Intense Electron Fluxes Research Articles

Observation of Thunderstorm Ground Enhancements with intense fluxes of high-energy electrons

The high altitude (∼3200m above sea level) of Aragats Space Environmental Center (ASEC) and low elevation of the thunderclouds provides a good opportunity to detect Thunderstorm Ground Enhancements (TGEs), particles of which rapidly attenuate in the atmosphere. In 2012, we have estimated the energy spectra of several TGEs and revealed significant electron fluxes extended till 30–40MeV. Measured in the one and the same event gamma ray and electron fluxes allow to estimate the height of the thundercloud above the detector. Proceeding from the energy spectra and the height of the cloud we estimate the electron spectra on the exit from the electric field of the thundercloud, the number of excess electrons in the cloud and avalanche multiplication rate.

TEC Enhancement due to Energetic Electrons Above Taiwan and the West Pacific

The energetic electrons of the inner radiation belt during a geomagnetic disturbance can penetrate in the forbidden range of drift shells located at the heights of the topside equatorial ionosphere (< 1000 km). A good correlation was previously revealed between positive ionospheric storms and intense fluxes of quasi-trapped 30-keV electrons at ~900 km height in the forbidden zone. In the present work, we use statistics to validate an assumption that the intense electron fluxes in the topside equatorial ionosphere can be an important source of the ionization in the low-latitude ionosphere. The data on the energetic electrons were obtained from polar orbiting satellites over the periods of the 62 strong geomagnetic storms from 1999 to 2006. Ionospheric response to the selected storms was determined using global ionospheric maps of vertical total electron content (VTEC). A case-event study of a major storm on 9 November 2004 provided experimental evidence in support to the substantial ionization effect of energetic electrons during positive ionospheric storms at the low latitudes. Statistical analysis of nine magnetic storms indicated that the VTEC increases coincided with and coexisted with intense 30-keV electron fluxes irrespective of local time and phase of geomagnetic storm. We concluded that extremely intense fluxes of the 30-keV electrons in the topside low-latitude ionosphere can contribute ~ 10 30 TECU to the localized positive ionospheric storms.

Wp index: A new substorm index derived from high‐resolution geomagnetic field data at low latitude

Geomagnetic field data with high time resolution (typically 1 s) have recently become more commonly acquired by ground stations. Such high time resolution data enable identifying Pi2 pulsations which have periods of 40–150 s and irregular (damped) waveforms. It is well‐known that pulsations of this type are clearly observed at mid‐ and low‐latitude ground stations on the nightside at substorm onset. Therefore, with 1‐s data from multiple stations distributed in longitude around the Earth's circumference, substorm onset can be regularly monitored. In the present study we propose a new substorm index, the Wp index (Wave and planetary), which reflects Pi2 wave power at low‐latitude, using geomagnetic field data from 11 ground stations. We compare the Wp index with the AE and ASY indices as well as the electron flux and magnetic field data at geosynchronous altitudes for 11 March 2010. We find that significant enhancements of the Wp index mostly coincide with those of the other data. Thus the Wp index can be considered a good indicator of substorm onset. The Wp index, other geomagnetic indices, and geosynchronous satellite data are plotted in a stack for quick and easy search of substorm onset. The stack plots and digital data of the Wp index are available at the Web site (http://s‐cubed.info) for public use. These products would be useful to investigate and understand space weather events, because substorms cause injection of intense fluxes of energetic electrons into the inner magnetosphere and potentially have deleterious impacts on satellites by inducing surface charging.

On relation between mid-latitude ionospheric ionization and quasi-trapped energetic electrons during 15 December 2006 magnetic storm

We report simultaneous observations of intense fluxes of quasi-trapped energetic electrons and substantial enhancements of ionospheric electron concentration (EC) at low and middle latitudes over the Pacific region during the geomagnetic storm on 15 December 2006. Electrons with energy of tens of keV were measured at altitude of ∼800–900km by POES and DMSP satellites. Experimental data from COSMIC/FS3 satellites and global network of ground-based GPS receivers were used to determine height profiles of EC and vertical total EC, respectively. A good spatial and temporal correlation between the electron fluxes and EC enhancements was found. This fact allows us to suggest that the quasi-trapped energetic electrons can be an important source of ionospheric ionization at middle latitudes during magnetic storms.

Particle-in-cell simulations for virtual cathode oscillator including foil ablation effects

We have performed two- and three-dimensional, relativistic, electromagnetic, particle-in-cell simulations of an axially extracted virtual cathode oscillator (vircator). The simulations include, for the first time, self-consistent dynamics of the anode foil under the influence of the intense electron beam. This yields the variation of microwave output power as a function of time, including the role of anode ablation and anode–cathode gap closure. These simulations have been done using locally developed particle-in-cell (PIC) codes. The codes have been validated using two vircator designs available from the literature. The simulations reported in the present paper take account of foil ablation due to the intense electron flux, the resulting plasma expansion and shorting of the anode–cathode gap. The variation in anode transparency due to plasma formation is automatically taken into account. We find that damage is generally higher near the axis. Also, at all radial positions, there is little damage in the early stages, followed by a period of rapid erosion, followed in turn by low damage rates. A physical explanation has been given for these trends. As a result of gap closure due to plasma formation from the foil, the output microwave power initially increases, reaches a near-flat-top and then decreases steadily, reaching a minimum around 230 ns. This is consistent with a typical plasma expansion velocity of ∼2 cm/μs reported in the literature. We also find a significant variation in the dominant output frequency, from 6.3 to 7.6 GHz. This variation is small as long as the plasma density is small, up to ∼40 ns. As the AK gap starts filling with plasma, there is a steady increase in this frequency.

Suprathermal electron flux peaks at stream interfaces: Signature of solar wind dynamics or tracer for open magnetic flux transport on the Sun?

The high variability of the intensity of suprathermal electron flux in the solar wind is usually ascribed to the high variability of sources on the Sun. Here we demonstrate that a substantial amount of the variability arises from peaks in stream interaction regions, where fast wind runs into slow wind and creates a pressure ridge at the interface. Superposed epoch analysis centered on stream interfaces in 26 interaction regions previously identified in Wind data reveal a twofold increase in 250 eV flux (integrated over pitch angle). Whether the peaks result from the compression there or are solar signatures of the coronal hole boundary, to which interfaces may map, is an open question. Suggestive of the latter, some cases show a displacement between the electron and magnetic field peaks at the interface. Since solar information is transmitted to 1 AU much more quickly by suprathermal electrons compared to convected plasma signatures, the displacement may imply a shift in the coronal hole boundary through transport of open magnetic flux via interchange reconnection. If so, however, the fact that displacements occur in both directions and that the electron and field peaks in the superposed epoch analysis are nearly coincident indicate that any systematic transport expected from differential solar rotation is overwhelmed by a random pattern, possibly owing to transport across a ragged coronal hole boundary.

Plasma generation and expansion at the anode surface in a Virtual Cathode Oscillator

We have performed two- and three-dimensional, relativistic, electromagnetic particle-in-cell simulations of an axially-extracted Virtual Cathode Oscillator (vircator). The simulations include, for the first time, self-consistent dynamics of the anode foil under the influence of the intense electron beam. This yields the variation of microwave output power as a function of time, including the role of anode ablation and anode-cathode gap closure. These simulations have been done using locally-developed Particle-in-Cell (PIC) codes. The codes have been validated using two vircator designs available from the literature. The simulations reported in the present paper take account of foil ablation due to the intense electron flux, the resulting plasma expansion and shorting of the anode-cathode gap. The variation in anode transparency due to plasma formation is automatically taken into account. We find that damage is generally higher near the axis. Also, at all radial positions, there is little damage in the early stages, followed by a period of rapid erosion, followed in turn by low damage rates. A physical explanation has been given for these trends. As a result of gap closure due to plasma formation from the foil, the output microwave power initially increases, reaches a near-"flat-top" and then decreases steadily, reaching a minimum around 230 ns. This is consistent with a typical plasma expansion velocity of ~2 cm/us reported in the literature. We also find a significant variation in the dominant output frequency, from 6.3 to 7.6 GHz. This variation is small as long as the plasma density is small, up to ~40 ns. As the AK gap starts filling with plasma, there is a steady increase in this frequency.

Hybrid simulation of electrode plasmas in high-power diodes

New numerical techniques for simulating the formation and evolution of cathode and anode plasmas have been successfully implemented in a hybrid code. The dynamics of expanding electrode plasmas has long been recognized as a limiting factor in the impedance lifetimes of high-power vacuum diodes and magnetically insulated transmission lines. Realistic modeling of such plasmas is being pursued to aid in understanding the operating characteristics of these devices as well as establishing scaling relations for reliable extrapolation to higher voltages. Here, in addition to kinetic and fluid modeling, a hybrid particle-in-cell technique is described that models high density, thermal plasmas as an inertial fluid which transitions to kinetic electron or ion macroparticles above a prescribed energy. The hybrid technique is computationally efficient and does not require resolution of the Debye length. These techniques are first tested on a simple planar diode then applied to the evolution of both cathode and anode plasmas in a high-power self-magnetic pinch diode. The impact of an intense electron flux on the anode surface leads to rapid heating of contaminant material and diode impedance loss.

Quantum-mechanical models for photo-ionization: Uni-directional electron re-scattering by a laser pulse

The interaction of a hydrogen atom with a linearly (z-) polarized laser pulse is described by numerical solution of the three-dimensional Schrödinger equation. Photo-ionization of the ground state, with pulses having three or more optical cycles at photon energies well above the ionization potential and maximum intensity 1015Wcm−2, yields symmetric opposite fluxes of electrons preferentially in the +z and −z directions. One-cycle laser pulses can lead to modest symmetry breaking, e.g., more intense electron fluxes in the +z direction than in the −z direction, depending on the carrier-envelope phase (CEP) of the pulse. Production of uni-directional electron fluxes, similar to those observed in Coulomb scattering, calls for laser pulses with stronger intensity, or lower carrier frequency, or shorter duration with appropriate CEP, e.g., half-cycle pulses in the attosecond time domain. Here, uni-directionality is achieved by a four-step mechanism: (i) photo-ionization, (ii) turn-around of the electron, (iii) scattering from the atom's core and (iv) drift in the forward direction.

Particle precipitation during ICME‐driven and CIR‐driven geomagnetic storms

Interplanetary coronal mass ejections (ICME) and corotating interaction regions (CIR) alter the parameters of the solar wind and interplanetary magnetic field (IMF) that affect conditions in the Earth's magnetosphere and particle precipitation in the auroral zone. We perform a superposed epoch study of the effects of ICME‐dominated and CIR‐dominated solar wind on particle precipitation during geomagnetic storms. We use data from a set of 38 CIR events and 33 ICME events. Particle precipitation is inferred from cosmic noise absorption (CNA) recorded by the riometer at Abisko. The electron flux intensity at geosynchronous orbit close to the location of the riometer is taken from the synchronous orbit particle analyzer (SOPA) onboard the Los Alamos National Laboratory (LANL) satellite LANL‐01A. The results show that mean CNA is more intense during the main phase of ICME‐driven storms. In contrast, mean CNA remains elevated for a much longer period during CIR‐driven storms indicating prolonged periods of particle precipitation. Enhanced CNA over a sustained period of time is observed during CIR‐driven storms that are categorized as only weak or moderate in terms of the response that they drive in the Dst index (Dst &gt;−100 nT). This result indicates that events which may be considered geomagnetically ineffective have a significant effect on particle precipitation in the auroral zone. The elevated CNA observed during CIR‐driven storms is accompanied by elevated electron flux intensity, measured at geosynchronous orbit, over all channels in the 50–500 keV range at all local times.

Planetary, solar and astrophysical relativistic electrons: Common energization mechanisms?

Direct observations or deduced analysis indicate clearly that formation of intense fluxes of relativistic electrons is an important ingredient in the evolution of numerous active magnetized plasma systems. Examples of relativistic electron energization include the recovery phase of a planetary magnetic storm, post solar flare coronal activity and the afterglow of gamma ray bursts. It is suggested that there exists a universal mechanism, which may explain electron energization at the vastly different magnetized plasma environments. The favorite configuration consists of an inhomogeneous magnetic field anchored at a given magnetic structure and excitation of whistler waves due to external injection of low-energy non-isotropic electrons. The energization proceeds as a bootstrap process due to interaction with the propagating whistler waves along the inhomogeneous magnetic field.

The electron formations under the radiation belts at L-shells 1.2–1.9

We continue to analyze the distribution of electron fluxes with energy 30–500 keV under the radiation belts at low and middle latitudes ( L = 1.2–1.9) using experimental data obtained onboard ACTIVE satellite. Special attention is given to altitudinal distribution of electron fluxes and detailed analysis of these electron formations. We observe three main regions of electron flux registration that seem to exist constantly under the radiation belts. These regions are: magneto-conjugated to SAA region (in the north hemisphere), local zone of low intense electron flux accumulation to the west of SAA, and extensive region in the north hemisphere to the east. The analysis of experimental data obtained from ACTIVE satellite (orbit height 500–2500 km) shows that electron fluxes are registered in the wide altitude range up to 1100 km. It is shown that these formations have complicated initial structure with two regions of flux maximums: at L = 1.3 and L = 1.6–1.8. We compare particle data with low frequency (LF) data (ARIEL-4 satellite) and high frequency (HF) data (CORONAS-I satellite). Also we discuss the possible mechanisms of the appearance of these formations under the radiation belts.

IMAGE FUV and in situ FAST particle observations of substorm aurorae

Images from the IMAGE Wide‐band Imaging Camera (WIC) and Spectrographic Imager (SI) channels SI‐12 and SI‐13 were compared to in situ data taken by FAST during several substorms. FAST spacecraft observations have shown that the high latitude auroral ionosphere has several distinct regions. Intense auroras are seen in regions of upward directed quasi static electric fields and of Alfven wave accelerated superthermal electrons. In two of the cases presented, the satellite passed through an active poleward propagating substorm surge on its duskward flank. Both show that the superthermal wave accelerated component to be on the polar cap boundary of the surge, and that it could be distinguished from quasi static field “inverted V” precipitation which occurred at the more equatorward parts of the auroral oval. In one of these cases, the surge was accompanied by intense ion outflow. Three cases showed the FAST satellite passing through the substorm aurora at midnight or the dawn side outside of the surge and the wave accelerated electrons were less clearly separated from the inverted V type precipitation. The wave accelerated electrons were seen to be part of very short‐lived transient events, i.e., bursts. The region of auroral forms, associated with Alfven waves exhibit relatively soft auroral precipitation with very intense electron fluxes. By comparing the intensity of the WIC and SI‐13 channels of IMAGE FUV, it is possible sometimes to distinguish optically between the two types of regions. Global imaging of the two regions would allow the separation of quasi‐static plasma convection regions containing inverted V‐s from regions of Alfven wave driven electrons signifying substorm related magnetic field dynamics.

A study of long-term strong dawn-dusk asymmetry of the earth's magnetosphere in 1991

A study of dawn-dusk asymmetry of the Earth's magnetosphere was made by the indirect way using data from a middle-energy-range (E: ∼ 80/1000 keV) electron semiconductor spectrometer onboard the geosynchronous satellite Gorizont from July, 1991 to April, 1992. In July-September, 1991 the diurnal variation of the examined fluxes had a number of unusual features. The most interesting feature was existence of local maxima on the diurnal distribution of electron flux intensity in dawn and dusk sectors. Observed features of the flux distributions could be explained as appeared due to the particle drift in the strong dawn-dusk asymmetry of the magnetospheric magnetic field. In the presented case, probably, the intrinsic factor was the main cause stabilising the dawn-dusk asymmetric geomagnetic field.

Fluxes of relativistic electrons in low-Earth orbit during the decline of solar cycle 22

Highly relativistic electron events (HREs) contain some of the longest lasting and most energetically intense electron fluxes measured in low-Earth orbit. Their short-term effects on astronauts and space-based electronic systems as well as their long-term influence on the terrestrial climate must be evaluated using measured electron fluxes spanning the ranges of solar inputs. We have used measurements from the High Energy Particle Spectrometer (HEPS) on Upper Atmosphere Research Satellite (UARS) to develop a database of energy- and pitch-angle-resolved electron fluxes. The HEPS data were acquired during the late part of the maximum and the declining phase of solar cycle 22, the latter phase being when HREs are thought to peak in frequency and intensity. We show average differential energy spectra and the limits of variation as a function of energy. The HEPS data shows that the flux of electrons with energies around 1 MeV lasts longer than does the flux of lower energy, but still relativistic, electrons. The data are used to estimate the probability of encountering a selected flux of electrons during similar phases of the solar cycle.

Proton-Electron Reactions as Precursors of Anomalous Nuclear Events

In some experiments, intense electron fluxes were made to encounter high proton concentrations to achieve p + e fusions. Anomalies were observed: The electron energies were often below the threshold energy, and the cross-section results were unexpectedly high. A twofold mechanism consisting of hydrogen squeezed atom formation and of virtual neutron absorption is suggested to justify the observed anomalous nuclear events. The hypothesis is extended to the d + e reaction.

Near-Equatorial Electrons as Measured onboard the MirSpace Station

Some results of studying the electrons with energies of tens to hundreds of keV at the low and near- equatorial geomagnetic latitudes by using the instruments Sprut-V and Ryabina-2 onboard the Mirspace station in 1991 are presented. It is found that at L< 1.2 the enhanced electron fluxes are sporadically detected, being localized within three longitudinal intervals, 180° W–0°–15° E, 90°– 120° E, and 160° E–180°–135° W. The most intense electron fluxes are observed at the lower edge of the near-equatorial boundary of the inner radiation belt on longitudes of the South Atlantic Anomaly between 14 and 20 h MLT. The occurrence of electron bursts does not depend on the geomagnetic disturbance level. A hardening of the electron spectra is observed near the geomagnetic equator. At L< 1.1, the more energetic particles are located closer to the geomagnetic equator. The results are compared with the data on the low-frequency waves and fields at low and near-equatorial latitudes obtained by the Ariel-4and San Marco Dsatellites, as well as by the spacecraft and ground-based observations of the thunderstorm global distribution. The thunderstorms are considered as a possible source of electron production near the geomagnetic equator.

Stimulated desorption of atoms and molecules from bodies in the outer solar system

Laboratory data is needed on electronically-induced desorption from low-temperature solids: ices, organics, hydrated salts, glasses and certain minerals. Many bodies in the outer solar system are bombarded by relatively intense fluxes of fast ions and electrons as well as solar UV photons. This can cause both changes in their optical reflectance as well as desorption of atoms and molecules from their surfaces. Stimulated desorption produces Na and K 'atmospheres' above the 'rocky' surfaces of the moon and Mercury and H2O, H2 and O2 'atmospheres' about icy outer-solar system bodies. Since theses bodies contain other surface materials, direct detection by spacecraft or remote detection by telescopes of the desorbed atoms and molecules can be used, along with laboratory data, to determine the surface composition and geological processes occurring on distant bodies. This paper describes the relevance of stimulated desorption to the ambient neutrals and plasma in Saturn's magnetosphere, in preparation for CASSINI's arrival, and to the production of atmospheres on the moons of Jupiter being studied by the Galileo spacecraft.

Some features of electron diurnal variation at geostationary orbit

The paper studies the diurnal variation of electron fluxes at the geostationary orbit. Data were being acquired from a middle-energy-range (E: ∼80–1000 keV) electron semiconductor spectrometer on the Gorizont satellite from July, 1991 to April, 1992. During as long as two months (July–September) we were observing appearance of different energy electron flux intensity maxima in the diurnal distribution in dusk and dawn sectors which may be explained by features of the particle drift in the strong dawn-dusk asymmetric magnetosphere and by passing through a quasi-trapped region.

Numerical modelling of the thermospheric and ionospheric effects of magnetospheric processes in the cusp region

Abstract. The thermospheric and ionospheric effects of the precipitating electron flux and field-aligned-current variations in the cusp have been modelled by the use of a new version of the global numerical model of the Earth's upper atmosphere developed for studies of polar phenomena. The responses of the electron concentration, ion, electron and neutral temperature, thermospheric wind velocity and electric-field potential to the variations of the precipitating 0.23-keV electron flux intensity and field-aligned current density in the cusp have been calculated by solving the corresponding continuity, momentum and heat balance equations. Features of the atmospheric gravity wave generation and propagation from the cusp region after the electron precipitation and field-aligned current-density increases have been found for the cases of the motionless and moving cusp region. The magnitudes of the disturbances are noticeably larger in the case of the moving region of the precipitation. The thermospheric disturbances are generated mainly by the thermospheric heating due to the soft electron precipitation and propagate to lower latitudes as large-scale atmospheric gravity waves with the mean horizontal velocity of about 690 m s–1. They reveal appreciable magnitudes at significant distances from the cusp region. The meridional-wind-velocity disturbance at 65° geomagnetic latitude is of the same order (100 m s–1) as the background wind due to the solar heating, but is oppositely directed. The ionospheric disturbances have appreciable magnitudes at the geomagnetic latitudes 70°–85°. The electron-concentration and -temperature disturbances are caused mainly by the ionization and heating processes due to the precipitation, whereas the ion-temperature disturbances are influence strongly by Joule heating of the ion gas due to the electric-field disturbances in the cusp. The latter strongly influence the zonal- and meridional-wind disturbances as well via the effects of ion drag in the cusp region. The results obtained are of interest because of the location of the EISCAT Svalbard Radar in the cusp region and the associated observations at lower latitudes that will be possible using the existing EISCAT UHF and VHF radars. The paper makes predictions for both these regions, and these predictions will be tested by joint observations by ESR, EISCAT UHF/VHF and other ground-based ionosphere/thermosphere observations.