bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic field line reconnection experiments 2. Plasma parameters
Authors: Gekelman W. , Stenzel R. L.
Published: February 2008

Detailed measurements of density, temperature, and potentials of a laboratory plasma undergoing magnetic field line reconnection are reported. The plasma column (n ≃1012 cm−3, Te ≃5 eV, B0 ≃20 G) is subject to a time‐varying transverse magnetic field with X‐type neutral point (B⊥max ≃100 G, Δt ≃100 µs). Time‐ and space‐resolved probe measurements show rapid electron heating giving rise to further ionization up to neutral burnout. Density and temperature exhibit strong spatial nonuniformities in all directions as well as significant temporal fluctuations. The plasma potential increases in the direction of the induced electric field, indicating the presence of axial space charge separation. Electrostatic fields also develop perpendicular to the applied fields and can exceed the latter in magnitude. The knowledge of the basic plasma parameters is essential in explaining the observed magnetic field configurations, plasma flows, and resistivity, which are described separately.
Temperature gradient effects on the stability of magnetospheric plasmas
Authors: Migliuolo S. , Patel V. L.
Published: February 2008

The linear stability of magnetospheric plasmas to low‐frequency electromagnetic perturbations is investigated, for the case where there exist equilibrium density and temperature gradients, as well as temperature anisotropies. The effects of the temperature gradients on the behavior of drift‐compressional modes are given special attention. The effects of a gradient in the equilibrium magnetic field, required for hydrostatic equilibrium, are included to lowest nonvanishing order. The model is valid for moderate β magnetospheric plasmas. A two‐component (hot and cold) multispecies plasma is considered, and a kinetic linear dispersion relation is derived, for arbitrary Larmor radius ordering. The destabilizing effects of the gradient in the perpendicular temperature (orientations are measured with respect to the unperturbed magnetic field) are discussed.
Cluster and channel effect phase bunchings by whistler waves in the nonuniform geomagnetic field
Authors: Matsumoto Hiroshi , Omura Yoshiharu
Published: February 2008

A test particle simulation has been carried out on the characteristic behavior of resonant electrons in a monochromatic whistler wave propagating along the nonuniform geomagnetic field. The geomagnetic field is approximated by a parabolic field around the equator. In addition to a phase bunching of untrapped electrons due to the inhomogeneity of the magnetic field, found by Vomvoridis zand Denavit (1979), another type of phase bunching of initially untrapped and later trapped electrons is found to take place in the parabolically nonuniform magnetic field. The former is called channel effect phase bunching, and the latter is called cluster effect phase bunching. The difference of the cluster effect phase bunching from the channel effect bunching as well as from the conventional phase bunching in a uniform magnetic field is discussed. The relative importance of these phase bunchings in forming resonant currents in the generation process of VLF‐triggered emissions is also discussed.
Occurrence distributions of VLF hiss and saucer emissions over the southern polar region
Authors: Yoshino Takeo , Ozaki Takayuki , Fukunishi Hiroshi
Published: February 2008

Occurrence regions of VLF hiss and saucer emissions over the southern polar region have been studied statistically from Isis 1 and 2 VLF data which were received at Syowa station (L=6.0), Antarctica. It is found that saucers occur both in the dayside and in the nightside just as VLF hiss emissions, and spatial distribution of the saucer emission region is quite similar to the distribution of downward field‐aligned currents given by Iijima and Potemra [1976]. It is also found that saucers are observed at an altitude range of 500–4000 km in winter, while they are observed only at altitudes higher than 3000 km in summer. These results suggest that saucers are excited by upflowing ionospheric electron fluxes and that the growth rate depends on the electron density of the background.
Spectral characteristics of precipitating electrons associated with visible aurora in the premidnight oval during periods of substorm activity
Authors: Tanskanen P. J. , Hardy D. A. , Burke W. J.
Published: February 2008

Three late evening passes of the DMSP/F2 satellite over the northern auroral zone have been studied using simultaneous visible emissions and measurements from a zenith‐looking, 16‐channel, electron spectrometer. All three orbits occurred during periods of substorm activity; the second and third passes were consecutive. The auroral oval is conveniently divided into three latitudinal segments: a most poleward bright arc; a region of structured, inverted‐V precipitation; and the diffuse auroral region. The most poleward bright arc is characterized by directional fluxes occasionally in excess of 1010 (cm² s sr)−1 carried by two populations with temperatures of ∼100 eV and ∼600 eV. These fluxes, which apparently continue well into substorm recovery, are not easily reconciled with a simple model for pressure balance in the magnetotail. Presumably they reflect not well understood dynamic processes in the distant magnetotail. In the second regions precipitating electrons had average energies in excess of 1 keV and had spectral shapes that were either quasi‐thermal or monoenergetic peaks superimposed on a secondary‐electron background. Beams of low‐energy (<1 keV) electrons frequently found in this region are consistent with localized field‐aligned potential drops flickering on and off at altitudes not much greater than that of the satellite. In the diffuse auroral region the average energy of electrons from the central plasma sheet ranged up to 5 keV. In isolated patches within the diffuse auroral region and near its equatorward boundary, electrons with energies ≤100 eV and fluxes exceeding 1010 (cm² sr keV)−1 were found in all three cases. We interpret these electrons as part of an originally cold plasma that became detached from the plasmasphere due to time‐varying convective electric fields. The electrons were subsequently heated by the Landau damping of electromagnetic ion‐cyclotron waves generated by hot, gradient‐curvature drifting plasma sheet protons. Features of the diffuse auroral region during substorms are found to persist on time scales of the 100 min between passes.
The kinetic equation of the field‐aligned particle flux distribution function
Authors: Tamao Tsutomu
Published: February 2008

Starting from the continuity equation of the guiding center distribution function, we have obtained the kinetic equation which describes the field‐aligned particle flux distribution per unit magnetic intensity, V∥f/B, for adiabatic processes in a magnetized plasma under the constraint of the magnetic moment conservation. In addition to the total change along a particle dynamical orbit, the derived equation contains a term due to the convergence or divergence of the particle drift motions which depend on a sign of charges. In the bounce‐averaged configuration, effects of this additional term on the localized accumulation of the trapped particle population are examined in association with the stationary, large‐scale convection in the magnetosphere. It is shown that the main contribution to the local charge accumulation in the field‐aligned current region comes from the curvature drift motion due to the perturbed magnetic field relating to the field‐aligned current. Another utilization of the kinetic equation is demonstrated in obtaining an expression of the differential energy spectrum of precipitating particles from a magnetically trapped region.
Equatorial disc and dawn‐dusk currents in the frontside magnetosphere of Jupiter: Pioneer 10 and 11
Authors: Jones D. E. , Thomas B. T. , Melville J. G.
Published: February 2008

Observations by Pioneer 10 and 11 show that the strongest azimuthal fields are observed near the dawn meridian (Pioneer 10) while the weakest occur near the noon meridian (Pioneer 11), suggesting a strong local time dependence for the corresponding radial current system. Modeling studies of the radial component of the field observed by both spacecraft suggest that the corresponding azimuthal current system must also be a strong function of local time. Both the azimuthal and the radial field component signatures exhibit sharp dips and reversals, requiring thin radial and azimuthal current systems. There is also a suggestion that these two current systems either are interacting or are due, at least in part, to the same current. We suggest that a plausible current model consists of the superposition of a thin, local time independent, azimuthal current system plus the equatorial portion of a taillike current system that extends into the dayside magnetosphere.
The lower hybrid density drift instability with cold plasma
Authors: Gary S. Peter , Ashour‐Abdalla Maha
Published: February 2008

The linear Vlasov dispersion relation for the lower hybrid density drift instability is studied in a four component (hot electrons and protons, cold electrons and protons) plasma. The introduction of a cold ion population monotonically reduces the maximum growth rate of the instability. Reduction of Tc/Th, the ratio of temperatures of the cold and hot plasmas, reduces both the real frequency and the growth rate of the instability. Near Tc/Th=10−2 a higher frequency branch of this instability emerges and for fixed nc/nh exhibits an increasing maximum growth rate as Tc/Th decreases further. The ratio Tc/Th for the ions is the crucial parameter and deserves detailed magnetospheric studies.
E and F region electric fields over dip equator
Authors: Prakash S. , Muralikrishna P.
Published: February 2008

The horizontal east‐west drift velocity VE of ionisation irregularities in E region, and the vertical drift velocity VF of electrons in F region over Jicamarca (dip latitude ≃1°) are used to estimate the average diurnal variation of the east‐west components of the electric fields in these two regions. The F region field is estimated from VF by using the relationship derived earlier by Woodman. The E region field is estimated from VE by using a relationship different from the one used earlier by Balsley and Woodman and is derived by using more realistic electrojet and conductivity models. The E region electric field thus obtained is found to be weaker at least by a factor of 3 than that estimated by Balsley and Woodman. A comparative study shows that the east‐west electric field in the F region is, most of the time, stronger than that in the E region, and also that the ratio of the E region field to the F region field systematically increases from forenoon to afternoon hours, and from pre‐midnight to post‐midnight hours.
Auroral electron acceleration and atmospheric interactions: (1) Rocket‐borne observations and (2) Scattering calculations
Authors: Pulliam D. M. , Anderson H. R. , Stamnes K. , Rees M. H.
Published: February 2008

A Terrier‐Malemute rocket was launched from Poker Flat, Alaska, on March 9, 1978, over a stable premidnight auroral arc. It carried instrumentation to measure electric and magnetic fields and particle fluxes. The electron intensity in 13 fixed energy intervals from 0.04 to 40 keV was measured over 180° of pitch angle every half spin at ∽2.5 rps. The intensity was generally isotropic over the upper hemisphere with the total energy flux and the spectral hardness greater in the visible arc than elsewhere. Field alignment of low‐energy electrons occurred at the edges of the arc, with higher energies involved toward the center, and in two bursts within the arc. The interaction of the measured downward intensity with the neutral atmosphere (below apogee altitude ∼320 km) was modeled by transport theory, including inelastic and multiple‐elastic scattering of electrons by neutrals. The upcoming intensity calculated there‐from agrees with the measured upcoming intensity so that no collective effects, including parallel electric fields, need be postulated. The downward intensity at high energy within the discrete arc was fit to a thermal plasma accelerated (at some high altitude) through a parallel potential drop V0 (Evans, 1974). Electrons with energy E ≤|eV0| ⩽6 keV are produced, in this model, by scattering on neutrals and specular reflection from the potential barrier above. The calculated downward intensity of electrons with E ⩽|eV0| fits the measured intensity well enough, in the arc, that no other interactions need be postulated. We infer that in this type of aurora the interaction of electrons with the atmosphere and ionosphere below several hundreds of kilometers is satisfactorily described by collisional scattering.
Periodic fluctuations in the Earth‐ionosphere waveguide
Authors: Bernhardt Paul A. , Price Kent M. , Crary James H.
Published: February 2008

VLF phase and amplitude measurements made in 1967 at Byrd Station, Antarctica, using 18.6‐kHz transmissions from NLK, Washington, have been analyzed for lunar‐induced and hebdomadal variations. The VLF propagation path was 14,250 km in length and nearly constant in longitude. The lunar‐induced variations are found to be ±18° in phase and ±0.26 dB in amplitude and are explained by height changes in the D region of the ionosphere. The hebdomadal variation in VLF amplitude shows a 0.46‐dB increase during the Sunday daylight hours, relative to the Monday‐Saturday average, and is ascribed to man‐made changes in the D region.
Numerical simulations on ion acoustic double layers
Authors: Sato T. , Okuda H.
Published: February 2008

A comprehensive numerical study of ion acoustic double layers has been performed for both periodic and nonperiodic systems by means of one‐dimensional particle simulations. For a nonperiodic system, an external battery and a resistance are used to model the magnetospheric convection potential and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated potential buildup across the system increase with the system length. The potential jump ΔϕD across a single double layer is approximately eΔϕD/Te ≈ 1 and the distance between two consecutive double layers is typically 1000 Debye length, where e and Te are the electronic charge and temperature. There is little interaction among double layers, and each double layer behaves almost independently of the others. The maximum increase of plasma energy through the enhanced resistance associated with double layer formation is found to be about 15% of the initial plasma energy for the parameters used in the simulations. The resistivity takes its maximum value at the instance when the double layers are just formed and then drops to almost zero afterwards, indicating the presence of a superconducting phase due to the formation of a quasistable Bernstein‐Green‐Kruskal type equilibrium. The equilibrium is, however, unstable with respect to the emission of ion acoustic solitons, and the double layers eventually decay as the solitons carry the energy away from the double layers propagating through a plasma toward the downstream direction.
Plasma irregularities in the tropical F‐region detected by OI 7774 Å and 6300 Å nightglow measurements
Authors: Sahai Y. , Bittencourt J. A. , Teixeira N. R. , Takahashi H.
Published: February 2008

Simultaneous measurements of the permitted OI 7774 Å and the forbidden OI 6300 Å nightglow emissions were carried out at Cachoeira Paulista (geographic 22.7°S, 45.0°W), Brazil, during the period of April 1978 to March 1979. Both the emissions were observed with tilting filter‐type photometers. During spread‐F conditions, on several nights, both the emissions showed simultaneous short‐time large intensity depletions, indicating the presence of large‐scale irregularities in the F‐region. Data for the period September‐October 1978 are presented and discussed. The depletions observed are possibly associated with the passage of F‐region holes or bubbles drifting across the sky.
5–50‐m wavelength plasma instabilities in the equatorial electrojet 2. Two‐stream conditions
Authors: Hanuise C. , Crochet M.
Published: February 2008

New multifrequency measurements with a HF radar in the equatorial electrojet have extended the range of wavelengths investigated during high drift velocity conditions to 50 m. It is shown that the so‐called type 1 spectra can be detected at all wavelengths. Their phase velocity has a value given by the threshold for instability in the full dispersion equation and is constant with elevation angle and time when corrected for neutral wind effect. Spectral width increases with wave number, following a law Kn, n ∼0.7, but is constant with elevation angle. Ratio of spectral width to mean Doppler shift is of the order of unity at the lowest wave number and decrease as K−n, n ∼0.6. These results are compared to the existing numerical simulations and theoretical works.
On a theory of temporal fluctuations in the electrostatic potential structures associated with auroral arcs
Authors: Silevitch M. B.
Published: February 2008

This paper deals with the description of a mechanism that could cause the generation of large‐amplitude temporal oscillations in the structure of the electron acceleration region of an auroral arc. The fluctuations are triggered by the fact that a self‐consistent steady state can disrupt as the mobile plasma electrons rearrange themselves into a more ‘stable’ configuration on a time scale characterized by the electron transit time across the acceleration region. During this rearrangement the ions remain essentially frozen. A cyclic behavior results, since the ions eventually respond, thus driving the system back toward its original steady state. The period of these oscillations is approximately the ion transit time. We obtain a description of those characteristics of the steady state necessary for the generation of fluctuations. As a specific example, we consider the recent one‐dimensional auroral double layer model of Kan and Lee showing that it exhibits a negative dynamic resistance. This propoerty is necessary for the production of periodic (∼10 Hz) modulations in the precipitating electron flux. This result suggests explanations for two kinds of events observed to be correlated with auroral arcs. These are the quasi‐periodic flickering aurora and the existence of low‐frequency modulations in the envelope of electrostatic hydrogen cyclotron waves.
The relationship of field‐aligned currents to electrostatic ion cyclotron waves
Authors: Cattell Cynthia
Published: February 2008

Two sources of free energy for driving ion cyclotron waves have been observed on the S3‐3 satellite: field‐aligned currents and ion beams. Since the waves are destabilized by the thermal electron drift and not the current, before correlating observations of field‐aligned currents with ion cyclotron waves, it is first necessary to determine that the current is primarily carried by thermal electrons. Comparisons of the current carried by energetic particles with the current measured by the magnetometer during several events shows that this is sometimes the case. Statistical studies indicate that the field‐aligned current density is correlated with the spectral density during ion cyclotron events. The combination of the results of this report and those of Kintner et al. (1979) is consistent with the hypothesis that the observed ion cyclotron waves are driven by a combination of ion beams and electron drift. However, the available data set does not unambiguously identify the free energy source.
Upstream waves and particles: An overview of ISEE results
Authors: Tsurutani Bruce T. , Rodriguez Paul
Published: February 2008

This issue contains results presented at the Upstream Wave and Particle Workshop held at the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California on April 15–16, 1980. This overview article summarizes the results of the collective ISEE work. Several critical scientific problems remaining to be solved are mentioned with the hope that readers may be sufficiently aroused to attempt to study/solve them. In conclusion, some obvious astrophysical implications are discussed.
Measurements of bow shock particles far upstream from the Earth
Authors: Anderson K. A.
Published: February 2008

Electrons and ions moving upstream frequently appear at distances up to 240 RE from earth at times when the direction of the interplanetary magnetic field allows their propagation from the bow shock. Strong asymmetries in the ion angular pitch angle distribution are often observed, a consequence of the sharp gradient in guiding center density and very weak scattering. The gradient is due to the restricted spatial region over which these particles are accelerated. The solar wind electric field, E=−Vsw × Bimf acts on these particles and produces striking effects in both the ion angular distributions and the ion energy spectra. The frequent occurrence of these effects implies that the source region of the diffuse ions at the bow shock is not more than a few times 104 km.
On the location of the source for the energetic electron layer at the polar magnetopause and its relation to magnetic reconnection
Authors: Formisano V. , Domingo V. , Wenzel K.‐P.
Published: February 2008

The existence of a layer of energetic (≳20 keV) electrons along the magnetopause, extending from the polar cusp region to the distant magnetotail, has been established by measurements on various spacecraft. We have performed a statistical study of electron flux and spectral measurements above 0.5 MeV observed in different regions of the magnetopause accessible to HEOS 2, with the aim of identifying the source for this magnetopause electron layer. The measurements along the polar magnetotail (i.e., adjacent to the plasma mantle), along the mid‐latitude dayside magnetopause (i.e., adjacent to the dayside plasma boundary layer), and on both sides of the magnetosheath/polar cusp interface (i.e., in the exterior polar cusp and in the entry layer) have been separately analyzed and are statistically compared. We conclude that escape of electrons from the magnetosphere can be excluded as a significant source for the tail magnetopause layer on the basis of the observed intensities, of the spectra, and of the frequency of appearance of electrons outside those magnetopause regions which lie adjacent to the outer trapping zone. The electron intensities in the exterior polar cusp region are found to be correlated with the north/south component of the interplanetary magnetic field (IMF). High intensity levels are observed when the IMF is directed southward (BZ <0), and low levels when the IMF points northward (BZ >0). The electron flux in the exterior cusp region at times of southward IMF and at the near‐earth polar magnetotail at times of northward IMF is well correlated with the number of field lines carried by the solar wind towards the magnetosphere (expressed by the product of solar wind speed and interplanetary field magnitude). We interpret this as strong evidence that acceleration processes associated with magnetic reconnection occur at the magnetopause at those times. Local acceleration near the high‐latitude magnetopause appears therefore to be a prime source for the magnetopause electron layer.
Auroral arc electrodynamic parameters measured by AE‐C and the Chatanika Radar
Authors: de la Beaujardière O. , Vondrak R. , Heelis R. , Hanson W. , Hoffman R.
Published: February 2008

Auroral arc electrodynamic parameters are studied using coordinated measurements between the AE‐C satellite and the Chatanika radar. On January 4, 1978, the spacecraft twice crossed an east‐west aligned auroral arc at widely spaced longitudes, spanning more than 3 hours in local time. The Chatanika radar was scanning in elevation at a magnetic longitude equidistant from the two AE‐C crossings. The electric field pattern around this arc was remarkably similar at the three longitudes. Equatorward of the arc the north‐south field was very intense (≳60 mV/m), whereas poleward of the arc it was small (∼10 mV/m). The east‐west field was small and almost constant across the arc. The same arc was observed by the radar for about 1 hour, and this electric field pattern did not change, even though the arc location, intensity, and width changed substantially. The ion and electron temperature variations around this arc were also studied. For a given electric field the AE‐C measured ion temperature was substantially different during each of the arc crossings. This dissimilarity is attributed to differences in the F region neutral wind at the two longitudes. We show that the electric field variations are consistent with the existence of polarization charges within the arc, even though the electric field remained small poleward of the arc.
The effects of cold plasma on the Kelvin‐Helmholtz instability
Authors: Melander Barbara G. , Parks George K.
Published: February 2008

This article studies the effect of a two‐component plasma (hot and cold) on the shear driven Kelvin‐Helmholtz instability. The theory incorporates an ion distribution function with a shear flow parallel to the ambient magnetic field and a density gradient perpendicular to both. The electrostatic and electromagnetic modes of the instability are studied in the limit of hydromagnetic frequencies. The dispersion relation for the electrostatic case is obtained by solving the Vlasov equation for the perturbed ion and electron densities that are then used in the quasi‐neutrality condition. The electromagnetic dispersion relation is obtained by solving the coupled Vlasov and Maxwell equations. For low β(=4πNkT/B²), the electromagnetic analysis yields two uncoupled modes. One is related to the Alfvén mode and the other to the ion acoustic mode. The Alfvén mode exists only in a finite β plasma, while in the limit β → 0, the ion acoustic mode becomes purely electrostatic. The effect of cold plasma on the two modes is studied for a wide variety of parameters (velocity shear, density gradient, wave number, plasma β, and flow velocity). The results show that the ion acoustic mode is stabilized by the presence of very small amounts of cold plasma. For β ≪1, the Alfvén mode is found to dominate over the ion acoustic mode when a sufficiently large background of cold plasma is present. The results applied to the magnetosphere show that the ionosphere plays an important role in determining the type of waves that are generated by a sheared plasma flow and indicate whether the flow boundary is unstable to the Kelvin‐Helmholtz instability.
On the significance of including the thermal motion of ions in determining the ion distribution behind a satellite
Authors: Samir Uri , Widjaja D.
Published: February 2008

A comparative investigation concerning the spatial distribution of ions in the wake of small bodies was conducted using the theoretical wake models of Call (1969) and Parker (1976). Results for bodies with RD=2 and RD=5 (where RD=R0/λD, R0 is radius of the body, and λD is ambient Debye length), with a Te equal to the ambient electron temperature (e and k are electronic charge and Boltzmann's constants, respectively), and for the ionic Mach numbers S=2, 4, 6, 8 are presented. Since the main physical difference between the models is in the consideration of the thermal motion of ions (Parker) versus ignoring this component (Call), a comparison between the models yields the quantitative significance of this component in determining the distribution of ions in the wake of artificial satellites. The application of this result to future experiments to be conducted on board the Spacelab and for any other large space platform in the area of space plasma physics is mentioned.
Relationships between the AE and DST indices during geomagnetic storms
Authors: Akasofu S.‐I.
Published: February 2008

During moderately disturbed periods, the AE and Dst indices have a simple linear relationship. However, it is shown that their relationship is considerably different during geomagnetic storms. As the |Dst| index grows above 50γ, the AE index levels off and tends to decrease. This finding may have interesting implications in understanding the formation of the ring current belt.
Conjugacy of electron microbursts and VLF chorus
Authors: Rosenberg T. J. , Siren J. C. , Matthews D. L. , Marthinsen K. , Holtet J. A. , Egeland A. , Carpenter D. L. , Helliwell R. A.
Published: February 2008

Information on the location of microburst source regions is limited. One measurement at L ≈ 8.5 placed the source within 4 RE of the ionosphere. Measurements at 5≲ L ≲6, though less conclusive, suggested that source regions may be located either near the equatorial plane or at higher magnetic latitudes along the field line. This paper reports simultaneous observations of bremsstrahlung X rays and VLF radiowave emissions that reveal a detailed correlation between electron microbursts precipitated in one hemisphere and chorus elements of rising frequency recorded at the conjugate point. The measurements were made at Roberval, Canada, and Siple Station, Antarctica (L ≈ 4.1), during magnetic substorms on July 9 and 15, 1975. The relationship between electron energy (50 ≲ E ≲ 200 keV) and wave frequency ( ≲ f ≲4 kHz), and the measured time difference (0.01 s ≤Δt ≤0.13 s) between detection of the electrons and waves at ionospheric conjugate points are consistent with near‐equatorial cyclotron resonance interactions occurring outside the plasmasphere. In both cases, the observations could be accounted for if a diffusive‐equilibrium distribution of electron density along the field line was assumed. The so‐called ‘collisionless’ (or R−4) model of electron density was not in accord with the observations. Some evidence is found for a separation of the wave growth and electron scattering regions. Evidence is also found indicating that the process of electron scattering requires a finite time, up to ∼80 ms under the conditions of these observations. The present results suggest that microburst generation regions are located within 20° of the equator on subauroral field lines.
Infrasonic oscillations in the F2 region associated with severe thunderstorms
Authors: Raju D. G. Krishnam , Rao M. Srirama , Rao B. Madhusudana , Jogulu C. , Rao C. Poornachandra , Ramanadham R.
Published: February 2008

Phase path variations of F2 region echoes on 5.6 MHz over Waltair (17°43′N; 83°18′ E) are found to exhibit prominent short‐period reversals on some occasions during summer evening hours. The observed waves have periods in the range of 0.5 to about 5 min. The spectral content of the ionospheric waves is found to vary from one event to another. These disturbances are apparently associated with severe local thunderstorms in the troposphere and are interpreted as ionospheric manifestations of acoustic waves generated in the storm sources. The mechanical oscillations excited during the pulsating growth of a thundercloud are the likely source of the observed ionospheric disturbances. A simple model for the generation of acoustic waves by the developing thunderstorms is suggested.
On the role of the lower hybrid drift instability in substorm dynamics
Authors: Huba J. D. , Gladd N. T. , Drake J. F.
Published: February 2008

Recent studies of the lower hybrid drift instability have shed new light on the role of this mode in field reversed plasmas. For substorm magnetotail conditions we find that the lower hybrid drift instability can penetrate to the neutral line and can dissipate magnetic energy at a rate WB ≃4 × 1017 erg/s. Thus this instability is capable of playing a major role in the onset of substorms and providing resistivity for reconnection processes in the context of the neutral line substorm model.
On the application of numerical models to the inverse mapping of solar wind flow structures
Authors: Pizzo Victor J.
Published: February 2008

The widely used constant velocity technique is capable of mapping solar wind structures seen near 1 AU back to the vicinity of the sun with only limited accuracy. This report points out that relatively sophisticated MHD numerical models can be applied to this ‘inverse’ mapping problem, promising better accuracy, especially in the region of the stream front.
Rocket measurements of the solar spectral irradiance during solar minimum, 1972–1977
Authors: Rottman G. J.
Published: February 2008

Five sounding rocket experiments conducted between December 1972 and March 1977, a period spanning solar minimum between cycles 20 and 21, provide full disc solar irradiance data in the spectral range 120–190 nm. The five measurements have been combined to give a solar minimum reference table. This spectrum is compared with other measurements obtained during the same time period. A table of intensities for the strong emission lines at wavelengths between 120 and 190 nm is presented.
The role of hiss in magnetospheric chorus emissions
Authors: Koons H. C.
Published: February 2008

Many researchers have reported that narrowband hiss emissions are simultaneously present with ELF chorus emissions outside of the plasmasphere. In data from the SCATHA satellite, chorus emissions are often observed to start at frequencies that are within a hiss band. Hiss band spectra averaged for 6.4 s with a resolution of 5 Hz are very smooth. Relative maxima are typically less than 2 dB above adjacent minima. Spectra obtained on a 200‐ms sample show large variations in amplitude between adjacent bins with relative maxima 10–15 dB above adjacent minima. Electrons in a narrow range of energies and pitch angles can be organized in phase by the Doppler‐shifted cyclotron resonance with the larger‐amplitude spectral components in the hiss band. The bandwidth of the cyclotron resonance is found to be sufficiently narrow so that the electrons are not dephased by waves in adjacent portions of the highly structured spectrum. The amplitude of the hiss is sufficient to significantly phase bunch the electrons in the calculated interaction time. The chorus emission is then generated as the phase‐bunched electrons moved adiabatically along the geomagnetic field line. No evidence for monochromatic input waves such as power line harmonic radiation is found in the SCATHA data within the hiss bands from which chorus is observed to be triggered. This mechanism can also account for the chorus emissions detected at frequencies above a hiss band in the Jovian magnetosphere.
Plasma density features associated with strong convection in the winter high‐latitude F region
Authors: Sojka J. J. , Raitt W. J. , Schunk R. W.
Published: February 2008

We combined a simple plasma convection model with an ionospheric‐atmospheric composition model in order to study the plasma density features associated with strong convection in the winter high‐latitude F region. Our numerical study produced time‐dependent, three‐dimensional, ion density distributions for the ions NO+, O2+, N2+, O+, N+, and He+. We covered the high‐latitude ionosphere above 42° N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. From our study, we found the following: (1) For strong convection, the electron density exhibits a significant variation with altitude, latitude, longitude, and universal time. A similar result was obtained in our previous study dealing with a weak convection model. (2) For strong convection, ionospheric features, such as the main trough, the aurorally produced ionization peaks, the polar hole, and the tongue of ionization, are evident but they are modified in comparison with those found for slow convection. (3) For strong convection, the tongue of ionization is much more pronounced than for weak convection. (4) The polar hole that is associated with quiet geomagnetic activity conditions does not form when the plasma convection is strong. (5) For strong convection, a new polar hole appears in the polar cap at certain universal times. This new polar hole is associated with large downward, electrodynamic plasma drifts. (6) For strong convection, the main or mid‐latitude electron density trough is not as deep as that found for a weak convection model. However, it is still strongly UT dependent. (7) The ionospheric parameters NmF2, hmF2, and the topside plasma density scale height exhibit an appreciable variation over the polar region at a given UT.
Observations of effects from magnetospheric cusp movement during a solar proton event
Authors: Brown R. R. , Barcus J. R. , Stauning P. , Karas R. H.
Published: February 2008

The interplanetary magnetic field underwent a strong southward turning at the location of the ISEE 3 spacecraft, with Bz (in satellite coordinates) decreasing from +15γ to −15γ in the interval from 1540 UT to 1600 UT on August 20, 1979. Solar wind speed measurements at the spacecraft indicated that the southward turning of the IMF should have reached the front of the magnetosphere around 1625 UT. At that time the solar proton event of August 18, 1979, was still in progress. Observations from balloon‐borne and ground‐based instrumentation in Greenland in that period, around 1415 magnetic local time, showed an expansion of the polar cap, the cusp moving southward by at least 5° in latitude in 15 min, starting around 1635 UT. From changes in the energetic photon spectrum at balloon altitude, it is shown that the proton cutoff energy at Sondre Strømfjord, Greenland, prior to the cusp motion was in the range 6–10 MeV.
Charged particle distributions and electric field measurements from S3‐3
Authors: Mizera P. F. , Fennell J. F. , Croley D. R. , Gorney D. J.
Published: February 2008

Comparisons of electron and proton distribution functions are made with dc electric field measurements as the S3‐3 satellite crossed a series of high‐latitude acceleration regions near local dusk on July 29, 1976. Potential drops, from parallel electric fields, are inferred from charged particle distributions using adiabatic theory and compared with potentials calculated from measured perpendicular electric fields. There exists a one to one spatial relationship between strong dc electric field enhancements in the form of electric field reversals and acceleration signatures of auroral particles. From the charged particle and electric field analysis, we conclude that electric fields, parallel to B, can extend above and below the satellite altitude near 7500 km when strong electrostatic field reversals are encountered. Within the uncertainties of our analysis, the potential drop below the satellite is comparable to the potential calculated from the individual electrostatic structures crossed by the satellite. There are, in addition, particle signatures that imply a source of strong acceleration was located above and relatively close to the satellite. These accelerated electrons are coincident with auroral hiss and ion conics. In addition to regions of acceleration that extended only fractions of a degree in latitude, there was a broad ‘inverted V structure’ near the polar cap boundary where strong perpendicular electric fields were embedded, giving rise to large variations in the inferred potential below the satellite.
Energy spectrum of ions accelerated through Fermi process at the terrestrial bow shock
Authors: Terasawa Toshio
Published: February 2008

The observed energy spectra of the upstream energetic ions (up to ∼ 150 keV per charge) are compared with the expectations from a first‐order Fermi acceleration process, i.e., a multiple reflection process between the bow shock and the upstream wave field. The escape of particles into the far upstream region (≳ several tens to 100RE) is found important for the formation of the energy spectrum. The predicted energy spectrum has exponential dependence on energy likeN(E)dE∼ exp (−E/Ec)dE, which is consistent with the observation. One of the remarkable features of the observation, the invariance of the abundance ratios among various ion species when evaluated at the same energy per charge, can also be explained by the Fermi acceleration process: At the same energy per charge, the elementary acceleration process at the shock front is more efficient for particles of higher mass to charge ratio (M/Q), while the scattering process in the upstream waves is less efficient for these particles. It is shown that the above two effects compensate each other and make the energy spectra of accelerated particles independent of particle species when evaluated by energy per charge unit.
A laboratory experiment on EM backscatter from Farley‐Buneman and gradient drift waves
Authors: Alport M. J. , D'Angelo N. , Pécseli H. L.
Published: February 2008

Results are reported of a laboratory experiment on Bragg backscatter of 3‐cm microwaves by turbulent waves driven by the Farley‐Buneman and gradient drift instabilities. The present work is the third in a series of laboratory experiments performed to test, under controlled conditions, prevalent ideas on EM scattering by equatorial and high‐latitude ionospheric waves and irregularities.
On the three‐body recombination of O(³P) + CO
Authors: Slanger T. G.
Published: February 2008

This comment is in reference to a misconception that has crept into the literature concerning the reaction
. There have now been several references (McElroy and Donahue, 1972; McElroy et al. 1973; Sze and McElroy, 1975; Stewart el al., 1980) to a rate coefficient for this reaction of 2 × 10−37 cm6 molec−2 s−1 attributed to Simonaitis and Heicklen (1972). These authors did indeed study this reaction, and reported a rate coefficient of 1.6 × 10−32 exp (−4100/RT) cm6 molec−2 s−1 with N2O as a third body. However, the figure of 2 × 10−37 cm 6 molec−2 s−1 comes directly from the paper of Slanger et al. (1972) and is a calculation for M=CO2 at 200° K. It is based on temperature‐dependent data obtained for M=CO and includes a multiplicative factor of 1.6, CO2 having been found to be that much more efficient than CO as a third body at 300°K.
Measurements of plasma wave spectra in Jupiter's magnetosphere
Authors: Scarf F. L. , Gurnett D. A. , Kurth W. S.
Published: February 2008

The Voyager 1 and 2 plasma wave instruments had to be designed without direct knowledge of the intensities or spectral characteristics of waves in Jupiter's magnetosphere, the possible environmental problems at Jupiter, or the possible in‐flight interference effects from Voyager subsystems. The wave instruments operated continuously during the 1979 Voyager encounters, and now we can assess in detail the performance of the receiver/spacecraft system within the magnetosphere of Jupiter. We present compressed plots of E field averages for all of the 16‐channel spectrum analyzer data from the Voyager 1 and 2 magnetosphere traversals to provide an overall framework for the discussion. We illustrate the importance of considering peaks as well as averages by using 16‐channel measurements from the first inbound and last outbound bow shock for Voyager 2. We also present selected wideband measurements from the waveform receivers to demonstrate how many important wave bursts are variable in times less than or comparable to the 4‐s scan period of the 16‐channel analyzer. These signal characteristics could not be determined by using the 16‐channel analyzer data alone. In addition, we show how the continuous frequency coverage of the waveform data link provides extremely valuable information on the complex spectra of Jovian plasma waves. These wideband frames also lead to the identification of significant variable interference effects associated with the changing interaction between spacecraft subsystems and the Jupiter plasma environment.
Composition of nonthermal ions in the Jovian magnetosphere
Authors: Hamilton D. C. , Gloeckler G. , Krimigis S. M. , Lanzerotti L. J.
Published: February 2008

We present observations from Voyager 1 and 2 of nonthermal ions from H through Fe in the Jovian magnetosphere using the low‐energy particle telescope (LEPT), one of the two sensors of the low‐energy charged particle (LECP) experiment. At ∼1 MeV/nucleon the major constituents of the ion population were H, He, C, O, Na, S, and the hydrogen molecules H2 and H3. Relative to He, the abundance of H and H3 at equal energy/nucleon was highest in the outer magnetosphere, the abundance of O, Na, and S was highest in the inner magnetosphere, and the abundance of C was constant throughout the magnetosphere. He and C may be of largely solar origin, while H2, H3, O, Na, and S are largely of local origin. The variations in abundance ratios were accompanied by a general hardening of the energetic particle spectra near 1 MeV/nucleon with decreasing radial distance. We are able to find a parameter η, assumed to be a species‐dependent constant times energy/nucleon, in terms of which the flux ratios among most species do not change with radial distance. These ‘invariant’ ratios indicate that there are approximately equal numbers of nonthermal O, S, and He ions, with the abundance of H ions being a factor of ∼15 higher. The large ratio changes at equal energy/nucleon can then be ascribed to the changing spectral slopes. The parameter η may be reasonably identified with energy/charge, in which case we are able to deduce relative charge to mass ratios for H, He, C, O, and S. If He is doubly ionized, we find that the nonthermal carbon has an approximate charge state of +6, typical of solar wind particles, while oxygen and sulfur have low charge states (+2 to +4), typical of local plasma sources. Spectral changes over the range of ∼30 to ∼16 RJ, in this interpretation, are consistent with particle energization by inward radial diffusion conserving the first adiabatic invariant. In the Jovian magnetotail, at the time of the Voyager 2 outbound pass, the energetic particle population was a combination of Jovian particles with soft spectra and interplanetary particles (probably of solar flare origin) with much harder spectra. Above ∼1 MeV/nucleon the interplanetary particles were dominant. Beyond ∼160 RJ, in the ‘magnetospheric wind’ region, the nonthermal ion intensity increased and reflected an oxygen‐and sulfur‐rich composition typical of the middle magnetosphere. Two short‐lived intensity increases were observed at ∼290 RJ which had heavy ion abundance ratios and spectra similar to those found in the inner magnetosphere. The release of these particles was apparently associated with the arrival at Jupiter of a fast solar wind stream.
The formation of arcs in the dynamic spectra of Jovian decameter bursts
Authors: Goldstein Melvyn L. , Thieman James R.
Published: February 2008

A model is presented that can account for several features of the dynamic spectral arcs observed at decameter wavelengths by the planetary radio astronomy experiment on Voyagers 1 and 2. We first show that refraction of an extraordinary mode wave initially excited nearly orthogonal to the local magnetic field is significantly influenced by the local plasma density, being greater the higher the density. We assume that the source of the decameter radiation lies along the L=6 flux tube and that the highest frequencies are produced at the lowest altitudes, where both the plasma density and magnetic field gradients are largest. We further assume that the decameter radiation is emitted into a thin conical sheet, consistent with both observation and theory. In the model the emission cone angle of the sheet is chosen to vary with frequency so that it is relatively small at both high and low frequencies, but approximately 80° at intermediate frequencies. The resulting emission pattern as seen by a distant observer is shown to resemble the observed arc pattern. The model is compared and contrasted with examples of Voyager radio data.