Vertical Component Of Electric Field Research Articles

Rapid fluctuations of stratospheric electric field following a solar energetic particle event

[1] During January, 2005, there were several large X-class solar flares and associated solar energetic particle (SEP) events. Coincidentally, the MINIS balloon campaign had multiple payloads aloft in the stratosphere above Antarctica measuring dc electric fields, conductivity and x-ray flux. One-to-one increases in the electrical conductivity and decreases to near zero of both the vertical and horizontal electric field components were observed in conjunction with an increase in particle flux at SEP onset. Combined with an atmospheric electric field mapping model, these data are consistent with a shorting out of the global electric circuit and point toward substantial ionospheric convection modifications. Additionally, two subsequent, rapid changes were detected in the vertical electric field component several hours after SEP onset. These changes result in similar fluctuations in the calculated vertical current density. We will describe how rigidity cut-off dynamics may be crucial in understanding these sudden jumps in the vertical electric field.

On the electro–dynamical characteristics of the fog

The electrical properties of the fog are described on the basis of full-scale aeroelectrical observations and theoretical modeling. The measured electric field and spectrum of its pulsations are given along with the simultaneous amplitude–time series of the vertical component of electric field and electric current. Fog is shown to increase the intensity of electric-field pulsations by more than an order of magnitude. Nevertheless, in the majority of observations, the exponent of the spectrum does not differ drastically from the spectrum exponents typical for fair-weather conditions. The results of structure–time analysis offer the possibility of specifying two types of electrical states of fog: one of them is characterized by aeroelectric structure generation and another, by chaotic structure–time variations. Possible mechanisms of electric-field profiles and spectra formation are discussed with allowance for fog-particle charging, neutral gas turbulence and aeroelectric structures in the fog.

Propagation of Radar Pulses from a Horizontal Dipole in Variable Dielectric Ground: A Numerical Approach

We numerically investigate the propagation of radar type short pulses from a horizontal dipole in the presence of some simple models of inhomogeneous ground with a flat surface. We use 3-dimensional (3-D) pseudospectral time domain (PSTD) and 2-D finite difference time domain forward modeling to determine the range and azimuth dependence of electric field components and to simulate events in a moveout profile. The models are: (i) a uniform half space with either high or low conductivity; (ii) a vertical dielectric wedge; (iii) a surface thin layer with a monocline wedge overlaid on the dielectric half space. Our homogeneous results agree with the analytical solutions, and more clearly show the significant vertical electric field component, which occurs for all models. The incorporation of an anomalous dielectric quadrant does not affect the air wave and only complicates ground wave propagation near the boundary. Modeling of a monocline dielectric wedge shows predictable subsurface reflections and refractions, some of which are highly dispersive events, depending on the direction of propagation. We present two field examples that appear to demonstrate some of our findings. We conclude that air waves make suitable references for moveout profiles regardless of dielectric complications, and that our results provide some insight into the interpretation of unique events seen in moveout profiles.

The relationship between variations of the atmospheric electric field in the southern polar region and thunderstorm activity

Observations of the atmospheric, near-surface vertical electric field component E z have been carried out at the Russian–Antarctic station, Vostok, since 1998 under the framework of a cooperative Russian–Australian project. Only data satisfying “fair weather” conditions are selected for the subsequent analyses. Behavior of E z field at Vostok station is compared with thunderstorm occurrence determined from a network of ELF magnetic field measurements in April 1998 and with simultaneous VLF emission measurements at Halley Bay (Antarctica). We find no correlation between the 5 min averages of E z and the lightning flashes intensity or between E z and VLF emissions, although significant correlation between E z and VLF emissions is observed in particular cases. The same statistical results have been obtained from a comparison of hourly averaged values. Moreover, even the mean diurnal variation of electric field derived for 10 fine weather days in April 1998 turned out to be inconsistent with the mean diurnal variation of the lightning flashes for the same days. Reasons of these inconsistencies are discussed.

On the lithosphere‐atmosphere coupling of seismo‐electromagnetic signals

Employing borehole and terrestrial antennas, vertical electric field components of the naturally occurring very low frequency electromagnetic emissions at the frequency of 3 kHz have been monitored simultaneously at Agra (geographic latitude 27.8°N, longitude 78°E), India, from 15 March 1999 to 30 September 1999. This period of observation included a major seismic swarm activity in the months of March and April which occurred in the Chamoli hills of north India, the next two months of May and June being quiet with respect to local lightning and spheric activities, and the rest of the three months from July to September being highly disturbed due to local lightning and thunderstorm activities. The abnormal electric field changes occurred in the form of noise bursts of varying amplitude and duration and included three kinds of data: (1) noise bursts observed by borehole antenna only, (2) noise bursts observed by terrestrial antenna only, and (3) noise bursts observed by both the antennas. We find that the occurrence of the first kind of data is positively correlated with major seismic activities in the region over the period of observations. The third kind of data indicates coupling between the two antennas dominated overall by atmospheric emissions. The long distance propagation of the seismo‐electromagnetic emissions through the middle layer crust working as waveguide or through seismic faults is found to be associated with large attenuation ≈13 dB/km. Hence, the observation of the emissions at Agra, about 400 km from Chamoli, is interpreted in terms of leakage to the atmosphere through “windows” of low conductivity in the skin layer near the epicenter, possibly produced by some geophysical formations as discussed by other workers and then propagation in the Earth‐ionosphere waveguide.

Horizontal structure of the electric field in the stratiform region of an Oklahoma mesoscale convective system

This analysis combines vertical electric field components Ez observed by two research aircraft flying horizontally at two levels, with vertical soundings of thermodynamic parameters and Ez made by five balloons, to produce a quasi‐three‐dimensional view of the space charge distribution in the trailing stratiform cloud region behind a mesoscale convective system (MCS) that developed in central Oklahoma late in the afternoon of 2 June 1991. The balloons were launched serially at one‐hour intervals from two sites separated by 80 km along a north‐south line as the MCS moved eastward, yielding two east‐west time‐height cross‐sections of the Ez structure within the quasi‐steady state trailing stratiform region behind the MCS. The balloon measurements are consistent with a vertical stack of five rearward‐ and downward‐sloping horizontal sheets of charge of alternating polarity, beginning at the bottom with a negative charge layer below the 0°C level and a positive layer near the 0°C level. This structure persisted for more than 2 hours. The two aircraft flew back and forth along a north‐south line through the balloon launch sites during the balloon launch period. Aircraft measurements demonstrated that the vertical electric field (Ez) at constant altitude varied in the north‐south direction. The peak magnitudes of Ez deduced from the airborne instrument systems agreed with the magnitudes deduced from the balloon measurements at the aircraft altitudes of 4.5 km and 5.8 km AGL. Rapid reversals in polarity of Ez with peak magnitude >50 kV m−1 observed by the aircraft at 4.5 km, just above the 0°C level, confirms the thin concentrated positive charge layer observed there by balloons and suggests that this charge layer is undulating above and below 4.5 km altitude, at least in the north‐south direction. Microphysically, this layer contained large aggregates and pockets of low cloud liquid water concentration. At the 5.8 km level, the polarity of Ez was always positive but the magnitude varied from zero to 25 kV m−1. Aircraft‐observed Ez at both altitudes varied on horizontal scales of ∼10 km or greater at both levels, suggesting that the charge density derived using the one‐dimensional infinite‐layer Gauss's law approximation applied to the balloon soundings of Ez is valid in this study. These observations show that layers of charge can persist for hours as they advect rearward in a storm‐relative sense, possibly due to continuing in situ charge separation, and/or due to weak dispersion, slow recombination and slow settling of charge attached to low mobility low terminal velocity ice hydrometeors.

Solving a Two-Dimensional Telegraph Equation with Anisotropic Parameters

We solve a two-dimensional telegraph equation with anisotropic parameters, which models the propagation of electromagnetic waves in the Earth–ionosphere waveguide, in the frequency range 0.1-30 Hz. The results are generalized to allow for the Earth's sphericity and the horizontal inhomogeneity of the waveguide. It is shown that the resonance character of reflection from the ionosphere at frequencies below 10 Hz becomes pronounced for the horizontal magnetic-field components and for the vertical electric-field component of a horizontal dipole. In the case of low solar activity under nighttime conditions, the oscillations in the frequency dependences of the field components are much more pronounced compared with the case of high solar activity.

Optical studies of the ionospheric irregularities over the brazilian region by nocturnal images of the OI 630 nm emission

This study is an extension of previous statistical studies (Sobral et al., 1990, 1991, 1999) of both the local time and latitude variations of the zonal drift velocities of ionospheric plasma depletions, over the Brazilian low latitude station Cachoeira Paulista — CP (22.54°S, 45.00°W). The past studies were based on OI 630 nm scanning photometer data and the present one is based on digital OI 630 nm airglow images obtained by an all-sky imager system. These data were gathered between October 1998 and October 1999, at CP. The present results show that, in general, the velocities clearly tended to decrease with local time. Such a decrease should be associated with decreasing intensity of the vertical component of the ambient electric field which, in turn can be accounted for by recombination. All zonal drifts obtained for the 18 nights were eastwards. During equinox, the velocities clearly tended to decrease with local time at lower rates as compared with spring and summer. The highest and lowest zonal drift velocities, from all three seasons considered here, were observed to be in the summer ≈180 ms −1 at 21:45 LT, and in the spring ≈25 ms −1 at 03:15 LT, respectively. Ionospheric plasma bubbles were detected out to the maximum extra-tropical geographical latitude of ≈28° S, which was the highest latitude position analyzed in this study.

Variations of the atmospheric electric field in the near‐pole region related to the interplanetary magnetic field

Variations in the atmospheric, near‐surface vertical electric field component Ez measured at the Russian Antarctic station Vostok in 1998 are analyzed in conjunction with changes of the interplanetary magnetic field (IMF). A total of 134 days were selected which satisfied the “fair weather” conditions, that is, days with absence of high winds, falling or drifting snow, clouds, and electric field “pollution” from the station's power plant. It is shown that the average diurnal variation of Ez for these days follows the global geoelectric field “fair ‐ weather” diurnal variation: the “Carnegie” curve, which describes the global electric circuit formed by the thunderstorm activity occurring mostly over equatorial regions. The Ez diurnal variation shows strong seasonal dependence: it is maximal (∼40% of the average daily magnitude) in summer but gradually reduces through the equinoctial months and is almost negligible during the austral winter. Ez at Vostok is strongly affected by variations in both the IMF By and Bz components. The influence of By is dominant during geomagnetic daytime hours (1100–1400 UT at Vostok): Ez increases with By in the range from −10 to +10 nT. The IMF Bz effect is mainly seen at dawn (Ez decreases with Bz) and dusk (Ez increases with Bz).

Electric‐field changes of lightning observed in thunderstorms

During the Summer and Fall of 1998 we launched five balloon‐borne instruments into thunderstorms to observe changes in the vertical component of electric field caused by lightning. Four of these were for measurement of field change only. The fifth was part of a larger package that included a gamma radiation detector and a GPS receiver on board. We have processed electric‐field‐change data from two of these flights. We discuss examples of field changes observed at altitude and compare them with data from the National Lightning Detection Network (NLDN) for cloud‐to‐ground lightning flashes that were coincident in time. Limits on time resolution and timing accuracy prevent unambiguous identification of the lightning processes that caused the field changes. It appears that they may have been caused by charge movements relatively near the instruments as compared with the ground‐strike location of coincident flashes.

Spatially resolved exciton trapping in a voltage-controlled lateral superlattice

With spatially resolved photoluminescence experiments we demonstrate voltage-controlled trapping of excitons in a submicron scale lateral potential superlattice imposed on a semiconductor quantum well. The potential modulation is achieved by two interdigitated field-effect electrodes on top of the sample surface. Both parallel and vertical electric field components strongly modify the optical properties of the quantum well. We show that the lateral modulation of the strength of the quantum confined Stark effect results in an effective lateral exciton potential that can be probed by spatially resolved measurements of the excitonic luminescence. We demonstrate that excitons may be confined to the regions of strongest vertical fields, in which the effective exciton energy is lowest. Spatial resolution of the observed photoluminescence signal allows for a qualitative understanding of the exciton transport and trapping process.

TSS‐1R vertical electric fields: Long baseline measurements using an electrodynamic tether as a double probe

This paper presents measurements of vertical electric fields obtained using the Tethered Satellite System (TSS) as an electrodynamic double probe. During five hours of TSS‐1R deployment from the space shuttle Columbia in February 1996, observations of induced tether potential were gathered over a baseline from 2 to 20 km in the mid and low latitude F‐region ionosphere. The corresponding electric fields derived from the potential measurements are found to be consistent with previous satellite and ground‐based measurements for similar ionospheric conditions. The data are unique and demonstrate a new capability for measuring the vertical component of the ionospheric electric field. Comparison of the measured electric field at different tether deployment lengths for corresponding local times reveal that the vertical component of the ambient electric field exists on scales of at least 20 km.

DC polarization electric field, current density, and plasma density measurements in the daytime equatorial electrojet

Measurements of the vector DC electric field, current density, and plasma number density were gathered in the daytime equatorial electrojet on a sounding rocket launched from Alcântara, Brazil. The data set provides a self‐consistent picture of the electrodynamics of the daytime electrojet, permitting a detailed comparison of the altitude profiles of the vertical component of the DC electric field, Evert, the current density, J, and the plasma number density, Ne. Good agreement in the upper electrojet region between both the magnitude and the profile of the plasma drifts, calculated independently from Evert/B and Jzonal/qNe, demonstrates that the equatorial electrojet is a Hall current consisting of electron motion driven by a vertical DC electric field. The data support the basic Cowling conductivity ideas of electron flow at the dip equator within a narrow conducting layer in which the ions are at rest.

Spectral characteristics of Schumann resonances observed in central Europe

The vertical electric field component in the frequency range of Schumann resonances has regularly been measured at the Nagycenk Observatory in Hungary, in Central Europe since May 1993. The actual peak frequencies and the amplitudes belonging to them are determined for the first three modes. Each mode has its own character and they show distinct daily and seasonal variations. The recurrence tendency of these variations from year to year is also presented. The significant annual and semiannual variations of the amplitudes support the suggestion that the Schumann resonance as a global phenomenon is sensitive to small temperature variations in the tropical atmosphere.

Direct determination of 3D forces applied on a particle suspended in an electrodynamic chamber

The main motivation of the present work is to enable one to carry out a direct quantitative measurement of 3D force balance applied on a suspended particle in an electrodynamic chamber (EDC). For this, the absolute values of electric field parameters are essential. Both horizontal and vertical electric field components were analysed theoretically and experimentally. From the theoretical analysis of the motion of a charged particle in an EDC, two relationships relating motion parameters to electric field strength were found. These relationships were validated experimentally from measurements of 17 polystyrene and char particles with various densities and sizes. Consequently, the absolute 3D field parameters were determined. This method was used to determine the absolute value of the photophoretic force (PPF) and the free convection force (FCF) applied on a suspended particle. In these experiments, the particle was irradiated horizontally by a focused laser beam. Consequently, the PPF was developed horizontally whereas the FCF was developed vertically. The present measurement indicated that the PPF is much smaller than the FCF, in contrast to previous reports.

Measurement of horizontal electric fields associated with distant cloud‐to‐ground strokes

A broadband sensor for the horizontal component of the electric field associated with lightning discharges was developed. The vertical electric field component contaminating the output of this sensor was, on the average, only about 0.5% of the output. Simultaneous measurement of both vertical and horizontal electric field components, associated with lightning striking at more than 16 km away, confirms that the horizontal electric field is accurately evaluated from the measured vertical electric field with the help of the wave tilt formula, irrespective of the propagation path or the polarity of the cloud‐to‐ground stroke. From this simultaneous measurement, it is possible to estimate the effective conductivity and permittivity of the ground in the vicinity of the measuring site. These local electrical parameters are independent of those of the ground beneath the propagation path, which are estimated by comparing the attenuated electromagnetic waves propagated over land with relatively unattenuated electromagnetic waves propagated over seawater. The estimation becomes easier by measuring the horizontal electric field, as it is more sensitive to the attenuation.

ELF/VLF propagation measurements in the Atlantic during 1989

The vertical electric field component was measured by a group of the Ukrainian Institute of Radio Astronomy on board the Professor Zubov scientific vessel during April 1989 at latitudes from 30°S to 50°N. Results of the amplitude measurements in the Atlantic of natural ELF radio signals and those from the VLF navigation system “Omega” at its lowest frequency of 10.2 kHz are given. Characteristics were obtained of the moving ship as the field-site for the ELF observations. Variations in the ELF radio noise amplitude recorded at tropical latitudes agree with the computed data for the model of three continental centres of lightning activity. The VLF results were obtained by the “beat” technique providing the simplest narrow-band amplitude registration. Range dependencies of the field amplitudes from A (Norway), B (Liberia) and F (Argentina) stations have been analysed. The VLF attenuation factor was estimated for the ambient day conditions along the four cardinal directions. This allowed the detection of a statistically significant attenuation difference between the east-west and west-east propagation paths. The VLF radio signal was also used as a probe to evaluate the effective height of the vertical electric antenna and to calibrate the ELF noise amplitudes.

A modified technique to locate the sources of ELF transient events

An algorithm is proposed for the location of the sources of ELF transient events which occur in the Schumann resonance range. The procedure yields a uniformly rotating vector in the frequency domain. The vector is formed out of the recorded vertical electric and horizontal magnetic field components. The changes of this vector with frequency provide a pair of equations for the evaluation of two of the three unknown parameters: these are the distance from the source, phase and attenuation constants of the waveguide.

ELF radio wave propagation in a locally nonuniform Earth‐ionosphere cavity

The vertical electric field component of the ELF radio wave propagating in the spherical Earth‐ionosphere cavity with a localized nonuniformity is studied. The analysis is performed in the framework of Born's approximation of the perturbation theory applied to the Stratton‐Chu integral equation. Both the vertical electric dipole and the horizontal grounded wire antenna are considered as the ELF field sources. It is shown that different effects can arise within the nonuniform waveguide depending on the disturbance position between or beyond the endpoint of the propagation path that are conditioned by the vectorial nature of the radio wave. Backscatter is the prevailing effect in the case of impedance or height disturbances. A localized nonuniformity can bring forth pattern rotation of the horizontal wire antenna and at the same time an amplitude modification of its lobes.

On the assumption of the Earth's surface as a perfect conductor in atmospheric electricity

The assumption of considering the Earth's surface as a plane perfect conductor is examined. The electric field produced due to a point charge or a model thundercloud in the atmosphere and the field changes produced due to a leader in a lightning flash have been calculated if the Earth's surface, instead of a perfect conductor, is considered as a dielectric of finite dielectric constant and zero conductivity. It is shown that when the dielectric constant of the surface is <10, the horizontal and vertical components of electric field may be comparable to each other at comparatively large distances from the charge. The net electric field in such a case may be inclined from the vertical by as much as 45° or even more. At different distances, the field changes caused due to the leader in a lightning flash change not only its magnitude but direction as well. Certain igneous and metamorphic rocks with low moisture contents, fine‐grained sand when it is dry or has a moisture content of <1% or is at low temperatures, and ice at very low temperatures of <−50°C or oriented such that its c axis is perpendicular to the direction of electric field have dielectric constant values < 10 and conductivity < 10−9 S/m. Therefore, for some regions, such as polar regions, high‐latitude regions covered with sea ice or dry sand, hot and dry regions covered with sand in the midst of vast deserts, and regions covered with hot and dry igneous and metamorphic rocks, the average representative values of dielectric constant and conductivity of the surface may be such that the Earth's surface at those places cannot be assumed as a perfect conductor. Consequently, the assumption of treating the Earth's surface as an insulating surface generally taken for fast field changes during a stepped leader in a lightning flash, may be extended for much slower field changes occurring even in fair weather. It needs to be mentioned, however, that thunderstorm activity is generally minimal in most of the regions mentioned above. It is proposed that instead of measuring only the vertical component of electric field, as is normally done, a measurement of the electric field vector will give a fifil description of the intensity of the electric field at some places.