Impulse Electric Field Research Articles

Partially transmitted lightning signals recorded by pioneer Venus orbiter

Impulsive electric fields appearing on all four frequency channels of the Pioneer Venus electric field detector in the night ionosphere of Venus are characteristic of lightning generated signals. Based on our knowledge of the electron density and magnetic field in the Venus ionosphere, we suggest that lightning waves could be partially transmitted upwards into the ionosphere. The leakage of these lightning waves into the ionosphere on encountering electron density holes may be treated as reradiation into the ionosphere from the hole. Since this radiation pattern is frequency dependent, we should not expect to see all frequency components for every lightning stroke observed.

Magnetohydrodynamic theories of solar flares

Our current understanding of the MHD of the flare process is summarised, with some emphasis on processes which produce strong impulsive electric fields and current filamentation. As an introduction, a description of the two main types of flare (i.e., simple-loop and two-ribbon) is given, together with an account of the two branches of reconnection theory (tearing modes and the Petschek-Sonnerup mechanism). Modern numerical experiments of reconnection suggest impulsive bursty acceleration of particles in many small regions of width a hundred kilometres or less. This is followed by a discussion of the eruptive instability thought to initiate a large flare and of the reconnection process of energy release. Finally, the role of emerging flux and horizontally moving satellite sunspots is discussed briefly.

Hydrogen atoms perturbed by some periodic impulsive electric fields

Calculations on a classical hydrogen atom, perturbed by equal and equally spaced electric field impulses, are compared with analogous quantal calculations performed by Dhar et al. (1983). The classical and quantal ionisation probabilities are of the same order of magnitude. Classical stochasticity is observed. Then calculations on a classical hydrogen atom, perturbed by alternating electric field impulses, are compared with calculations performed by Leopold, Percival and Jones et al. (1980), on a hydrogen atom perturbed by a microwave field. The two systems exhibit similar mechanisms of ionisation.

Observations of large magnetospheric electric fields during the onset phase of a substorm

A large (30‐mV/m peak) impulsive westward electric field was observed in the midnight, low latitude, dipole L = 7.5 region of the earth's magnetospheric tail at the onset of a large substorm. The measurements were made with the long, 179‐m baseline, cylindrical electric field probes carried by ISEE 1. The electric field impulse was coincident with a sharp 60 nT steplike change in the x component of the magnetic field at the satellite and the onset of a sharp 60 nT decrease in the H component of the field at a magnetic observatory near the subconjugate point. The 2‐min envelope of the westward Ey field correlates with the time derivative ∂Bx/∂t of the collapsing magnetic field attributed to the decrease in the cross‐tail current. Associated with this inductive impulse, large electric field variations are also observed on time scales of tens of seconds to tens of milliseconds. The low‐frequency (10 s) wave variations show a coherent phase relationship between the electric and magnetic field that changes from correlative to anti‐correlative during the event. Higher frequency (t < 1 s) turbulent electrostatic fields of similar magnitude are present throughout the event. These large time‐dependent electric fields seem to have the proper amplitude, duration, and timing relative to the auroral substorm sequence to explain the energetic proton enhancements frequently observed near midnight both at synchronous orbit and in the magnetotail at times of substorm onsets. The azimuthal direction of Ey (westward) for this event appears to conflict with the IMP 6 observations of an eastward Ey at higher latitudes under similar conditions. However, these observations are in agreement when magnetotail collapse is viewed in terms of a sharp reduction in the anti‐solar tension on auroral field lines as opposed to interpretations based solely on the effects of a sudden decrease in the cross‐tail current sheet.

Persistence of two-state resonances in a hydrogen atom under the influence of a periodic impulsive field

Very-long-lived two-state resonances are observed in numerical studies of a hydrogen atom interacting with a periodic impulsive electric field. These resonances are discussed in the light of a simple exactly soluble two-state, weak-field model. No evidence of chaotic motion is observed.

Simulation of high-voltage breakdown in the post-arc column

A simple model of the nonequilibrium discharge in molecular gas has been developed based on the assumption that partition of heavy species is governed by the common kinetic temperature of heavy particles. The model has been used to simulate high-voltage breakdown in the post-arc column in nitrogen at a pressure of 20 atm. Axial homogeneity has been assumed and electrode effects were neglected. The initial conditions were given by the arbitrary radial distributions of the electron and heavy-particle temperatures. The electric-field impulse was applied to the column after a period of forced cooling, which lasted approximately 30 μs. The gas sustained fields of up to 18 kV cm−1 and breakdown occurred at 24 kV cm−1.

Formulation of the linearized Vlasov-fluid model for a sharp-boundary screw pinch

A theoretical formulation is derived for analyzing linearized equations appropriate to a straight, cylindrical, sharp-boundary screw pinch within the framework of the Vlasov-fluid model. Surrounding the plasma is a cylindrical conducting wall, and there is a nonconducting vacuum between the plasma and the wall. By introducing a perturbation-dependent transformation of the phase space and linearizing about a zeroth-order state which depends on the perturbation, the linearized equations of Freidberg’s Vlasov-fluid model are put into a form which would be correct for a hypothetical problem in which the plasma boundary is a rigid cylinder. The effects of the impulsive electric field at the actual perturbed boundary are taken into account in the zeroth-order state. The boundary conditions at the perturbed plasma boundary are continuity of the normal component of B and vanishing of the normal component of the net current density.

Pi-2 pulsations as a result of evolution of an Alfvén impulse originating in the ionosphere during a brightening of aurora

It is assumed that the original impulse producing Pi-2 pulsations is generated in the ionosphere at the moment of a brightening of aurora. The electric field is known to decrease in the auroral arc almost by an order of magnitude. The electric impulse that appears will be transferred along magnetic field lines and reflected from the ionosphere of the opposite hemisphere, forming the standing Alfvén wave. The electric field impulse of 100 mV m is capable of causing magnetic field oscillations of order of 100 γ. Reflection of the Alfvén impulse from the ionosphere with horizontal inhomogeneities corresponding to different forms of auroras is studied. The following is found: (a) the resonance is possible only for harmonics with the rotating vector of polarization; (b) the resonance periods appear to depend essentially on the ionospheric conductivity; this may bring a significant error into determination of the magnetospheric plasma density from the pulsation periods; (c) the auroral zone exerts a screening influence on the pulsations excited at latitudes higher than the zone itself.

Plasma waves in the dayside polar cusp: 2. Magnetopause and polar magnetosheath

During the outbound pass of Nov. 1, 1968, Ogo 5 sporadically encountered the low-altitude polar cusp at low magnetic latitudes. The spacecraft remained in the cusp beyond six earth radii, and it then traversed the interface region between the magnetospheric cusp and the magnetosheath. Two large scale discontinuities were detected in this sheath-cusp transition region, and several possible interpretations are evaluated here. At 1427 UT, local changes in magnetic field orientation and the variation in ULF magnetic power spectral density were typical of shifts detected at the magnetopause, although the spacecraft did not traverse a true boundary of warm plasma at this point. The second discontinuity, detected at 1456 UT, resembled a collisionless shock, and it was characterized by observations of intense, impulsive VLF electric field bursts and rapid local variations in both total ion flux and differential electron flux. The simplest interpretation is that Ogo 5 had traversed a standing shock within the sheath.