Found 919 results
Authors: Wygant J, Mozer F, Temerin M, Blake J, Maynard N, et al.
Title: Large amplitude electric and magnetic field signatures in the inner magnetosphere during injection of 15 MeV electron drift echoes
Abstract: Electric and magnetic fields were measured by the CRRES spacecraft at an L-value of 2.2 to 2.6 near 0300 magnetic local time during a strong storm sudden commencement (SSC) on March 24, 1991. The electric field signature at the spacecraft at the time of the SSC was characterized by a large amplitude oscillation (80 mV/m peak to peak) with a period corresponding to the 150 second drift echo period of the simultaneously observed 15 MeV electrons. Considerations of previous statistical studies of the magnitude of SSC electric and magnetic fields versus local time and analysis of the energization and cross-L transport of the particles imply the existence of 200 to 300 mV/m electric fields over much of the dayside magnetosphere. These observations also suggest that the 15 MeV drift echo electro. . .
Date: 08/1994 Publisher: Geophysical Research Letters Pages: 1739–1742 DOI: 10.1029/94GL00375 Available at:
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Authors: Li Xinlin, Roth I, Temerin M, Wygant J R, Hudson M K, et al.
Title: Simulation of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC
Abstract: We model the rapid (∼ 1 min) formation of a new electron radiation belt at L ≃ 2.5 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the CRRES satellite. Guided by the observed electric and magnetic fields, we represent the time-dependent magnetospheric electric field during the SSC by an asymmetric bipolar pulse that is associated with the compression and relaxation of the Earth's magnetic field. We follow the electrons using a relativistic guiding center code. The test-particle simulations show that electrons with energies of a few MeV at L > 6 were energized up to 40 MeV and transported to L ≃ 2.5 during a fraction of their drift period. The energization process conserves the first adiabatic invariant and is enhanced due to resonance of the el. . .
Date: 11/1993 Publisher: Geophysical Research Letters Pages: 2423–2426 DOI: 10.1029/93GL02701 Available at:
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Authors: Chiu Y T, Nightingale R W, and Rinaldi M A
Title: Simultaneous Radial and Pitch Angle Diffusion in the Outer Electron Radiation Belt
Abstract: A solution of the bimodal (radial and pitch angle) diffusion equation for the radiation belts is developed with special regard for the requirements of satellite radiation belt data analysis. In this paper, we use this solution to test the bimodal theory of outer electron belt diffusion by confronting it with satellite data. Satellite observations, usually over finite volumes of (L, t) space, are seldom sufficient in space-time duration to cover the relaxation to equilibrium of the entire radiation belt. Since time scales of continuous data coverage are often comparable to that of radiation belt disturbances, it is therefore inappropriate to apply impulsive semi-infinite time response solutions of diffusion theory to interpret data from a finite window of (L, t) space. Observational limitat. . .
Date: 04/1988 Publisher: Journal of Geophysical Research Pages: 2619 - 2632 DOI: 10.1029/JA093iA04p02619 Available at:
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Authors: West H I, Buck R M, and Davidson G T
Title: The Dynamics of Energetic Electrons in the Earth’s Outer Radiation Belt During 1968 as Observed by the Lawrence Livermore National Laboratory’s Spectrometer on Ogo 5
Abstract: An account is given of measurements of electrons made by the LLNL magnetic electron spectrometer (60–3000 keV in seven differential energy channels) on the Ogo 5 satellite in the earth's outer-belt regions during 1968 and early 1969. The data were analyzed to identify those features dominated by pitch angle and radial diffusion; in doing so all aspects of phase space covered by the data were studied, including pitch angle distributions and spectral features, as well as decay rates. The pitch angle distributions are reported elsewhere. The spectra observed in the weeks after a storm at L ∼3–4.5 show the evolution of a peak at ∼1.5 MeV and pronounced minima at ∼0.5 MeV. The observed pitch angle diffusion lifetimes are identified as being the shortest decays observed and are found t. . .
Date: 04/1981 Publisher: Journal of Geophysical Research Pages: 2111 - 2142 DOI: 10.1029/JA086iA04p02111 Available at:
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Authors: Holzworth R H, and Mozer F S
Title: Direct Evaluation of the Radial Diffusion Coefficient near L = 6 Due to Electric Field Fluctuations
Abstract: The radial diffusion coefficient for radiation belt particles near L=6 has been calculated from the measured electric field fluctuations. Simultaneous balloon flights in August 1974 from six auroral zone sites ranging 180° in magnetic longitude produced the electric field data. The large scale slowly varying ionospheric electric fields from these flights have been mapped to the equator during the quiet magnetic conditions of this campaign. These mapped equatorial electric fields were then Fourier transformed in space and time to produce power spectra of the first two terms of the global azimuthal electric field. From these power spectra the radial diffusion coefficient has been calculated.
Date: 06/1979 Publisher: Journal of Geophysical Research Pages: 2559 - 2566 DOI: 10.1029/JA084iA06p02559 Available at:
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Authors: Lyons Lawrence R, and Thorne Richard Mansergh
Title: Equilibrium Structure of Radiation Belt Electrons
Abstract: The detailed quiet time structure of energetic electrons in the earth's radiation belts is explained on the basis of a balance between pitch angle scattering loss and inward radial diffusion from an average outer zone source. Losses are attributed to a combination of classical Coulomb scattering at low L and whistler mode turbulent pitch angle diffusion throughout the outer plasmasphere. Radial diffusion is driven by substorm associated fluctuations of the magnetospheric convection electric field.
Date: 05/1973 Publisher: Journal of Geophysical Research Pages: 2142 - 2149 DOI: 10.1029/JA078i013p02142 Available at:
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Authors: Lanzerotti L J, and Morgan Caroline G
Title: ULF Geomagnetic Power near L = 4, 2. Temporal Variation of the Radial Diffusion Coefficient for Relativistic Electrons
Abstract: Measurements at conjugate points on the ground near L = 4 of the power spectra of magnetic-field fluctuations in the frequency range 0.5 to 20 mHz are used as a means of estimating daily values for the relativistic-electron radial-diffusion coefficient DLL for two periods in December 1971 and January 1972. The values deduced for L−10 DLL show a strong variation with magnetic activity, as measured by the Fredricksburg magnetic index KFR. The radial-diffusion coefficient typically increases by a factor of ∼10 for a unit increase in KFR. When KFR ≲ 2, it is generally found that DLL ≲ 2 × 10−9 L10 day−1 for equatorially mirroring electrons having a first invariant M = 750 Mev/gauss; a value of DLL ∼4 × 10−7 L10 day−1 is deduced for one day on which the mean KFR was 4.5. The. . .
Date: 08/1973 Publisher: Journal of Geophysical Research Pages: 4600 - 4610 DOI: 10.1029/JA078i022p04600 Available at:
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Authors: Tomassian Albert D, Farley Thomas A, and Vampola Alfred L
Title: Inner-Zone Energetic-Electron Repopulation by Radial Diffusion
Abstract: A quantitative study of the intrusion of natural electrons into the inner radiation zone during and after the geomagnetic storm of September 2, 1966, shows that the transport is consistent with a radial-diffusion mechanism in which the first two invariants are conserved. Except for the 3-day period of the storm main phase when data were missing, the radial-diffusion coefficient is D = 2.7 × 10−5 L7.9 μ−0.5 day−1 in the range 1.7 ≤ L ≤ 2.6 and 13.3 ≤ μ ≤ 27.4 Mev gauss−1. This value could be produced by variation of a large-scale electric field across the magnetosphere having an amplitude of 0.28 mv / m and a period of 1600 sec. Electric fields having approximately these characteristics have been inferred from previous observations of the motion of whistler ducts within t. . .
Date: 07/1972 Publisher: Journal of Geophysical Research Pages: 3441 - 3454 DOI: 10.1029/JA077i019p03441 Available at:
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Authors: Lyons Lawrence R, and Thorne Richard Mansergh
Title: Parasitic Pitch Angle Diffusion of Radiation Belt Particles by Ion Cyclotron Waves
Abstract: The resonant pitch angle scattering of protons and electrons by ion cyclotron turbulence is investigated. The analysis is analogous to that recently performed for electron interactions with whistler mode waves. The role played by the intense band of ion cyclotron waves, predicted to be generated just within the plasmapause during the decay of the magnetospheric ring current, is evaluated in detail. Loss rates resulting from parasitic interactions with this turbulence are determined for energetic protons and relativistic electrons.
Date: 10/1972 Publisher: Journal of Geophysical Research Pages: 5608 - 5616 DOI: 10.1029/JA077i028p05608 Available at:
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Authors: Lanzerotti L J, Maclennan C G, and Schulz Michael
Title: Radial Diffusion of Outer-Zone Electrons: An Empirical Approach to Third-Invariant Violation
Abstract: The near-equatorial fluxes of outer-zone electrons (E>0.5 Mev and E>1.9 Mev) measured by an instrument on the satellite Explorer 15 following the geomagnetic storm of December 17–18, 1962, are used to determine the electron radial diffusion coefficients and electron lifetimes as functions of L for selected values of the conserved first invariant µ. For each value of µ, the diffusion coefficient is assumed to be time-independent and representable in the form D = DnLn. The diffusion coefficients and lifetimes are then simultaneously obtained by requiring that the L-dependent reciprocal electron lifetime, as determined from the Fokker-Planck equation, deviate minimally from a constant in time. Applied to the data, these few assumptions yield a value of D that is smaller by approximately a. . .
Date: 10/1970 Publisher: Journal of Geophysical Research Pages: 5351 - 5371 DOI: 10.1029/JA075i028p05351 Available at:
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Authors: Birmingham Thomas J
Title: Convection Electric Fields and the Diffusion of Trapped Magnetospheric Radiation
Abstract: We explore here the possible importance of time-dependent convection electric fields as an agent for diffusing trapped magnetospheric radiation inward toward the earth. By using a formalism (Birmingham, Northrop, and Fälthammar, 1967) based on first principles, and by adopting a simple model for the magnetosphere and its electric field, we succeed in deriving a one-dimensional diffusion equation to describe statistically the loss-free motion of mirroring particles with arbitrary but conserved values of the first two adiabatic invariants M and J. Solution of this equation bears out the fact that reasonable electric field strengths, correlated in time for no longer than the azimuthal drift period of an average particle, move particles toward the earth at a rate at least an order of magnitud. . .
Date: 05/1969 Publisher: Journal of Geophysical Research Pages: 2169 - 2181 DOI: 10.1029/JA074i009p02169 Available at:
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Authors: Schulz Michael, and Eviatar Aharon
Title: Diffusion of Equatorial Particles in the Outer Radiation Zone
Abstract: Expansions and contractions of the permanently compressed magnetosphere lead to the diffusion of equatorially trapped particles across drift shells. A general technique for obtaining the electric fields induced by these expansions and contractions is described and applied to the Mead geomagnetic field model. The resulting electric drifts are calculated and are superimposed upon the gradient drift executed by a particle that conserves its first (μ) and second (J = 0) adiabatic invariants. The noon-midnight asymmetry of the unperturbed drift trajectory (resulting from gradient drift alone) is approximated by means of a simple model. In this model the angular drift frequency is found to be the geometric mean of a particle's angular drift velocities at noon and midnight. The radial diffusion . . .
Date: 05/1969 Publisher: Journal of Geophysical Research Pages: 2182 - 2192 DOI: 10.1029/JA074i009p02182 Available at:
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Authors: Vernov S N, Gorchakov E V, Kuznetsov S N, Logachev Yu. I, Sosnovets E N, et al.
Title: Particle fluxes in the outer geomagnetic field
Abstract: The outer geomagnetic field comprises the outer radiation belt, consisting of electrons with energies of 104–107 ev, and the unstable radiation zone. The outer radiation belt is bounded on its inner side by a gap, which is at various times located at a distance of 2.2–3.5 RE and in which a considerable precipitation of electrons from radiation belts occurs, possibly owing to a high intensity of electromagnetic waves. The boundary separating the outer radiation belt from the unstable radiation zone is at λ ∼ 71° and ∼9 RE in the equatorial plane on the sunlit side, and at 7–8 RE in the equatorial plane on the nightside. Beyond this, the unstable radiation zone extends out to the magnetosphere boundary and up to λ ∼ 77° on the sunlit side, and out to 14–15 RE on the nightsi. . .
Date: 02/1969 Publisher: Reviews of Geophysics Pages: 257-280 DOI: 10.1029/RG007i001p00257 Available at:
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Authors: Farley Thomas A
Title: Radial Diffusion of Starfish Electrons
Abstract: A study of the change in electron intensities in the Starfish electron belt from January 1, 1963, to November 3, 1965, indicates that radial diffusion, both inward and outward from L of 1.40, was a significant loss mechanism for these electrons during this period. For L values of 1.20 and below, the indicated steepening of the pitch-angle distributions during this period has been interpreted as the result of a radial diffusion source for each L shell concentrated near the geomagnetic equator. Since pitch-angle diffusion lifetimes are not well known for 1.20 < L < 1.65, a definitive radial diffusion coefficient cannot be computed from these data. A maximum reasonable diffusion coefficient (mean square displacement per unit time) computed for this range of L for this period has a minimum at . . .
Date: 07/1969 Publisher: Journal of Geophysical Research Pages: 3591 - 3600 DOI: 10.1029/JA074i014p03591 Available at:
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Authors: Newkirk L L, and Walt M
Title: Radial Diffusion Coefficient for Electrons at 1.76 < L < 5
Abstract: Radial diffusion by nonconservation of the third adiabatic invariant of particle motion is assumed in analyzing experiments in which electrons appeared to move across field lines. Time-dependent solutions of the Fokker-Planck diffusion equation are obtained numerically and fitted to the experimental results by adjusting the diffusion coefficient. Values deduced for the diffusion coefficient vary from 1.3 × 10−5 RE²/day at L = 1.76 to 0.10 RE²/day at L = 5. In the interval 2.6 < L < 5, the coefficient varies as L10±1. Assuming a constant electron source of arbitrary magnitude at L = 6 and the above diffusion coefficients, the equatorial equilibrium distribution is calculated for electrons with energies above 1.6 Mev. The calculation yields an outer belt of electrons whose radial distr. . .
Date: 12/1968 Publisher: Journal of Geophysical Research Pages: 7231 - 7236 DOI: 10.1029/JA073i023p07231 Available at:
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Authors: Newkirk L L, and Walt M
Title: Radial Diffusion Coefficient for Electrons at Low L Values
Abstract: An empirical evaluation of the diffusion coefficient for trapped electrons diffusing across low L shells is obtained by adjusting the coefficient to account for the observed radial profile and the long-term decay rate of the trapped electron flux. The diffusion mechanism is not identified, but it is assumed that the adiabatic invariants µ and J are conserved. The average value of the coefficient for electrons > 1.6 Mev energy is found to decrease monotonically from ∼4 × 10−6 RE²/day at L = 1.16 to ∼2 × 10−7 RE²/day at L = 1.20.
Date: 02/1968 Publisher: Journal of Geophysical Research Pages: 1013 - 1017 DOI: 10.1029/JA073i003p01013 Available at:
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Authors: Kennel C, and Petschek H
Title: Limit on Stably Trapped Particle Fluxes
Abstract: Whistler mode noise leads to electron pitch angle diffusion. Similarly, ion cyclotron noise couples to ions. This diffusion results in particle precipitation into the ionosphere and creates a pitch angle distributon of trapped particles that is unstable to further wave growth. Since excessive wave growth leads to rapid diffusion and particle loss, the requirement that the growth rate be limited to the rate at which wave energy is depleted by wave propagation permits an estimate of an upper limit to the trapped equatorial particle flux. Electron fluxes >40 kev and proton fluxes >120 kev observed on Explorers 14 and 12, respectively, obey this limit with occasional exceptions. Beyond L = 4, the fluxes are just below their limit, indicating that an unspecified acceleration source, sufficient . . .
Date: 01/1966 Publisher: Journal Geophysical Research Pages: 1-28 DOI: 10.1029/JZ071i001p00001 Available at:
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Authors: Kennel C F
Title: Velocity Space Diffusion from Weak Plasma Turbulence in a Magnetic Field
Abstract: The quasi‐linear velocity space diffusion is considered for waves of any oscillation branch propagating at an arbitrary angle to a uniform magnetic field in a spatially uniform plasma. The space‐averaged distribution function is assumed to change slowly compared to a gyroperiod and characteristic times of the wave motion. Nonlinear mode coupling is neglected. An H‐like theorem shows that both resonant and nonresonant quasi‐linear diffusion force the particle distributions towards marginal stablity. Creation of the marginally stable state in the presence of a sufficiently broad wave spectrum in general involves diffusing particles to infinite energies, and so the marginally stable plateau is not accessible physically, except in special cases. Resonant particles with velocities much . . .
Date: 12/1966 Publisher: Physics of Fluids Pages: 2377 DOI: 10.1063/1.1761629 Available at:
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Authors: Falthammar C -G
Title: Effects of time-dependent electric fields on geomagnetically trapped radiation.
Abstract: Large-scale electric potential fields in the magnetosphere are generally invoked in theories of the aurora. It is shown in the present article that irregular fluctuations of such fields cause a random radial motion of trapped energetic particles by violating the third adiabatic invariant. When the first and second invariants are conserved, any radial motion of the particles is associated with a corresponding energy change. Some particles move outward and others inward; but, if there is a source in the outer magnetosphere and a sink farther in, there will be a net inward transport and an associated net energy gain. This mechanism supplements that of particle transport by magnetic disturbances, which has already been discussed in the literature. The transport and acceleration of energetic pa. . .
Date: 06/1965 Publisher: Journal of Geophysical Research Pages: 2503–2516 DOI: 10.1029/JZ070i011p02503 Available at:
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