bluuebunny/crossref_metadata_2025 huggingface dataset:
Direction finding of ELF hiss emissions in a detached plasma region of the magnetosphere
Authors: Hayakawa M. , Ohmi N. , Parrot M. , Lefeuvre F.
Published: February 2008

Wave normal directions and wave distribution functions of ELF hiss emissions in a detached plasma region of the magnetosphere have been determined, using data from the geostationary satellite GEOS 2 located in the equatorial plane at L = 6.6. Three different methods of direction finding have been utilized: (1) Means's method based on the hypothesis of a single plane wave, (2) the maximum likelihood method, assuming a few plane waves, and (3) the maximum entropy method of determining the wave distribution function. An intercomparison of the results from those methods has proven that they provide very reliable and definite information on the wave normals. From analyses of two equatorial ELF hiss events it is found that the wave distribution function is composed of a single peak (i.e., the waves have a single propagation direction) and that the wave normals of the ELF hiss originating in the detached plasma region make very small angles with the Earth's magnetic field; also, we wore able to make an experimental estimate of the angular width of the unstable cone of the emissions. Both our initial direction finding results in the equatorial plane and the corresponding previous results at higher geomagnetic latitudes are compared with theoretical predictions, assuming that the waves are generated by the electron cyclotron instability due to medium‐energy (3–30 keV) electrons. It is concluded that all of the characteristics (morphology and direction‐finding results) are consistent with the electron cyclotron instability.
Convection electric fields and electrostatic potential over 61° < Λ < 72° invariant latitude observed with the European Incoherent Scatter Facility: 1. Initial results
Authors: Alcaydé D. , Caudal G. , Fontanari J.
Published: February 2008

Convection electric fields are observed with the European Incoherent Scatter Common Program CP‐3 which probes the F2 region of the auroral ionosphere between 61° and 72° invariant latitude for 24‐hour runs. Several examples of convection fields are discussed, corresponding to various levels of magnetospheric activity. The principal characteristics of the convection drifts are discussed in the light of indices of magnetospheric activity level. It is shown that depending on the level of magnetospheric activity as revealed by the Kp index, the two‐cell convection pattern is more or less present in the field of view of the radar and that the convection velocities around dawn and dusk increase with increasing activity. A method is described which assumes that the 24‐hour convection pattern is due to a steady state potential viewed by the radar rotating with the earth under its ionospheric induced structures; as this assumption can be wrong, in some extreme circumstances of very high and unsteady magnetospheric activity, a test is proposed to ascertain the validity of the method. Inferred potential distributions are then discussed; it is shown in particular that the potential drop from dawn to dusk increases with the magnetospheric activity index Kp. A preliminary analysis of the shapes and positions of the two convection cells is then presented.
Study of a QP/GP event at very high latitudes
Authors: Lanzerotti L. J. , Maclennan C. G. , Medford L. V. , Carpenter D. L.
Published: February 2008

We report on the observation and analysis of a quasi periodic (QP) VLF emission and geomagnetic pulsation (GP) event, a QP/GP event, observed for several hours around local noon at high geomagnetic latitudes at the South Pole station. We believe that this is the highest latitude QP/GP event reported. The narrow‐band magnetic pulsation (f ∼ 30 mHz) suggests that at this time the dayside magnetic field lines connecting South Pole to the magnetosphere were closed. This conclusion is supported by an investigation of the interplanetary magnetic field (IMF) conditions at the time of the event and modeling of the polar cap region of the magnetosphere. The results show that the South Pole location would be expected to be inside the boundary for closed magnetic field lines. The polarizations of the observed hydromagnetic wave were primarily right‐handed throughout the interval, changing slowly to left‐handed beginning approximately 2 hours after local noon. The polarizations and the orientation of the IMF (essentially radial) suggest that the hydromagnetic energy source was upstream waves.
Limits on ion radial diffusion coefficients in Saturn's inner magnetosphere
Authors: Paonessa Mark , Cheng Andrew F.
Published: February 2008

Voyager low energy charged particle (LECP) ion phase space densities at constant first and second adiabatic invariants have been used to place limits on the rate of radial diffusion of energetic ions (30 keV to 1 MeV) in Saturn's inner magnetosphere. Upper and lower limits to the radial diffusion coefficient, DLL, are deduced from physical requirements on the rates of diffusion and loss. Lower limits to DLL are obtained between L = 4 and L = 9 by requiring the rate of inward diffusion to be just large enough to balance satellite sweeping losses. An approximate upper limit on DLL is obtained by requiring the rate of inward diffusion not to be so large as to predict observable ultraviolet aurora on plasma torus L shells. Both methods make no assumption about the functional form of DLL. An independent upper limit to DLL is obtained by assuming various functional forms for DLL and requiring the inferred loss rate of energetic ions to be less than the strong diffusion rate. If DLL is near the lower limit found in this work, then satellite sweeping accounts for a large fraction of the total ion losses. If DLL is near the upper limit, then ion losses can approach 10% of the strong diffusion rate. In this case, ion losses are dominated by wave‐particle interactions, and sweeping losses are relatively unimportant.
Scatter‐free propagation of low‐energy protons in the magnetosheath: Implications for the production of field‐aligned ion beams by nonthermal leakage
Authors: Burgess David , Luhmann J. G.
Published: February 2008

We investigate the scatter‐free propagation of low‐energy (1–5 keV) protons in the magnetosheath by following test particle trajectories in a model of the magnetosheath fields previously obtained from gasdynamic simulations. We concentrate on those ions energized by near‐specular reflection at the quasi‐perpendicular shock: the reflected‐gyrating ions. Our results indicate that for the most common orientations of the interplanetary field, it is unlikely that such ions when scattered in pitch angle behind the near‐perpendicular bow shock (θBn⩾80°) can contribute to upstream field‐aligned beams leaving the bow shock at shock‐normal angles (θBn) greater than 45°. Reflected‐gyrating ions similarly scattered behind the quasi‐perpendicular shock (θBn ⩾45°) are more likely to contribute to such beams by leaking from the bow shock close to where they entered the magnetosheath.
Laboratory observations of ion cyclotron waves associated with a double layer in an inhomogeneous magnetic field
Authors: Alport M. J. , Cartier S. L. , Merlino R. L.
Published: February 2008

Observations of coherent electrostatic ion cyclotron (EIC) waves associated with a strong, magnetized double layer are presented. The double layers are produced in a weakly ionized argon plasma by applying a positive potential to an electrode plate located in the diverging magnetic field region of a cylindrical plasma column. Ionization within the electrode sheath is essential to the formation of these double layers. The resulting V‐shaped potential structures have extended parallel, oblique and perpendicular (to B) electric field components. The frequency of the ion cyclotron instability is dependent upon the magnetic field strength at the position of the parallel potential structure. The properties of EIC waves in the presence of the double layer are discussed in relation to the possible excitation mechanisms (field‐aligned currents, ion and electron beams, and perpendicular E fields).
Ar+ in the terrestrial ionosphere
Authors: Fox J. L.
Published: February 2008

The Ar+ densities in the terrestrial ionosphere are computed for both low and high solar activity models. The reaction N2+(υ > 0) + Ar → N2 + Ar+ is found to be a significant source of Ar+, nearly equal to photoionization and electron impact ionization in the high solar activity model. Peak densities of Ar+ of 11 cm−3 near 190 km and 22 cm−3 near 220 km are predicted for the low and high solar activity models. It is suggested that a simultaneous measurement of Ar+ and Ar densities would provide a test for the presence of vibrationally excited N2+ in the terrestrial ionosphere.
Cosmic ray density gradients related to north‐south asymmetry in activity on the Sun
Authors: Swinson D. B. , Shea M. A. , Humble J. E.
Published: February 2008

Data are presented from underground cosmic ray telescopes in both the northern and southern hemispheres from 1965 to 1983, analyzed as a function of interplanetary magnetic field (IMF) sense, to examine the long‐term properties of the cosmic ray density gradient perpendicular to the ecliptic plane, ▽Np. Yearly cosmic ray solar diurnal variation vectors for IMF (B) away from and toward the sun are obtained; these vectors include a contribution from the B × ▽Np anisotropy, from which the predominant direction of the perpendicular gradient, ▽Np, is inferred. These data are compared with the north‐south asymmetry in activity on the sun for the same period, based both on comprehensive flare index data and on solar events associated with type II radio emission. The cosmic ray data up to the 1969–1971 solar polar field reversal are consistent with a perpendicular cosmic ray gradient pointing southward, observed by telescopes in both hemispheres. The solar activity data indicate a statistically significant excess of activity in the sun's northern hemisphere from 1959 through 1970, which may well be the cause for this southward perpendicular cosmic ray gradient during this period. After the 1969–1971 reversal the solar activity data become reasonably symmetrically divided between the two solar hemispheres. The northern hemisphere cosmic ray data show some evidence of a northward pointing cosmic ray gradient after 1971, while data from the southern hemisphere telescopes continue to indicate a southward pointing gradient. These results can be accounted for if the resultant perpendicular cosmic ray gradient is the sum of two gradients—a north‐south symmetric gradient that reverses upon reversal of the sun's polar magnetic field, along with a larger north‐south asymmetrical gradient that is due to north‐south asymmetry in activity on the sun.
Aperture plane potential control for thermal ion measurements
Authors: Olsen R. C. , Chappell C. R. , Burch J. L.
Published: February 2008

Thermal plasma measurements from the Dynamics Explorer 1 spacecraft using an aperture bias in the outer plasmasphere and over the polar cap show the existence of cold plasma (T ⩽1 eV) which may otherwise be hidden from the particle detector by positive spacecraft potentials. Operations of the retarding ion mass spectrometer instrument with the external aperture plane biased up to −8 V with respect to the spacecraft reveal the existence of low‐energy (few eV) field‐aligned flows over the polar cap. Electrostatic models of the spacecraft indicate that if the spacecraft potential is more than a few volts positive, there can be a saddle point, or an electrostatic barrier, inhibiting the effectiveness of the aperture bias. Comparison of the aperture bias experiments with the electrostatic models shows that the aperture bias is successful in allowing the measurement of those field‐aligned flows with kinetic energy greater than the predicted barrier height but is less effective in aiding the measurement of the isotropic background. The addition of electron measurements from the high‐altitude plasma instrument allows the determination of the spacecraft potential when it is greater than +5 V. This additional information allows us to determine that the dayside polar wind (reported by Sojka et al., 1983) is supersonic, up to Mach 5.
A quasi‐local theory of the E × B instability in the ionosphere
Authors: Fu Z. F. , Lee L. C. , Huba J. D.
Published: February 2008

It is found that a new transient wave mode, which will be termed the “quasi‐local mode”, is associated with the E × B instability in the presence of a velocity shear. This quasi‐local wave mode is different from the nonlocal and the local eigenmodes, both of which have been studied extensively. The quasi‐local mode has the following novel properties: (1) the quasi‐local mode evolves from the local wave mode; (2) the wave number of the quasi‐local mode increases with time; and (3) the wave mode grows, reaches a saturation level, then decays due to the increase of wave number. This mode may be responsible for the observed short wavelength turbulence (i.e., λ < 1 km) in the E and F regions of the ionosphere in the presence of strong velocity shear.
Solar wind Fe and CNO measurements in high‐speed flows
Authors: Ipavich F. M. , Galvin A. B. , Gloeckler G. , Hovestadt D. , Bame S. J. , Klecker B. , Scholer M. , Fisk L. A. , Fan C. Y.
Published: February 2008

We present solar wind Fe charge state and density measurements from two time periods of high‐speed solar wind occurring during a flare‐associated driver plasma and two time periods during coronal hole‐associated high‐speed streams. This constitutes the first reported measurements of Fe charge states in coronal hole‐associated high‐speed streams. The observations, made with the ultralow energy charge analyzer (ULECA) sensor on ISEE 3, indicate that the iron in the driver plasma solar wind was predominately of charge state 15 or 16, indicative of an unusually high coronal temperature (∼4×106 K). In contrast, the Fe charge state distributions in the coronal hole‐associated high‐speed streams peak at 9 or 10, indicating a much lower coronal temperature (∼1.4×106 K). We also present the charge state distribution of the CNO group in one coronal hole‐associated stream and find an ionization temperature of (1.3±0.3) × 106 K. Combining the ULECA measurements with proton observations made with the Los Alamos National Laboratory solar wind instrument on ISEE 3, we find that the speed of solar wind iron is equal to that of hydrogen in the driver plasma but is substantially higher (by about the Alfvén speed) in the coronal hole flows. Both the iron‐hydrogen velocity difference and the calculated temperature gradient from the corona to 1 AU suggest that although the driver plasma expansion was nearly adiabatic, an extended energy input existed for the coronal hole flows. The abundance ratio Fe/H, relative to the nominal interstream value, is found to be enhanced by a factor of ∼2 in the driver plasma and depressed by a factor of ∼2 in the coronal hole‐associated solar wind.
A model for conjugate coupling from ionospheric dynamos in the acoustic frequency range
Authors: Jacobson A. R.
Published: February 2008

A model is developed for estimating the Pedersen currents driven in the conjugate ionosphere by an oscillatory ionospheric dynamo associated with acoustic waves in the upper atmosphere. The model is electrostatic within each ionosphere but uses Alfvén waves in the intervening geomagnetic flux tube. The acoustic frequency range (f ∼ 10¹–10² mHz) considered here allows for coupling to the geomagnetic micropulsation spectrum. Exercises of the model show that the conjugate coupling could be both efficient and observable (by HF sounding). During the daytime the preferred observational mode would be of plasma compression in the upper E region. During the nighttime, only observations of F‐region plasma convection would be possible. Daytime and nighttime coupling efficiencies differ markedly because of a variation in ionospheric boundary condition at the foot of the flux tube.
Pitch angle diffusion in morningside aurorae: 1. The role of the loss cone in the formation of impulsive bursts of precipitation
Authors: Davidson G. T.
Published: February 2008

Pitch angle diffusion of energetic electrons is important in morningside diffuse aurorae, equatorward of the auroral oval, where the plasma is shielded from the influence of large‐scale electric fields. Morningside aurorae exhibit complex spatial and temporal structure. The temporal structure is addressed in a treatment which includes the principal elements of the feedback between pitch angle diffusion and VLF wave growth. A time‐dependent bounce‐averaged pitch angle diffusion equation is derived for the electron flux in and near the loss cone. The diffusion equation includes backscatter from the atmosphere. The atmospheric backscatter is represented by an empirical model in which the pitch angle distribution in the loss cone is approximated by a Taylor series in the sine of the pitch angle. The backscatter model is adjusted to match detailed computations performed with a Fokker‐Planck code for the scattering and slowing of energetic electrons in the atmosphere. Solutions of the pitch angle diffusion equation—both steady state and time‐dependent—are used to compute anisotropies and estimate growth rates of VLF whistler mode waves. The electrons' anisotropy is most sensitive to the diffusion rate near the transition from weak to strong diffusion, where the anisotropy may become so low that VLF wave growth is halted. The principal effect of loss cone filling during an episode of strong diffusion is a sharp increase in the minimum resonant energy for wave growth and a rapid decrease of the growth rate. The characteristic time scales for wave growth and quenching due to changes in the anisotropy are of the order of 0.1–1 s and 2–10 s, respectively. The interaction of growth and decay of waves leads to precipitation bursts on a time scale of 1–50 s. The theory explains many observations of impulsive electron precipitation throughout the outer trapping regions at energies above 20–25 keV. Whether the theory can explain auroral precipitation pulsations at energies below 25 keV without invoking other wave modes remains unresolved.
Gigahertz scintillations and spaced receiver drift measurements during Project Condor Equatorial F Region Rocket Campaign in Peru
Authors: Basu Santimay , Basu Sunanda , LaBelle J. , Kudeki E. , Fejer B. G. , Kelley M. C. , Whitney H. E. , Bushby A.
Published: February 2008

Radar backscatter at 50 MHz, rocket, and VHF/GHz scintillation measurements of spread F irregularities at the magnetic equator in Peru were made during the Project Condor campaign in March 1983. The paper discusses the coordinated set of observations on two evenings, March 1 and March 14, 1983, when the altitude of the F region peak differed by more than 150 km. The full complement of equatorial spread F phenomena, namely, the occurrence of 3‐m plume structures and VHF/GHz scintillations, were recorded on both these evenings. It was found that the radar backscatter with extended plumes occurs in association with maximum 1.7‐GHz scintillations. This established that the height‐integrated rms electron density deviation of ∼200‐m scale irregularities causing 1.7‐GHz scintillations maximizes in extended 3‐m plume structures. The magnitude of 1.7‐GHz scintillations recorded at high elevation angles (∼76°) near the magnetic equator did not exceed a value of S4 = 0.2 (4 dB) in contrast to the near saturated 1.5‐GHz scintillations routinely observed at Ascension Island near the crests of the equatorial anomaly of F2 ionization. The observed scintillation magnitudes at 1.7 GHz have, however, been found to be compatible with the ambient F region and the irregularity parameters measured by the rocket. The spectral index n of scintillations has been found to be relatively less steep (n ∼ −3) on March 1, 1983, when the F region was high, and the index is steep (n ∼ −5) on March 14, 1983, when the F region was at a lower altitude. The F region rocket, however, measured nearly identical one‐dimensional spectral indices of intermediate‐scale irregularities on both evenings, compatible with the less steep spectral index of scintillations. The irregularity drift velocities measured by the spaced receiver scintillation measurements were in general agreement with the radar interferometer results except that the spaced receiver drifts were 20% higher. The zonal drift was observed to be ∼100 m/s on the night of March 1 and ∼200 m/s on the night of March 14. This result may be a consequence of the day‐to‐day variability of the measured zonal neutral winds and field line integrated Pedersen conductivities.
Greater than 0.1‐Hz ULF magnetic pulsations measured at South Pole, Antarctica
Authors: Arnoldy R. L. , Cahill L. J. , Eather R. H. , Engebretson M. J.
Published: February 2008

South Pole pulsation activity at frequencies greater than 0.1‐Hz is analyzed in this study and found to consist predominantly of large‐amplitude, irregular pulsations (Pi 1) closely correlated with overhead auroral activity. These pulsations therefore have two diurnal maxima related to the substorm polar expansion nightside aurora and cusp or dayside aurora. The dependence of this magnetic nightside Pi activity at South Pole on Kp and interplanetary magnetic field parameters is consistent with a strong substorm correlation. As found at lower latitudes, when pulsating aurora is evident in the photometric data there can be a good detailed correlation between the auroral luminosity fluctuations and the magnetic pulsations, suggesting that the pulsations are locally produced by overhead currents driven by the particle precipitation. Nightside Pi activity is often of larger‐amplitude than the dayside Pi and appears in bursts of pulsations having 5 to 20 minsduration. The burst‐like character arises because of the rapid poleward expansion of discrete auroral forms from the nightside auroral oval, as is evident in the South Pole photometric data. South Pole nightside auroral magnetic pulsations generally commence well after the onset of similar auroral magnetic pulsations recorded at Siple, Antarctica, a subauroral location. One third of the hours during which structured, band‐limited pulsations (Pc 1) are observed at the low‐latitude, Siple, Antarctica, location also contain Pc 1 observed at South Pole. When it is possible to identify similar structures in Pc 1 between South Pole and Siple they are in phase, in contrast to out of phase structures for opposite hemisphere stations. This supports horizontal ducting of Pc 1 from lower‐latitudes to South Pole. However, there often appears much more structure at South Pole than recorded at Siple, suggesting many paths of horizontal propagation from multiple lower‐latitude sources if the signals are not generated on South Pole field lines. The pronounced inverse correlation of South Pole Pc 1 with magnetic activity means that the magnetic field topology and/or ionospheric conditions associated with substorm activity preclude the possible propagation of Pc 1 to South Pole from lower‐latitudes when the magnetic activity is high.
Electrical changes of the polar ionosphere during magnetospheric substorms
Authors: Ahn B.‐H. , Kamide Y. , Akasofu S.‐I.
Published: February 2008

Changes of the distribution of the potential, electric fields, ionospheric currents, field‐aligned currents, the Joule heat production rate, the particle energy injection rate and the total energy dissipation rate are examined in detail by comparing them at a presubstorm epoch and the maximum epoch for several substorms on March 17, 18, and 19, 1978. The data sets are obtained on the basis of the magnetic records from the six International Magnetospheric Study meridian chains of observatories by using the computer code developed by Kamide et al. (1981) and the conductivity model developed by Ahn et al. (1983b). A number of global features that are found to be common to most of the substorms examined in this study include the following: (1) The positive potential cell in the morning sector extends into the evening sector during substorms. (2) When it is intensified, the westward electrojet on the nightside tends to flow equatorward of the positive potential ridge. (3) The so‐called “Harang discontinuity” may be identified as the ridge of the negative potential cell. (4) The distribution of field‐aligned currents determined by our method is more complicated than the statistical pattern obtained by polar orbiting satellites. (5) The basic ionospheric current pattern is fundamentally the same during a fairly quiet period, a slightly disturbed period and a substorm period. (6) The highest Joule heat production occurs along the westward extension of the westward electrojet, while the particle energy injection rate is high along the westward electrojet in the morning sector.
The role of energetic O+ precipitation in a mid‐latitude aurora
Authors: Ishimoto M. , Torr M. R. , Richards P. G. , Torr D. G.
Published: February 2008

We show that fluxes of precipitating energetic O+ that have been observed by satellites in the topside ionosphere can explain the magnitude of the N2+(1 N) (first negative) 3914‐Å and N2(2 P) (second positive) 3371‐Å emission rate observed during a mid‐latitude aurora over Logan, Utah (41° N, 111°W), on September 21–22, 1982. Heavy particle precipitation has previously been invoked to explain the anomalously high populations in the upper vibrational levels of the N2+(1 N) system that are evident in the observed emissions. The N2(2 P) 3371‐Å emission rate in the observed aurora was a factor of 4‐7 less than the observed 3914‐Å emission rate, whereas the rate is a factor of 2 less for a typical electron aurora. A model is used to investigate the impact of precipitating heavy ions on the atmosphere. The model has been improved over previous models in three ways: first, the neutral atmosphere now includes N2 as well as O. Second, measured values rather than theoretical values are used for the elastic scattering differential cross sections, and third, emission rates from energetic O and N2 by heavy particle collisions and their “ionization by‐product” low‐energy secondary electrons are evaluated. The measured cross sections are smaller than those of the previous models and more strongly forward scattering than the values used in our previous studies, allowing the energetic atoms to penetrate more deeply into the atmosphere. As a result, the peak energy deposition is lowered to approximately 180 km from the 270‐ to 350‐km peak of the earlier calculations. The bulk of the energy of the precipitating flux goes into heating of the neutral atmosphere (∼82%), while a significant fraction (∼16%) of the energy is carried by an upward moving neutral escape flux. The escape flux is 13% N2 and 87% O. The remaining 3% of the incident O+ energy goes into ionization and excitation. The nocturnal thermospheric heating rate and ionization rate during one of these events can be equivalent to the daytime EUV heating and ionization rates. We conclude that the characteristics of the observed spectrum can be explained by energetic O+ precipitation to within the uncertainties of the inputs to the model.
Radial and latitudinal gradients in the interplanetary magnetic field: Evidence for meridional flux transport
Authors: Thomas Barry T. , Slavin James A. , Smith Edward J.
Published: February 2008

An analysis is presented of the magnetic field data obtained by the Pioneer 10 and 11 spacecraft in the outer heliosphere, with regard to radial and latitudinal gradients in the field components and magnitude. At first sight the field data appear to conform fairly well with the predictions of the Parker model. However, when the data obtained by Pioneer are compared with data from earth orbiting satellites, it is found that time variations are significantly affecting the field throughout the low‐latitude heliosphere. Removing these time variations allows a significant departure from the Parker model to emerge. The field magnitude and directions are found to be consistent with meridional flux transport from the equatorial plane towards higher heliographic latitudes. Such meridional transport could be driven by higher pressure near the solar equator. Enhanced pressure would be expected on the basis of the increased intensity of the spiral field in that region. However, another possible source of increased pressure is associated with the heating that occurs in compressive solar wind interaction regions and the large field magnitudes that occur in these regions both of which may be enhanced at low latitudes at least at the radial distances sampled thus far. Finally, evidence is presented which suggests a solar cycle dependence in the degree of meridional flux transport.
A simple model of auroral electrodynamics compared with HILAT measurements
Authors: Doyle M. A. , Burke W. J. , Hardy D. A. , Bythrow P. F. , Rich F. J. , Potemra T. A.
Published: February 2008

Simultaneous measurements of cold plasma drift velocities, magnetic field perturbations, and precipitating electron fluxes with instrumentation on board the HILAT satellite provide an opportunity to correlate Birkeland current densities, electric fields, and ionospheric conductivities in the region of an auroral form. Typical plasma parameters such as ion density, temperature, and composition and electron density and temperature are also available. On July 17, 1983, the satellite crossed the northern auroral zone in the early morning, magnetic local time sector. As the satellite crossed a bright auroral form, recorded by the auroral imager‐mapper, the particle spectrometer detected a 2 orders of magnitude increase in the flux of >10‐keV electrons. The precipitating electrons of this event produced a double inverted‐V structure embedded in the large‐scale, region 2 field‐aligned current sheet. This paper presents calculations of the component of the electric field along the satellite trajectory and perpendicular to the auroral form, given the Birkeland current feeding the auroral form and conductivities derived from particle precipitation data. This electric field component emerges as a solution to the current continuity equation j∥ = −▽ · (Σ · E) in the infinite current sheet approximation with appropriate boundary conditions. Emphasis is placed on accurately representing the Birkeland current density in the region of the bright auroral form. In general, large‐scale features are well represented by the calculations. Although small‐scale features are not well tracked, calculations of the auroral zone potential drop and the height‐integrated Joule heating varied by less than 2% from measured values. During this particular pass the ionospheric Joule heating exceeded the particle energy deposition along the satellite trajectory by a factor of 2.6.
Narrow‐band Jovian kilometric radiation: Occurrence, polarization, and rotation period
Authors: Daigne Gérard , Leblanc Yolande
Published: February 2008

A statistical analysis of the narrowband Jovian kilometric radiation, or nKOM, observed by the planetary radio astronomy experiment (Voyager 1 and Voyager 2) from January to December 1979, is reported. Occurrence, polarization, and rotation period are studied. The sense of circular polarization changes with magnetic latitude of the observer. Left‐hand polarized emission is associated with the northern hemisphere, which suggests a radiation mechanism in the ordinary mode. The emission is beamed in magnetic latitude with an obscuration at the equator, and the measured axial ratio increases with the magnetic latitude of the observer. The nKOM source regions do not rotate with a single period and coherent phase. Long‐term variations in the rotation are shown, the dominant regimes being system III and 2.5–3% corotation lags. During sequences of corotation with system III, the nKOM events are observed mainly in the ranges 40° and 300° central meridian longitude.
Perturbation of the solar wind in a model terrestrial foreshock
Authors: Skadron George , Holdaway Robert D. , Scholer M.
Published: February 2008

We analyze the perturbation of the solar wind in the earth's foreshock. The foreshock is modeled as a planar magnetic flux tube having a 15 RE half width. Within the flux tube the upstream energetic particle pressure is assumed to fall monotonically to zero at the flux tube boundary and decline in the upstream direction with a scale length of 8 RE. The incident solar wind is assumed to flow uniformly with a velocity of 400 km s−1, a density of 8 cm−3, a pressure of 50 eV cm−3, and a magnetic field of 4γ directed parallel to the flow. The solar wind density, velocity, and magnetic field within the foreshock are described by the steady state ideal MHD equations. We find that (1) the vector solar wind velocity perturbation rotates from the sunward to the transverse direction with increasing distance from the axis of the flux tube, (2) the peak solar wind deflection is located ∼3 RE within the flux tube boundary, (3) a central upstream pressure of 200 eV cm−3 produces a maximum deceleration of 6 km s−1 and a maximum deflection of 1.3°, (4) a central upstream pressure of 600 eV cm−3 produces a maximum deceleration of 19 km s−1 and a maximum deflection of 3.6°, and (5) the deflection and deceleration are accompanied by perturbations of the solar wind density and magnetic field. These perturbations are largest near the flux tube boundary where both form spikes having a width of ∼2 RE. For a 600 eV cm−3 central pressure those spikes have amplitudes of 2 cm−3 and 1γ, respectively. We have analyzed the linearized flow problem analytically and reduced the solutions to quadrature. These solutions are found to be good approximations to the numerical nonlinear solutions for moderate values of the upstream particle pressure.
Simulations of high Mach number perpendicular shocks with resistive electrons
Authors: Quest Kevin B.
Published: February 2008

The structure of high Mach number perpendicular shocks is examined using a simulation code which treats the ions as macroparticles and the electrons as a resistive massless fluid. It is shown that stable, stationary shock solutions can be found for Alfvén Mach numbers MA between 5 and 60 for upstream plasma β = 1, where β is defined as the ratio of the plasma pressure to the magnetic pressure, provided that the upstream resistive diffusion length is much smaller than the ion inertial length c/ωpi. If the resistive diffusion length is larger than 0.4c/ωpi, then the magnetic field overshoot is damped, and an imbalance in the electron momentum equation results in a periodic fluctuation of the fraction of reflected ions. In the limit MA ≤ 10, the magnetic field overshoot and the fraction of reflected ions increase with increasing MA, consistent with earlier results. At higher Mach numbers the fraction of reflected ions peaks at approximately 40% and the magnetic field overshoot increases at a much slower rate. These results are consistent with simple scaling laws derived from the electron momentum equation. The importance of upstream β and electron inertial effects are discussed.
On the interchange instability
Authors: Rogers B. , Sonnerup B. U. Ö
Published: February 2008

We reexamine the standard method for analyzing the stability of planetary magnetospheres against interchange motions of magnetic flux tubes and the plasma contained in them. This method consists of finding the change in potential energy ε = ∫ [p/(γ ‐ 1) + ρϕ] dV of two tubes of equal flux which exchange position, leaving the energy of the surrounding plasma and field unchanged. As an illustration, we study a cylindrically symmetric plasma with an embedded purely toroidal magnetic field. Our results for this geometry and for the nonrotating case are as follows. (1) The standard method, which takes into account changes in internal energy, p/(γ ‐ 1), and gravitational energy, ρϕ, but not magnetic energy has been claimed to be valid for vanishing plasma pressure. We show it to be correct up to and including terms of order β, β being the ratio of plasma to magnetic pressure. (2) Toroidal equilibria having β of order unity or larger can be analyzed by interchanging tubes of unequal flux such that to first order in the displacement the surroundings are left unperturbed and by taking into account changes in the magnetic energy, B²/2µ0, of the two tubes. (3) Such equilibria can also be analyzed by considering the displacement of a single flux tube, taking into account resulting changes in the energy of the tube as well as the environment. For rotating equilibria we find that the standard method of replacing ρϕ by ρ(ϕ ‐ r²Ω²/2) in ε only gives a sufficient condition for stability. However, for the cylindrical equilibrium an exact marginal condition can be obtained from energy arguments, provided Coriolis effects are taken into account.
Plasma boundaries in the inner magnetosphere
Authors: Horwitz J. L. , Menteer S. , Turnley J. , Burch J. L. , Winningham J. D. , Chappell C. R. , Craven J. D. , Frank L. A. , Slater D. W.
Published: February 2008

Plasma boundaries in the inner magnetosphere are investigated with measurements chiefly by the DE 1 and 2 spacecraft. The boundaries studied here are: (1) the low‐energy (or thermal) ion transition (LEIT) frequently observed at or near the conventional plasmapause density gradient, defined here as the outer boundary of observable, cold, isotropic light ions and transition to warm field‐aligned ions; (2) the earthward or inner edges of the plasma sheet electrons having pitch angles near 90° and the three energies 100 eV, 1 keV, and 10 keV; and (3) the equatorward boundaries of precipitating auroral oval electrons at those same energies. Some simultaneous observations of the aurora are also examined. Observations reported here have been obtained in the evening and the morning local time sectors; however, it is found that distinct equatorward boundaries of the auroral oval and the plasma sheet are infrequently observed in the morning sector, and the report focuses on boundary measurements in the evening sector (mainly 1800–2300 MLT). These measurements show that in the evening sector, the LEIT and the 100‐eV inner edge of the electron plasma sheet are normally coincident to within identification uncertainties (∼0.3L), and these are reasonably coincident with the field lines threading the 100‐eV equatorward edge of the auroral electron precipitation. These boundaries respond similarly to variations in magnetic activity. A characteristic electron energy dispersion is typically observed in the plasma sheet inner edges at the different energies, with the lower‐energy boundaries located earthward of the boundaries at higher energies. The dispersion appears to increase from the midnight sector toward dusk, and also to decrease with increasing magnetic activity. It is suggested that these boundaries are reasonably sensitive and accurate signatures, in the evening sector, of the boundary between closed and open convection trajectories as determined by the convection electric field, and that the evening sector characteristic electron plasma sheet energy dispersion is similarly governed by the convection pattern so that the inner edges may be regarded as the Alfvén layers at those energies.
Differential cross sections for scattering of 0.5‐, 1.5‐, and 5.0‐keV hydrogen atoms by He, H2, N2, and O2
Authors: Newman J. H. , Chen Y. S. , Smith K. A. , Stebbings R. F.
Published: February 2008

This paper reports measurements of absolute cross sections, differential in angle, for scattering of 0.5‐, 1.5‐, and 5.0‐keV hydrogen atoms by He, H2, N2, and O2 at laboratory scattering angles between 0.1° and 5°. The measured cross sections are the sums of those for elastic and inelastic collisions having a fast H atom product and are needed for calculating energy transfer to the upper atmosphere from precipitating ring current particles.
Anomalous outward diffusion and associated heating of iogenic ions in the Jovian magnetosphere
Authors: Abe Takashi , Nishida Atsuhiro
Published: February 2008

Heavy ions in the Jovian plasma disc can be heated as they diffuse outward under the influence of the centrifugal force if they are scattered with an effective collision frequency which is comparable to their gyrofrequency. The purpose of this paper is to see if the random electric fields having temporal and spatial scales of the ion gyration can act as sufficiently efficient scattering agents. The diffusion process is studied by numerically tracing the trajectories of sets of heavy ions subjected to the centrifugal force and the random electric field. The random field of inferred intensity is found to produce significant diffusion of heavy ions. These ions are heated to the level of the kinetic energy of the local corotational motion. We suggest that the above mechanism contributes in supplying the high‐temperature heavy ions to the outer Jovian plasma disc.
Radiation of plasma waves by a conducting body moving through a magnetized plasma
Authors: Barnett Alan , Olbert Stanislaw
Published: February 2008

There are many situations of interest in space and astrophysics which consist of a conducting body moving through a magnetized plasma. It is well known that large conducting objects which move slowly across magnetic field lines radiate low frequency (Alfvén) waves. In this paper we study the interaction between a plasma and a moving conductor in order to estimate the total power radiated at all frequencies. Toward this end, we develop a formalism which permits us to compute the response of the plasma to an external current source. We then derive an integral equation which relates the source current to the electrical properties of the conducting body. Since the integral equation is prohibitively difficult to solve, we estimate the total radiated power for simple geometries using energy conservation and a source current deduced by physical reasoning. We find in general that radiation is produced at all frequencies for which one of the plasma modes has zero phase velocity in some direction. The mechanism by which this radiation is produced is analogous to Cherenkov radiation. In the cold plasma approximation, in a plasma for which ωp² ≫ Ωe² and V² ≪ cA² ≪ c², there is radiation in three frequency bands: ω < Ωi, ωLH < ω < Ωe, and ωp < ω < ωUH, where V is the speed of the body, cA is the Alfvén speed, c is the speed of light in vacuum, ω is the frequency of the radiation, and Ωi, ωLH, Ωe, ωp, ωUH are the ion cyclotron, lower hybrid, electron cyclotron, plasma, and upper hybrid frequencies, respectively. To gain a better understanding of the properties of the plasma waves in these frequency bands, we present polar plots of the phase and group velocities of these waves. Finally, we present estimates of radiated power for a sphere and for a cylinder of arbitrary size. We find that a wire 10 km long and 1 mm in radius radiates about 40 watts. The Jovian satellite Io, known to be a strong source of waves in the first frequency band, also radiates 2.9×10−7 times as much power in the second frequency band.
Viscous pumping and the spin‐down of thermospheric gyres and jets
Authors: Walterscheid R. L. , Schubert G.
Published: February 2008

Strong gyres and jets can be generated at auroral latitudes in the thermosphere by enhanced electric fields during geomagnetic substorms. Typical height profiles of ion density suggest that the ion drag force should generate large curvature in the vertical profile of the winds in the highly viscous region of the thermosphere above about 200 km. It is proposed that the poststorm spin‐down of these gyres and jets proceeds via Ekman circulations driven by the curvatures in the height profiles of the winds. Analytic and numerical calculations of the ageostrophic winds forced by curvature in model geostrophic wind profiles show that the ageostrophic wind speeds and directions depend mainly on the kinematic viscosity in the region of curvature and the total change in shear in the geostrophic wind. Ageostrophic wind speeds for typical thermospheric jets can exceed 200 m s−1 (about 50% of the jet winds). Spin‐down times of thermospheric jets and cyclonic gyres by the Ekman pumping mechanism are estimated at ≲6 hours.
Stability of the Io Torus
Authors: Huang T. S. , Siscoe G. L.
Published: February 2008

We investigate the inherent stability of the coupled neutral‐plasma Io torus. Under the assumptions that the neutrals arise through sputtering by corotating torus ions and that the ions move radially by centrifugally driven diffusion, we find that the equilibrium state properties of the Io torus depend on two quantities: the sputtering yield and Jupiter's ionospheric Pedersen conductance. For fixed values of these quantities, the torus equilibrium state is stable. When the torus neutral and ion densities deviate from the equilibrium state, the perturbations decay without oscillating, with a decay time near 1 day for the neutrals and near 60 days for the ions. The growths of the neutrals and ions from seed populations are computed. The torus evolves directly to its equilibrium state.
Disruption of a coronal streamer by an eruptive prominence and coronal mass ejection
Authors: Illing R. M. E. , Hundhausen A. J.
Published: February 2008

We describe and analyze in detail the coronal mass ejection of 18 August 1980, using images from the coronagraph on the Solar Maximum Mission (SMM) satellite. The event occurred at the site of a large coronal helmet streamer and evolved into the three‐part structure of a bright frontal shell, followed by a relatively dark space surrounding a bright filamentary core as seen in many mass ejections of the SMM epoch. The bright core can be identified as material from a prominence whose eruption was observed from the ground; this identification is based on (1) the looplike and filamented appearance of the core, (2) its motion along a trajectory that is a good extrapolation of the motion deduced from ground‐based observations of the prominence eruption, and (3) direct observations of Hα emission when the core is in the coronagraph field of view. The mass of the frontal shell is equal to that of the coronal helmet streamer (to the ∼30% accuracy with which mass estimates can be made), indicating that the shell is the coronal material previously in the helmet streamer, displaced and set into motion by the erupting prominence and surrounding cavity. The mass ejected in the bright core (or prominence) is estimated to be ∼50% larger than the “coronal” material in the frontal loop. The total mass of 2.5×1015 g and energy of 5×1031 ergs estimated for this mass ejection are both greater than in typical ejections of the Skylab era but are comparable to the average mass and energy in an interplanetary shock wave.
Analysis of the prominence associated with the coronal mass ejection of August 18, 1980
Authors: Athay R. Grant , Illing Rainer M. E.
Published: February 2008

Coronal mass ejections detected with the Solar Maximum Mission coronagraph/polarimeter are often accompanied by erupting prominence material observed both in Hα and in the electron scattering continuum. Hα emission is concentrated in bright filaments moving radially outward. The same filaments are seen in the electron scattering continuum as regions of enhanced brightness. In this paper we develop a diagnostic method based on the observed Hα and continuum brightness to derive the electron density, line of sight thickness, and degree of ionization of hydrogen as functions of the temperature of the prominence filaments. Our method differs from that of Poland and Munro (1976) in the treatment of Ly α excitation. Analysis of data from the event of August 18, 1980, illustrates that the rising prominence material has decreased density, increased temperature, and increased ionization of hydrogen relative to quiescent prominences in the lower corona. Hydrogen is found to be 90–99% ionized, electron densities are near 108 cm−3, and the temperature is near 20,000 K. The increased ionization is due mainly to the decreased density. Use of the results is made here and in an accompanying paper by Illing and Hundhausen to determine the total mass ejected in the event.