Showing papers on "Electric field published in 1979"

Magnetosphere-ionosphere coupling

Abstract: A simple two-dimensional model of the magnetosphere-ionosphere system is discussed in which a localized electromotive force applied across a magnetic field line at t=0 is shown to propagate along the magnetic field with the Alfven velocity. The perpendicular electric field is assumed to reverse direction across the field line. Since the perpendicular electric field is limited in space, the propagation involves parallel electric fields whose magnitude depends on the characteristic scale length of the applied emf and the local plasma parameters. The electric field pulse associated with the ‘shock’ front is reflected at the ionosphere and propagates back to the source region. The finite Pedersen conductivity in the ionosphere damps the wave, and a steady state current system is established in the order of several hours. The parallel electric field can accelerate ions and electrons.

Electric field depinning of charge density waves

Abstract: The pinning of charge-density waves by impurities is considered in systems that exhibit at least short-range order in three dimensions. Impurities are classified into strong and weak with quite different pinning properties. The pinning of spin-density waves is weak and the phase values at impurity sites are almost random, in agreement with a recent experiment. The electric field required to depin the charge-density wave is estimated. The coupling between a drifting charge-density wave and carriers either from a remnant Fermi surface or thermal excitation is considered. Attention is focused on umklapp scattering of carriers by phasons as a coupling mechanism at finite temperature. The conductivity in the high-electric-field depinned limit can be large. Dislocations in the charge-density-wave lattice are examined with particular emphasis on the piecewise motion of the charge-density wave through the motion of dislocations. We also discuss the generation of dislocations by the analog of Frank-Read sources. The unusual nonlinear conductivity observed in Nb${\mathrm{Se}}_{3}$ is interpreted in terms of depinning of charge-density waves. The possibility of observing similar effects in other systems is briefly examined.

Liquid-Crystal Lens-Cells with Variable Focal Length

Abstract: Liquid-crystal cells shaped like a plano-convex lens or a plano-concave lens are prepared. The focal length can be varied from the value fe for an extraordinary ray, where the liquid-crystal cell takes a homogeneous alignment, to fo for an ordinary ray, where it takes a homeo-tropic alignment, by applying an electric field or a magnetic field across the lens-cell. The focal length in the lens-cell with the homogeneous alignment can also be switched between fe and fo. This is done by switching the direction of polarization of the incident light by applying a voltage across a TN cell sandwiched between the polarizer and the lens-cell. Since the thickness of the liquid-crystal layers increases in the lens-cells, the optical transmission properties are investigated as a function of the cell thickness.

Electric field effect on the thermal emission of traps in semiconductor junctions

Abstract: Electric field effects on the thermal emission of traps in a diode have been studied. Calculations were performed and compared with experimental data on deep centers in GaAs. The results are consistent with a thermal equivalent of the optical Franz‐Keldysh effect.

An explanation for anomalous equatorial ionospheric electric fields associated with a northward turning of the interplanetary magnetic field

Abstract: Anomalous reversals of the zonal equatorial electric field component have some- times been observed when the interplanetary mag- netic field turns northward from a steady south- erly direction. We suggest that this reversal is associated with a sudden change in the convection electric field in the magnetosphere and present measurements to support this explanation. Al- though slower variations in the convection field are shielded from the low latitude ionosphere by polarization charges at the inner edge of the ring current, these charges may require an hour or more to vary. A sudden decrease in the cross- tail electric field will thus be accompanied by a dusk-dawn perturbation electric field across the inner magnet o s phe re.

Characterization of the electron mobility in the inverted l100g Si surface

Abstract: The effective mobility of electrons in the inverted 〈100〉 Si surface was measured over a wide range of temperatures, gate voltages, and back-bias voltages. At a first glance the mobility appears to be strongly dependent on the channel surface doping. When the data were reanalyzed under a new approach where the mobility is plotted as a function of an effective perpendicular electric field experienced by the inversion layer, a universal curve has developed from the experimental data which indicates that the inversion layer mobility is not a function of doping density in the range (N A 2 system and not a parameter sensitive to nominal process variations encountered in the present n-channel Si-Gate Technology.

Polar cap electric field structures with a northward interplanetary magnetic field

Abstract: Polar cap electric fields patterns are presented from times when the S3-2 Satellite was near the dawn-dusk meridian and IMF data were available. With Bz ≥ 0.7 γ, two characteristic types of electric field patterns were measured in the polar cap. In the sunlit polar cap the convection pattern usually consisted of four cells. Two of the cells were confined to the polar cap with sunward convection in the central portion of the cap. The other pair of cells were marked by anti-sunward flow along the flanks of the polar cap and by sunward flow in the auroral oval. These observations are interpreted in terms of a model for magnetic merging at the poleward wall of the dayside polar cusp. The sunward flow in the auroral zone is not predicted by the magnetic model and may be due to a viscous interaction between the solar wind and magnetosphere. The second type, which was observed in some of the summer hemisphere passes and all of the winter ones, was characterized by an electric field pattern which was very turbulent, and may be related to inhomogeneous merging.

Stare auroral radar observations of Pc 5 geomagnetic pulsations

Abstract: The Stare (Scandinavian twin auroral radar experiment) auroral radar system has been used to measure ionospheric electric fields associated with Pc 5 geomagnetic pulsations With this system, electric fields are derived from the drift velocity of radar auroral irregularities The spatial resolution is 20 km over a 200,000-km² grid, and the temporal resolution is 20 s It has been found that the oscillating electric field associated with a hydromagnetic field line resonance produces poleward moving, bandlike regions of radar aurora, which are aligned in the east-west direction The drift of the irregularities within these bands is alternately eastward and westward The Stare electric field data have been used in conjunction with the Biot-Savart Law and an assumed height-integrated conductivity of 8–10 Ω−1 to calculate the ground magnetic disturbance It has been found that the H and Z are well predicted, whereas D is generally underestimated These results are consistent with a 90° rotation of the magnetic polarization ellipse in the ionosphere By Fourier analyses of the Stare data it is found that the half-power latitudinal width of the field line resonance is typically 100 km in the ionosphere Moreover, the north-south electric field undergoes a 180° phase shift about the resonance as predicted by theory The data have been used to estimate equatorial plasma densities for 6 < L < 7, and values of the order of 20 cm−3 have been obtained However, these determinations are strongly affected by distortions of the geomagnetic field from a dipolar geometry In summary, (1) the experimental results strongly support the hydromagnetic field line resonance theory of pulsations; (2) the magnetic polarization ellipse is indeed rotated through 90° by the ionosphere; (3) the phenomena previously observed by auroral radar workers in association with Pc 5 pulsations were related to the electric field of the hydromagnetic wave near resonance; and (4) auroral radar measurements can be used to estimate the equatorial magnetospheric plasma density in the region 5 < L < 8

Sliding-Mode Conductivity in Nb Se 3 : Observation of a Threshold Electric Field and Conduction Noise

Abstract: Two new effects associated with Fr\"ohlich sliding-mode conductivity have been observed in Nb${\mathrm{Se}}_{3}$ First, nonlinear resistance is observed only after a well-defined threshold field is reached Second, electric fields above the threshold result in noise in the potential difference across a current biased specimen We interpret the threshold field as direct evidence of charge-density wave depinning and the noise as a result of charge-density wave motion

Equatorial electric fields during magnetically disturbed conditions 2. Implications of simultaneous auroral and equatorial measurements

Abstract: Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally intriguing, is the evidence presented for a close relationship between the zonal equatorial electric field and the time derivative of the ring current induced magnetic field. Another class of events seems related to rapid changes of magnetospheric convection and a temporary imbalance between the field external to the plasmasphere and the shielding charges in the Alfven layer. Examples of both rapid increases and decreases are presented. The latter seems oftern to be related to a northward turning of the interplanetary magnetic field.

An observed relation between magnetic field aligned electric fields and downward electron energy fluxes in the vicinity of auroral forms

Abstract: Using electron observations in the vicinity of, and over, auroral forms obtained from three rocket flights, we have found that the net downward electron energy flux generally varied as V², where V is the magnetic-field-aligned electric potential difference inferred from the peak in the observed energy spectra of precipitating electrons. We show that this relation implies that V is proportional to the net downward number flux of electrons from the magnetosphere to the auroral ionosphere and thus that increases in V and increases in the net downward number flux of electrons are equally responsible for the enhanced electron energy deposition responsible for auroral forms. This also indicates a direct physical connection may exist between V and the net downward electron number flux.

Characterization of lightning return stroke electric and magnetic fields from simultaneous two‐station measurements

Abstract: The paper presents a characterization of Florida lightning return stroke electric and magnetic fields derived from simultaneous measurements of the fields at two separate stations, one station being within 15 km of the lightning, the other at either about 50 or 200 km from the lightning. Also presented are: (1) examples of correlated wave forms, (2) typical first and subsequent stroke wave forms over the distance range 1.0-200 km, and (3) the following statistical data from which the typical wave forms were derived: for electric field, rise time, initial peak value, ramp starting time, ramp slope, value at 170 microsec, ratio of value at 170 microsec to initial peak, zero-crossing time for 50 and 200 km wave forms; for magnetic fields, time of hump following initial peak, ratio of hump value to initial peak value, zero-crossing time for 50 and 200 km wave forms. Return stroke electric and magnetic field characteristics appear to be independent of location in Florida.

Equatorial electric fields during magnetically disturbed conditions 1. The effect of the interplanetary magnetic field

Abstract: Radar measurements of E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east-west component of the IMF appears to be unimportant, but the north-south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east-west electric field during both daytime and nighttime. This is not always true, however; the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMF B/sub z/ is large and southward but not varying drastically. In this latter case the equatorial perturbations start nearly simultaneously with the onset of auroral substorms, while in the previous case they usually correlate with the onset of the substorm recovery phase. These observations indicate that the IMF does not affect the equatorial electric fields directly. Rather, it is changes in the magnetospheric electric fields and the auroral zone electric field and conductivity distribution (which may or may not be triggered by IMF changes) which alter the worldwide ionospheric current flow and electric field pattern, of which the equatorial observations are an indication.

The dc and ac electric field, plasma density, plasma temperature, and field‐aligned current experiments on the S3‐3 satellite

Abstract: Measurements of dc electric fields, field-aligned currents, the plasma density, and wave electric fields and density fluctuations have been made for the first time at auroral zone altitudes between 1000 and 8000 km on the S3-3 satellite. The design and operation of the various detectors that made these measurements is described, and some typical scientific results are presented. These include the observations that the high altitude auroral zone plasma density is typically 5–50 particles/cm³, that field-aligned currents exceeding the electrostatic ion cyclotron instability threshold are often observed in regions of ion cyclotron wave emission and accelerated upgoing ions, that the auroral zone electric field penetrates the plasmapause to cause deviations from corotation of the plasmasphere, and that the energetic electron high latitude trapping boundary is sometimes equatorward of the last closed magnetic field line, as determined by the reversal in the poleward electric field component.

Frequency dependence of dielectric loss in condensed matter

Abstract: The dielectric response of condensed matter below microwave frequencies has been known to depart from the Debye behavior, sometimes to the point of being unrecognizable and yet the generally accepted interpretations of the departures have seldom deviated from the Debye philosophy of simple relaxation phenomena in noninteracting systems. It was recently recognized, from a synoptic view of the experimental data involving a wide range of materials, that there exists a remarkable universality of dielectric response behavior regardless of physical structure, types of bonding, chemical type, polarizing species, and geometrical configurations. This strongly suggests that there should exist a correspondingly universal mechanism of dielectric polarization in condensed matter. The present work proposes such a universal mechanism associated with the existence of some ubiquitous very-low-energy excitations in the system. These excitations exhibit an infrared-divergent-like response to transitions of the polarizing species induced by a time-varying electric field in the dielectric and give rise to the universal dielectric response.

Plasma wave turbulence at the magnetopause - Observations from ISEE 1 and 2

Abstract: An investigation of plasma wave electric and magnetic fields in the vicinity of the magnetopause using measurements from the ISEE 1 and 2 spacecraft is presented. Strong electric and magnetic field turbulence is often observed at the magnetopause; the electric field spectrum of this turbulence extends from less than a few hertz to over 100 kHz, and the magnetic field from a few hertz to about 1 kHz. Similar turbulence spectra are observed in association with flux transfer events and possible 'inclusions' of boundary layer plasma in the magnetosphere. Two possible plasma instabilities, the electrostatic ion-cyclotron and the lower-hybrid-drift instability, should explain the broad-band electric field turbulence; the narrow-band electrostatic emissions near the local electron plasma frequency are believed to be plasma oscillations or electrostatic waves near the upper-hybrid-resonance frequency.

Finite Element Solution for Electric Fields of Coronating DC Transmission Lines

Abstract: Analytical computation of steady-state corona losses on HVDC transmission lines presupposes knowledge of two quantities: of the electric field vector and of the space charge. Both quantities could be sought in the entire interelectrode space, but it is mandatory to know them at least at electrode surfaces.

Simulation studies of ionospheric electric fields and currents in relation to field‐aligned currents, 2. Substorms

Abstract: Computer simulation studies of the electric fields and currents in the global ionosphere produced by field-aligned electric currents for quiet periods are conducted. The steady state equations for current conservation are solved numerically by assuming (1) several divided regions of the global earth (such as the polar cap, auroral zone, and middle-low latitudes), (2) exponentially distributed anisotropic electric conductivities for each zone with a continuous change at the boundaries of the regions, and (3) exponentially distributed downward and upward field-aligned current intensities in the auroral region, assumptions based on our current knowledge of auroral phenomena and geomagnetic variations as well as rocket and satellite measurements of field-aligned currents. Resultant computer-plotted diagrams include equipotential contours of the electric fields, vector distributions of the electric fields and currents, and electric current patterns equivalent to the magnetic field effect produced by the field-aligned and real ionospheric currents. One of the merits of this simulation method is that the three-dimensional current system can roughly be estimated from the equivalent current system obtained from ground-based geomagnetic data alone. This paper also provides a foundation for a similar study of substorms. The following main results are obtained: (1) Conductivity inhomogeneity alters considerably the electric field pattern that has previously been obtained by assuming the uniform conductivity distribution. (2) Even a slight conductivity enhancement along the nightside auroral belt results in a large modification of the electric field. (3) The existence of the strong conductivity gradients and the field-aligned currents in the equatorward half of the auroral oval reduces the electric field in the middle and low latitudes. This corresponds to the ‘shielding’ effect of the electric field inside the Alfven layer in the magnetotail. (4) Seasonal changes in the polar cap conductivities cause surprisingly large effects on the electric fields and currents. (5) The equivalent ionospheric currents differ significantly from real ionospheric currents in both intensity and direction.

Theory of Non-Ohmic Conduction from Charge-Density Waves in Nb Se 3

Abstract: A theory of non-Ohmic conduction from depinning of charge-density waves by an electric field is presented. It is based on Zener-type tunneling of the charge-density waves across a gap at the Fermi surface that is determined by the pinning frequency. The theory applies to relatively pure specimens for which the pinning is due to approach to commensurability or cooperative action of impurities.

Effects of coronae on electric fields beneath thunderstorms

Abstract: Intense electric fields beneath thunderstorms produce electrical discharges (coronae) at the tips of trees, bushes and other sharp objects attached to the surface of the earth. We find typical corona current densities of about 1 nA m−2 in an 8 kV m−1 field at the ground. The ions released into the air limit the magnitude of the field at the ground to about 10kV m−1. Our measurements beneath thunderstorms with a balloon-borne electric field meter show that the magnitude of the field a hundred metres above the ground is several times larger than at the ground; in one case the field 300 metres above ground was 6 times that at the ground. The substantial thickness of the space charge layer and the speed with which it vanishes when the electric field strength declines imply that the charge carriers have substantial velocities (0.4m s−1) either because their mobilities are high or because they are carried by air motions. Coronae also influence the time behaviour of the electric field at the ground. The field at the ground often changes very rapidly after a lightning flash. The rate of change decreases as the field approaches the value it had prior to the flash. In contrast, the field a hundred metres above the ground, which is often above most of the influence of space charge produced by coronae, increases more uniformly (linearly) during the time interval between lightning flashes. This behaviour is similar to that of the field farther aloft in the interior of the cloud. Our numerical simulations of the shapes of recovery curves indicate that the corona current density is more accurately described by a cubic function than by a quadratic function of the electric field strength at the ground. Despite strong influences of coronae, three properties of the field at the ground accurately reflect what happens above the space charge layer. First, the rapid changes in electric field during a lightning flash are not usually affected by corona space charge. Second, when the field at the ground is nearly constant it usually has the same polarity as the field above the space charge layer. And third, when the field strength at the ground is nearly zero, and when certain other conditions are met, the time rate of change of the field at the ground is the same as that above the space charge layer.

Characteristics of the inverted-V event

Abstract: An attempt is made to determine the origin of the inverted-V precipitating electrons and mechanisms that could create the inverted-V structure. The energy and pitch angle structures are compared with predictions from several theories that have been proposed to explain the origin of inverted-V events. Data from the AE-D satellite indicate that the origin of the inverted-V precipitating electrons is in the magnetosphere, the most probable regions being the plasma sheet and the neutral sheet. The energy and pitch angle distributions show that electrons are trapped between the mirror points and the electric field potential. The observations suggest that field-aligned precipitating electrons have been heated, probably when they were accelerated by the parallel electric field. Qualitatively, the detailed structures of the inverted-V events favor the theory of anomalous resistivity.

Theory of electrokinetic‐magnetic anomalies in a faulted half‐space

Abstract: Fluid motion in the vicinity of a vertical fault separating regions of different streaming potential coefficient can produce an external magnetic field of observable magnitude. If tectonic stress changes along the fault produce fluid motion, the magnetic field changes would be indicative of stress changes, and might precede severe fault motion. The largest component of the magnetic field is oriented parallel to the strike of the fault. Magnetic field changes produced by this mechanism will have electric fields associated with them with similar time variation; this is in contrast to magnetic field changes produced by changes in susceptibility or remanent magnetization, which have no associated electric field. Experiments aimed at the detection of tectonomagnetic effects should include electric field sensors to help in determining the source of any observed variations. The hypothesis of Mizutani and Ishido (1976) that the magnetic field changes associated with the Matsushiro earthquake swarms were produced by electrokinetic currents seems reasonable.

Intense electrostatic waves near the upper hybrid resonance frequency

Abstract: Plasma wave measurements using instruments on the Imp 6 and Hawkeye satellites are utilized in a study of very intense electrostatic waves near the upper hybrid resonance frequency in the region just outside the plasmapause. Studies of these electrostatic disturbances show that the events occur at local times and at magnetic latitudes varying from the equator to 50 deg, and the polarization of these waves is such that the wave electric field vector is oriented perpendicular to the geomagnetic field. In most cases the center frequency of the intense waves corresponds to an (n + 1/2) fg(-) harmonic near the upper hybrid resonance frequency. The hot distribution on function is described for a few events showing temperature anisotropy and a loss cone distribution. A possible mechanism for producing intense waves near the upper hybrid resonance frequency is suggested, and evidence which indicates that the intense electrostatic waves may be a source of nonthermal continuum radiation is given.

Finite length thermal equilibria of a pure electron plasma column

Abstract: The electrons of a pure electron plasma may be in thermal equilibrium with each other and still be confined by static magnetic and electric fields. Since the electrons make a significant contribution to the electric field, only certain density profiles are consistent with Poisson’s equation. The class of such distributions for a finite length cylindrical column is investigated. In the limit where the Debye length is small compared with the dimensions of the column, the density is essentially constant out to some surface of revolution and then falls off abruptly. The falloff in density is a universal function when measured along the local normal to the surface of revolution and scaled in terms of the Debye length. The solution for the shape of the surface of revolution is simplified by passage to the limit of zero Debye length.

The motion of depleted plasma regions in the equatorial ionosphere

Abstract: Depleted plasma regions in the equatorial ionosphere and their associated motions have been observed by a variety of ground-based, rocket-borne, and satellite instruments. Various theories, based primarily on the Rayleigh-Taylor instability mechanism, have been proposed for the formation and motion of these bubbles. Numerical studies in the past have incorporated local electron density depletions, with Pedersen conductivities involving local ion-neutral collision frequencies. Realizing that bubbles are actually depleted magnetic flux tubes, we investigate the vertical E × B motion of these depleted regions, incorporating flux tube integrated quantities of electron content and Pedersen conductivity. A simple expression for the polarization electric field E1 inside the depleted flux tube is used. The resulting calculations show that the vertical bubble velocity as a function of time critically depends on the background ionospheric electric field and that this dependence extends to much greater heights than was previously thought. Bubbles which are initiated at 350-km altitude (1900LT) with a 5% depletion in electron content attain an upward velocity of 200 m/s at 1920 LT when the background electric field is 0.6 mV/m. Bubble altitude at this time is 447 km with an 88% depletion in electron content. In the absence of an ambient electric field, 1 hour is required for the vertical bubble velocity to reach 200 m/s.