar cycle, i.e., the shock‐producing ones should present a bimodal distribution.
Long‐term total solar irradiance variability during sunspot cycle 22
Authors: Lee Robert B. , Gibson M. Alan , Wilson Robert S. , Thomas Susan
Published: February 2004

Total solar irradiance measurements from the 1984‐1993 Earth Radiation Budget Satellite (ERBS) active cavity radiometer and 1978‐1993 Nimbus 7 transfer cavity radiometer spacecraft experiments are analyzed to detect the presences of 11‐, 22‐, and 80‐year irradiance variability components. The analyses confirmed the existence of a significant 11‐year irradiance variability component, associated with solar magnetic activity and the sunspot cycle. The analyses also suggest the presence of a 22‐ or 80‐year variability component. The earlier Nimbus 7 and Solar Maximum Mission (SMM) spacecraft irradiance measurements decreased approximately 1.2 and 1.3 Wm−2, respectively, between 1980 and 1986. The Nimbus 7 values increased 1.2 Wm−2 between 1986 and 1989. The ERBS irradiance measurements increased 1.3 Wm−2 during 1986‐1989, and then decreased 0.4 Wm−2 (at an annual rate of 0.14 Wm−2yr−1) during 1990‐1993. Considering the correlations between ERBS, Nimbus 7, and SMM irradiance trends and solar magnetic activity, the total solar irradiance should decrease to minimum levels by 1997 as solar activity decreases to minimum levels, and then increase to maximum levels by the year 2000 as solar activity rises. The ERBS measurements yielded 1365.4 ± 0.7 Wm−2 as the mean irradiance value with measurement accuracies and precisions of 0.2% and 0.02%, respectively. The ERBS mean irradiance value is within 0.2% of the 1367.4, 1365.9, and 1366.9 Wm−2 mean values for the SMM, Upper Atmosphere Research Satellite (UARS), and Space Shuttle Atmospheric Laboratory for Applications and Science (ATLAS 1) Solar Constant (SOLCON) active cavity radiometer spacecraft experiments, respectively. The Nimbus 7 measurements yielded 1372.1 Wm−2 as the mean value with a measurement accuracy of 0.5%. Empirical irradiance model fits, based upon 10.7‐cm solar radio flux (F10) and photometric sunspot index (PSI), were used to assess the quality of the ERBS, Nimbus 7, SMM, and the UARS irradiance data sets and to identify irradiance variability trends which may be caused by drifts or shifts in the spacecraft sensor responses. Comparisons among the fits and measured irradiances indicate that the Nimbus 7 radiometer response shifted by a total of 0.8 Wm−2 between September 1989 and April 1990 and that the ERBS and UARS radiometers each drifted approximately 0.5 Wm−2 during the first 5 months in orbit.
On Ba+ production in the CRIT II Experiment
Authors: Liou K. , Torbert R. B.
Published: February 2004

Analysis of particle data from the CRIT II experiment, studying Alfvén's critical ionization velocity (CIV) effect, shows that the density of newly created ions (presumably Ba+ from the shaped‐charge beam) is consistent with the increase in total plasma density measured by the independent RF plasma probe on board (Swenson et al., 1990) at the most active time period. We model this ion production using the measured electron flux data and the neutral barium model of Stenbaek‐Nielsen et al. (1990a). To identify the main source mechanisms which may contribute most to the barium ionization, a simple model for barium ion density at the payload location is developed based on Liouville's theorem. We estimate that the electron impact ionization is responsible for 90% of the barium ion production observed by CRIT II in the first release and up to 45% in the second release. By employing a “two‐state approximation” calculation (Rapp and Francis, 1962), the Ba‐O+ charge exchange cross section is found to range from about 2.0 × 10−17 cm2 at a velocity of 4 km/s to 2.0 × 10−15 cm2 at a velocity of 20 km/s. This result suggests that the Ba‐O+ charge exchange is probably dominant among all the non‐CIV ionization processes. By considering the charge exchange process in our density model, the barium ion densities are calculated for the two releases on CRIT II. The comparison between the model results and the observed data is found to be reasonably consistent if the cross sections, as calculated above, are multiplied by 0.3 for the first release and 1.0 for the second release. Our result suggests that the charge exchange process could be the most important non‐CIV ionization mechanism in the CRIT II experiment and it should be considered carefully case by case in CIV experiments.
Low‐frequency fluctuations in the magnetosheath near the magnetopause
Authors: Denton Richard E. , Gary S. Peter , Li Xinlin , Anderson Brian J. , LaBelle James W. , Lessard Marc
Published: February 2004

There are four low‐frequency modes which may propagate in a high‐beta nearly bi‐Maxwellian plasma. These are the magnetosonic, Alfvén, ion acoustic, and mirror modes. This manuscript defines a procedure based on linear Vlasov theory for the unique identification of these modes by use of transport ratios, dimensionless ratios of the fluctuating field and plasma quantities. A single parameter, the mode deviation, is defined which characterizes the difference between the theoretical transport ratios of a particular mode and the observed ratios. The mode deviation is calculated using the plasma and magnetic field data gathered by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module spacecraft to identify the modes observed in the terrestrial magnetosheath near the magnetopause. As well as determining the mode which best describes the observed fluctuations, it gives us a measure of whether or not the resulting identification is unique. Using 17 time periods temporally close to a magnetopause crossing, and confining our study to the frequency range from 0.01 to 0.04 Hz, we find that the only clearly identified mode in this frequency range is the mirror mode. Most commonly, the quasi‐perpendicular mirror mode (with wave vector k roughly perpendicular to the background magnetic field B0) is observed. In two events the quasi‐parallel mirror mode (k ∥ B0) was identified.
A three‐dimensional analysis of the electron radiation belt by the Salammbô code
Authors: Beutier Thierry , Boscher Daniel
Published: February 2004

Using diffusion theory, the first results for a phase space three‐dimensional model of the electron radiation belt are presented. The model is based on the numerical solution of a diffusion equation which takes into account the deceleration of electrons by free and bounded thermospheric and ionospheric electrons, pitch angle diffusion by Coulomb and wave‐particle interactions and radial diffusion by magnetic and electric field perturbations. Sources of two types are included. Alone, the cosmic ray albedo neutron decay (CRAND) internal source gives results much lower than measured values, though with the addition of an external source, the orders of magnitude for the fluxes are reasonable, suggesting that the belt is created and maintained by the injections occuring during storms and substorms.
The influence of intermediate‐scale variations in the heliospheric magnetic field on the transport of galactic cosmic rays
Authors: Fisk L. A. , Schwadron N. A.
Published: February 2004

Variations in the heliospheric magnetic field occur on most scales including those lying intermediate between the gyro‐radii of galactic cosmic rays and heliocentric radial distance. It is demonstrated that a correlation exists between these intermediate‐scale variations in the magnetic field and the variations in the cosmic ray distribution function that result from the field variations. This correlation will affect the average transport of galactic cosmic rays by significantly altering the patterns of gradient and curvature drifts in the heliosphere. During the current solar cycle, the altered drift patterns can lead to larger radial gradients of the galactic cosmic rays and significantly smaller latitude gradients than is expected only from drifts in the mean magnetic field.
A study of dayside auroral bright spots seen by the Viking Auroral Imager
Authors: Vo H. B. , Murphree J. S.
Published: February 2004

Instantaneous Viking optical images at UV Lyman‐Birge‐Hopfield wavelength are used to study the occurrence of dayside auroral bright spots versus the upstream solar wind parameters observed by the IMP 8 spacecraft. A survey study of 68 passes indicates that dayside auroral bright spots are most likely observed in the afternoon sector, most commonly have one to four spots simultaneously, and most commonly are separated by 0.25‐0.75 MLT. They also occur most commonly with the following solar wind conditions: high speed (>500 km/s), low density, By < 0, and interplanetary magnetic field in the radial direction; but they have no dependence on Bz, Bx, or solar wind pressure. This suggests that dayside auroral bright spots are caused by alternating field‐aligned current regions that map to plasma vortices formed in the magnetospheric boundary layer by the Kelvin‐Helmholtz instability.
Plasma turbulence enhanced current collection: Results from the plasma motor generator electrodynamic tether flight
Authors: Katz I. , Lilley J. R. , Greb A. , McCoy J. E. , Galofaro J. , Ferguson D. C.
Published: February 2004

The plasma motor generator (PMG) experiment, launched June 26, 1993, was a tethered system of two identical plasma contactors connected via a 500‐m conducting tether. The experiment was designed to demonstrate the ability of plasma contactors to provide a low‐impedance connection between a spacecraft and the ionosphere for both the electron emission and collection. The flight data indicate that plasma contactors enhance electron collection and emission by both neutralizing the electron space charge and scattering electrons across the geomagnetic field lines. Up to a 0.3 A steady current flowed along the tether in a circuit completed through the ionosphere. An analytical model for plasma contactor interaction with a background plasma which incorporates electron scattering by plasma waves is compared with the flight data. Good agreement between the model and the data is achieved for an effective scattering frequency equal to one twentieth of the local plasma contactor plasma frequency.
Banded electron structures in the plasmasphere
Authors: Burke William J. , Rubin Allen G. , Hardy David A. , Holeman Ernest G.
Published: February 2004

The low‐energy plasma analyzer on CRRES has detected significant fluxes of 10‐eV to 30‐keV electrons trapped on plasmaspheric field lines. On energy‐versus‐time spectrograms these electrons appear as banded structures that can span the 2 < L < 6 range of magnetic shells. We present an example of banded electron structures, encountered in the nightside plasmasphere during the magnetically quiet January 30, 1991. Empirical analysis suggests that two clouds of low‐energy electrons were injected from the plasma sheet to L < 4 on January 26 and 27 while the convective electric field was elevated. The energies of electrons in the first cloud were greater than those in the second. DMSP F8 measurements show that after the second injection, the polar cap potential rapidly decreased from >50 to <20 kV. Subsequent encounters with the lower‐energy cloud on alternating CRRES orbits over the next 2 days showed a progressive, earthward movement of the electrons’ inner boundary. Whistler and electron cyclotron harmonic emissions accompanied the most intense manifestations of cloud electrons. The simplest explanation of these measurements is that after initial injection, the Alfvén boundary moved outward, leaving the cloud electrons on closed drift paths. Subsequent fluctuations of the convective electric field penetrated the plasmasphere, transporting cloud elements inward. The magnetic shell distribution of electron temperatures in one of the banded structures suggests that radiative energy losses may be comparable in magnitude to gains due to adiabatic compression.
Modeling the Earth's magnetospheric magnetic field confined within a realistic magnetopause
Authors: Tsyganenko N. A.
Published: February 2004

Empirical data‐based models of the magnetospheric magnetic field have been widely used during recent years. However, the existing models (Tsyganenko, 1987, 1989a) have three serious deficiencies: (1) an unstable “de facto” magnetopause, (2) a crude parametrization by the Kp index, and (3) inaccuracies in the equatorial magnetotail Bz values. This paper describes a new approach to the problem; the essential new features are (1) a realistic shape and size of the magnetopause, based on fits to a large number of observed crossings (allowing a parametrization by the solar wind pressure), (2) fully controlled shielding of the magnetic field produced by all magnetospheric current systems, (3) new flexible representations for the tail and ring currents, and (4) a new “directional” criterion for fitting the model field to spacecraft data, providing improved accuracy for field line mapping. Results are presented from initial efforts to create models assembled from these modules and calibrated against spacecraft data sets.
Effects of zonal winds and metallic ions on the behavior of intermediate layers
Authors: Osterman G. B. , Heelis R. A. , Bailey G. J.
Published: February 2004

The characteristics of intermediate layers formed by zonal and meridional winds and those containing significant metallic ion concentrations are examined. Also investigated, in addition to layers, are differences in the ionization background and their effect on layer development. Calculations show that both meridional and zonal winds may contribute to layer formation and that in combination, these wind systems may create multiple layers or even single layers lying between regions of significant wind shear. Metallic ions, if present in the valley region, will be transported into any layer formed and cause the enhancements to assume altitude profiles that are significantly different from those expected when layers are populated solely by molecular ions.
On the uniqueness of linear moving‐average filters for the solar wind‐auroral geomagnetic activity coupling
Authors: Vassiliadis D. , Klimas A. J.
Published: February 2004

The relation between the solar wind input to the magnetosphere, υBSouth, and the auroral geomagnetic index AL is modeled with two linear moving‐average filtering methods: linear prediction filters and a driven harmonic oscillator in the form of an electric circuit. Although the response of the three‐parameter oscillator is “simpler” than the filter's, the methods yield similar linear timescales and values of the prediction‐observation correlation and the prediction χ². Further the filter responses obtained by the two methods are similar in their long‐term features. In these aspects the circuit model is equivalent to linear prediction filtering. This poses the question of uniqueness and proper interpretation of detailed features of the filters such as response peaks. Finally, the variation of timescales and filter responses with the AL activity level is discussed.
Solar wind double ion beams and the heliospheric current sheet
Authors: Hammond C. M. , Feldman W. C. , Phillips J. L. , Goldstein B. E. , Balogh A.
Published: February 2004

Double ion beams are often observed in the solar wind, but little work has been done in relating these beams to structures within the solar wind. Double ion beams are observed as beams of a given ion species and charge state occurring at two different energies. We use the three‐dimensional ion plasma instrument on board the Ulysses spacecraft to look for evidence of such beams associated with the heliospheric current sheet. In a subset chosen independently of plasma parameters consisting of 8 of over 47 crossings of the current sheet made during the in‐ecliptic phase of the Ulysses mission we find that these double ion beams are always present on either side of the current sheet. The double beams are present in both the proton and helium species. The secondary beam typically has a higher helium abundance, which suggests that these beams are formed in the helium‐rich corona rather than in interplanetary space. The double beams are not present in the interior of the current sheet. Neither collisions nor effects of plasma beta can account for the disappearance of the double beams inside the current sheet in all eight cases. We postulate that these beams are formed by reconnection occurring near the Sun in the boundary region between the open field lines of the coronal holes and the closed field line region of the heliospheric current sheet. Such a scenario would be consistent with previous X ray measurements which suggest that reconnection is occurring in this region.
The fine‐scale structure of the outer plasmasphere
Authors: Moldwin Mark B. , Thomsen Michelle F. , Bame Samuel J. , McComas David , Reeves Geoffrey D.
Published: February 2004

The density and temperature structure of the low‐energy ion population in the outer plasmasphere is examined by using data from Los Alamos National Laboratory's three‐dimensional magnetospheric plasma analyzer at synchronous orbit. We define the “outer plasmasphere” as regions of dense, cold plasma observed at synchronous orbit, with no attempt to distinguish between the main plasmasphere or detached plasma regions existing beyond the plasmapause. We find that for moderate to high levels of geomagnetic activity the outer plasmasphere typically has a fine‐scale density structure. The amount of variability in the density generally increases with increasing geomagnetic activity, as indicated by Kp, and the most variable intervals are associated with substorm activity. The dense (>10 ions cm−3), cold (≈1 eV), plasmaspherelike plasma is adjacent to, and often interspersed with, low‐density (1–10 ions cm−3), warm (2–10 eV), “troughlike” plasma regions. We find that occasionally these two temperature populations can coexist, but that most often they do not. The scale size of the fine‐scale structure in the dense, cold plasma regions often is of the order of 1000 km or less. These observations suggest that fine‐scale density structure in the dusk sector of the outer plasmasphere is imposed by penetrating substorm electric fields.
A review of plasma interactions with spacecraft in low Earth orbit
Authors: Hastings D. E.
Published: February 2004

All spacecraft interact in some manner with the plasma environment in space, either the natural environment or a self‐induced environment. Early work on plasma spacecraft interactions focused on geosynchronous altitudes where the primary effect is spacecraft charging from the non‐Maxwellian high‐energy plasma environment. This work has been extensively reviewed. In the last several years, there have been a number of measurements in low Earth orbit (LEO) which, when combined with models, have revealed a rich variety of plasma interaction phenomena at these low altitudes. These are reviewed in this work. These include charging on polar orbits, ram and wake flows, use of high‐voltage power systems in space, arcing on high‐voltage solar arrays, noise generation in self induced plasma clouds around large, active spacecraft such as the shuttle, anomalous ionization of emitted neutral gases, use of electrodynamic tethers and plasma contactors and phenomena associated with the use of electrically propelled rockets.
Flow‐aligned jets in the magnetospheric cusp: Results from the Geospace Environment Modeling Pilot Program
Authors: Weiss L. A. , Reiff P. H. , Weber E. J. , Carlson H. C. , Lockwood M. , Peterson W. K.
Published: February 2004

The extended flight of the Airborne Ionospheric Observatory during the Geospace Environment Modeling (GEM) Pilot program on January 16, 1990, allowed continuous all‐sky monitoring of the two‐dimensional ionospheric footprint of the northward interplanetary magnetic field (IMF) cusp in several wavelengths. Especially important in determining the locus of magnetosheath electron precipitation was the 630.0‐nm red line emission. The most striking morphological change in the images was the transient appearance of zonally elongated regions of enhanced 630.0‐nm emission which resembled “rays” emanating from the centroid of the precipitation. The appearance of these rays was strongly correlated with the Y component of the IMF: when the magnitude of By was large compared to Bz, the rays appeared; otherwise, the distribution was relatively unstructured. Late in the flight the field of view of the imager included the field of view of flow measurements from the European incoherent scatter radar (EISCAT). The rays visible in 630.0‐nm emission exactly aligned with the position of strong flow jets observed by EISCAT. We attribute this correspondence to the requirement of quasi‐neutrality; namely, the soft electrons have their largest precipitating fluxes where the bulk of the ions precipitate. The ions, in regions of strong convective flow, are spread out farther along the flow path than in regions of weaker flow. The occurrence and direction of these flow bursts are controlled by the IMF in a manner consistent with newly opened flux tubes; i.e., when |By| > |Bz|, tension in the reconnected field lines produce east‐west flow regions downstream of the ionospheric projection of the x line. We interpret the optical rays (flow bursts), which typically last between 5 and 15 min, as evidence of periods of enhanced dayside (or lobe) reconnection when |By| > |Bz|. The length of the reconnection pulse is difficult to determine, however, since strong zonal flows would be expected to persist until the tension force in the field line has decayed, even if the duration of the enhanced reconnection was relatively short.
Observation and modeling of compressional Pi 3 magnetic pulsations
Authors: Matsuoka Hitoshi , Takahashi K. , Yumoto K. , Anderson B. J. , Sibeck D. G.
Published: February 2004

Compressional magnetic pulsations with irregular waveforms and periods longer than 150 s (here termed Pi 3) have been studied by using data from Active Magnetospheric Particle Tracer Explorers Charge Composition Explorer (AMPTE/CCE) and GOES 5 and 6 in the dayside magnetosphere and compared with signatures on the ground at low latitudes by using data from Kakioka station (L = 1.25). On the ground, the pulsations appear in the horizontal component. A study of 17 such concurrent events during a 2‐month period in 1986 reveals the following pulsation characteristics. (1) The peak‐to‐peak amplitudes in space (δBT) and on the ground (δH) are comparable and are in the range of 0.5–7 nT. (2) On the ground the pulsations can be seen at all local times, even at midnight, while at geostationary orbit they are observed only on the dayside with a clear amplitude maximum at noon. (3) The pulsations on the ground lag those observed by CCE near local noon, and the lag increases as the local time separation between CCE and the ground station increases. The time lag is 1–2 min longer when the ground station is on the nightside than when it is on the dayside. (4) The time lag between pulsations observed at geostationary orbit and near noon by CCE varies systematically with local time and is about 2 min per 6 hours of local time separation. These observations indicate that some nightside pulsations in the Pi 3 band have dayside origins. The position dependence of the pulsation amplitude can be explained well by changes in the magnetopause current, which are in turn presumably caused by changes in the solar wind dynamic pressure. The time lags observed in space are consistent with signal propagation in the MHD fast mode, but the variation in space‐ground time lags with ground station local time must be attributed to another mechanism.