bluuebunny/crossref_metadata_2025 huggingface dataset:
A theory of incoherent scattering of radio waves by a plasma, 5. The use of the Nyquist Theorem in general quasi‐equilibrium situations
Authors: Swartz Wesley E. , Farley Donald T.
Published: February 2008

The Nyquist or fluctuation‐dissipation theorem applies strictly only to linear systems in thermal equilibrium. However, it can also be used successfully to calculate fluctuating quantities in systems in quasi‐equilibrium, a familiar example being a circuit with elements at different temperatures. An analogous calculation can be carried out for a plasma, considering each particle species as a separate element of the system. One calculates the spontaneous force generated by each species (with its own temperature and mean drift velocity) and also a set of transfer functions which relate each of these forces to the electron perturbations which are responsible for the scattering. The important point to realize in the plasma case is that, with this approach, the electric field perturbations, which couple the species together, enter the calculation only through the transfer function and are not involved in the statistics of the ‘generalized forces.’ The results obtained apply for multiple ion species with unequal temperatures, unequal mean drift velocities, unequal charges (including negative), etc., and agree with similar calculations based on the dressed particle approach.
Refinement of the aeronomically determined rate coefficient for the reaction of N2+ with O
Authors: Torr D. G.
Published: February 2008

An earlier aeronomic determination of the rate coefficient for the reaction
using Atmosphere Explorer data indicated a small increase in k1 with ion temperature, contrary to laboratory observations. This was incorrectly attributed to neglect of an increase in the N2+ recombination rate with vibrational excitation. Recent aeronomical results have shown that the rate coefficient for charge exchange of O+(²D) with N2 is about an order of magnitude smaller at thermal temperatures than at energies greater than 0.5 eV (i.e., energies at which laboratory measurements have been made). It is shown that the use of the smaller charge exchange rate coefficient coupled with recent results on N2 quenching of O+(²D) yields a temperature dependence in excellent agreement with the laboratory results for k1.
The magnetotail magnetic field
Authors: Beard David B.
Published: February 2008

The magnetic vector potential for points throughout the magnetosphere has been obtained by integrating over a model magnetotail current system. Parameterized functions of x, y, z have then been fit to the potential at these points. The curl of the resultant vector potential function matches the computed magnetic field closely. The final expression for the field presented in this work is a good representation of the field from an arbitrarily thick (or thin) current sheet which diminishes antisolarward from the earth and returns on the surface of the magnetosphere.
Scattering of terrestrial kilometric radiation at very high altitudes
Authors: Alexander J.K. , Kaiser M.L. , Rodriguez P.
Published: February 2008

On a number of occasions during the 3.5‐yr operating lifetime of Rae 2, we observed strong terrestrial kilometric radiation when the spacecraft was over the far side of the moon and when the low‐altitude terrestrial magnetosphere was completely obscured from view. If these deep lunar occultation events are used to infer radio source locations, then we find that the apparent source must sometimes be situated at geocentric distances of 10–40 RE or more. From an analysis of these events, we show that they are probably due to propagation effects rather than the actual generation of the emission at such large distances. The kilometric radiation can be generated near the earth at auroral latitudes and subsequently strongly scattered in the magnetosheath and nearby solar wind to produce the large apparent distances. The most likely scatterers are density inhomogeneities in the magnetosheath plasma and ion plasma waves in the magnetosheath and the upstream solar wind.
Frequency asymmetry in the upshifted and downshifted plasma lines induced by an HF wave at Arecibo
Authors: Muldrew D. B.
Published: February 2008

The Langmuir waves responsible for the HF‐wave‐induced plasma lines observed during ionospheric heating experiments at Arecibo are generated and propagate to the point of detection, in field‐aligned iontzation ducts. These Langmuir waves grow parametrically in the ducts at the height in the ionosphere at which the HF wave electric field is strongest. If it is assumed that there is a positive density gradient upward along the duct, then the observed ion acoustic frequency asymmetry between the upshifted and downshifted plasma lines can be explained. Agreement can be obtained between experimental and theoretical values for the frequency asymmetry and for the growth rates of the plasma line for a scale length along the magnetic field direction of about 40 km. A 40‐km‐scale length is less than that which would be expected during the day in the ambient plasma. However, it is probably not an unreasonable value for a duct under the influence of HF heating. A 40‐km scale length also leads to a height differential of about 55 m between the points at which the waves responsible for the upshifted and downshifted plasma lines are detected by the Arecibo radar. The model also implies that the intensity of the upshifted plasma line would be greater than that for the downshifted plasma line.
Nonlinear Landau damping in the ionosphere
Authors: Kiwamoto Yasuhito , Benson Robert F.
Published: February 2008

A model is presented to explain the nonresonant waves which give rise to the diffuse resonance observed near 3/2 fH by the Alouette and Isis topside sounders, where fH is the ambient electron cyclotron frequency. These waves are the result of plasma wave instabilities driven by anisotropic electron velocity distributions initiated by the high‐power (400 W) short‐duration (100 µs) sounder pulse. In a strictly linear analysis these instability‐driven waves will decay owing to Landau damping on a time scale much shorter than the observed time duration of the diffuse resonance. Calculations of the nonlinear wave‐particle coupling coefficients, however, indicate that the diffuse resonance wave can be maintained by nonlinear Landau damping of the sounder‐stimulated 2fH wave. This 2fH wave is always observed with a time duration longer than that of the diffuse resonance wave, a finding which indicates that it is available as an energy source for the proposed nonlinear mechanism. The time duration of the diffuse resonance is determined by the transit time of the instability‐generated and nonlinearly maintained diffuse resonance wave from the remote short‐lived hot region back to the antenna. The model is consistent with the Alouette/Isis observations and clearly demonstrates the existence of nonlinear wave‐particle interactions in the ionosphere. Such interactions have been observed in the laboratory and have long been speculated as being important in the energetics of the earth's magnetosphere and ionosphere.
Do field‐aligned auroral particle distributions imply acceleration by quasi‐static parallel electric fields?
Authors: Whalen B.A. , Daly P.W.
Published: February 2008

Charged particle observations from several high‐altitude sounding rocket flights launched from Churchill Research Range into auroral events when magnetic‐field‐aligned electron precipitation was observed are presented. Large field‐aligned enhancements were observed near the edges of regions of intense electron precipitation (auroral arcs), while only small or no enhancements were observed inside these regions. Field alignment was spread over a large energy range, at times from 0.5 to 60 keV, and showed no enhancement near the characteristic peak in the energy spectrum. These and other observations are compared with predictions of models involving acceleration by quasi‐static parallel electric fields, including the possibility of beam‐plasma instability effects, and are shown to be inconsistent. Acceleration by broadband electrostatic waves is suggested as a possible energization mechanism for field‐aligned particles.
Properties of spike events in auroral radio absorption
Authors: Hargreaves J.K. , Chivers H.J.A. , Nielsen E.
Published: February 2008

This paper considers the spatial extent and the spectral index of spike events in auroral radio absorption observed with riometers. On the evidence of narrow‐ and wide‐beam observations at more than one radio frequency and satellite particle data, it is shown that the typical spike event extends for only tens of kilometers in the ionosphere, compared with several hundred kilometers for auroral absorption in general. The spectral index is found to be close to 2.0, as for the general absorption, implying that the spike absorption is not produced at an unusually low altitude. It is concluded that for spike events the electron precipitation is very intense, is not unusually energetic, and is spatially restricted.
Two‐dimensional potential double layers and discrete auroras
Authors: Kan J.R. , Lee L.C. , Akasofu S.‐I.
Published: February 2008

This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc (of a width less than the gyrodiameter of the plasma sheet protons) and with the formation of the inverted V precipitation region (of a width much greater than the proton gyrodiameter). The former is embedded in the latter, and both are associated with field‐aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two‐dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter (corresponding to the visible auroral arc) we obtain solutions in which the field‐aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter (corresponding to the inverted V structure) we obtain solutions in which the potential drop is confined to a distance on the order of the Debye length. The electric field in our two‐dimensional double‐layer model is the zeroth‐order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first‐order field due to current instabilities or turbulences. The maximum potential in our two‐dimensional double‐layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.
Recombination of NO+ in the mid‐latitude trough and the polar ionization hole
Authors: Torr M.R. , Torr D.G.
Published: February 2008

The dissociative recombination of NO+ with electrons is further examined using a sample of Atmosphere Explorer data from the mid‐latitude ionization trough. The electron temperature for this data sample covered a range of 2500°K, thus allowing an accurate determination of the temperature dependence of the rate coefficient. The results confirm our earlier determinations which were made from a large data base, and the rate coefficient α is found to be inversely proportional to the electron temperature. We investigate the possibility of a neglected process in the NO+ chemistry which, if it were included, might result in a smaller temperature dependence of α. Such a source would require a direct dependence on electron temperature. A possible candidate is associative recombination of energetic N(²D) with O. The results confirm recent measurements which find that this process cannot be significant. The NO+ chemistry is a very sensitive indicator of chemical equilibrium conditions. Using measurements of the relevant parameters made in the polar ionization hole, we find that horizontal drifts do not appear to be significant in this region.
EUV observations of the equatorial aurora
Authors: Paresce Francesco
Published: February 2008

The extreme ultraviolet telescope on the Apollo‐Soyuz mission observed the equatorial aurora from an altitude of 220 km on four separate occasions in July 1975 in quiet geomagnetic conditions (Ap=6). In all cases signals well above ambient background in the 50 to 150‐Å, 114 to 150‐Å, 170 to 600‐Å, and 500 to 780‐Å bands were recorded as the spacecraft moved across the equator and the instrument viewed the atmosphere below it. The observed emissions are confined to a band roughly 10° to 20° in width, the peak emission occurring in the range ∼ −15° to +2° magnetic latitude. No enhancement in the 1350 to 1550‐Å channel was noted. The observed signals are interpreted as recombination radiation of energetic helium and, possibly, oxygen ions originating in the terrestrial ring current.
Experiments on nonlinear effects of strong ion cyclotron wave turbulence
Authors: Böhmer H. , Fornaca S.
Published: February 2008

Laboratory experiments on strong ion cyclotron wave turbulence are reported, which show features similar to those occurring in the polar magnetosphere above auroral arcs. Measurements of ion heating, the ion velocity distribution function, and the saturated wave amplitude which is shown to agree with resonance‐broadening theory, are reported. The appearance of suprathermal electrons and a phenomenon that can be described as electron flux disruption are also reported. Radial hot ion transport is observed, and the possibility of filamentation of the instability is discussed.
Plasma electron observations in the vicinity of magnetic holes
Authors: King J.H. , Ogilvie K.W. , Behannon K.W.
Published: February 2008

A search of Mariner 10 electron plasma and magnetic field measurements has revealed 14 examples of narrow, well‐defined interplanetary field depressions. Eleven of these events are associated with electron enhancements, five with significant magnetic field direction changes, and six without. Thus even though such magnetic depressions usually coincide with electron enhancements at energies of ∽100 eV, these enhancements cannot always be the result of magnetic reconnection. It seems likely that some events involve local acceleration, possibly the result of reconnection, while others may involve electrons injected onto the field line at a remote point.
Determination of the auroral O(¹S) production sources from coordinated rocket and satellite measurements
Authors: Sharp W.E. , Torr D.G.
Published: February 2008

Over the years there have been numerous theories advances to explain the production of the O(¹S) state in aurora as well as the fact that the variation with altitude of the emission from O(¹S) is the same as that from the N2+ first negative (1 NG) band system. In reality the source function for O(¹S) does not covary with N2+ (1 NG) but has a smaller scale height. The covariation is due to quenching of the source function by O(³P). In a flight of the Michigan Airglow Payload into a remarkably steady aurora the profile of 5577‐Å was obtained. The steadiness of the aurora allows the profile to be differentiated for direct comparison to theory. By using the simultaneous measurements of the secondary electron flux and ionospheric densities the electron‐atom impact and O2+ dissociative recombination source functions are found to be inadequate below 160 km. The remaining source can be adequately explained by N2(A³Σ) + O → O(¹S) + N2.
Interaction of interplanetary shock waves with the bow shock‐magnetopause system
Authors: Grib S.A. , Brunelli B.E. , Dryer M. , Shen W.‐W.
Published: February 2008

The collision of interplanetary shock waves with the bow shock wave‐magnetopause system is considered both in the gas‐dynamic and magnetohydrodynamic approximations. It is shown that the shock wave is reflected from the magnetopause as a rarefaction wave which, in turn, is reflected from the rearward side of the bow shock. This secondary rarefaction wave arrives at the magnetosphere after a time interval of 3–5 min after the interplanetary shock wave's arrival. The rarefaction wave decreases the flow pressure on the magnetosphere and causes the reverse (i.e., outward) motion of the magnetopause. With the help of an approximate solution of the differential equations the problem of rarefaction wave reflection from the magnetosphere is considered. The law of the subsolar point motion of the magnetosphere during the abrupt shock‐like perturbation is obtained. The experimental data confirm the theoretical results.
Laboratory studies of O++ reactions of ionospheric importance
Authors: Howorka F. , Viggiano A.A. , Albritton D.L. , Ferguson E.E. , Fehsenfeld F.C.
Published: February 2008

The rate constants for the reactions of O++ ions with several molecules and atoms have been measured. For reaction with N2 the rate constant was found to be (1.6±0.6) × 10−9 cm³ s−1, which agrees very well with an earlier laboratory study but which is considerably larger than the upper limit deduced from satellite observations.
Effect of displaced geomagnetic and geographic poles on high‐latitude plasma convection and ionospheric depletions
Authors: Sojka J.J. , Raitt W.J. , Schunk R.W.
Published: February 2008

We assumed that the ionospheric plasma at high latitudes has a tendency to corotate about the geographic pole and that magnetospheric convection is relative to the geomagnetic pole. With this assumption we calculated plasma drift patterns over the polar cap for a range of constant magnetospheric electric fields as well as for asymmetric electric fields with enhanced plasma flow on either the dawnside or the duskside of the polar cap. We calculated the drift patterns in both the geographic inertial and the geomagnetic inertial frame taking into account the displacement between the geographic and geomagnetic poles. We found that this displacement between the poles has an important effect on the plasma drift patterns. In particular, we found the following: (1) A time‐independent magnetospheric electric field produces a flow pattern in the magnetic inertial frame that does not vary with universal time. (2) This flow pattern becomes UT dependent in the geographic inertial frame because of the motion of the geomagnetic pole about the geographic pole. (3) The UT variation of the plasma flow pattern in the geographic inertial frame occurs on a time scale that is comparable to satellite orbital periods and that is much less than typical plasma convection flow times over the polar cap. (4) In the geographic inertial frame the main region of very low speed flow is not centered at 1800 LT but moves from about 1300 to 2300 LT during the course of a day. (5) In the geographic inertial frame a throatlike feature appears at certain universal times owing to the relative motion of the geographic and geomagnetic poles. This feature is not seen in the geomagnetic inertial frame and is not connected with our model of the magnetospheric electric field. These results and others described in the paper have important implications for both the interpretation of satellite data related to high‐latitude ionospheric dynamics and the formation of ionospheric troughs.
Evolution of ion cyclotron instability in the plasma convection system of the magnetosphere
Authors: Kaye Stanley M. , Kivelson Margaret G. , Southwood David J.
Published: February 2008

Liouville's theorem and approximate but extremely accurate expressions which reflect the invariance of µ and J can be used to determine analytically the evolution of an adiabatically convecting energetic particle distribution. Features of the convecting distribution which are reproduced by our model include positive pitch angle anisotropy, regions in velocity space in which ∂f/∂v⊥ >0, and the energy dependence of the degree of particle injection. The energy dependence of the injection yields upper and lower cutoffs to the distribution within the plasmasphere, and only an upper cutoff outside. We have used this approach to study the evolution of ion cyclotron waves in a convecting particle distribution, and have found that the upper cutoff to the distribution restricts the growth of these waves, both on and off the geomagnetic equator, to a narrow range of frequencies which grow only inside the plasmasphere. In addition, we found that the upper cutoff limits wave growth to a few hours on either side of dusk. We have examined the results for two source distributions, a power law and a Maxwellian, and we found that for distributions with equivalent mean energies the power law is unstable over a greater range of frequencies and radial distances than the Maxwellian.
On energy dependent modulation of the ULF ion flux oscillations observed at small pitch angles
Authors: Su S.‐Y. , Konradi A. , Fritz T. A.
Published: February 2008

The characteristics of the ultralow frequency oscillations in the ion fluxes observed at small pitch angles by the National Oceanic and Atmospheric Administration detector telescopes on board ATS 6 are again examined. The present report concentrates on the dramatic variation of the flux modulations detected in various energy channels during a single event which occurred on February 18, 1975. The wave amplitude is observed to be larger in a higher energy channel with energies from 100 keV to 150 keV and to decrease toward the lower energy channels. The lowest‐energy protons (25–33 keV) in general are seldom seen to be oscillating, but in this event they display a low‐amplitude oscillation which is 180° out of phase with the adjacent channel. Such energy dependent modulation of the flux oscillation is thought to be a consequence of the wave particle resonant interaction. However, the prediction of the bounce resonant interaction is not consistent with the observations of both the energy dependent variation of the flux amplitudes and a 180° change in the oscillation phase in the adjacent low‐energy channels that occurred in the February 18, 1975, event. Since the shape of the undisturbed particle distribution can also determine the variation of the particle perturbation at various energies, the first‐order particle distribution derived in a homogeneous plasma with a uniform magnetic field is examined without any specification of the wave mode. When the average particle distribution during the wave observation is used together with a parallel wave electric field that presumably causes the flux modulation at small pitch angles, a reasonable agreement is found between the variation of flux modulation derived from the slope of the average particle distribution and that from the experimental observation.
Equatorial hiss in the topside ionosphere
Authors: Morgan M. G.
Published: February 2008

Equatorial hiss seen in the topside ionosphere by the Dartmouth experiment on Ogo 6, using an electric dipole antenna, is described. The observations are consistent with wave normal positions intermediate between the geomagnetic field and the resonance cone. Unlike that seen by Gurnett (1968) on Injun 3, using a loop antenna, the hiss is seen over the full range of altitudes from perigee to apogee (400–1100 km). There is a significant local time dependence, with concentration in the dawn and dusk sectors. Simultaneous occurrence with spread F would appear to be no more than coincidental. The possibility of spacecraft effects has been discounted. A search by Hoffman (1977) for equatorial electron fluxes such as those found by Heikkila (1971) has been negative. Thus the underlying cause of the hiss remains unknown. The hiss occurs in two distinct forms, ‘spiky’ and ‘nonspiky.’ No parameter has been found which clearly determines which type will occur, although there is some local time dependence. The hiss is most intense at the lowest frequency observed (20 Hz), but the spiky form may extend above 15 kHz and occasionally even to 200 kHz. Although it is largely confined to the equatorial zone, two instances were found when this hiss extended to middle latitudes and two when it occurred in the polar cap. In one of the latter it coexisted with the usual auroral hiss. A reassessment of synoptic recordings made at Huancayo during the International Geophysical Year has reaffirmed the absence of hiss, as well as whistlers, on the ground at the magnetic dip equator.
Ion transport in the topside ionosphere at Arecibo
Authors: Vickrey James F. , Swartz Wesley E. , Farley Donald T.
Published: February 2008

Incoherent scatter measurements at Arecibo can determine the separate vector drift velocitites of O+ and H+ ions in regions where the two species are mixed. At times the field‐aligned drifts are actually in opposite directions in regions where the H+‐O and O+‐H charge exchange reactions are important. Here we present observations of the structure and dynamics of the topside ionosphere for 2 days, one in summer and one in winter. Measurements on August 15–16, 1976, showed upward daytime fluxes of both species totaling about 2–4 × 108 cm−2 s−1. During the night the net flux was generally downward, averaging about 1 × 108 cm−2 s−1. On January 15–16, 1977, the net upward daytime flux was smaller (∼1 × 108 cm−2 s−1), with the proton flux remaining slightly downward. During the night of January 15–16 the average downward flux was again about 1 × 108 cm−2 s−1. The total upward flux through 754 km integrated from 0800 to 1600 LT on August 15–16 was ∼8.6 × 1012 cm−2, which was roughly 60% of the estimated total protonospheric content at 1500 LT. The total downward nighttime‐integrated flux in the August observations was about 4 × 1012 cm−2. The August data thus suggest a net (24 hour) upward flux. The January data are less complete but suggest a possible net downward flux. If these 2 days can be taken as being typical, they imply some interhemispheric transport from summer to winter.
Bouncing ion clusters in the Earth's magnetosphere
Authors: Quinn J. M. , McIlwain C. E.
Published: February 2008

Mirroring clusters of ions have been observed by the UCSD auroral particles experiment on ATS 6. The dayside clusters are confined to the equatorial region, while the nightside events are low pitch angle and presumably associated with auroral processes. The bounce period of the clusters allows determination of the ion mass, and heavy ions have been observed.
Numerical simulation of global formation of auroral arcs
Authors: Miura Akira , Sato Tetsuya
Published: February 2008

Global simulation of auroral arcs is performed, based on the feedback theory of auroral arcs (Sato, 1978), for a three‐dimensionally coupled ionosphere‐magnetosphere system which includes two pairs of large‐scale Birkeland currents, large‐scale polar cap electric fields, and a day‐night asymmetry of the electron density distribution. Simulation results have shown that auroral arcs are formed in the dark sector of the auroral oval, more preferentially in the evening sector. They usually appear in multiples with a shape elongating in the east‐west direction, each arc being a couple of thousand kilometers in length and 10 to 40 km in width. A pair of small‐scale, upward and downward, Birkeland currents is associated with each arc, the density of which becomes 10 to 200 µA/m² at 110‐km height, and the intensity of the associated electrojet reaches 5 to 20 kA. Each arc is strongly polarized in the direction of the large‐scale north‐south current so that the electric field inside the arc is reduced considerably from its ambient value. What controls the formation of auroral arcs (growing speed, locations, arc width, etc.) is examined in detail. For example, the arc width becomes sharper, as the bounce time of the Alfvén wave decreases. The overall structure of auroras is largely dependent upon the large‐scale Birkeland current, the electric field, and the electron density distribution in the auroral oval.
Interaction between ELF‐VLF emissions and magnetic pulsations: Quasi‐periodic ELF‐VLF emissions associated with Pc 3–4 magnetic pulsations and their geomagnetic conjugacy
Authors: Sato Natsuo , Kokubun Susumu
Published: February 2008

The characteristics of quasi‐periodic (QP) ELF‐VLF emissions with periods of 10–150 s and their relationships to magnetic pulsations are studied by using data obtained from Syowa and Mizuho Stations in Antarctica and at Husafell in Iceland, which is located near the geomagnetic conjugate point of Syowa. From the coherency analysis between QP emissions and Pc 3–4 magnetic pulsations it is found that the coherency between the D component of magnetic pulsations and the intensity fluctuations of QP's is much higher than that between the H component of magnetic pulsations and QP's. It is also found that the propagation time of magnetic pulsations (HM waves) from the interaction region between magnetic pulsations and QP's in the magnetosphere to the ground is 20–30 s. These properties are observed at conjugate‐pair stations with good conjugacy. The results strongly suggest that QP emissions are modulated by compressional mode Pc 3–4 magnetic pulsations near the equatorial plane in the outer magnetosphere.
Occurrence and lifetimes of discrete auroras near midnight
Authors: Krukonis A.P. , Whalen J.A.
Published: February 2008

All‐sky camera photographs from flights of the Air Force Geophysics Laboratory (AFGL) airborne ionospheric observatory have been used to investigate discrete auroras in the midnight sector of the auroral oval. The photographs were taken at intervals of 1 min throughout flight durations of 5–10 hours near 69° (±4°) corrected geomagnetic latitude; the 12 flights totaling 93 hours provide ∼5600 frames. For each flight the photographs have been assembled into a montage format which permits perception of individual frames and also, in the aggregate, reveals individual events of auroral activation with measurable lifetimes. The discrete auroras observed in this way, when classified into four categories of activity, active (A), moderate (M), quiet (Q), and no discrete aurora visible (N), exhibit frequencies of occurrence of 22, 37, 24, and 17%, respectively. The lifetimes of auroras in categories A, M, and Q occur predominantly in a group which maximizes between 10 and 20 min with another lesser group which maximizes near 2 hours. Ten to 20 min is also characteristic of the duration of plasma flows observed in the plasma sheet, and thus it is suggested that discrete auroras may be associated with these flows.
The half‐wave rectifier response of the magnetosphere and antiparallel merging
Authors: Crooker N.U.
Published: February 2008

In some ways the magnetosphere behaves as if merging occurs only when the interplanetary magnetic field (IMF) is southward, and in other ways it behaves as if merging occurs for all IMF orientations. An explanation of this duality is offered in terms of a geometrical antiparallel merging model which predicts merging for all IMF orientations but magnetic flux transfer to the tail only for southward IMF. This is in contrast to previous models of component merging, where merging and flux transfer occur together for nearly all IMF orientations. That the problematic duality can be explained by the model is compelling evidence that antiparallel merging should be seriously considered in constructing theories of the merging process.
Correlation between λ4278‐Å Optical emissions and a Pc 1 Pearl Event observed at Siple Station, Antarctica
Authors: Mende S.B. , Arnoldy R.L. , Cahill L.J. , Doolittle J.H. , Armstrong W.C. , Fraser‐Smith A.C.
Published: February 2008

Detailed correlations were observed between the amplitude envelope of Pc 1 pulsations and zenith 4278 N2+ intensity at Siple Station, Antarctica, (L=4.2) on August 1, 1977. Conjugate Pc 1 data at Roberval show a similar amplitude envelope and an approximate antiphase relationship. The frequency‐time spectrogram of the ULF data shows none of the increasing dispersion associated with bouncing waves; i.e., the Pc 1 pulsation event is a periodic hydromagnetic emission. Analysis of the time delay between the particle‐induced optical emission and the waves (42 s) using the ion cyclotron resonance theory shows that the delay is consistent with the resonance of Pc 1 and MeV protons near the northern conjugate of the Siple field line. Alternately, resonance theory using He+ or O+ ions as the interacting hot particles does fit the data if the interaction region is off the equator. The intensity of the measured light is higher than that which can be expected from precipitation of ions of normally observed densities.
Latitudinal oscillations of plasma within the Io torus
Authors: Cummings W.D. , Dessler A.J. , Hill T.W.
Published: February 2008

We calculate the equilibrium latitude and the period of oscillations about this equilibrium latitude for plasma in a centrifugally dominated tilted dipole magnetic field representing Jupiter's inner magnetosphere. For a hot plasma the equilibrium latitude is the magnetic equator; for a cold plasma it is the centrifugal equator; for a warm plasma it is somewhere in between. In the small‐tilt‐angle approximation, the latitudinal oscillation period of a cold particle in the centrifugal potential field is P0=PJ/31/2, where PJ is the rotation period of Jupiter. For a warm plasma the magnetic mirror force causes the bounce period to be decreased slightly. These results are applicable to the plasma injected by Io to form the torus of plasma surrounding Jupiter. We adopt an illustrative model in which atoms are sputtered from the Jupiter‐facing hemisphere of Io and escape Io's gravity to be subsequently ionized some distance from Io. Ionization generally does not take place at the equilibrium latitude, and the resulting latitudinal oscillations provide an explanation for the irregularities in electron concentration within the torus, as reported by the radio astronomy experiment aboard Voyager 1.
On the convective properties of magnetospheric Bernstein Waves
Authors: Barbosa D.D.
Published: February 2008

Recent observations of electrostatic electron cyclotron harmonic waves have been organized very well within the framework of magnetospheric Bernstein waves. A number of effects that result simply from convective properties of these waves are examined. The roles of wave trapping in plasma density depressions and partial trappings near the magnetic equator are considered. A number of future wave observations are suggested that can improve our understanding of this magnetospheric wave phenomenon.
Radar observations of cleft dynamics
Authors: Foster J.C. , Stiles G.S. , Doupnik J R.
Published: February 2008

The ionospheric F region is perturbed by low‐energy particle precipitation in the cleft. On January 28–29, 1977, UT an ionospheric density enhancement associated with the cleft was monitored continuously by the Chatanika incoherent scatter radar during a 6‐hour period including an onset and recovery of global substorm activity. A strongly southward interplanetary magnetic field (IMF) brought the cleft into the field of view of the radar (invariant latitudes less than 75°). The observed motions of the cleft included a rapid equatorward excursion (∼4° Λ/h) to 70°Λ before occurrence of a major substorm intensification, continued location at low magnetic latitude during substorm expansion, and a poleward retreat to ∼73.5°Λ during substorm recovery in response to a northward turning of the IMF. The latitudinal width of the cleft density enhancement varied from less than 1° during the presubstorm equatorward motion to ∼4° after substorm recovery. F region densities immediately poleward of the cleft were reduced by a factor of 10 from their quiet time value.
Electron collisional effects on lower hybrid drift instabilities in the ionosphere
Authors: Sperling J.L. , Goldman S.R.
Published: February 2008

Electron collisional as well as ion collisional effects have a significant effect on the stability analysis of lower hybrid drift modes in the ionosphere. Electron collisions stabilize the modes and cause a density gradient threshold for the instability not previously calculated. This threshold results in restrictions on the interpretation of 155‐ and 415‐MHz backscatter results as being due to lower hybrid drift instabilities and suggests measurements to determine whether the instability can account for the backscatter.
6300‐Å airglow meridional intensity gradients
Authors: Herrero F.A. , Meriwether J.W.
Published: February 2008

Airglow meridional intensity gradients (MIG) that moved from east to west with the antisolar meridian have been observed during times of considerable magnetic activity. The magnitude of the gradient is around 0.1 R/km or more. We believe the MIG phenomenon develops as a result of a velocity gradient that is produced by the meeting of opposing meridional neutral winds. The northern wind system arises from the auroral heating at high latitude that produces meridional winds penetrating to low latitudes in the summer hemisphere. The southern wind system is produced by the equatorial midnight pressure bulge that is formed by the thermal tides of the lower atmosphere combined with the in situ forcing by EUV radiation absorption in the daytime. In a magnetic storm the merging of the two wind systems produces a sharp front over a latitudinal width of several hundred kilometers. North of the front the ionosphere is elevated, and the airglow is weak. South of the front the ionosphere is depressed, and the airglow is enhanced with a surface brightness of the order of 100 R. The conceptual model that evolved from these observations accounts for the overall behavior of the MIG as well as the normal midnight collapse. A simple calculation shows that the MIG can be used to estimate the meridional velocity gradient as well as the magnitude of the winds in the midnight pressure bulge.
The solar spectral irradiance 1200–2550 Å at solar maximum
Authors: Mount George H. , Rottman Gary J. , Timothy J. Gethyn
Published: February 2008

Full‐disk solar spectral irradiances at solar maximum were obtained in the spectral range 1200–2550 Å at a spectral resolution of approximately 1 Å from rocket observations above White Sands, New Mexico, on June 5, 1979. Comparison with measurements made near solar minimum indicates approximately a factor of 2.5 increase in the irradiance at 1200 Å, a 20% increase near 1800 Å, and no increase within our measurement errors (±15%) above 2100 Å. Irradiances in the range 1800–2100 Å are in excellent agreement with previous measurements, but those in the 2100‐ to 2550‐Å range are significantly lower. The intensities of strong emission lines at wavelengths below 1850 Å are also reported.
Microstructure of the interplanetary magnetic field near 4 and 5 AU
Authors: Parker G.D.
Published: February 2008

Seventy‐two days of vector magnetic field measurements from Pioneer 10 and 11 are analyzed for information about magnetic field fluctuations in the quiet solar wind near 4 and 5 AU. Calculated as functions of frequency over the range 4 × 10−5 to 9 × 10−3 Hz, directional properties of magnetic field fluctuations are presented and are discussed with reference to theoretical predictions for MHD plane waves. The distributions of maximum variance directions computed from ≃500 spectral matrices for each spacecraft are peaked along the normal to the plane of the minimum variance direction and the mean magnetic field. This orientation is expected for a planar, small‐amplitude Alfvén wave with a minimum variance direction close to the wave vector. Noting also that magnetic fluctuations tend to conserve field magnitude, as is required for Alfvénic fluctuations, we infer that single small‐amplitude Alfvén waves are occasionally present in the temporal and frequency bands analyzed. However, statistics of the relative spatial orientations of the mean field and the minimum and maximum variance directions permit that waves with wave vectors not well approximated by the minimum variance direction, Alfvén wave ensembles, finite‐amplitude waves, and nonplanar fluctuations may also be present. Assuming that the minimum variance direction approximates the wave vector when a small‐amplitude wave is present, we note that (1) among those data in which the field fluctuations behave in accord with theoretical predictions for single, planar, small‐amplitude MHD waves, observations suggest the predominance of the Alfvén mode over the fast and slow modes and (2) there is a general lack of observational support for theoretical models of outward propagating plane Alfvén waves of solar origin.
A test of two theories for the low‐frequency cutoffs of nonthermal continuum radiation
Authors: Shaw Robert R. , Gurnett Donald A.
Published: February 2008

Two theories have been proposed that differently identify the frequencies of the low‐frequency cutoffs of nonthermal continuum radiation. The first of these theories states that the two low‐frequency cutoffs occur at the local plasma frequency and R=0 cutoff frequency, with the continuum radiation propagating in the ordinary mode between the cutoffs and a mixture of ordinary and extraordinary mode above the upper cutoff. The second theory suggests that the two low‐frequency cutoffs occur at the local L=0 cutoff frequency and plasma frequency, with the continuum radiation being generated by Cerenkov emission in the Z mode between the local plasma frequency and upper hybrid resonance frequency. Mode coupling at the local plasma frequency was suggested to generate continuum radiation in the ordinary mode which freely propagates to remote regions of the magnetosphere. In this paper, several examples of continuum radiation observed in the outer magnetosphere by Imp 6 and ISEE 1 are analyzed in detail, and it is shown that these cutoff frequencies occur at the local plasma frequency and R=0 cutoff frequency. In addition, no substantive evidence is found in the outer magnetosphere for a component of continuum radiation propagating in the Z mode.
Upper limit on the electric field along a magnetic O line
Authors: Vasyliunas Vytenis M.
Published: February 2008

The electric field along a magnetic neutral line of the O type can be estimated by the method previously applied by Alfvén to neutral sheets, with the same result: the line integral of the electric field along the neutral line, multiplied by the elementary charge, is at most equal to twice the magnetic energy per particle. The same upper limit, within a numerical factor of order unity, is obtained from a hydromagnetic calculation where the plasma flow toward the O line is balanced by outflow within the narrow region where the hydromagnetic coupling between the flow and the electric field breaks down. The same upper limit can also be derived from nonsteady models with a nonzero curl of the electric field (no E × B inflow) or with a nonzero divergence of the mass flux density (no outflow), as well as from a model that involves anomalous resistivity when the current density exceeds a threshold value. The derived upper limit implies that the maximum energy that is gained by a particle that drifts along the O line is not significantly greater than the typical energy of a plasma sheet particle; hence simple acceleration by electric fields along magnetic O lines cannot account for the energetic component of the charged particle population in the magnetotail.
Coordinated study of equatorial scintillation and in situ and radar observations of nighttime F region irregularities
Authors: Basu Santimay , McClure J.P. , Basu Sunanda , Hanson W.B. , Aarons J.
Published: February 2008

A coordinated set of Atmospheric Explorer E (AE‐E) satellite in situ, VHF radar backscatter, and scintillation measurements performed during 1977 over a common ionospheric volume is used to study the relationship between the plasma depletions or bubbles, the extended 3‐m irregularity structures known as plumes and bursts of scintillation activity or patches in the nighttime equatorial F region. It is shown that in the early evening hours saturated VHF and UHF scintillation and 3‐dB fluctuations (propagation path in the east‐west plane where the effect of anisotropy is least) at 1.54 GHz are obtained in association with strong 50‐MHz radar backscatter, implying near simultaneous (∼min) excitation of large scale (∼km to 100 m) and 3‐m irregularities. In this early developed phase of irregularities, the AE‐E in situ measurements detect strong fluctuations of ion concentration with very sharp spatial gradients. The power spectra of these fluctuations in the scale length range of 10 km‐100 m conform to a power law variation with one‐dimensional spectral index ∼1.5. The postmidnight period, on the other hand, is found to be characterized by an absence of radar backscatter and presence of only marginal GHz scintillation activity. However, strong VHF scintillations and somewhat weaker UHF activity is found to persist. The AE‐E measurements indicate that during the late phase, the spatial gradients of ion concentration become shallower and the spectral intensity of the irregularities <500 m decreases by about two orders of magnitude as compared with that recorded during the onset phase. The irregularity spectrum conforms to a quasi‐gaussian description with correlation lengths of the order of a kilometer, which corresponds to the Fresnel dimensions of VHF scintillation observations. The implications of the observed spatial structures and the level of ambient concentration on the generation of 3‐m irregularities and scintillation modeling are discussed.
On the modifications of the whistler mode instability in the magnetosphere in the presence of parallel electric field by cold plasma injection
Authors: Misra K.D. , Singh B.D.
Published: February 2008

Dispersion relation for the whistler mode waves in an anisotropic warm magnetoplasma in the presence of a parallel electric field has been derived. The modifications in the whistler mode instability produced by cold plasma injection to an infinite uniform anisotropic plasma (A <1) in the presence of a parallel electric field have been studied. This study has been performed with the plasma parameters similar to those observed in the equatorial magnetosphere at 6.6 RE. The electric field is found to have pronounced effect for small values of nc/nw and extends the range of instability in k space toward higher wavelengths. The cold plasma injection increases the range of instability in k space toward lower wave lengths. The effects of electric field seem to be insignificant for large values of nc/nw.
Measurements of potential of a cylindrical monopole antenna on a rotating spacecraft
Authors: Kellogg Paul J.
Published: February 2008

Measurements of antenna potential on the Helios 1 spacecraft are presented and discussed. Normally, the antenna potential varies by about 6 V between positions normal to the sun line and pointing at the sun. The behavior of the potential indicates that Ly α and shorter wavelengths determine the potential; longer wavelengths only create photoelectrons which cannot escape. As expected, there is usually a voltage spike when the antenna is shadowed. We do not measure this voltage. Sometimes this spike is not present, which is puzzling, but which allows us to estimate the potential variations on an antenna which is not shadowed. The spectrum is then roughly (Fourier coefficient) 2 V × (2fo/f)² where fo is the spacecraft spin frequency, and f is an even harmonic of the spin frequency.
Hα and Hβ emission cross sections for low‐energy H and H+ collisions with N2 and O2
Authors: Van Zyl B. , Neumann H.
Published: February 2008

Absolute cross sections for the emission of Balmer alpha and Balmer beta radiations from H and H+ collisions with N2 and O2 are reported. The H and H+ projectile energies ranged between about 50 eV and 2.5 keV. For projectile energies above 300 eV, the contributions to these radiations from decay of the long‐lived 3s and 4s excited states of hydrogen were resolved. The emission cross sections for the case of H atom impact were found to be substantially larger than those for H+ impact. The results are discussed within the context of their application to analysis of the hydrogen aurora.