Evidence for a collision-free hydromagnetic shock in interplanetary space.
Collision-free hydromagnetic shock observed simultaneously in interplanetary space on October 7, 1962 by Mariner II and Explorer XIV
INTERPLANETARY SPACE↗
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A cosmic-ray-mediated shock in the solar system
It is pointed out that the flare-induced blast wave of Aug. 4, 1972, the most violent disturbance in the solar wind on record, produced cosmic rays with an efficiency of about 50%. Such a high efficiency is predicted by the self-regulating production model of cosmic-ray origin in shocks. Most interplanetary shocks, according to simple theoretical analysis, are not strong enough to produce cosmic rays efficiently. However, if shock strength is the key parameter governing efficiency, as present interplanetary data suggest, then shocks from supernova blasts, quasar outbursts, and other violent astrophysical phenomena should be extremely efficient sources of cosmic rays.
Eichler, D.↗
Evidence for a collision-free hydromagnetic shock in interplanetary space
Evidence for collision-free hydromagnetic shock in interplanetary space
SHOCK WAVE↗
Spatial dependence of the local diffusion coefficient measured upstream of the November 12, 1978 interplanetary traveling shock
Characteristics of wuprathermal particles accelerated by quasi-parallel interplanetary traveling shocks have been generally explained in terms of a first order Fermi mechanism. Such models require diffusive scattering of particles upstream of the shock. This scattering is characterized by a local diffusion coefficient, kappa, which is determined by the local power density of waves in the upstream region. The dependence of the diffusion coefficient of suprathermal upstream protons on distance from the November 12, 1978 interplanetary traveling shock using a different approach is studied. Unlike previous studies this method, which is based on measurements of particle streaming and intensity gradients, does not rely on predictions. The local spatial variations of Kappa upstream of the November 12, 1978 shock have been chosen for study because the characteristics of this quasi-parallel shock have been extensively studied, and also because of its favorable geometry (i.e. B field nearly radial).
Gloeckler, G.↗
Solar flare shocks in interplanetary space and solar flare particle events
Data on particle events resulting from three solar flares are examined to determine the effect of shocks on the population of protons at energies not less than 30 MeV. The arrival of the shock is found to mark the start of the decay phase of the particle event, and changes in particle anisotropy are found to be related to features in the shock structure. Two distinct modes of particle propagation are found to exist: a direct component, and a second component which has a time scale of days and is seen in two of the flares which also produced interplanetary shock. In addition, a model is described in which the protons are accelerated by the shocks, and it is shown to be in agreement with observations.
Evenson, P.↗
A test of Lee's quasi-linear theory of ion acceleration by interplanetary traveling shocks
Lee's (1983) quasi-linear theory of ion acceleration is tested using ISEE-3 measurements of the November 12, 1978 quasi-parallel interplanetary shock. His theory accounts with varying degrees of precision for the energetic proton spatial profiles; the dependence of the spectral index of the power law proton velocity distribution upon the shock compression ratio; the power law dependence of the upstream proton scalelength upon energy; the absolute magnitude of the upstream proton scale length; the behavior of the energetic proton anisotropy upstream and downstream of the shock; the behavior of the alpha-particle proton ratio upstream; the equality of the spatial scale lengths at the shock of the upstream waves and of the protons that resonate with them; and the dependence of the integrated wave energy density upon the proton energy density at the shock. However, the trace magnetic field frequency spectra disagree with his theory in two ways. The part of the spectrum that can resonate with the observed protons via first-order cyclotron resonance is flat, whereas Lee's theory predicts an f exp - 7/4 frequency dependence for the November 12 shock. Higher frequency waves, which could not resonate with the observed upstream protons, increased in amplitude as the shock approached, suggesting that they too were generated by the shock.
Kennel, C. F.↗
Energetic ions upstream of the earth's bow shock during an energetic storm particle event
Simultaneous observations of low-energy protons and alpha particles from ISEE 3 far upstream and from ISEE 1 close to the earth's bow shock during the passage of an interplanetary shock wave with its associated energetic storm particles are presented. Intensities, spectra, and anisotropies of the energetic storm particles are modified due to the interaction of these particles with the earth's bow shock. An intensity spike observed at ISEE 1 during the passage of the interplanetary shock is interpreted as being due to postacceleration of energetic storm particles at the bow shock by the first-order Fermi mechanism. The spikes observed at ISEE 1 after the passage of the interplanetary shock are most probably due to reflection of the energetic storm particles at the bow shock.
Scholer, M.↗
Motion of shocks through interplanetary streams
A model for the motion of flare-generated shocks through interplanetary streams is presented which illustrates the effects of a stream-shock interaction on the shock strength and geometry. It is a gasdynamic calculation based on Whitham's (1958) method and on an empirical approximation for the relevant characteristics of streams. The results show that the Mach number of a shock can decrease appreciably to near unity in the interaction region ahead of streams and that the interaction of a spherically symmetric shock with a spiral-shaped corotating stream can cause significant distortions of the initial shock-front geometry. The geometry of a shock discussed by Lepping and Chao (1972) is qualitatively explained by this model.
Burlaga, L. F.↗
Coupled hydromagnetic wave excitation and ion acceleration at interplanetary traveling shocks
A theory for the self-consistent configuration of upstream hydromagnetic waves, upstream energetic storm particle (ESP) events, and downstream postshock ion enhancements at interplanetary traveling shocks is presented. The observations of upstream ultralow frequency waves and those ESP events and postshock enhancements which exhibit approximately isotropic ion distributions in the solar wind or shock frame are briefly reviewed. The theory of Lee (1982) for application to interplanetary traveling shocks is modified and analytical solutions for the wave spectrum as a function of wavenumber and z are presented along with the ion omnidirectional distribution functions as functions of energy and z for all ion species. The theory quantitatively explaines the observed features of the shock-associted energetic ions and predicts the configuration of upstream hydromagnetic waves.
Lee, M. A.↗
Interplanetary Fast Shocks and Associated Drivers Observed through the Twenty-Third Solar Minimum by WIND Over its First 2.5 Years
A list of the interplanetary (IP) shocks observed by WIND from its launch (in November 1994) to May 1997 is presented. Forty two shocks were identified. The magnetohydrodynamic nature of the shocks is investigated, and the associated shock parameters and their uncertainties are accurately computed using a practical scheme which combines two techniques. These techniques are a combination of the "pre-averaged" magnetic-coplanarity, velocity-coplanarity, and the Abraham-Schrauner-mixed methods, on the one hand, and the Vinas and Scudder [1986] technique for solving the non-linear least-squares Rankine-Hugoniot shock equations, on the other. Within acceptable limits these two techniques generally gave the same results, with some exceptions. The reasons for the exceptions are discussed. It is found that the mean strength and rate of occurrence of the shocks appears to correlated with the solar cycle. Both showed a decrease in 1996 coincident with the time of the lowest ultraviolet solar radiance, indicative of solar minimum and start of solar cycle 23, which began around June 1996. Eighteen shocks appeared to be associated with corotating interaction regions (CIRs). The distribution of their shock normals showed a mean direction peaking in the ecliptic plane and with a longitude (phi(sub n)) in that plane between perpendicular to the Parker spiral and radial from the Sun. When grouped according to the sense of the direction of propagation of the shocks the mean azimuthal (longitude) angle in GSE coordinates was approximately 194 deg for the fast-forward and approximately 20 deg for the fast-reverse shocks. Another 16 shocks were determined to be driven by solar transients, including magnetic clouds. These shocks had a broader distribution of normal directions than those of the CIR cases with a mean direction close to the Sun-Earth line. Eight shocks of unknown origin had normal orientation well off the ecliptic plane. No shock propagated with longitude phi(sub n) >= 220 +/- 10 deg, this would suggest strong hindrance to the propagation of shocks contra a rather tightly winding Parker spiral. Examination of the obliquity angle theta(sub Bn) (that between the shock normal and the upstream interplanetary magnetic field) for the full set of shocks revealed that about 58% was quasi-perpendicular, and some were very nearly perpendicular. About 32% of the shocks were oblique, and the rest (only 10%) were quasi-parallel, with one on Dec. 9, 1996 that showed field pulsations. Small uncertainty in the estimated angle theta(sub Bn) was obtained for about 10 shocks with magnetosonic Mach numbers between 1 and 2, hopefully significantly contributing to studies researching particle acceleration mechanisms at IP shocks, and to investigations where accurate values of theta(sub Bn) are crucial.
Mariani, F.↗
Turbulence, Structures, and Diffusive Shock Acceleration
Diffusive shock acceleration (DSA) is thought to be the primary acceleration at shock waves. While this acceleration mechanism has been very successful in explaining many observations of energetic particles in astrophysics and heliophysics, recent observations suggest that DSA, at least its simplest version, may not be adequate in explaining observations of acceleration of particles at the termination shock and some interplanetary shocks. Meanwhile, turbulence and its structures like flux ropes and current sheets have been proposed to have important effects on accelerating particles into high energies. The goal of this project is to carefully examine and extend theories of particle acceleration including the DSA and recently developed reconnection acceleration associated with turbulence structures.
79 ASTRONOMY AND ASTROPHYSICS↗
Acceleration of energetic particles
Acceleration of some particles from the background plasma to highly superthermal energies is a common feature of collisionless shocks in interplanetary space. The complete in situ measurements of bulk flows, thermal plasma, electromagnetic waves and energetic particles available for interplanetary shocks both suggest and test the models of shock acceleration in the solar system and the rest of the universe. This tutorial will review the present state of shock acceleration theory. Scatter-free acceleration by grad B drift in the plasma electric field E = -V x B/c, and diffusive acceleration resulting from scattering by Alfven waves in the plasma on both sides of the shock are discussed. The diffusive theory in simple steady state gives power-law spectra, but also shows the effects of time-dependent shocks and injection rates, escape and other losses, the self-consistent Alfven wave spectra, and plasma flow fields affected by diffusive energetic particle acceleration.
Forman, M. A.↗
The Transmission of ULF Waves From the Solar Wind to the Magnetosphere: An Analysis of Some Critical Aspects
Several critical aspects may influence the analysis of the relationship between the solar wind (SW) and magnetospheric fluctuations, for example, the characteristics and frequency of SW fluctuations that are expected to impinge the magnetosphere may not be the same when they are observed by spacecraft located at different places in front of the magnetosphere; similarly, the choice of analytical methods adopted for the spectral analysis might influence the frequency estimate (as well as the wave identification itself) both in the SW and magnetosphere. Focusing our attention on these aspects, we present an analysis of SW compressional fluctuations (f ≈ 1–5 mHz), following two interplanetary shocks observed by two interplanetary spacecraft, regarded as two different situations in terms of spacecraft separation and distance from the magnetosphere. Our results show that some differences in the characteristics of SW fluctuations emerge when the same stream is observed at different places and confirm the critical role of analytical methods in determining fluctuation characteristics. We compared aspects of SW fluctuations with those of magnetospheric fluctuations following the sudden impulses due to the impact of interplanetary shocks. For this scope, we examined observations by two satellites at geostationary orbit and at several ground-based stations. We found that the magnetospheric fluctuations were related to compressional SW fluctuations approximately at the same frequencies, with no evidence for wave activity of internal origin or directly driven by the shock impact.
ULF waves↗
Ion thermalization in the earth's bow shock
Interplanetary magnetic field role in counterstreaming ion-ion instability in ion thermalization process for earth bow shock
Papadopoulos, K.↗
Plasma wave experiment for the ISEE-3 mission
Results of analyses of data received from a scientific instrument designed to study solar wind and plasma wave phenomena on the ISEE-3 mission are discussed in two papers prepared for publication. A study of plasma wave levels in and interplanetary magnetic field orientation preceding observations of interplanetary shocks by the satellite infers that quasi-parallel, interplanetary shocks are preceded by foreshocks whose presence is not obviously attributable to scattering of ion beams generated at quasi-perpendicular zones of these interplanetary shocks. Investigations of whistler mode turbulence in the disturbed solar wind resulted in various indirect lines of evidence indicating that these whistler waves are generated propagating at large angles to the local interplanetary field, a fact which helps identify possible free energy sources for their growth.
Scarf, F. L.↗
Shock waves in the interplanetary medium.
Shock waves in interplanetary medium caused by sudden expansion of solar corona following flare
CORONA↗
Pioneer Solar Plasma and Magnetic Field Measurements in Interplanetary Space During August 2-17, 1972
Solar wind plasma and magnetic field measurements from Pioneers 9 and 10 during August 2-17, 1972, reveal complex and large-amplitude variations on a one-hour time scale and numerous discontinuities. During this time period an approximate radial alignment of the two spacecraft as seen from the Sun occurred with heliocentric distances of 0.8 AU for Pioneer 9 and 2.2 AU for Pioneer 10, both at 45 deg east of the Earth's solar longitude. The peak hourly average solar wind proton bulk velocity measured at Pioneer 9 was 990 km sec (exp -1) during hour 0 UT of August 5. The peak hourly average proton number density was 62 cm (exp -3) during hour 11 UT of August 3. The peak solar wind speeds are generally much reduced at Pioneer 10 compared with those observes at Pioneer 9. The peak 30 minute average magnetic field magnitude was 85 gamma during 1245 - 1315 UT of August 3. The Pioneer 9 data indicate passage of four fast forward interplanetary shocks, and one slow forward interplanetary shock.
Mihalov, J. D.↗
Particle acceleration by an interplanetary shock-pair seen at Ulysses at 3.15 AU
Observations from the HI-SCALE instrument on Ulysses of the ions and electrons associated with an interplanetary shock-pair at about 3.15 AU are presented. An empirical model is used to derive the evolution of the particle distribution in the solar wind frame. The forward shock is shown to be the primary source of ion acceleration, while the weaker and younger reverse shock is found to trap particles in its vicinity. There is also evidence of electron acceleration at the forward shock. We find evidence of multiple shock encounters for both ions and electrons.
Tappin, S. J.↗