bluuebunny/crossref_metadata_2025 huggingface dataset:
Substorm introduction of ≤ 1‐keV magnetospheric ions into the inner plasmasphere
Authors: Newell Patrick T. , Meng C.‐I.
Published: February 2008

Observations from the ion detectors on Defense Meteorological Satellite Program satellites F6 and F7 have revealed an interesting phenomenon, namely the existence of isolated and latitudinally narrow regions of ion precipitation up to ∼1 keV well within the plasmasphere. Using the almost continuous coverage afforded by the 101‐min polar orbits of these satellites, we are able to document in detail the process whereby such isolated precipitation patterns are established. Prolonged intense substorm activity is observed to introduce plasma of sub‐keV energy from the earthward edge of the plasma sheet to deep within the plasmasphere (at least L = 2.4). The plasma introduction occurs over a confined magnetic local time (MLT) range extending from somewhere postmidnight to about 0830 MLT. Because of their much more rapid pitch‐angle scattering into the loss cone, the energetic electrons are lost within one or two hours, whereas the ions can persist for at least a day. After being injected into low L values, the ions begin to corotate, thereby forming latitudinally narrow and well‐isolated structures of ion precipitation far below the instantaneous auroral oval. The total number of ions injected over a several‐hour span can be very roughly estimated to be ∼1025. Because of certain similarities of the injection process to observations by Lennartsson and Sharp (1982) and to the magnetic storm time observations of Shelley et al. (1972) and Strangeway and Johnson (1984), it is likely that the low‐latitude precipitating ions are O+.
Sporadic narrowband radio emissions from Uranus
Authors: Kurth W. S. , Gurnett D. A. , Scarf F. L.
Published: February 2008

Among several different types of radio emissions discovered at Uranus during the Voyager 2 encounter in January 1986 is a very sporadic, bursty signal which consists of very narrow bands lying in the frequency range from about 3 to 10 kHz. The bursty emission was virtually undetectable from the dayside portion of the Voyager 2 trajectory but was observed out to beyond 300 RU during the outbound trajectory through the predawn sector. While the narrowband tones making up this emission are reminiscent of escaping continuum radiation observed near earth, Jupiter, and Saturn, the Uranian signals show large amplitude variations on time scales of 1 s, suggesting a very different type of generation mechanism.
Polar cap F layer patches: Structure and dynamics
Authors: Weber E. J. , Klobuchar J. A. , Buchau J. , Carlson H. C. , Livingston R. C. , de la Beaujardiere O. , McCready M. , Moore J. G. , Bishop G. J.
Published: February 2008

Coordinated measurements of F region plasma patches were conducted on February 3/4, 1984, from Thule and Sondrestrom, Greenland. Optical, ionosonde, amplitude scintillation, total electron content (TEC), and incoherent scatter radar measurements were combined to reveal several new aspects of the structure and transport of these localized regions of enhanced F region ionization. For the first time these patches were directly tracked flowing in the antisunward direction over distances of 3000 km from the center of the polar cap to the poleward edge of the auroral oval. Quantitative measurements of TEC show increases of 10–15 TEC units within the patches, above a background polar cap value of 5 TEC units. Amplitude scintillation measurements show the presence of ionospheric irregularities through the entire patch, with a weak indication of stronger scintillation on the trailing (or E × B unstable) edge.
Correlated electron and X ray measurements of quiet time electron precipitation: A comparative study of Bremsstrahlung production and transport in the atmosphere
Authors: Gaines E. E. , Imhof W. L. , Francis W. E. , Walt M. , Rosenberg T. J.
Published: February 2008

Five cases of X ray observations from balloons coordinated with measurements of precipitating electrons were obtained during passes of the polar‐orbiting satellite P78‐1 near Siple, Antarctica (L ∼ 4.1), the launch point of the balloons. The observations, made during a geomagnetically quiet period in late December 1980 to early January 1981, showed small enhancements of the X ray fluxes (E > 25 keV) and moderate trapped electron fluxes (E > 68 keV) with pitch angle distributions extending into the edge of the loss cone sufficient to produce the ≲0.5 dB of cosmic noise absorption recorded by the Siple 30‐MHz riometer. Bremsstrahlung production and transport in the atmosphere were calculated using the measured electron fluxes, energy spectra, and pitch angle distributions for the source. The X ray fluxes and spectra calculated for the balloon altitudes were in good agreement with those measured from the balloons when the total energy deposition from electrons, E > 10 keV, exceeded 2×10−3 erg/cm² s. The observed electron fluxes show that a significant continuous electron precipitation occurs at the western edge of the South Atlantic magnetic anomaly even at times of low geomagnetic activity.
Spectral characteristics of interchange turbulence
Authors: Hassam A. B. , Hall W. , Huba J. D. , Keskinen M. J.
Published: February 2008

The spectral characteristics of turbulence associated with the two‐dimensional magnetized Rayleigh‐Taylor instability in the presence of a background neutral gas are studied. Particular attention is paid to comparing the electrostatic potential spectra obtained in the ion‐neutral collision‐dominated case with the spectra from the ion inertia‐dominated case. The time‐averaged one‐dimensional spectra along kx and ky for the collisional case are found to be Px ∝ kx−3.7±0.3 and Py ∝ ky−4.6±0.3, respectively, where x is the direction of the density gradient and gravity. Correspondingly, the spectra for the inertial case are given by Px ∝ kx−3.8±0.2 and Py ∝ ky−3.8±0.2. Thus the potential spectrum in the collisional case shows a marked anisotropy in contrast to that of the inertial case, which is isotropic and exhibits Kolmogorov scaling. The anisotropy in the collisional case is attributed to the frictional nature of the turbulence and the suppression of inertial overshoots. Application of these results to ionospheric turbulence is discussed.
Periodic amplitude variations in Jovian continuum radiation
Authors: Kurth W. S. , Gurnett D. A. , Scarf F. L.
Published: February 2008

An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both 5 and 10 hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by the position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clocklike modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude‐solar wind alignment to the amplitude of the continuum radiation implies that the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.
Linearly polarized magnetic fluctuations at comet Giacobini‐Zinner
Authors: Gary S. Peter , Winske Dan
Published: February 2008

The fully electromagnetic linear Vlasov dispersion equation for instabilities in a homogeneous, magnetized plasma is solved. Parameters appropriate to conditions observed during the ICE encounter with comet Giacobini‐Zinner are used to study the polarization of electromagnetic instabilities driven by the relative streaming of two ion components. If the ion/ion relative drift is near the Alfvén speed, the associated long‐wavelength modes may be approximately linearly polarized at relatively small angles of propagation with respect to the magnetic field. The relatively inhomogeneous plasma background of the comet may impose such oblique propagation, so that this result provides an alternate explanation to the observations of linearly polarized waves near the comet.
A closed nonlinear model of wave‐particle interactions in the outer trapping and morningside auroral regions
Authors: Davidson G. T. , Chiu Y. T.
Published: February 2008

A closed system of three nonlinear coupled equations is presented, phenomenologically describing the source and loss mechanisms for waves and particles in the outer trapping regions. The principal variable parameters are total particle flux, diffusion rate, and wave growth rate. The equations combine elements suggested in earlier work to represent distinct aspects of the coupled interactions. The equations include effects of particle drift and wave propagation transverse to the magnetic field lines. The behavior of the system is examined in the linearized approximation of small amplitude perturbations, to define the parameter space regions where oscillatory or growing solutions appear. It is shown that auroral electron precipitation pulsations at a frequency of ∼0.1 Hz can occur in a limited region where oscillatory solutions are found that grow at a rate comparable with their frequency. A stationary, nongrowing solution is found with a characteristic frequency of about 3 Hz which might appear as a modulation of the particle precipitation flux. Other growing solutions are found with characteristic periods so long that they are probably not important in the outer trapping regions which are disturbed by substorms at intervals of hours to days. Spatial scales are not set by the coupled equations but must be determined by external influences.
Transverse deflection and dissipation of small plasma beams and clouds in magnetized media
Authors: Cheng Andrew F.
Published: February 2008

Propagation of a quasi‐neutral plasma beam or cloud across a magnetic field is considered for the case where the transverse dimension of the beam or cloud is sufficiently small compared to ion gyroradii. This situation commonly arises for active experiments in near‐earth space. Two mechanisms are presented for transverse deflection of a beam or cloud in the ‐ v0 × B0 direction where v0 is the velocity relative to the ambient medium. In the first, asymmetric escape of ions from an electrically polarized beam or cloud causes transverse deflection by means of a rocket effect. The transverse deflection distance is estimated to be a few times the initial transverse dimension of the beam or cloud. Dissipation occurs within a few times the thermal ion transverse crossing time. In the second mechanism, asymmetric charging results from localized accumulation of incident ions from the ambient medium. This excess positive charge distorts electric equipotentials and drives electron Hall currents that maintain an asymmetric compressed magnetic field region. The asymmetry of the magnetic stress contributes to transverse deflection with the same sign as the rocket effect. The asymmetric magnetic field also focuses incident ions to yield the localized charge accumulation. These ideas are qualitatively consistent with observations of the Active Magnetospheric Particle Tracer Explorers artificial comet releases.
Substorm effects on spectral structures of Pc 1 waves at synchronous orbit
Authors: Ishida Juro , Kokubun Susumu , McPherron Robert L.
Published: February 2008

Pc 1 waves observed at synchronous orbit are studied using magnetic field data from the flux gate magnetometer on board ATS 6. The data were obtained in the interval of June to September in 1975 when the satellite was located at the geographic equator at 36° east longitude near the geomagnetic equator (geomagnetic latitude ∼−3°). It is found that spectral structures of Pc 1 waves are significantly affected by variations of the magnitude of the local magnetic field near the geomagnetic equator. Spectral bands of Pc 1 waves are usually confined to the frequency range below the helium gyrofrequency (fHe+) when Pc 1 waves appear on the afternoon side accompanied by a decrease in the ambient magnetic field during substorms. In the daytime, Pc 1 waves often occur in association with an increase in the ambient magnetic field caused by a magnetospheric compression. In such cases, Pc 1 waves tend to appear in the frequency range above fHe+. The sense of polarization is left‐handed for most waves as was noted in previous studies. It is suggested from the linear growth rate analysis that the absence of Pc 1 waves in the frequency range above the helium gyrofrequency during substorms is mainly due to an increase in the energetic proton flux.
Observation of the O I ultraviolet intercombination emissions in the terrestrial dayglow
Authors: Bowers C. W. , Feldman P. D. , Tennyson P. D. , Kane M.
Published: February 2008

Spectroscopic observations have been made of the terrestrial ultraviolet dayglow (850–1850 Å) using newly developed instrumentation in a sounding rocket payload. The atmospheric conditions and viewing geometry were such as to suppress nitrogen emissions relative to those from atomic oxygen. This permitted the identification and measurement of the weak O I 1173‐Å (3s′ ³D0 ‐ 2p4 ¹D) intercombination multiplet and the 1641‐Å (3s ³S0 ‐ 2p4 ¹D) line as well as the strong 989‐Å and 1304‐Å emissions. The 1173‐Å emission rate increased at lower altitudes, while the 989‐Å emission, from the same upper level, decreased at lower altitudes. This behavior is consistent with the radiative entrapment model of Meier (1982) and the laboratory value of the 1173‐Å/989‐Å branching ratio of 1.5 × 10−4 (Morrison, 1985). The 1641‐Å/1304‐Å emission ratio is also consistent with a radiative entrapment model and a branching ratio near 5.0 × 10−6. Lack of detection of the 1484‐Å (3s′ ³D10 ‐ 2p4 ¹S0) intercombination line allows an upper limit to be placed on the 1484‐Å branching ratio, confirming that emission in this line is less significant in depleting the 3s′ ³D0 term than is 1173‐Å emission.
An upper limit on the sizes of shepherding satellites at Saturn's ring G
Authors: Van Allen James A.
Published: February 2008

An accurate analytical theory of the absorption of energetic magnetospheric particles by an inert satellite is developed for the case in which the radius b of the satellite is much less than the equatorial gyroradius rg of the particles and in which rg is in turn much less than the radius r of the satellite's orbit. In previous interpretations of Pioneer 11 observations an estimate of the lifetime against absorption of energetic protons (E > 80 MeV) at Saturn's ring G has been made. This lifetime is used in the framework of the absorption theory to establish an upper limit on the sizes of shepherding satellites associated with the ring. The resulting upper limit, ignoring the absorption of the optically observed particulate matter, is ∑i = 1N bi2 = 6 km2 (uncertain by a factor of 2) for an assemblage of N satellites of various radii bi. It is noted that ring G lies outside the Roche limit. No shepherding satellites at ring G were detected optically by Voyagers 1 and 2, though the lower limit of sensitivity of this technique was b ≈ 10 km for an albedo exceeding 0.1 and the searches were not comprehensive in longitudinal coverage.
Low‐altitude ISIS 1 observations of auroral radio emissions and their significance to the cyclotron maser instability
Authors: Benson Robert F. , Wong H. K.
Published: February 2008

Low‐altitude ISIS 1 observations are presented which support the cyclotron maser instability as the generation mechanism of most, but not all, auroral radio emissions. The observations confirm the ability of the mechanism to generate different wave modes and harmonics as the ratio of the plasma frequency to gyrofrequency ƒN/ƒH increases depending on the form of the energetic electron distribution function. The present observations correspond to conditions where ƒN/ƒH is always larger than 0.2 and is typically ∼1.0. The observations and instability growth rate calculations indicate that second harmonic radiation in the extraordinary and the Z modes is directly generated at low altitudes. By far the most common signals observed near ISIS 1 perigee, however, are in the fundamental Z and whistler modes. The observations and calculations in the case of the Z mode suggest that the pertinent process involves a maser that does not saturate, i.e., that group velocity effects are important. The whistler mode is the most intense signal observed at low altitudes. Since the cyclotron maser generated whistler mode waves have peak growth rates for downward field‐aligned propagation, they should be able to penetrate the ionosphere. This process may provide the explanation of occasional reports, dating back to the International Geophysical Year time period, of ground level detection of radio noise (∼100 kHz) associated with the aurora.
Doppler radio observations of 3‐meter irregularities in the polar cap E region
Authors: Sofko G. J. , Koehler J. A. , Haldoupis C. , McKibben M. J. , McNamara A. G.
Published: February 2008

The first VHF Doppler radar system to measure echoes from ionospheric plasma instabilities in the polar cap was set up in 1982 in the Northwest Territories. High‐resolution spectra were achieved through the use of CW transmissions. A scattering volume over Sachs Harbour (geomagnetic latitude ∼77°) was defined by the intersection of the narrow antenna beams from the two widely spaced transmitter arrays (at Inuvik and Cambridge Bay) and the common receiver array (at Fort Franklin). The two bistatic radio links so formed had bisectors which differed in azimuth by 60°, and which were at mean magnetic aspect angles of ∼9° and 13° from perpendicularity with the earth's field. In this report, Doppler spectra are presented for a moderately disturbed period on July 7, when the scattering region was in the polar cap. In spite of this scattering location, the Doppler spectra show all the usual spectral types (I, II, and III) typical of the auroral zone. Although type III (ion cyclotron) echoes might have been anticipated at these large aspect angles (the k∥/k⊥ ratio could be as large as 0.25) in association with strong polar cap field‐aligned currents, the presence of the type I and II echoes is not explicable on the basis of present two‐stream and gradient drift instability theories. Whereas the spectral types in the polar cap and auroral zone show substantial similarities, the temporal morphology of the polar cap echoes is quite different from that of auroral zone echoes.
Dust charges, cloud potential, and instabilities in a dust cloud embedded in a plasma
Authors: Havnes O. , Goertz C. K. , Morfill G. E. , Grün E. , Ip W.
Published: February 2008

We consider a finite‐sized dust cloud embedded in an infinite plasma. The dust cloud will generally be at a different potential from that of the ambient plasma, and particles which enter the cloud are accelerated or decelerated. We treat the two limiting cases: in case A, particles are not thermalized within the cloud, and in case B, the plasma is thermalized in the cloud interior to form a Maxwellian plasma with densities given by Boltzmann relations as functions of the local cloud potential. Qualitatively, both cases lead to similar results: In a tenuous cloud the dust cloud potential is low while the dust potentials are close to those of single isolated dust particles. In dense dust clouds the cloud potential approaches a maximum while the dust potentials decreases to zero with increasing dust density. However, the exact values of the potentials can differ considerably for the two cases for the same set of other cloud and ambient plasma parameters. Also, for case A we may have several sets of solutions for the two potentials, all giving charge balance in the cloud and current balance to the dust. We find, however, that case A may not easily be formed for all ranges of dust densities because the charging of dust can take a longer time than the time for scattering processes to lead to internal Boltzmann distributions for both plasma particle types. On the other hand, we expect semistable cases intermediate between case A and case B with multiple solutions to be found. Instabilities through the creation of double layers and transitions between two solutions may occur and lead to events in dust clouds. We suggest that such events may possibly occur in cometary comas and in planetary rings and lead to changes in the dust cloud structure. Conditions relevant for multiple solutions will probably be rather short‐lived, at most a few times 10 days, before scattering collisions with diffusion in velocity space turn the plasma velocity distribution into that of case B. In this case there is only one solution for the potentials for each set of cloud and plasma parameters.
Three‐dimensional simulation of an active magnetospheric release
Authors: Brecht Stephen H. , Thomas V. A.
Published: February 2008

The early time dynamics of an AMPTE release in the solar wind is studied using a three‐dimensional particle simulation. The results of the simulation explain the dynamics of the solar wind ions, release ions, and the current system that the release sets up. It is found that, within the limits of charge quasi‐neutrality and the recognition of differential reference frames caused by the inertia of the release ions, the cross‐field motion of the ions can be understood. It is also found in these simulations that the convection of the magnetic field around the release is asymmetric and that the solar wind ion interaction is also asymmetric. From this feature and the correlation between the three‐dimensional and two‐dimensional simulations it is seen that the AMPTE releases produce physics that is somewhat different from that of a planet or a comet.
Field‐aligned currents associated with substorms in the vicinity of synchronous orbit: 1. The July 5, 1979, substorm observed by SCATHA, GOES 3, and GOES 2
Authors: Nagai T. , Singer H. J. , Ledley B. G. , Olsen R. C.
Published: February 2008

Magnetic field topology and field‐aligned current signatures in the vicinity of synchronous orbit are examined for a substorm on July 5, 1979. Changes from taillike to dipolar field geometry propagate earthward near the midnight meridian during the substorm. The major field‐aligned currents producing a negative D perturbation at and around synchronous orbit are downward currents flowing into the auroral ionosphere on L shells greater than the synchronous spacecraft L shell. Although these currents are located initially on higher L shells, they shift toward the lower L shells as the change from taillike to dipolar fields propagates earthward. There may exist upward field‐aligned currents located on smaller L shells in the limited longitudinal region near the meridian where mid‐latitude D perturbations change their sign.
E and F region study of the evening sector auroral oval: A Chatanika/Dynamics Explorer 2/NOAA 6 comparison
Authors: Senior C. , Sharber J. R. , de la Beaujardière O. , Heelis R. A. , Evans D. S. , Winningham J. D. , Sugiura M. , Hoegy W. R.
Published: February 2008

Simultaneous data obtained with the Chatanika incoherent scatter radar and the Dynamics Explorer 2 (DE 2) and NOAA 6 satellites are used to relate the locations of the precipitating particles, field‐aligned currents, and E and F region ionization structures in the evening‐sector auroral oval. The auroral E layer observed by the radar extends about 2° equatorward of the electron precipitation region, and its equatorward edge coincides with the equatorward edges of the region 2 field‐aligned current and intense convection region (E ≃ 50 mV/m). It is shown that precipitating protons are responsible for part of the E region ionization within the electron precipitation region as well as south of it. E region density profiles calculated from ion spectra measured by the DE 2 and NOAA 6 satellites are in fairly good agreement with the Chatanika data. In the F region, a channel of enhanced ionization density, elongated along the east‐west direction and having a width of about 100 km, marks the poleward edge of the main trough. It is colocated with the equatorward boundary of the electron precipitation from the central plasma sheet. Although enhanced fluxes of soft electrons are observed at this boundary, the energy input to the ionospheric electron gas, calculated from the radar data, shows that this ionization channel is not locally produced by this soft precipitation, but that it is rather a convected feature. In fact, both the trough and the ionization channel are located in a region where the plasma flows sunward at high speed, but the flux tubes associated with these two features have different convective time histories. Keeping in mind that several processes operate together in the F region, our data set is consistent with the following trough and ionization channel formation mechanisms. (1) The mid‐latitude trough, located equatorward of the electron precipitation region, is mainly the result of transport and enhanced recombination due to large electric fields. Flux tubes on the low‐latitude edge of the trough have most probably corotated eastward before flowing sunward at higher latitudes where magnetospheric convection predominates. The trough thus forms by recombination during the long time the flux tubes stagnate in the region where the flow reverses. (2) Flux tubes associated with the ionization channel have drifted antisunward in the polar cap before drifting sunward in the auroral zone. Its formation results from the distortion of polar cap F region ionization structures, due to the incompressibility of the flow.
Detailed spectral structure of magnetospheric electron bursts precipitated by lightning
Authors: Goldberg R. A. , Curtis S. A. , Barcus J. R.
Published: February 2008

We have analyzed the temporal structure of electron fluxes precipitated by lightning that was measured at night over Wallops Island, Virginia, during August 1984. Given the high time resolution of our data for two independent lightning‐induced precipitation bursts, we are able to identify a component of the precipitating electrons almost certainly due to equatorial wave‐particle interactions involving equatorial electron cyclotron resonance (EECR) with whistlers which produce pitch angle scattering. These bursts also contain other precipitating electrons, possibly due to off‐equatorial pitch angle scattering by the electron cyclotron resonance (ECR) process or, more likely in our opinion, an off‐equatorial wave‐particle interaction leading to field‐aligned electron acceleration. In particular, we have shown that the precipitated electron fluxes of equatorial origin are characterized by a very steep spectral power exponent of about −20 above 100 keV. In contrast, the other non‐EECR fluxes are much harder, with a spectral power exponent of about −2 between 40 and 400 keV. As a consequence, the energy deposition of the other electron fluxes may be equal to or possibly exceed that of the equatorial interaction fluxes. We conclude that study of lightning‐produced electron fluxes from the perspective of pitch angle scattering alone may neglect other processes that significantly contribute to total energy transfer into the lower atmosphere. Furthermore, we find that the EECR wave‐particle interaction produces precipitation fluxes that are well described simply by the kinematics involving the wave and electron transit times to and from the magnetic equator.
On the interpretation of different flow vectors of different ion species in the magnetospheric boundary layer
Authors: Lundin R. , Stasiewicz K. , Hultqvist B.
Published: February 2008

Recent measurements of the ion composition in the magnetospheric boundary layer indicate that the boundary layer may contain clouds of magnetosheath plasma which are gradually becoming mixed with the magnetospheric plasma. A significant difference between flow vectors of different ion species (≈50–100 km/s) implies that an ideal MHD equation E + V × B = 0, does not fully describe the macroscopic plasma flow inside such inhomogeneities. An analysis based on the first‐order drift theory indicates that gradients of the partial ion pressure and of the magnetic field could induce differential ion drifts comparable in magnitude to the electric drift velocity. We discuss some implications of these results on the physics of solar wind‐magnetosphere interactions.
Latitudinal gradient of energetic particles in the outer heliosphere during 1985–1986
Authors: Decker R. B. , Krimigis S. M. , Venkatesan D.
Published: February 2008

We report a measurement of a sustained latitudinal gradient of 70‐MeV galactic cosmic ray protons using data from the interplanetary probes Voyager 1 and 2 and the earth‐orbiting satellite IMP 8 during a 1‐year period from mid‐1985 to mid‐1986. Starting in early 1985 the intensity of cosmic rays at Voyager 2 began increasing faster than that at Voyager 1. By mid‐1985 the intensity at Voyager 2 (helioradius 17 AU, heliolatitude ∼0°) exceeded and remained higher than that at Voyager 1 (helioradius 24 AU, heliolatitude ∼26°) for at least 14 solar rotations. Using the Voyager 2‐IMP 8 data to correct for the radial gradient, we determine an average latitudinal gradient during this period of (−0.53 ± 0.10)% deg−1 or (−0.38 ± 0.11)% deg−1 (i.e., intensity decreasing northward of the solar equatorial plane), assuming either a constant radial gradient or one that decreased at an average rate of −0.025% AU−1 AU−1, as was the case during 1984, respectively. In addition, we present Voyager data at very low (≳30 keV) ion energies which are associated with acceleration at corotating shocks. These ions also exhibit a latitudinal gradient (∼ −3% deg−1), with lower intensities at higher latitudes, and serve to highlight changes that occurred in the interplanetary medium in early 1985.
Pioneer Venus and near‐Earth observations of interplanetary shocks
Authors: Mihalov J. D. , Russell C. T. , Knudsen W. C. , Scarf F. L.
Published: February 2008

Twenty‐three transient interplanetary shocks observed near earth during 1978–1982, and mostly reported in the literature, have also been identified at the Pioneer Venus Orbiter spacecraft. There seems to be a fairly consistent trend for lower shock speeds, farther from the sun. Shock normals obtained using the Pioneer Venus data correspond well with published values from near earth. By referring to the portion of the Pioneer Venus plasma data used here from locations at longitudes within 37° of earth, it is found that shocks are weaker at earth, compared with closer to the sun.
Stability of the polar wind
Authors: Barakat A. R. , Schunk R. W.
Published: February 2008

The classical polar wind is an ambipolar outflow of thermal plasma from the terrestrial ionosphere at high latitudes. At altitudes above about 3000 km, the H+ flow becomes supersonic and collisionless, and the H+ velocity distribution becomes non‐Maxwellian. The non‐Maxwellian features include a temperature anisotropy, with the parallel H+ temperature greater than the perpendicular temperature (Ti∥ > Ti⊥), and an asymmetry, with an elongated tail in the upward direction. These distortions from a Maxwellian increase as the H+ gas escapes in the diverging geomagnetic field, and at 10 earth radii the parallel‐to‐perpendicular temperature ratio is about 50 and the elongated tail is sufficiently long to move the drift velocity point off the peak of the distribution function. The stability of these highly non‐Maxwellian H+ velocity distributions was studied with regard to the excitation of electrostatic waves and the plasma was found to be remarkably stable for a wide range of electron temperatures (0.1 ≤ Te/Ti∥ ≤ 10). This indicates that the various macroscopic formulations of the classical polar wind are valid. The stability of a perpendicularly heated polar wind was also studied, assuming bulk perpendicular heating of H+ in the cusp, followed by the subsequent convection of the heated plasma into the polar cap. Two regions of instability were found. For high electron temperatures (Te/Ti∥≳5), the plasma is unstable for Ti⊥/Ti∥ > 4, while for lower electron temperatures the plasma is unstable only for Ti⊥/Ti∥ > 30.
Wavelength dependence of electrostatic plasma wave propagation in the auroral E region
Authors: Moorcroft D. R.
Published: February 2008

The propagation of electrostatic plasma wave packets in the auroral E region has been studied using kinetic theory and is found to confirm previous results obtained using fluid theory, which showed that the wave packet travels at high speed nearly parallel to the magnetic field, except possibly for a small height interval in which it is reflected upward. The principal effect of decreasing the plasma wavelength is to increase the group velocity and to sharpen any reversal in propagation. Effects on the propagation of enhanced electron collision frequencies are also examined. It is shown that under some circumstances it might be possible to observe these wave packet motions experimentally. By comparing propagation speeds with estimates of wave packet lifetimes, it is found that linear growth rates can probably not be used to estimate amplitudes of meter scale waves.
Latitudinal variations of nighttime enhancements in total electron content
Authors: Balan N. , Rao P. B.
Published: February 2008

Latitudinal variations of the various characteristics of nighttime anomalous enhancements in total electron content (TEC) are presented by considering TEC data from the ATS series of satellites for a 2‐month period from a number of stations in the northern hemisphere extending from 2° to 63° dip latitude. The latitudinal variations of the various TEC enhancement characteristics are found to be strikingly similar, and they reveal a pattern of cyclic variation with two distinct minima, one at 30°N and the other at 60°N (dip latitude). The TEC enhancements show a strong positive correlation with geomagnetic activity at middle and high latitudes and no significant correlation at low latitudes. The observed pattern of the latitudinal vaiations of the TEC enhancements is discussed in the light of the potential source mechanisms.
Three‐dimensional structure of the coronal magnetic field and the solar wind speed distribution projected on the photosphere in 1974
Authors: Hakamada Kazuyuki
Published: February 2008

Since the solar wind and coronal holes were relatively steady in 1974, the average distribution of the solar wind speed on the source surface and that of the line‐of‐sight component of the photospheric magnetic fields (B1) can be constructed, with fair accuracy, by the superposed epoch analysis. The three‐dimensional structure of the coronal magnetic fields is then computed from this average map of B1 based on the potential model. The average distribution of the solar wind speed on the source surface, obtained from interplanetary scintillation observations, is then projected onto the photosphere along the open field lines in the corona. The high‐speed regions thus projected are compared with the He I (1083 nm) coronal holes and are found to have a similar geometry. The results are also suggestive that the solar wind does not blow out uniformly from the vicinity of a coronal hole and that the speed is higher at the east side in that region than at the west side. The slower speed regions on the source surface have a sinusoidal structure in heliographic latitude‐longitude coordinates and are similar to the brightness distribution of the K corona and the structure of closed field line regions projected onto the photosphere.
Simultaneous observation of monochromatic and variable period geomagnetic pulsations
Authors: McDiarmid D. R. , Nielsen E.
Published: February 2008

On February 4, 1983, following a storm sudden commencement, a monochromatic and a variable period pulsation were simultaneously observed by the Scandinavian Twin Auroral Radar Experiment (STARE) and Sweden and Britain Radar Experiment (SABRE) radar systems. Both pulsations differed from previously analyzed examples of their class. The phase of the monochromatic pulsation increased linearly with latitude rather than decreased. Its amplitude remained relatively constant over the latitude interval of linear phase change. The variable period pulsation experienced a change of orientation of its essentially linear polarization diagram in association with a discontinuity of its period. The variable period pulsation was thus manifest in both the toroidal and poloidal components. The results are discussed in terms of recent developments in theoretical pulsation modeling.
Empirical high‐latitude electric field models
Authors: Heppner J. P. , Maynard N. C.
Published: February 2008

Electric field measurements from the Dynamics Explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn‐dusk OGO 6 measurements (J. P. Heppner, 1977). The analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. Paralleling the previous analysis, the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the Y component of the interplanetary magnetic field. The objective, which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns, is met by deriving one pattern (model BC) for the northern hemisphere with a +Y interplanetary magnetic field (IMF) and southern hemisphere with a −Y IMF and two patterns (models A and DE) for the northern hemisphere with a − Y IMF and southern hemisphere with a +Y IMF. The most significant large‐scale revisions of the OGO 6 models are (1) on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the IMF Y component, (2) on the nightside where a westward flow region poleward from the Harang discontinuity appears under model BC conditions, and (3) magnetic local time shifts in the positions of the convection cell foci. The modeling above was followed by a detailed examination of cases where the IMF Z component was clearly positive (northward). Neglecting the seasonally dependent cases where irregularities obscure pattern recognition, the observations range from reasonable agreement with the new BC and DE models, to cases where different characteristics appeared primarily at dayside high latitudes. The analysis of these differences for strong +Bz conditions, using passes through different MLT zones, led to finding that the deviations from both the BC and DE models could be modeled by extending the evening cell foci toward, and beyond, noon with a deformation that roughly resembles a rotational twist of the extended evening cell. The morning cell accommodation to the model BC deformation produces a narrow tongue of eastward convection near 75° invariant latitude on the dayside. The model DE deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 MLT sector. In both cases, the deformations of the two‐cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern. Thus the nightside dilemmas that plague three‐ and four‐cell models designed to explain sunward convection in polar regions under +Bz conditions do not appear.
A unified theory of anomalous resistivity and Joule heating effects in the presence of ionospheric E region irregularities
Authors: St.‐Maurice J. ‐P.
Published: February 2008

This paper describes how large‐amplitude plasma waves in the E region can simultaneously change the conductivity of the plasma and heat the electrons, and how these two processes are actually related to one another and to overall energy balance requirements. We show how to relate the wave‐enhanced transport properties to the turbulent state of the plasma, and, ultimately, to broadband electric field and density fluctuation levels. We point out that in theories for which enhanced diffusion effects are used to saturate the unstable waves, care should be taken not to have wave amplitudes that exceed the limits provided by full turbulence estimates; we use an earlier theory proposed by Ichimaru to obtain such an estimate. We also stress that anomalous diffusion is, at most, two‐dimensional, and that the momentum equation is therefore not affected by anomalous diffusion in the magnetic field direction. On the other hand, we show that what little wave energy there is in the magnetic field direction could be important for wave heating purposes. We show how to combine, in general, the parallel wave heating rate and heating produced by the increase in perpendicular conductivity and compare, in that light, various calculations done to date on this subject.
On transient electric fields observed in chemical release experiments by rockets
Authors: Marklund G. , Brenning N. , Holmgren G. , Haerendel G.
Published: February 2008

As a follow‐up to the successful chemical release experiment Trigger in 1977, the Trigger Optimized Repetition rocket was launched from Esrange on October 24, 1984. As in the Trigger experiment, a large‐amplitude electric field pulse of 200 mV/m was detected shortly after the explosion. The central part of the pulse was found to be clearly correlated with an intense layer of swept up ambient particles behind a propagating shock front. The field was directed toward the center of the expanding ionized cloud, which is indicative of a polarization electric field source. Expressions for this radial polarization field and the much weaker azimuthal‐induced electric field are derived from a simple cylindrical model for the field and the expanding neutral cloud. Time profiles of the radial electric field are shown to be in good agreement with observations.
Initial results from the operation of two argon ion generators in the auroral ionosphere
Authors: Erlandson R. E. , Cahill L. J. , Pollock C. J. , Arnoldy R. L. , Scales W. A. , Kintner P. M.
Published: February 2008

Two argon ion generators were operated during a sounding rocket flight from Sondre Stromfjord, Greenland, on February 10, 1985. The ion generators were flown to investigate ion beam dynamics and beam effects on the ionosphere. The other major purpose of the flight was investigation of auroral electrodynamics as the rocket passed over auroral arcs. One generator emitted an ion beam perpendicular to the magnetic field and the other a beam parallel to the field. The ion generators were on a subpayload that was separated from the main payload early in the flight. Ion detectors, an electric field meter and wave receivers were carried on the main payload to provide diagnostic measurements during the ion beam operations. Seventeen operations of the generators were observed over a 480‐s interval before the rocket reentered the atmosphere. There was evidence of heating of the ionosphere around the subpayload during each ion beam emission. Ions of energy 100 to 200 eV, the ion beam energy range, were observed at the main payload during the first seven operations of each generator, with payload separation distances up to 800 m, reaching the main payload from directions appropriate for beam ions. In addition, there were also ions reaching the detectors during beam operations, with higher and lower energies and different directions than those expected from the beam ions. Waves were observed during most of the first seven operations of each beam. Hydrogen, helium and oxygen cyclotron harmonics were observed in some of the perpendicular‐beam operations. Waves were weak or absent during the first and third parallel‐beam operations at separation distances near 80 and 320 m. In general the waves generated by the parallel beam were weaker than those generated by the perpendicular beam. The parallel beam waves were line emissions, some at approximate multiples of the hydrogen cyclotron frequency, between 5 and 7 kHz, near the lower hybrid frequency. During the fourth perpendicular gun operation, with separation distance 380 m and near peak altitude, absorption lines, separated by the hydrogen cyclotron frequency, were observed in the auroral hiss band.
Effects of thermospheric motions on the polar wind: A time‐dependent numerical study
Authors: Gombosi T. I. , Killeen T. L.
Published: February 2008

This paper presents the results of a numerical study investigating the effects of low‐altitude short‐duration plasma heating episodes (such as horizontal frictional heating) on transient heavy ion outflows from the polar ionosphere using a time‐dependent model. In a previous set of calculations, where the effects of high‐altitude transient heat sources were investigated, the low‐altitude neutral atmosphere (z < 800 km) acted as a very efficient heat sink, absorbing most of the energy conducted to this region and thus preventing large differences between the ion and neutral temperatures. One purpose of the present study was to investigate whether realistic, specified low‐altitude frictional heating rates, based on published experimental data, can result in elevated ion temperatures and lift a part of the heavy ion population over the gravitational barrier before the extra energy is lost to the neutral atmosphere. In our model calculations the specified heating generated an upflowing O+ disturbance (with a normalized peak flux of ∼108 cm−2 s−1) moving upward along the open magnetic field line with a velocity of ∼2 km/s. The spatial extent of the disturbance was approximately equal to the disturbance velocity times the duration of the heat source. The model results provide a possible mechanism to explain recent European Incoherent Scatter observations of high‐latitude O+ upwellings.
On the height variation of the equatorial F region vertical plasma drifts
Authors: Pingree J. E. , Fejer B. G.
Published: February 2008

We have used improved incoherent scatter radar measurements at the Jicamarca Radio Observatory to study the height variation of the F region vertical plasma drift velocity (driven by the zonal electric field) during moderately quiet conditions. Preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km, but with considerable day‐to‐day variations in the value of the slope. On the average, the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours. Simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere. The time dependence of the Jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at F region heights over Arecibo.
Do flux transfer events cause long‐period micropulsations in the dayside magnetosphere?
Authors: Gillis E. J. , Rijnbeek R. , Kling R. , Speiser T. W. , Fritz T. A.
Published: February 2008

Russell and Elphic (1979) suggested the possibility that flux transfer events (FTEs) generate long‐period micropulsations in the outer, dayside magnetosphere. We examine the reasons for this hypothesis and present results of two pulsation surveys designed to test it. In the first survey, observations of micropulsations by GOES 2 are compared with ISEE 3 and IMP observations of interplanetary magnetic field (IMF) direction; since FTEs are highly correlated with southward IMF, we looked for a similar correlation between pulsations and southward IMF. In the second survey a catalogue of ISEE 1 and 2 magnetopause crossings is compared with magnetometer readings from GOES 2 and 3 to determine whether Pc 4 and Pc 5 pulsations are more likely to occur after FTEs have taken place. Our results indicate that there is a correlation between FTEs and transversely polarized Pc 4 pulsations with periods between 60 and 120 s but not between FTEs and Pc pulsations with periods greater than 120 s. This suggests that the generating (or driving) frequency associated with FTEs lies between 60 and 120 s.