bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron density and whistler mode propagation characteristics at 7000 km altitude in the auroral zone and polar cap
Authors: Temerin M.
Published: February 2008

A measurement of the electric field wave spectrum by the S3‐3 satellite has shown the upper frequency cutoff of the whistler mode wave to be below 16 kHz. This measurement shows that the electron density in the polar cap can be as low as 1 cm−3 at 7000 km. However, since the measurement is unique in the examined data set of the S3‐3 satellite, such low densities must be rare both in the polar cap and in the auroral zone, except perhaps in regions of upgoing ion beams where whistler mode waves are usually not detected. This low density was confirmed by a measurement of the local lower hybrid frequency. The spin modulation of the wave amplitude as a function of frequency was used to determine that the wave was propagating down the magnetic field line.
The distribution of topside spread F from in situ measurements by Defense Meteorological Satellite Program: F2 and F4
Authors: Young Eugene R. , Burke William J. , Rich Frederick J. , Sagalyn Rita C.
Published: February 2008

On the basis of 331 equatorial passes of two Defense Meteorological Satellite Program satellites at 840 km, we have determined that two distinct types of topside ion depletions occur in the evening sector during equinoctial periods. First, during the early evening (1854 LT) a smooth type of depletion occurs with over 80% probability of observation per pass. This feature is aligned parallel to the magnetic equator and is probably related to the equatorial fountain effect and general F region dynamics. Second, we have seen irregular depletions later in the evening (1936–2154 hours) which are the topside signatures of spread F. Their total probability of occurrence per pass increases from ∼20% at 1936 hours to ∼60% at 2154 hours. A statistical study of the entire data set has shown that spread F depletions occur only when the topside ion density surpasses a seasonally controlled threshold. Therefore longitudinal and local time variations of topside ion density are reflected in similar variations in the occurrence probability of spread F as reported both here and earlier. A detection model including orbit‐feature intersection geometry, the above mentioned threshold, and Poisson statistics has been empirically verified.
Temporal variations in the Siple Station conjugate area
Authors: Stassinopoulos E. G. , Lanzerotti L. J. , Rosenberg T. J.
Published: February 2008

The Siple Station conjugate locations in the northern hemisphere are examined for the epoch 1975–1990 according to the predictions of three internal source geomagnetic field models (IGRF 1980, MAGSAT 1980, Barraclough 1975) and one external field model (Mead/Fairfield) under quiet and disturbed conditions. The conjugate location systematically changes in the interval studied, making it imperative that changes be made in the locations of the northern hemisphere geophysical stations during the reactivation of Siple Station in 1985–1987.
Spectroscopy of the EUV (350–1400 Å) nightglow
Authors: Chakrabarti Supriya , Kimble Randy , Bowyer Stuart
Published: February 2008

We present time averaged spectra of the extreme ultraviolet nightglow in the 350 to 1400‐Å range at 8‐Å resolution. The uplooking spectrum is dominated by geocoronal and interplanetary resonantly scattered solar lines (HI 1216, HI 1026, O II 834, and He I 584 Å). The downlooking spectrum contains OI emission features from the nighttime ionosphere, including several previously unobserved features. In contrast to previously reported observations, no significant N2 Lyman‐Birge‐Hopfield emissions are evident in our data, and a 2‐σ upper limit of 135 R can be placed on this radiation for the time of our observations.
Modeling Jupiter’s magnetospheric currents using Pioneer data: Evidence for a low‐latitude cusp
Authors: Thomas Barry T. , Jones Douglas E.
Published: February 2008

The Jovian magnetospheric field measured by Pioneer 10 and 11 can be well modeled by a combination of current systems composing an azimuthally symmetric current disc, a dusk‐dawn current sheet in both the dayside and the nightside magnetosphere, and an image dipole to represent the effects of currents on the magnetopause. The inclusion of a dusk‐dawn current sheet in the dayside magnetosphere allows observations obtained both inbound and outbound to be simultaneously fit by an azimuthally symmetric current disc (i.e., without the need for local time dependent current densities). Similar disc current intensities are found to describe both Pioneer 10 and Pioneer 11 encounters. During the Pioneer 10 inbound passage the magnetopause was rapidly pushed inside the spacecraft position by a solar wind compression event. The changes that occurred in the magnetospheric field at this time can be described by relatively simple changes in our model parameters. When the field lines of our model are extended beyond the region of fitting, both the Pioneer 10 and the Pioneer 11 encounters give similar profiles with magnetopause distances that are consistent with the actual encounters. The most striking feature of the models is that they suggest that the Jovian cusp is at much lower latitudes than is the case with the earth’s magnetosphere.
The evanescence of striation parameters along the geomagnetic field
Authors: Sperling J. L.
Published: February 2008

The class of flutelike striation instabilities, including the Rayleigh‐Taylor and E × B gradient drift modes, acquire parallel variations as a result of the finite size and nonuniformity of the ionosphere. It is demonstrated that evanescence away from the source of free energy responsible for instability is the correct boundary condition that should be applied in the calculation of the eigenmodes for striations along the geomagnetic field. The appropriateness of the boundary condition arises because striation fields become more electrostatic at lower altitudes and cannot penetrate to the earth’s surface. Ion‐polarization currents and electromagnetic effects can limit the mapping of striation fields to the opposite conjugate zone, particularly when plasma densities are high and striations originate at higher geomagnetic latitudes.
Jovian magnetospheric neutral wind and auroral precipitation flux
Authors: Eviatar Aharon , Barbosa David D.
Published: February 2008

We propose a mechanism for the transport of energy from the rotation of Jupiter into the heavy ions whose precipitation into the atmosphere is responsible for the intense ultraviolet aurora. The process involves charge exchange of heavy ions in the Io torus, their flight to the outer magnetosphere as neutrals, and their reionization in a region where the pickup magnetic moment is large. The particles diffuse back inward adiabatically and are precipitated at 9 RJ with an energy exceeding 10 keV/nucleon. A field and flow model based on Voyager observations is used that defines a source region extending from 32 RJ to 80 RJ on the nightside. This region is capable of delivering 4×1013 W of power to the auroral region, well within the realm of the power required by observations. We also demonstrate that this mechanism provides a neutral planetary wind from Jupiter. The predicted wind will consist of two beams: one intense (5×1028 s−1) at 25 eV/nucleon and the other tenuous (1×1025 s−1) at 600 eV/nucleon and above. These neutral particles will appear as a suprathermal heavy ion component in the solar wind.
Uniformly spaced field‐aligned ionization ducts
Authors: Gross S. H. , Muldrew D. B.
Published: February 2008

MF and HF radio wave signals transmitted from topside sounders can often become trapped in magnetic‐field‐aligned ionization ducts located approximately vertically below the satellite. The resulting traces observed on ionograms are called combination mode traces. A number of cases of combination mode traces observed with the ISIS topside sounders were studied for passes over mid‐ and low‐latitude regions which exhibited distinguishable, nearly uniformly spaced traces on the ionograms typical of this type of propagation in the frequency range above 1 MHz. Associated extraordinary vertical and ducted traces were also evident in all cases. The ducted trace is interpreted as due to propagation in a duct encompassing the satellite at the time of measurement, whereas the combination mode traces are interpreted as due to ducts located well below the satellite. The simultaneous presence of a ducted trace and combination mode traces suggests the presence of a parallel system of ducts that are field aligned. On interpreting the ionograms for events studied by ray tracing, it was found that the ducts are separated by as much as 70 km transverse to their field alignment. The data indicate that, at times, the ducts may exist down to the F peak and may extend into the conjugate region as well. A multiplicity of ducts with such large, relatively uniform separations was not previously appreciated, and the mechanism for creating them in this fashion is not clear. One possibility for the even spacing of these irregularities is that they result from acoustic gravity waves at lower altitudes. Possible relationships to other geophysical phenomena, particularly equatorial phenomena, are discussed.
Jovian decametric arcs: An estimate of the required wave normal angles from three‐dimensional ray tracing
Authors: Menietti J. D. , Green J. L. , Gulkis S. , Six N. F.
Published: February 2008

A three‐dimensional ray tracing code which incorporates the O‐4 magnetic field model (Acuna and Ness, 1976) and a realistic plasma model has been used to model high‐curvature decametric arcs observed by the Voyager planetary radio astronomy instrument. Two examples of intense, isolated, vertex‐late, high‐curvature arcs were singled out for study. The source point wave normal angle was incremented at each of a full range of frequencies until the model rays identically matched the observed arcs of the planetary radio astronomy data. Several different Doppler shifts were assumed at the source point. By this procedure an accurate relationship between the wave normal angle Ψ and the frequency was obtained, with the variation being 70° < Ψ < 80°, and Ψmax = 80° for the arcs considered. As the assumed Doppler shift at the source point increased, the value of Ψmax was found to decrease, but the general shape of the Ψ(f) curve was unaffected. By comparing the ray tracing results with the independent results of Staelin (1981) regarding emission from beaming electrons, it was found that larger Doppler shifts (f/fg > 1.1) at the source point produce Ψmax > 70°, in agreement with the ray tracing results for the two arcs considered, only for υ∥ > 0.7 and υ∥/c > 0.32 (where υ∥ is the electron velocity parallel to B). Actual values of υ∥/υ are unknown, but independent observations indicate that υ∥/c ≈ 0.1. Since the low‐curvature arcs are believed to result from larger wave normal angles, our results indicate an upper limit to the Doppler shift of Jovian decametric emissions of f/fg < 1.1.
Observations of sunward propagating waves on the magnetopause
Authors: Nielsen E.
Published: February 2008

Observations of ionospheric electric fields during an ULF resonant event are used to infer the presence of waves on or near the magnetopause propagating toward the dayside. Simultaneous satellite measurements at geosynchronous orbit confirm the presence of these surface waves. Immediately following these observations a flux transfer event appears to have occurred (Goertz et al., 1984). It is speculated that the pulsations were associated with that event.
Simultaneous satellite and ground observations of ducted and nonducted VLF emissions: Generation region location and drift
Authors: Farley A. F. , Dowden R. L.
Published: February 2008

Discrete emissions received on the satellite ISIS 2 on August 15, 1978, corresponded closely with the emissions received on nearby ground stations. Over the first part of the pass the signals were more or less simultaneous and identical in shape, but later they appear on the satellite record in a slightly more dispersed form with about a quarter of a second additional delay, strongly suggestive of nonducted travel from the emission region to the satellite. Ray tracing is used to attempt to reconstruct this event and establish the generation region of the emissions.
O+ charge exchange in the polar wind
Authors: Barakat A. R. , Schunk R. W.
Published: February 2008

The continuity and momentum equations for ionospheric O+ were solved for typical polar cap conditions. Density profiles were obtained both with and without allowance for accidentally resonant charge exchange (ARCE) between O+ and H. It was found that ARCE acts to reduce the maximum (or limiting) O+ escape flux by less than 30% for typical atmospheric conditions (T∞ ≳ 1000 K) and by only a factor of about 3.5 for atmospheres with low exospheric temperatures (T∞ = 750 K). With allowance for ARCE the limiting O+ escape flux is of the order of 5×108 to 109 cm−2 s−1, depending on the atmospheric conditions, which easily accounts for the existing measurements. This indicates that, contrary to previous predictions, there is no O+ charge exchange barrier, and consequently, it is not necessary to have an acceleration mechanism at low altitudes in order to have an appreciable O+ escape flux. Instead, an O+ depletion at high altitudes due to some acceleration mechanism is sufficient to cause large O+ fluxes to escape from the ionosphere to the magnetosphere.
Temporal evolution of the solar wind and the formation of a standing shock
Authors: Habbal Shadia Rifai , Rosner Robert
Published: February 2008

The temporal evolution of the solar wind from one steady state to another is explored when momentum deposition produces multiple critical points in the flow. We show that the wind always evolves in time to a new steady state compatible with the solution of the steady state equation of motion. However, for the same initial state and identical asymptotic momentum deposition rate the temporal evolution pattern of the wind depends on the detailed time history of momentum addition and is therefore not unique. This feature plays an important role in the particular case when multiple (three in this study) steady states exist for identical boundary conditions; each one of these solutions is thus shown to be physically accessible. The details of the temporal evolution pattern of the wind reveal the formation of a shock discontinuity whenever the flow becomes supersonic at a critical point upstream from the initial critical point. If the flow remains supersonic at that inner critical point, the shock can become a standing one, depending on the strength and the temporal history of momentum addition. The results of this study indicate that the time scale required for the solar wind to evolve between steady states is of the order of 30–60 hours. Furthermore, the results also reveal the interesting and novel phenomenon that a standing shock is likely to develop in the inner solar wind flow within this time frame, in particular, in coronal hole regions with rapidly diverging geometries.
Association between energetic particle bursts and Birkeland currents in the geomagnetic tail
Authors: Lui A. T. Y. , Krimigis S. M.
Published: February 2008

IMP 8 observations in the geomagnetic tail of energetic particles at hundreds of keV and of the magnetic field are examined for a substorm period from 1700 to 1800 UT on March 3, 1976. For this interval, it is found that bursts of energetic protons detected at a downstream distance of ∼37 RE in the midnight tail region are accompanied by east‐west magnetic field perturbations indicative of Birkeland current sheets. The magnitude of the magnetic field perturbations ranges from ∼1 to 12 nT, corresponding to current densities of 1 to 9 mA/m when integrated over the current sheet thickness. These values are comparable to previous observations of Birkeland currents in the near‐earth tail (X > −20 RE) and with the auroral‐arc‐associated Birkeland current densities at low altitudes scaled out to the tail region. The favorable comparison suggests that the closure of small‐scale Birkeland current systems, at least in these instances, lies tailward of ∼40 RE. The observed Birkeland current system and the magnitude of current densities are found to be consistent with ion tearing instability in the tail. The inferred wavelength of the tearing mode along the tail axis is ∼2 to 17 RE. In the context of the tearing model, the presence of Birkeland currents and the occasional isotropic distribution of energetic electrons (Ee > 0.22 MeV) suggest that the energetic particle events in this study occur on closed magnetic field lines, even though strong tailward streaming dominates the particle anisotropy in these events.
Cross‐polar cap potential drop and the energy coupling function
Authors: Ahn B.‐H. , Akasofu S.‐I. , Kamide Y. , King J. H.
Published: February 2008

The cross‐polar cap potential Φpc on March 18 and 19, 1978, is determined by the numerical scheme developed by Kamide et al. (1981) on the basis of magnetic records from the six IMS meridian chain stations and others. The potential drop Φpc thus determined is correlated with the energy coupling function ϵ and the AE index. It is found that Φpc (kV) = 4.2×10−17 ϵ (erg/s) for 1018 erg/s < ϵ < 3.5×1018 erg/s and Φpc (kV) = 36 + 0.089 AE (nT). These results are in fair agreement with the satellite results obtained by Reiff et al. (1981). Thus, the ground‐based magnetometer inversion technique has been advanced to the point that Φpc can be inferred from the IMS meridian chain data with fair accuracy.
Formation of ion acoustic solitary waves upstream of the Earth's bow shock
Authors: Pangia M. J. , Lee N. C. , Parks G. K.
Published: February 2008

The turbulent plasma development of Lee and Parks is applied to the solar wind approaching the earth's bow shock region. The ponderomotive force contribution is due to ion acoustic waves propagating in the direction of the ambient magnetic field. In this case, the envelope of the ion acoustic wave is shown to satisfy the cubic Schroedinger equation. Modulational instabilities exist for waves in the solar wind, thereby predicting the generation of solitary waves. This analysis further identifies that the ion acoustic waves which exhibit this instability have short wavelengths.
Anisotropy observation of diffuse ions (>30 keV/e) upstream of the Earth's bow shock
Authors: Terasawa T. , Scholer M. , Ipavich F. M.
Published: February 2008

We have performed a detailed study of the temporal development of field‐aligned anisotropies and density gradient anisotropies during several diffuse ion events observed upstream of the earth's bow shock. A clear anticorrelation between the field‐aligned anisotropy and the particle intensity is found; in the solar wind frame this anisotropy, which is directed away from the bow shock, decreases as the particle flux increases. Furthermore, the field‐aligned anisotropy increases with increasing particle energy. In the strong scattering limit the one‐dimensional diffusion‐convection formalism predicts a decrease of the anisotropy with increasing energy. It is concluded that upstream escape is significant for higher energy particles and leads to the deviation from the prediction of the diffusion‐convection formalism. Quantitatively, the diffusion‐convection formalism predicts a field‐aligned anisotropy which is larger than measured for the lowest energy particles (∼30 keV/e). Along with the variation of the field‐aligned anisotropy, the appearance of a density gradient anisotropy was also observed. The observations are discussed in terms of a first‐order Fermi model for the upstream particles and in terms of a magnetospheric origin. It is concluded that field‐aligned anisotropy measurements obtained upstream of the bow shock cannot help to differentiate between the two possible models for the upstream population.
Perturbations in the velocity distribution in a collisionless plasma
Authors: Dungey J. W.
Published: February 2008

A range of phenomena important in space plasmas calls for simulation and can be approximated by the two‐dimensional geometry in which the magnetic field lines are straight and parallel and all gradients are perpendicular to the field. The design of simulations itself motivates analytical theory, in this case linear theory for a velocity distribution. A general formulation of linear theory with the unperturbed state stratified uses the method ofRobertson et al. [1981], the constants of the motion being energy W and canonical momentum Py. This is developed using the periodicity of any particle trajectory, leading to a simple condition determining the direction of energy exchange between resonant particles in an element dWdPy, and a wave, which is a generalization of the energization of a wave by an overtaking beam. A Larmor radius expansion is performed including the second harmonic of the trajectory frequency, but no higher harmonics, and including the gradient of the electric field, which would be essential for Kelvin‐Helmholtz instability. The objective is to determine the dependence of the perturbations on gyrophase. The important result is that the third Fourier component is of second order in the Larmor radius and the formulae are obtained for the Fourier components up to the second. When the Larmor radius expansion is valid, fine structure in the velocity distribution arises only from resonances. A less rigorous discussion of the opposite case, treating the magnetic field as weak, shows that particles faster than the phase speed pass through resonance in the sense of stationary phase. This generally dominates the perturbations, and generally these vary rapidly with gyrophase.
The effect of hydromagnetic waves on the shape of the plasmapause boundary
Authors: Daly R. A. , Hughes W. J.
Published: February 2008

We show that hydromagnetic wave electric fields could cause the fluctuations in cold plasma number density that have been observed as spacecraft cross the plasmapause. To explore the effects of a hydromagnetic wave electric field on the particles in the vicinity of the plasmapause we constructed a simple computer model of the flow of cold plasma in the equatorial plane of the magnetosphere. A hydromagnetic wave electric field which is localized in space and time is introduced. Particles are perturbed by the wave electric field. The resulting fluctuations in cold plasma number density are most evident in the dusk region and occur over both large (∼1 RE) and small (∼0.1 RE) distance scales. As these variations in the number density are similar to those observed, hydromagnetic wave electric fields could very well account for the density variations observed in the vicinity of the plasmapause boundary.
Global large scale structures in the F region
Authors: Gross S. H.
Published: February 2008

Measurements of neutral densities, neutral temperature, ion density and ion temperature by the Atmosphere Explorer C and E satellites exhibit fluctuations made up of coherent waves of scale sizes from hundreds to thousands of kilometers. The fluctuations in the AE‐C data are found at times of low magnetic activity to extend from the auroral region in one hemisphere across the equator to the corresponding region in the other hemisphere with little change in apparent wavelength. The fluctuations in the AE‐E data similarly exhibit at times of low magnetic activity nearly uniform wave structure encircling the equatorial belt. Typical examples of 2000 km waves in the AE‐C data and 1500 km waves in the AE‐E data are discussed. To explain these observations, it is suggested that during quiet periods the auroral belts excite quasi‐stationary waves distributed about the earth with coherent periods, possibly tidal, and scale lengths determined by the structure of the belts. According to this interpretation, TID's are manifestations of the transient waves that result from changes in magnetic activity with periods and scale sizes associated with the auroral excitation.
Coupling between the solar wind and the magnetosphere: CDAW 6
Authors: Tsurutani Bruce T. , Slavin James A. , Kamide Yohsuke , Zwickl Ronald D. , King Joseph H. , Russell Christopher T.
Published: February 2008

Interplanetary conditions (VBs V²Bs ε) are derived from ISEE 3 and IMP 8 field and plasma data for the two Coordinated Data Analysis Workshop (CDAW 6) intervals of study and are compared with various aspects of geomagnetic activity (AE, UT, derived Joule heating, electric potential, westward, eastward and total electrojet currents). The March 22 (day 81), 1979, interval contains two distinct periods of geomagnetic activity, both highly correlated with interplanetary features. The start of the first active interval is caused by a southward turning of the interplanetary magnetic field (IMF) associated with the passage of a heliospheric current sheet. The start of the second interval is related to a second IMF southward turning. The geomagnetic activity intensifies when the second crossing of the current sheet, and a ram pressure increase of 4 to 6, impinges on the magnetosphere. Because the interplanetary parameters VBs, V²Bs and ε decrease across the discontinuity, it is concluded that either additional energy is injected into the magnetosphere from the conversion of ram energy into magnetospheric substorm energy or some feature associated with current sheet crossing “triggers” the release of previously stored magnetosphere/magnetotail energy. It is not possible at this time to distinguish between these two possibilities. For day 81, VBs, V²Bs and ε were highly correlated with AL, AE, westward and equivalent currents with coefficients ranging from ∼0.75 to 0.90. The interplanetary parameters were significantly less correlated with geomagnetic activity in the second interval (days 90–91, 1979), with all correlation coefficients being less than 0.6. Several possible explanations for the latter result are (1) the scale of Alfvénic fluctuations was small in comparison to the size of the magnetosphere and the “upstream” spacecraft did not get an accurate indication of the solar wind impinging on the magnetosphere, or (2) during some periods of high and continuous activity, substorms are due to internal magnetospheric processes and occur randomly, independent of the interplanetary drivers.
Low energy (>130 eV) oxygen ions at the geosynchronous orbit during the CDAW 6 event of March 22, 1979
Authors: Stokholm M. , Amata E. , Balsiger H. , Candidi M. , Orsini S. , Pedersen A.
Published: February 2008

Anisotropic O+ ions were frequently observed by the GEOS 2 ion composition experiment in the energy range 4–130 eV, during the CDAW 6 event of March 22, 1979. These observations allow the study of the plasma flow in the electric and magnetic fields as known from data of other experiments in the geosynchronous orbit, in the noon, dusk and midnight sectors. By comparison of these measurements with plasma observations made by the ISEE 2 plasma experiment, at the same local time and at different latitudes, the observation of cold plasma streaming along magnetic field lines from the polar ionosphere to the equatorial magnetosphere is extended from the magnetotail to the near earth equatorial region.
Suprathermal O+ and H+ ion behavior during the March 22, 1979 (CDAW 6), substorms
Authors: Ipavich F. M. , Galvin A. B. , Scholer M. , Gloeckler G. , Hovestadt D. , Klecker B.
Published: February 2008

We present measurements of energetic (∼130 keV) O+ ions in the earth's magnetosphere during the two Coordinated Data Analysis Workshop 6 substorms on March 22, 1979. The behavior of thermal and suprathermal H+ (10–130 keV) and suprathermal He++ (30–130 keV/e) ions is also discussed. The observations were made with the University of Maryland/Max‐Planck‐Institut ultralow energy charge analyzer (ULECA) sensor on ISEE 1 at geocentric distances ∼16 to 7 RE in the earth's magnetotail. Approximately 15 min before the 1054 UT onset of the first substorm, energetic O+ ions are observed streaming tailward. H+ and He++ ions at all energies were generally streaming tailward from ∼1059 to 1115 UT, consistent with the presence of a near‐earth neutral line during this interval. From 1117 to 1124 UT the H+ and He++ ions were observed flowing earthward, suggesting that at ∼1117 UT the neutral line retreated tailward. A brief interval in the southern tail lobe, from ∼1124 to 1126 UT, was highlighted by an intense O+ beam streaming tailward; the O+/H+ ratio at 130 keV was 7±2. This suggests that high energy O+ ions may be accelerated directly out of the ionosphere. The recovery phase of the first substorm began a few minutes later and was characterized by large intensities of nearly isotropic suprathermal ions. The O+/H+ differential intensity ratio at 130 keV was quite large (∼1) during the recovery phase of both substorms.
Variable frequency VLF signals in the magnetosphere: Associated phenomena and plasma diagnostics
Authors: Carlson C. R. , Helliwell R. A. , Carpenter D. L.
Published: February 2008

Coherent variable frequency signals (ramps) extending from 1 to 8 kHz, injected into the magnetosphere from Siple Station, Antarctica (L=4.3) exhibit upper and lower cutoffs when received at the conjugate station, Roberval, Quebec. Ramp group delay measurements and ionospheric sounding data are used for the first time to determine the cold plasma density and L shell of the propagation path. Relationships among f, df / dt, and the “phase equator” for gyroresonance are calculated using second‐order resonance equations generalized to relativistic electrons. Observed upper cutoff characteristics are interpreted in terms of off‐equatorial gyroresonant interaction regions and ducted propagation limited to frequencies below half the local gyrofrequency. The observed lower cutoff frequencies varied systematically with transmitted ramp slope, suggesting a threshold in the resonant electron number density above which rapid temporal wave growth and saturation can occur. This concept is used to develop a hot plasma diagnostic technique which, for an assumed g(α)υ−n electron distribution, provides an estimate of the energy dependence n. A test of this technique is given using the data and a simplified wave‐particle interaction simulation. Additional aspects of the magnetospheric response to ramp injection, including emission triggering, are discussed.
The field‐aligned scale length of one‐dimensional double layers
Authors: Yamamoto Takashi , Kan J. R.
Published: February 2008

We have examined, by means of numerical simulation, the effects of the magnetic mirror, the backscattered primary electrons, and the magnetospheric hot ions on the field‐aligned scale length (L) of one‐dimensional double layers. In our simulation model, the external magnetic field is allowed to converge radially with spherical symmetry and a constant potential difference is applied across the system. The results show that the double‐layer scale length varies from: (1) localized (L ≳ 10λD) in the absence of the backscattered primary electrons and the magnetospheric hot ions; (2) partially extended (L ∼ 100λD < system length) if only the backscattered primary electrons are present; to become (3) fully extended (L ≲ system length and increase as system length increases) if both the backscattered primary electrons and the magnetospheric hot ions are present.
The galactic cosmic ray intensity minimum in the inner and outer heliosphere in solar cycle 21
Authors: Venkatesan D. , Decker R. B. , Krimigis S. M. , Van Allen J. A.
Published: February 2008

This paper investigates the occurrence of the cosmic ray intensity minimum during solar cycle 21 at widely separated locations in the heliosphere. The data include in situ measurements by cosmic ray detectors on the earth‐orbiting satellite IMP 8 (E ≳ 35 MeV), on the Voyagers 1 and 2 spacecraft (E ≳ 70 MeV), and on the Pioneers 10 and 11 spacecraft (E ≳ 80 MeV), located at distances from 1 to 27 AU. Note that Pioneer 10 and the other three spacecraft (Pioneer 11 and Voyagers 1 and 2) are on the opposite sides of the sun, with the latter moving toward the tail of the heliosphere. The data used in this study have been suitably corrected by removing solar flare particle contributions, Forbush decreases, and contamination by the radioisotope thermoelectric generator. It is evident that there exists a time delay in the occurrence of the cosmic ray intensity minimum registered by the IMP 8 and Pioneer 10 detectors, the latter being located at ∼27 AU. We show that the data from the four spacecraft in deep space are on an average consistent with the IMP 8 data at 1 AU when suitably corrected, using 3%/AU for the radial gradient and 500 km/s for the average speed of propagation. An overview of the intensity profiles reveals reasonable agreement among them. However, specific intensity features appear at times to propagate with speeds in excess of the average value of ∼500 km/s.
Geomagnetic influence on the muon charge ratio of cosmic rays
Authors: Allkofer O. C. , Dau W. D. , Jokisch H. , Klemke G. , Uhr R. C. , Bella G. , Oren Y.
Published: February 2008

The charge ratio of muons from cosmic radiation is strongly modified by the earth's magnetic field in the low‐energy region. With a magnetic spectrometer (DEIS project) erected at Tel‐Aviv this influence was studied in the momentum range from 10 to 200 GeV.
Deep space observations of the east‐west asymmetry of solar energetic storm particle events: Voyagers 1 and 2
Authors: Sarris E. T. , Decker R. B. , Krimigis S. M.
Published: February 2008

Measurements of energetic proton (Ep ≥ 520 keV) intensities by The Johns Hopkins University Applied Physics Laboratory instruments on board the Voyagers 1 and 2 deep space probes, during solar flare‐induced shock waves, indicate that the formation of solar energetic storm particle (ESP) events depends critically on the heliolongitudes of different locations on the large‐scale shock front with respect to the source flare site. It is shown that large ESP ion intensity enhancements are observed for solar flare sites to the east of the spacecraft meridian, whereas only weak ESP events are associated with shock crossings where the flare sites are west of the spacecraft meridian. The results are explained in terms of the average “interplanetary magnetic field‐shock front” configurations encountered by the Voyagers at various heliolongitudes of the solar flare‐generated shock wave, i.e., quasi‐perpendicular (quasi‐parallel) shocks for eastern (western) solar flare sites. These configurations suggest that efficient energetic proton acceleration processes operate at quasi‐perpendicular shock fronts consistent with the “grad‐B” shock drift acceleration mechanism.
Cold streams of ionospheric oxygen in the plasma sheet during the CDAW 6 event of March 22, 1979
Authors: Orsini S. , Amata E. , Candidi M. , Balsiger H. , Stokholm M. , Huang C. , Lennartsson W. , Lindqvist P.‐A.
Published: February 2008

During the March 22, 1979, substorm events the positive ion experiment on ISEE 2 (EGD) detected intense streams of low‐energy ions (mostly between 50 and 500 eV) moving tailward in the near‐earth magnetotail. The first clear observation of these streams was made about 30 min after the onset of the first substorm. On the basis of a comparison with simultaneous data from the ion composition experiment on ISEE 1, which was trailing ISEE 2 in the same orbit by about 2 RE, it is argued that these streams consisted primarily of O+ ions. From the analysis of the direction and energy of the streams we draw the following conclusions: (1) In addition to the bulk velocity along the magnetic field lines the streams also have a significant and varying perpendicular velocity due to E × B/B² drift. The GSE x and y components of the E × B/B² drift are generally toward the center of the magnetotail in the lobe and toward the tail flanks in the plasma sheet, in qualitative agreement with the field topology one obtains by mapping the north‐south electric field from the morning and evening auroral ovals well into the distant magnetotail, in a manner previously proposed in the literature. (2) The O+ flow speed and flow direction, as well as density and temperature, undergo strong fluctuations during the course of the two substorms. Some of these fluctuations seem to reflect an increased outflux of ionospheric O+ in connection with increasing magnetic activity, while others may be related to magnetotail movements. Certain oscillations of the flow direction and speed with periods ranging from 10 to 15 min may suggest a wavelike boundary between the plasma sheet and the lobes.
Anomalous resistivity and AE‐D observations of auroral electron acceleration
Authors: Lin C. S. , Rowland H. L.
Published: February 2008

Electron fluxes measured with high time resolution by AE‐D during narrow bursts of intense electron precipitation fluxes within inverted‐V events are compared with electron distributions obtained from particle simulations based on an anomalous resistivity model. The qualitative agreement between the AE‐D observations and the computer simulations is excellent. When the potential energy is small, both the AE‐D observations and the simulations indicate strongly field‐aligned electron beams; both also agree that the accelerated electrons undergo large pitch angle scattering when the potential drop increases above a certain critical value. Furthermore, the simulations show that electron distributions are isotropized progressively from low to high energy, in agreement with the AE‐D observation that the electron flux isotropization occurred first at lower energies. These results suggest that anomalous resistivity may play an important role in the acceleration of auroral particles.
Plasma‐depleted holes, waves, and energized particles from high‐altitude explosive plasma perturbation experiments
Authors: Wescott E. M. , Stenbaek‐Nielsen H. C. , Hallinan T. , Deehr C. , Romick J. , Olson J. , Kelley M. C. , Pfaff R. , Torbert R. B. , Newell P. , Föppl H. , Fedder J. , Mitchell H.
Published: February 2008

High explosive shaped charge experiments King Crab and Bubble Machines I and II, designed to perturb the ambient plasma and magnetic field, were flown above 460 km on Taurus Tomahawk rockets from Poker Flat in March 1980, 1981, and 1982, respectively. The last flights were a mother‐daughter combination with the instrumentation section remaining attached to the rocket. The detectors consisted of a single‐axis dipole electric field detector, a fixed bias cylindrical Langmuir probe, a three‐axis attitude magnetometer, and curved plated energetic ion and electron electrostatic analyzer. The first experiment, King Crab, revealed the existence of a barium plasma depleted region or dark hole of about 5 km diameter centered on the burst. All electric power to the instruments failed on the lift‐off of the 1981 Bubble Machine I, but useful optical data were obtained. The third flight a year later produced useful data from all but the electron detector on the electrostatic analyzer. Ground‐based optical and telluric field instrumentation recorded evidence for injection‐induced waves of about 5‐s period. Delay times indicate a slow (175–385 km/s) propagation from the burst point. Promptly following the release, auroral intensity ion beams were observed in the field‐aligned ion electrostatic analyzer, with energies up to 6.8 keV. Evidence suggests that these particles were not energized by the explosion but that they represent an existing ion conic population pitch angle scattered by the released barium into the view of the detector. Concerning locally produced electrostatic instabilities, the wave measurements of Bubble Machine II indicate that finite Larmor radius stabilization occurs for the weakly driven low (barium) density situation, but that shorter‐wavelength waves can occur early in the expansion event when the barium density is higher. These results are in reasonable agreement with a theory described by Sperling and Krall (1981).
Finite temperature effects on the evolution of ionospheric barium clouds in the presence of a conducting background ionosphere: 1. The simplest case: Incompressible background ionosphere, equipotential magnetic field lines, and an altitude‐invariant neutral wind
Authors: Zalesak S. T. , Chaturvedi P. K. , Ossakow S. L. , Fedder J. A.
Published: February 2008

We postulate that under realistic ionospheric conditions, barium ion clouds hundreds of meters in diameter can be long‐lived, quasi‐stable, nonbifurcating structures. These structures may resemble “tadpoles,” with a dense head, steep density gradients at the front, and a long, less dense tail. We assume that these structures are the final products of the recursive bifurcation of a considerably larger barium ion cloud, i.e., striations. The realistic ionospheric conditions to which we refer consist of a barium ion cloud with ion temperatures Ti of approximately 1000°K, coupled electrically to a background ionosphere of lower compressibility than itself, i.e., an F region. We show analytically that this combination of finite Ti and relatively incompressible background, combined with the simplifying assumptions of equipotential magnetic field lines and of a uniform, altitude‐invariant neutral wind, results in an effective diffusion of barium plasma but more importantly of total magnetic‐field‐line‐integrated Pedersen conductivity Σp. The diffusion coefficient has a special form which allows the inner portions of the cloud to diffuse slowly, giving the cloud a long lifetime, and allows the outer, less dense portions of the cloud to diffuse rapidly, preventing cloud bifurcation. Numerical simulations of the full nonlinear dynamics are then used to show that this diffusion does in fact give rise to quasi‐stable barium striations hundreds of meters in diameter. These findings are consistent with the linear analysis of Francis and Perkins (1975). The consequences of relaxing the above simplifying assumptions will be treated in subsequent papers in this series.
Effects of finite current channel width on the current convective instability
Authors: Satyanarayana P. , Chen J. , Keskinen M. J.
Published: February 2008

The effects of the finite current channel width on the current convective instability are studied both analytically and numerically. First, using a sharp boundary field‐aligned current distribution which has a finite width along the plasma density gradient, the dispersion relation is obtained analytically. It is found that for the long wavelength modes (kyd ≪ 1) where the nonlocal effects are most prominent, the growth rate γ is proportional to
in the collisional limit (νin ≫ |ω|), where d is the half width of the current channel, L is the plasma density gradient scale length,
is the field‐aligned current velocity, νin is the ion‐neutral collision frequency, and ω is the perturbation frequency. For the long wavelength modes in the inertial limit (νin ≪ |ω|) the growth rate γ scales as
, where α = 1/2 (2/3) for kz²/ky² Ωe/νei much less than (greater than) |ω|/Ωi, kz(ky) is the wave number parallel (perpendicular) to the magnetic field, Ωe(Ωi) is the electron (ion) gyrofrequency, and νei is the electron‐ion collision frequency. Numerical results are also presented for a diffuse boundary current velocity distribution. Applications to the high‐latitude ionosphere are discussed.
On the possibility that nonuniform ionospheric conductivity can cause a pulsation double resonance
Authors: McDiarmid D. R.
Published: February 2008

Recently, Glassmeier (1983, 1984) has discussed the consequences of nonuniform ionospheric conductivities on resonant Pc 4–5 electric field structure. One result of his work was the suggestion that ionospheric conductivity structure may have caused the pulsation double‐resonance event described by Nielsen and Allan (1983) in which a monochromatic pulsation was seen to resonate simultaneously at two different latitudes. Examination of this suggestion leads to the conclusion that although spatial conductivity variation may have contributed to the creation of the double resonance, it is unlikely to have been the sole cause.
On the divergence of the Hall Current in the westward traveling surge
Authors: Kan J. R. , Hollerbach R.
Published: February 2008

Recent observations suggest that the Hall current tends to be highly divergence free in the westward traveling surge. It is shown in a model calculation that the blockage of the Hall current from closure along field lines leads to a significant reduction of the divergence of the Hall current, but is not divergence free. The westward electrojet in our model is found to rotate counterclockwise around the leading edge of the surge and merge into the eastward electrojet. The difference in strength between the two electrojets at the head of the surge goes into the upward field‐aligned current. It is also shown that the conductivity enhanced by the discrete auroral precipitation does not contribute to the divergence of the Hall current provided that the electric fields are coplanar along a field line. The above results strongly suggest that the Hall current tends to be highly divergence free in regions of bright auroral forms, especially in the westward traveling surge.
EUV (300–900 Å) spectrum of polar cap and cusp emissions near local noon
Authors: Chakrabarti Supriya
Published: February 2008

Emissions in the 300‐to‐900‐Å wavelength range near the dayside oval were observed on April 5, 1979, over the south pole by the EUV spectrometer on board the STP78‐1 satellite. The spectra, obtained from 600 km, near local noon, are dominated by spectral lines of singly ionized atomic oxygen. Most prominent features in this passband are O II 538‐to‐539‐, 617‐, and O II 834‐Å emission lines, all of which have intensities exceeding 100 R. Several weak O II and N II features are present in the spectrum with intensities ranging from 10 to 60 R. In the same pass, we have also obtained EUV spectra from two distinctively different emission regions in the polar cap. A diffuse feature is probably excited by polar rain‐like soft particles, while a localized region shows bright emissions most lively excited by keV particles. The brightest spectral feature in this wavelength range is O II 834 Å, which was recorded in the latter region with an intensity exceeding 1 kR.
Helios spacecraft and Earth perspective observations of three looplike solar mass ejection transients
Authors: Jackson B. V. , Howard R. A. , Sheeley N. R. , Michels D. J. , Koomen M. J. , Illing R. M. E.
Published: February 2008

Three looplike mass ejection transients observed from earth with the SOLWIND coronagraph and the solar maximum mission coronagraph are imaged by Helios spacecraft zodiacal light photometers. Because the Helios spacecraft are not earth orbiting, views of these ejections from the two perspectives allow conclusions to be drawn about their three‐dimensional shapes. The mass ejection of May 24, 1979, in Helios data is concentrated in an outer structure followed by bright features separated by a region of depleted material. The ejections of June 18 and 29, 1980, appear restricted in position angle in Helios observations to less and the same, respectively, as in coronagraph observations. The observations imply that the ejections essentially retain their basic structure and speed out to heights (0.2–0.4 AU) observed by the Helios spacecraft.