A comparison of energetic storm protons to halo protons

Kahler, S. W.

doi:10.1007/bf00150668

Cited by 22 publications

(6 citation statements)

References 29 publications

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“…No attempt is made here to analyze this particular event in detail, since this would require plasma and magnetic field measurements in order to obtain the shock characteristics and calculate particle pitch angle distributions. The preshock duration of the intensity enhance-len and Ness, 1967; Kahler, 1969]. Most of these earlier models were reviewed and critically examined by Rao et al [1968], Singer [1970], and Datlowe [1972]; in each case it was concluded that the process whereby particles are accelerated locally at the shock front was most consistent with the observational data.…”

Section: Characteristics Of Shock-related Particle Enhancementsmentioning

confidence: 95%

The modulation of low‐energy proton distributions by propagating interplanetary shock waves: A numerical simulation

Decker¹

1981

J. Geophys. Res.

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A numerical simulation has been developed to study the formation in the intensities of ≲0.1‐ to ∼10.0‐MeV protons of the long‐lived energetic storm particle (ESP) events observed in association with the passage of flare‐produced fast mode MHD shocks. Protons are traced numerically backward in time from a given observation point (i.e., particle detector), through their adiabatic scatter‐free motion along the assumed laminar spiral interplanetary magnetic field (IMF), and finally through the shock discontinuity to their pre‐shock interaction state. An ambient proton can undergo at most one shock encounter, during which, as seen in the shock frame, the proton is accelerated by its effective ‘grad‐B drift’ along the induced electric field each time it crosses the shock. The time‐reversed calculation reveals which of the observed protons interacted with the shock, where the shock interaction occurred, and by how much each interacting proton's kinetic energy was increased at the shock. Time profiles of the omnidirectional and unidirectional protons fluxes are formed from the trajectories by invoking Liouville's theorem and an ambient proton unidirectional flux j ∼T−γ, where T is the kinetic energy and γ the spectral exponent. Simulation predictions are shown for different observed proton energies under various assumptions concerning the shock speed and strength, the slope of the ambient proton energy spectrum, the variation of the angle β1 between the shock surface and the upstream IMF vector, and the heliocentric radial position r of the observation point. The simulation model correctly recovers the gross features of the intensity variations, flux anisotropies, and energy spectra time evolutions of many observed ESP events. Representative simulation results predict shock‐induced enhancements in low‐energy proton fluxes that are characterized by (1) long, steady preshock or upstream rises to peaks before the shock arrival and abrupt declines following the shock passage; (2) peak enhancement amplitudes that increase for lower‐energy protons, stronger and faster shocks, softer ambient proton spectra, decreased β1 and increased r, (3) large, highly field‐aligned preshock flux anisotropies directed away from the sun along the IMF, (4) small postshock flux anisotropies nearly perpendicular to the magnetic field and directed towards the sun along the IMF, and (5) steadily softening preshock energy spectra that are steepest at the peak flux enhancement and slightly softer than the ambient spectra after the shock passage.

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Section: Characteristics Of Shock-related Particle Enhancementsmentioning

confidence: 95%

The modulation of low‐energy proton distributions by propagating interplanetary shock waves: A numerical simulation

Decker¹

1981

J. Geophys. Res.

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“…No widely accepted explanation for ESP events exists. Most models attempting to explain them invoke either interplanetary acceleration by the shock of a preexisting population of energetic particles [e.g., Axford and Reid, 1962;Rao et al, 1967;Fisk, 1971;Scholer and Morrill, 1975;Decker, 1979] or trapping of energetic particles behind the shock [e.g., Leinbach, 1962;Bryant et al, 1962;Kahler, 1969]. In general, interplanetary acceleration models have emphasized and have been most successful in explaining the preshock portions of ESP events; trapping models have primarily been concerned with the postshock phase of ESP events but have not been worked out in quantitative detail.…”

Section: Introductionmentioning

confidence: 99%

Interplanetary ions during an energetic storm particle event: The distribution function from solar wind thermal energies to 1.6 MeV

Gosling

Asbridge²,

Bame³

et al. 1981

J. Geophys. Res.

264

118

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Data from the Los Alamos Scientific Laboratory/Max‐Planck‐Institut fast plasma experiment on Isee 2 have been combined with data from the European Space Agency/Imperial College/Space Research Laboratory low‐energy proton experiment on Isee 3 to obtain for the first time an ion velocity distribution function f(ν) extending from solar wind energies (∼1 keV) to 1.6 MeV during the postshock phase of an energetic storm particle (ESP) event. This study reveals that f(ν) of the ESP population is roughly isotropic in the solar wind frame from solar wind thermal energies out to 1.6 MeV. Emerging smoothly out of the solar wind thermal distribution, the ESP f(ν) initially falls with increasing energy as E−2.4 in the solar wind frame. Above about 40 keV no single power law exponent adequately describes the energy dependence of f(ν) in the solar wind frame. Above ∼200 keV in both the spacecraft frame and the solar wind frame, f(ν) can be described by an exponential in speed (f(ν) ∝ e−ν/ν0) with ν0=1.05 × 108 cm s−1. The ESP event studied (August 27, 1978) was superposed upon a more energetic particle event which was predominantly field‐aligned and which was probably of solar origin. Our observations suggest that the ESP population is accelerated directly out of the solar wind thermal population or its quiescent suprathermal tail by a stochastic process associated with the shock wave disturbance. The acceleration mechanism is sufficiently efficient that ∼1% of the solar wind population is accelerated to suprathermal energies. These suprathermal particles have an energy density of ∼290 eV cm−3.

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“…The authors argued against the ESPs being trapped in a magnetic cloud, primarily on the basis of the lack of bi-directional anisotropies, and suggested that interplanetary acceleration by the shock associated with the Forbush decrease was the cause of the enhanced intensities. Kahler [1969] disagreed after performing his own survey of ESP events associated with magnetic sudden commencements using data from Explorers 12, 33, 34, and 35, Mariner 4, OGOs 1 and 3, Pioneer 6, and IMPs 3 and 4. The author argued that the association of ESP events with SEP events suggested that both particle populations were generated at the Sun (n.b.…”

Section: Early Observationsmentioning

confidence: 99%

Observations of Energetic Storm Particles: An Overview

2006

Solar Eruptions and Energetic Particles

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A comparison of energetic storm protons to halo protons

Cited by 22 publications

References 29 publications

The modulation of low‐energy proton distributions by propagating interplanetary shock waves: A numerical simulation

The modulation of low‐energy proton distributions by propagating interplanetary shock waves: A numerical simulation

Interplanetary ions during an energetic storm particle event: The distribution function from solar wind thermal energies to 1.6 MeV

Observations of Energetic Storm Particles: An Overview

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