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Journal ArticleDOI

Parallel and perpendicular electric fields in an aurora

01 Nov 1970-Planetary and Space Science (Pergamon)-Vol. 18, Iss: 11, pp 1563-1571
TL;DR: In this paper, the results of a rocket borne electric field experiment flown near local midnight from Andenes, Norway have been transformed to an Earth-fixed coordinate system and compared with plasma temperature and density measurements, energetic particle fluxes, and perpendicular electric field variations, to strengthen the earlier conclusion that ∼10 mV/m electric fields existed parallel to the magnetic field line during the flight.
About: This article is published in Planetary and Space Science.The article was published on 1970-11-01. It has received 97 citations till now. The article focuses on the topics: Electric field & Electric flux.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a general review of anomalous resistivity with emphasis on its applicability in space and more specifically on ionospheric plasmas is presented, addressed to the general ionosphere community rather than the specialist.
Abstract: This is a general review of anomalous resistivity with emphasis on its applicability in space and more specifically on ionospheric plasmas. It is addressed to the general ionospheric community rather than the specialist. Therefore a substantial amount of rigor has been sacrificed in favor of simplified physical pictures. However, several prescriptions are presented, on the basis of which one can compute the anomalous resistivity resulting from each specific mechanism. Following a conceptual discussion of resistivity a general formalism is presented for its computation on the basis of the spectrum of electric field fluctuations. On the basis of this it is shown that stable nonthermal plasmas can at most enhance resistivity by a few percent. The same is true for collisionally driven instabilities. From the current-driven instabilities, only the ion acoustic instability can produce a steady state anomalous resistivity. The rest result in transient resistivity and the appearance of hot electron or ion spots. A more satisfying picture emerges when the low-frequency turbulence that produces resistivity is excited parametrically by a high-frequency instability. The case where such a driver arises from the interaction of precipitating electrons is discussed in detail. Finally, the relevance of the various resistivity mechanisms and their importance in ionospheric electron acceleration is discussed. Although a large number of physical notions are well understood, the efforts toward their incorporation into a gross modeling picture remain embarrassingly small.

304 citations

Book
01 Jan 1976
TL;DR: In this paper, the origin and evolution of the solar system are analyzed, followed by experimental studies of plasma-solid reactions and chemical and mineralogical analyses of meteorites and lunar and terrestrial samples.
Abstract: The origin and evolution of the solar system are analyzed. Physical processes are first discussed, followed by experimental studies of plasma-solid reactions and chemical and mineralogical analyses of meteorites and lunar and terrestrial samples.

236 citations

Journal ArticleDOI
TL;DR: A review of the theoretical concepts and models describing the acceleration of auroral particles can be found in this article, where the dynamics of the particles are described, beginning with the adiabatic motions of particles in the converging geomagnetic field in the presence of parallel potential drops.
Abstract: The auroral zone ionosphere is coupled to the outer magnetosphere by means of field-aligned currents. Parallel electric fields associated with these currents are now widely accepted to be responsible for the acceleration of auroral particles. This paper will review the theoretical concepts and models describing this coupling. The dynamics of auroral zone particles will be described, beginning with the adiabatic motions of particles in the converging geomagnetic field in the presence of parallel potential drops and then considering the modifications to these adiabatic trajectories due to wave-particle interactions. The formation of parallel electric fields can be viewed both from microscopic and macroscopic viewpoints. The presence of a current carrying plasma can give rise to plasma instabilities which in a weakly turbulent situation can affect the particle motions, giving rise to an effective resistivity in the plasma. Recent satellite observations, however, indicate that the parallel electric field is organized into discrete potential jumps, known as double layers. From a macroscopic viewpoint, the response of the particles to a parallel potential drop leads to an approximately linear relationship between the current density and the potential drop. The currents flowing in the auroral circuit must close in the ionosphere. To a first approximation, the ionospheric conductivity can be considered to be constant, and in this case combining the ionospheric Ohm's Law with the linear current-voltage relation for parallel currents leads to an outer scale length, above which electric fields can map down to the ionosphere and below which parallel electric fields become important. The effects of particle precipitation make the picture more complex, leading to enhanced ionization in upward current regions and to the possibility of feedback interactions with the magnetosphere. Determining adiabatic particle orbits in steady-state electric and magnetic fields can be used to determine the self-consistent particle and field distributions on auroral field lines. However, it is difficult to pursue this approach when the fields are varying with time. Magnetohydrodynamic (MHD) models deal with these time-dependent situations by treating the particles as a fluid. This class of model, however, cannot treat kinetic effects in detail. Such effects can in some cases be modeled by effective transport coefficients inserted into the MHD equations. Intrinsically time-dependent processes such as the development of magnetic micropulsations and the response of the magnetosphere to ionospheric fluctuations can be readily treated in this framework. The response of the lower altitude auroral zone depends in part on how the system is driven. Currents are generated in the outer parts of the magnetosphere as a result of the plasma convection. The dynamics of this region is in turn affected by the coupling to the ionosphere. Since dissipation rates are very low in the outer magnetosphere, the convection may become turbulent, implying that nonlinear effects such as spectral transfer of energy to different scales become important. MHD turbulence theory, modified by the ionospheric coupling, can describe the dynamics of the boundary-layer region. Turbulent MHD fluids can give rise to the generation of field-aligned currents through the so-called α-effect, which is utilized in the theory of the generation of the Earth's magnetic field. It is suggested that similar processes acting in the boundary-layer plasma may be ultimately responsible for the generation of auroral currents.

231 citations

Journal ArticleDOI
TL;DR: The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally antisunward convection poleward and sunward convections equatorward of the electric field reversal location as mentioned in this paper.
Abstract: Simultaneous electric field and plasma observations with the low-altitude polar-orbiting satellite Injun 5 have provided a comprehensive survey of convection electric fields and their association with magnetospheric plasma phenomena. The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally antisunward convection poleward and sunward convection equatorward of the electric field reversal location. The electric field reversal is interpreted as the boundary between open and closed magnetic field lines. During local day the electric field reversal is observed to coincide with the equatorward boundary of the polar cusp. The plasma flow in the dayside polar cusp region is dominantly E-W, away from the stagnation point, the convection velocities typically being about 1 km/sec. At local evening, 'inverted V' electron precipitation bands are observed near or at the position of the electric field reversal. In the local late-evening sector the electric field reversal becomes less distinct, and often no single well-defined electric field reversal can be identified. In all cases the inverted V electron precipitation events are closely associated with large, typically greater than 30 mV/m, irregular electric field fluctuations with time scales of a few seconds or less.

220 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the nonlinear development of the feedback instability for a conjugate perturbation elongating in the east-west direction, having a width of several tens of kilometers at the ionospheric level, standing along the magnetic field line.
Abstract: Being fed by the large-scale magnetospheric convection, the coupled ionosphere-magnetosphere system is subject to a feedback instability for a conjugate perturbation elongating in the east-west direction, having a width of several tens of kilometers at the ionospheric level, standing along the magnetic field line. The growth time is as short as several minutes even when no hot electrons are involved in the field-aligned current. Nonlinear development of the feedback instability is numerically investigated, taking hot electrons into account. The following conclusions are obtained. (1) An auroral arc can develop within a few tens of seconds once hot electrons take part. (2) The induced potential associated with the arc can reach several hundred volts. This predicts that the upward field-aligned current may be provided by electrons with energies of the order of several hundred electron volts, provided anomalous resistivity or double layers develop. (3) The electron density enhancement is directly connected with the upward field-aligned current and hence the auroral arc. (4) The downward current is localized equatorward of the upward current, when the background electric field is westward. (5) The electrojet current can grow to a few thousand amperes, which can either be westward or eastward, depending on the direction of the electric field. (6) The induced electric field inside the arc is almost constant and different from outside. These results are consistent with the observational results.

219 citations

References
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Journal ArticleDOI
TL;DR: In this article, an electrodynamic heating mechanism is proposed to account for the precipitation of kilovolt energy electrons during an auroral disturbance, given the existence of an electric field transverse to the geomagnetic field caused by space charges in the magnetosphere, currents will flow along the magnetic field connecting the space charges to the conducting ionosphere.
Abstract: An electrodynamic heating mechanism is proposed to account for the precipitation of kilovolt energy electrons during an auroral disturbance. It is shown that given the existence of an electric field transverse to the geomagnetic field caused by space charges in the magnetosphere, currents will flow along the magnetic field connecting the space charges to the conducting ionosphere. It is shown that the longitudinal current deduced from magnetic observations can be of sufficient intensity to become unstable, resulting in growing ion acoustic waves. In the nonlinear limit these waves tend to inhibit current flows in a collisionless plasma and transform the ordered flow energy into turbulent energy, thus resulting in extreme electrodynamic heating of the electrons. The flow of these ‘hot’ electrons down the geomagnetic field lines is believed to be responsible for the bright aurora and accompanying ionospheric absorption.

131 citations

Journal ArticleDOI
TL;DR: In this article, five Nike-Apache rockets were launched from Kiruna, Sweden, carrying barium release and electron concentration experiments, and the magnitudes of the electric fields varied between 2 and 20 v/km.
Abstract: In April 1967 five Nike-Apache rockets were launched from Kiruna, Sweden, carrying barium release and electron concentration experiments. The component of the electric field transverse to the magnetic lines of force is derived from the motion of the ion clouds. The electron concentration measurements provide ionospheric conductivities. The magnitudes of the electric fields varied between 2 and 20 v/km. Their directions were northwestward for evening conditions and southwestward for morning conditions. The magnetic perturbations on the ground that would result from ionospheric currents derived on the basis of the measured fields and conductivities closely resemble the actual ground magnetometer data. The electric fields vary appreciably with space and time; they can even reverse their directions over distances of the order of 60 km.

101 citations

Journal ArticleDOI
TL;DR: Vector electric field and particle intensity measurements from sounding rocket launched into visible aurora were collected from the International Space Station (ISS) as mentioned in this paper, where they were used to detect the aurora.
Abstract: Vector electric field and particle intensity measurements from sounding rocket launched into visible aurora

93 citations

Journal ArticleDOI
TL;DR: The influence of electric currents along the magnetic field lines on the high-latitude F-layer ionosphere is investigated theoretically in this paper, where it is shown that a current of either sign leads to a reduction of the total electron content and the maximum density, if the charge carriers have to be produced in the ionosphere.
Abstract: The influence of electric currents along the magnetic field lines on the high-latitude F-layer ionosphere is investigated theoretically. It is shown that a current of either sign leads to a reduction of the total electron content and the maximum density, if the charge carriers have to be produced in the ionosphere. Low-energy precipitation leads to a corresponding increase. Extremely low densities in the topside ionosphere may be reached for ion currents of the order of 10-6 amp/m2 or electron currents of 10-3 amp/m2. Observational evidence exists for currents at least of the order of 10-6 amp/m2. It is suggested that the ionospheric trough, the F-layer storm, and other similar effects may be explained by field-aligned currents or plasma diffusion, which is also quantitatively accounted for by the present theory.

69 citations

Journal ArticleDOI
TL;DR: In this article, double-lungmuir probe detector systems have been successfully used on three rockets in the past two years to measure quasi-static and a.c. electric fields in the auroral zone ionosphere.

62 citations