[en] Significant intensity enhancements of low energy (0.10 to 10.0 MeV) solar ions are sometimes observed several hours prior to the passage of solar flare generated shock waves by satellites located in interplanetary space. The intimate temporal association between these energetic storm particle (ESP) events and the propagating shock strongly suggests that ambient particles are accelerated locally at the shock front. A computer model has been developed to numerically simulate the combined effects of a charged particle's energization at the shock and propagation to a satellite-borne particle detector at the observation point. A charged particle's adiabatic motion is assumed to be scatter-free along the laminar spiral interplanetary magnetic field (IMF). The interplanetary shock wave is taken as a suncentered spherical surface that expands radially outward. The plasma and field changes across the shock obey the jump conditions for a fast mode MHD shock wave. For a chosen shock model, a particle of specified observed kinetic energy and pitch angle at a given observation time and fixed observation point is followed numerically backward in time through the IMF and shock wave. The shock interaction is treated by solving the particle's exact orbit equations through the locally planar MHD shock discontinuity. The resultant trajectory relates the particle's phase space coordinates at the time of observation to those at a time immediately before shock interaction. The application of Liouville's theorem of the constancy of the single-particle distribution function along a dynamical phase space trajectory enables one to construct particle fluxes at the observation point by using an ensemble of numerically generated trajectories and a model of the ambient particle distribution

[en] An example is presented from a test particle simulation designed to study ion acceleration at oblique turbulent shocks. For conditions appropriate at interplanetary shocks near 1 AU, it is found that a shock with theta sub B n = 60 deg is capable of producing an energy spectrum extending from 10 keV to approx 1 MeV in approx 1 hour. In this case total energy gains result primarily from several separate episodes of shock drift acceleration, each of which occurs when particles are scattered back to the shock by magnetic fluctuations in the shock vicinity

[en] Solar flares often accelerate ions and electrons to relativistic energies. The details of the acceleration process are not well understood, but until recently the main trend was to divide the acceleration process into two phases. During the first phase elctrons and ions are heated and accelerated up to several hundreds of keV simultaneously with the energy release. These mildly relativistic electrons interact with the ambient plasma and magnetic fields and generate hard x-ray and radio radiation. The second phase, usually delayed from the first by several minutes, is responsible for accelerating ions and electrons to relativistic energies. Relativistic electrons and ions interact with the solar atmosphere or escape from the Sun and generate gamma ray continuum, gamma ray line emission, neutron emission or are detected in space by spacecraft. In several flares the second phase is coincident with the start of a type 2 radio burst that is believed to be the signature of a shock wave. Observations from the Solar Maximum Mission spacecraft have shown, for the first time, that several flares accelerate particles to all energies nearly simultaneously. These results posed a new theoretical problem: How fast are shocks and magnetohydrodynamic turbulence formed and how quickly can they accelerate ions to 50 MeV in the lower corona. This problem is discussed

[en] The cosmic ray radial gradient was determined during 1981-84 using data from very similar detectors onboard spacecraft Voyagers 1 and 2 (radial separation approx. 6 AU, heliolatitude separation approx. 25 deg.) and from the Earth-orbiting satellite IMP 8. The principal result is that the radial gradient over this period decreased at the rate approx. 2.0%/AU between 1 and 16 AU and approx. 0.6%/AU between approx. 16 and 22 AU

[en] This is a review of the fundamental physics of the interactions of charged particles treated individually while they interact with fast mode magnetohydrodynamic shocks. Numerical simulation and analytical theory are used to develop predictions of the expected characteristics of this process strong upstream anisotropies directed along the magnetic field and downstream anisotropies tending to be peaked more perpendicular to the field; relatively more of the enhancement of higher-energy particles occurring upstream; sensitive dependence on shock normal to magnetic field angle of the efficiency of energization. Observations which display all of the above characteristics are reviewed. Also discussed is the relationship of shock drift acceleration to the models for stochastic transport of charged particles in the vicinity of shocks. Extensions of this work in both the observational and theoretical approaches are discussed. 41 references

[en] The role played by shock-associated drifts during the diffusive acceleration of charged particles at collisionless MHD shocks is evaluated. In the rest frame of the shock, the total energy gained by a particle is shown to result from two coupled acceleration mechanisms, the usual first-order Fermi mechanism and the drift mechanism. When averaged over a distribution of particles, the ratio of the drift-associated energy gain to the total energy is found to be independent of the total energy at a given theta1 (the angle between the shock normal and the unperturbed upstream magnetic field) in agreement with theoretical predictions. No evidence is found for drift-associated deceleration, suggesting that drifts always augment acceleration. 35 references

[en] The process of charged particle acceleration in interplanetary shocks has been simulated for typical parameters. Since space probe observations of charged particle fluxes are the principle means of inferring the action of an acceleration mechanism, the simulation was designed to follow particles backwards in time from a given observing point, usually 1 A.U. This allowed a full diagnosis of which observed particles had interacted with an oncoming shock, where the interacting occurred, and by how much the energy had been changed by the shock interaction. Simple assumptions about the pre-shock energy spectrum allow the construction of a full temporal profile of the expected intensity, anisotropy, and energy spectrum. The simulations are apparently capable of reproducing the main features of the less than 10 MeV/nuc. ion flux enhancements observed at interplanetary shocks using only a laminar interplanetary magnetic field, Archimidean spiral, and a spherical oblique shock with typical speed, strength, and shock normal-magnetic field angle

[en] A numerical simulation has been developed to study the formation in the intensities of < or approx. =0.1-toapprox.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 japprox.T/sup -gamma/, 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

[en] Cosmic ray measurements obtained with integral detectors on Voyager 1 and 2 (E/sub p/> or approx. =70 MeV) moving toward the outer solar system and the earth-orbiting IMP 8 satellite (E/sub p/> or approx. =35 MeV) over the period late 1977 through mid-1982 are presented. During this period, Voyager 1 and 2 traversed the region from 1 to approx.13 AU and approx.10 AU, respectively, with little separation in heliolongitude; separation in heliolatitudde was also small (< or approx. =2⁰) through the end of 1980, at which time the trajectory of Voyager 1 changed toward higher ecliptic latitudes

[en] Data from the Johns Hopkins University Applied Physics Laboratory Charged Particle Measurement Experiment aboard Imp H and J were searched for solar flare produced intensity increases in >0.2-MeV electrons during the 26-month period from October 1972 through December 1974. Of the 44 solar electron events found during this period, 31 were isolated for a detailed statistical study. Systemtics among the characteristics of the electron profiles (e.g., peak intensity times and count rates) and those of the associated flares (e.g., Hα onset times, Hα importance class, heliocentric coordinates, etc.) were examined, and the significant results are presented in several scatter plots. The results reveal that the time delay between the flare onset and the arrival of the peak electron intensity at 1 AU (time to maximum) is a function of the flare's deviation in heliolongitude from the solar region which was well connected to the earth via a magnetic flux tube; the well-connected flares produced electron intensity maxima in the least time. The data also show that as the flare's deviation from the well-connected region increases, soft electron events are less likely to be observed, and the peak electron intensities are markedly decreased. No dependence of the time to maximum on the flare's heliolatitude is apparent. It is also found that solar flares with larger Hα areas tend to produce harder electron events