An ISEE/Whistler model of equatorial electron density in the magnetosphere
TL;DR: In this paper, an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8.9043 was presented for application to the local time interval 00-15 MLT, and a way to extend the model to the 15-24 MLT period is presented.
Abstract: Attention is given to an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8. Although the model is primarily intended for application to the local time interval 00-15 MLT, a way to extend the model to the 15-24-MLT period is presented. The model describes, in piecewise fashion, the 'saturated' plasmasphere, the region of steep plasmapause gradients, and the plasma trough. Within the plasmasphere the model profile can be expressed as logne - Sigma-xi, where x1 = -0.3145L + 3.9043 is the principal or 'reference' term, and additional terms account for: a solar cycle variation with a peak at solar maximum; an annual variation with a December maximum; and a semiannual variation with equinoctial maxima.
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TL;DR: In this article, a survey of wave data from the CRRES Plasma Wave Experiment for lower band (0.1-0.5f(ce)) and upper band ( 0.5-1.0f(c)) chorus was presented to assess whether these waves could play an important role in the acceleration of a seed population of electrons to relativistic energies during and following geomagnetic storms.
Abstract: Intense interest currently exists in determining the roles played by various wave-particle interactions in the acceleration of electrons to relativistic energies during/following geomagnetic storms. Here we present a survey of wave data from the CRRES Plasma Wave Experiment for lower band (0.1-0.5f(ce)) and upper band (0.5-1.0f(ce)) chorus, f(ce) being the electron gyrofrequency, to assess whether these waves could play an important role in the acceleration of a seed population of electrons to relativistic energies during and following geomagnetic storms. Outside of the plasmapause the chorus emissions are largely substorm-dependent, and all chorus emissions are enhanced when substorm activity is enhanced. The equatorial chorus (/ lambda (m) / 300 nT) with average amplitudes typically >0.5 mV m(-1) predominantly in the region 3 15 degrees) is strongest in the lower band during active conditions, with average amplitudes typically >0.5 mV m(-1) in the region 3 < L < 7 over a range of local times on the dayside, principally in the range 0600-1500 MLT, Consistent with wave generation in the horns of the magnetosphere. An inner population of weak, substorm-independent emissions with average amplitudes generally < 0.2 mV m(-1) are seen in both bands largely inside L = 4 on the nightside during quiet (AE < 100 nT) and moderate (100 nT < AE < 300 nT) conditions. These emissions lie inside the plasmapause and are attributed to signals from lightning and ground-based VLF transmitters. We conclude that the significant increases in chorus amplitudes seen outside of the plasmapause during substorms support the theory of electron acceleration by whistler mode chorus in that region. The results suggest that electron acceleration by whistle mode chorus during/following geomagnetic storms can only be effective when there are periods of prolonged substorm activity following the main phase of the geomagnetic storm.
509 citations
Cites background from "An ISEE/Whistler model of equatoria..."
...where Kp* is the maximum value of Kp in the previous 24 hours [Carpenter and Anderson, 1992], is marked on the amplitude and location plots as a thin white line....
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...The approximate position of the plasmapause, Lp, given by the expression Lp - 5.6 - 0.46Kp*, (1) where Kp* is the maximum value of Kp in the previous 24 hours [Carpenter and Anderson, 1992], is marked on the amplitude and location plots as a thin white line....
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TL;DR: The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts.
Abstract: The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance.
477 citations
Cites background or methods from "An ISEE/Whistler model of equatoria..."
...Statistical models such as Carpenter and Anderson (1992) or O’Brien and Moldwin (2003) treat the equatorial plasmasphere statistically, considering only large scale features, an inadequate approximation for radiation belt physics applications....
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...Also plotted are sunspot number, solar wind velocity, and the plasmapause location based on a statistical model (Carpenter and Anderson 1992)....
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TL;DR: In this article, the statistical properties of waves that violate the first and second adiabatic invariants are reviewed, leading to the loss and acceleration of high energy electrons in the outer radiation belt, and it is shown that statistically, the net effect of chorus waves is acceleration at MeV energies and loss at hundreds of keV energies.
412 citations
TL;DR: In this article, the authors used the combined Release and Radiation Effects Satellite (CRRES) sweep frequency receiver data to develop an empirical model of the plasmasphere and trough number density.
Abstract: Combined Release and Radiation Effects Satellite (CRRES) sweep frequency receiver data were used to develop an empirical model of the plasmasphere and trough number density The over 1000 CRRES orbits provided good statistical coverage of all local times between an L shell of 3 to 7 The CRRES density data were separated into plasmaspheric-like and trough-like by assuming a minimum density value for the plasmasphere as a function of L shell For the plasmasphere the average number density (in cm−3) as a function of L shell (3 ≤ L ≤ 7) was found to be: np = 1390 (3/L)48 ± 440 (3/L)36 For the trough the average number density (in cm−3) as a function of L-shell (3 ≤ L ≤ 7) and magnetic local time (0 ≤ LT ≤ 24) was found to be nt = l24 (3/L)40 + 36(3/L)35 cos({LT-[77(3/L)20+12]}π/12) ± {78 (3/L)47 + 17 (3/L)37 cos[(LT - 22)π/12]} No clear dependence on magnetic activity was found for either density model This empirical model is an improvement over earlier models in that it is continuous in local time and can be used to track densities based on refilling history The model standard deviations are representative of either early time or late time refilling of the trough or newly filled or saturated plasmaspheric densities
409 citations
TL;DR: Using quasi-linear diffusion coefficients for cyclotron resonance with field-aligned waves, the authors examined whether the resonant interactions with chorus waves produce a net acceleration or loss of relativistic electrons.
Abstract: [1] Relativistic electrons in the outer radiation belt are subjected to pitch angle and energy diffusion by chorus, electromagnetic ion cyclotron (EMIC), and hiss waves. Using quasi-linear diffusion coefficients for cyclotron resonance with field-aligned waves, we examine whether the resonant interactions with chorus waves produce a net acceleration or loss of relativistic electrons. We also examine the effect of pitch angle scattering by EMIC and hiss waves during the main and recovery phases of a storm. The numerical simulations show that wave-particle interactions with whistler mode chorus waves with realistic wave spectral properties result in a net acceleration of relativistic electrons, while EMIC waves, which provide very fast scattering near the edge of the loss cone, may be a dominant loss mechanism during the main phase of a storm. In addition, hiss waves are effective in scattering equatorially mirroring electrons and may be an important mechanism of transporting high pitch angle electrons toward the loss cone.
347 citations
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TL;DR: An English translation of the German version of the book has been published by as mentioned in this paper, which is based on the newly revised fifth edition of the original German version and contains more material than the German original.
Abstract: An English translation now joins the Russian and Spanish versions. It is based on the newly revised fifth edition of the German version of the book. The original edition has become very popular as a learning and reference source with easy to follow recipes and cross references for scientists in fields such as engineering, chemistry and the life sciences. Little mathematical background is required of the reader and some important topics, like the logarithm, are dealt with in the preliminaries preceding chapter one. The usefulness of the book as a reference is enhanced by a number of convenient tables and by references to other tables and methods, both in the text and in the bibliography. The English edition contains more material than the German original. I am most grateful to all who have in conversations, letters or reviews suggested improvements in or criticized earlier editions. Comments and suggestions will continue to be welcome. We are especially grateful to Mrs. Dorothy Aeppli of St. Paul, Minnesota, for providing numerous valuable comments during the preparation of the English manuscript. The author and the translator are responsible for any remaining faults and imperfections. I welcome any suggestions for improvement. My greatest personal gratitude goes to the translator, Mr. Zenon Reynaro wych, whose skills have done much to clarify the text, and to Springer-Verlag."
1,033 citations
TL;DR: In this article, the authors investigated the nature and origin of whistlers, which are sometimes observed at frequencies below 15 kc/s and were found to follow the lines of force of the earth's magnetic field.
Abstract: The paper, which is in two parts, describes an investigation of the nature and origin of the 'whistling atmospherics' or 'whistlers' which are sometimes observed at frequencies below 15 kc/s. The first part describes an experimental study of their properties, in the course of which a considerable number of whistlers were recorded and analyzed, and the law of the variation of their frequency with time determined. Some whistlers are heard to follow impulsive atmospherics, and these are found to be produced in the normal way by lightning strokes taking place within a distance of about 2000 km. Other whistlers are unaccompanied by atmospherics; they differ from the former type in several further respects. The diurnal and annual variations of the properties of both types of whistler have also been studied. In the second part of the paper a theory of the origin of the whistling atmospherics, originally due to Barkhausen (1930) and Eckersley (1935), is developed in detail. The theory proposes that they are due to waves which originate in normal impulsive atmospherics and travel through the outer ionosphere, following the lines of force of the earth's magnetic field and crossing over the equator at a great height. During their journey they become dispersed so as to arrive as 'whistlers'. They may be reflected from the earth's surface back along the same path, one or more times, to produce whistlers with increased dispersions. The effects responsible for the guiding of the waves along the lines of the geomagnetic field provide sufficient focusing action to prevent the energy from being spread unduly. Measurements of the degree of dispersion of the whistlers have been interpreted to yield information about the density of electrons in the atmosphere at very great heights. The density required seems considerably larger than could reasonably have been expected. If the free electrons are produced by ionization of the terrestrial atmosphere its temperature in these regions must be at least 7200 degrees K. The results might alternatively be explained on the assumption that the electrons are falling in from outside, and if this were so it might account for the relationship between the occurrence of whistlers and magnetic activity.
670 citations
TL;DR: The position of the knee in the density of magnetospheric ionization was measured on a high time-resolution basis using whistlers recorded during July and part of August 1963 as discussed by the authors.
Abstract: The position of the knee in the density of magnetospheric ionization was measured on a high time-resolution basis using whistlers recorded during July and part of August 1963. (The knee is an abrupt decrease in magnetospheric ionization density, frequently observed at field lines with an equatorial radius of about 4 RE.) The data were obtained at Eights (64°S dipole latitude) and Byrd (70°S dipole latitude) in the Antarctic. The whistler results and results from other experiments confirm that the knee is a regular feature of the magnetosphere. For conditions of steady, moderate geomagnetic agitation (Kp = 2–4), the diurnal variation in geocentric equatorial range to the knee is remarkably repeatable. It is characterized by (1) a slow inward movement of the knee on the nightside, covering about 1.5 RE in 10 hours; (2) a slight outward movement on the dayside covering about 0.5 RE and (3) a rapid outward shift in the late afternoon covering about 1 RE in 1 hour. During periods of changing magnetic activity, the knee position changes with at most a few hours' delay, moving inward with increasing magnetic activity. The results from Eights and Byrd may be generalized to describe a three-dimensional model of thermal ionization in the magnetosphere involving a dense (∼100 el/cm3) inner region and a tenuous (∼1 el/cm3) outer region separated by a sharp field-aligned boundary, the plasmapause. During the postmidnight hours, the inward motion of the knee involves a corresponding inward motion of the ionization just inside the plasmapause. The rapid outward shift of the knee near 1800 LT does not involve an outward plasma motion, but instead involves the presence of a region of ‘new’ high-density (∼100 el/cm3) plasma in the equatorial range of about 4–5 RE. Preliminary evidence shows that, at least in the period 0000–1700 LT, the ionization inside the plasmapause rotates at approximately the angular velocity of the earth.
557 citations
TL;DR: Magnetic activity effect on magnetospheric plasmapause position, measuring ion concentrations as function of local time from OGO 5 observations as mentioned in this paper, was used to measure ion concentrations in the magnetosphere.
Abstract: Magnetic activity effect on magnetospheric plasmapause position, measuring ion concentrations as function of local time from OGO 5 observations
326 citations
TL;DR: A quick reference guide to the plasmasphere can be found in this article, where a series of equatorial density profiles is shown to illustrate the reduction of plasmapause radius during brief periods of increased disturbance and the recovery of the plasosphere by various processes, particularly by filling from the underlying ionosphere.
Abstract: Recent research on the structure and dynamics of the magnetospheric thermal plasma indicates that the vast region above an altitude of ∼1000 km rivals the underlying ionosphere in complexity and that it is coupled to the lower region in complicated, physically important ways. An example involves the relation of the electron content of magnetospheric tubes of ionization to the electron content of the regular ionosphere. Tube volume between ∼1000 km and the magnetic equator varies rapidly over a relatively small range of tube end point latitudes, which gives rise to correspondingly rapid variations with latitude in coupled effects that involve interchange of ionization between the upper and lower regions. In the past, some correlative studies involving the plasmapause have been hindered by lack of information concerning (1) the unsteady nature of the process by which the disturbed-time plasmapause profile is established and (2) the fact that at most times and at most locations the plasmasphere-plasmapause system is in a state of recovery. A series of equatorial density profiles is shown to illustrate the reduction of plasmapause radius during brief periods of increased disturbance and the recovery of the plasmasphere by various processes, particularly by filling from the underlying ionosphere. A number of research results are presented as part of a ‘quick-reference guide’ to the plasmasphere. To the ionospheric observer, the plasmapause should appear to have a complex but generally predictable geometry as well as characteristic motions. A crude predictor of plasmapause L value (Lpp) in the post-midnight period as a function of magnetic disturbance is the formula Lpp = 5.7-0.47Kp, where Kp is the maximum 3-hour Kp value in the preceding 12 hours. A ground station at L ∼ 3.7 is recommended as optimum for observation of plasmapause-associated effects directly overhead. The plasmasphere is regularly perturbed by substorm-associated convection electric fields, and these apparently have important effects on the nightside ionosphere at middle latitudes. Other known departures of the plasmasphere from corotation are expected to have their counterparts in the ionosphere.
305 citations