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An unusual solar event involving the detection of a He-3/He-4 ratio of about 1.5 was observed with the aid of the cosmic-ray telescopes of OGO-V on May 28, 1969. A theory dealing with the production of H-2, H-3, and He-3 in solar events is considered together with the conditions which would have to be satisfied in order to explain the observed very high helium isotope ratio in terms of the theory.
A single active center was the origin of several solar flares observed in September, 1977. The longitude of the flares ranged from approximately 115 deg E to approximately 117 deg W. During this period Helios 1, Helios 2, Voyager 1 and Voyager 2 were extended over a range of approximately 120 deg in longitude, thus providing an opportunity to study the coronal transport of energetic solar flare particles. The result of a detailed study of the relative intensity and spectral shape of approximately 2-200 MeV protons and alphas at several solar longitudes has enabled the imposition of some criteria on models of coronal transport.
The elemental composition of energetic nuclei from seven major solar flare events were measured wit the cosmic ray detector systems aboard the Voyager 1 and 2 spacecraft. The energetic nuclei abundances differ significantly from those of photospheric material. They are enhanced relative to the photonsphere by a factor which is the ratio of abundance of an energetic nuclei species (relative to oxygen) over the corresponding abundance of photospheric material. This factor is common to all events and has a nonmonochromatic characteristic dependence on nuclear charge. This factor is roughly ordered by first ionization potential into two groups of elements, metallics and volatiles.
Within the past few years, instruments flown on satellites and space probes have made significant progress in measuring the elemental and isotopic composition of energetic heavy nuclei accelerated in solar flares. These new observations are discussed, focusing on: (1) the energy dependence of the elemental composition at energies not greater than 1 MeV/nucleon; (2) flare to flare variations in the composition; and (3) comparisons of the average solar particle abundances (Z not less than 2 and not greater than 28) with other measures of the solar composition, including photospheric, coronal, and solar wind observations. These comparisons have led to the suggestion that solar flares sample the composition of the corona. Isotopic measurements of heavy solar flare nuclei have recently added a new dimension to these studies. In particular, the isotopic composition of solar flare neon has been found to be significantly different from that measured in the solar wind, but consistent with the meteoritic component neon-A.
Measurements of the elemental composition of energetic nuclei with atomic numbers between 2 and 28 from seven major solar flares from September 1977 to May 1978 are presented. The abundance observations were made with the Low Energy Telescope systems of the cosmic ray detector systems on board the Voyager 1 and 2 spacecraft between 1 and 3 AU. Examination of the abundance ratios of the flare nuclei relative to oxygen reveals significant variations from event to event and between energetic nuclei and photospheric abundances, with an average composition, except for C and N, very similar to that of the galactic cosmic ray source. For the four flare events for which the elemental abundances exhibit no significant energy dependence in the energy range observed, it is found that the enhancement of energetic nuclei relative to their photospheric abundance are similar and not monotonic with atomic number, with the metallic nuclei showing an enhancement factor of approximately 5 and the volatiles showing one closer to 1.
Data from the solid-state detector on Explorer 35 are applied to a study of two intensity ratios in the sub-MeV per nucleon specific kinetic energy range for several energetic particle events. It is found that the intensity ratios vary markedly from event to event, particularly during the time history of the individual events. This implies that the ratios have no simple relationship to 'solar abundances' in the usual sense of the term. The pattern of the variability of each ratio is established; the ratio of He to ions with Z not smaller than 3 starts with a low value and increases as the event proceeds. The H/He ratio exhibits a qualitatively similar time history with marked relative enhancement of He early in an event. Differential diffusion of the various ionic species with differing magnetic rigidities is seen to be the dominant physical cause for the variabilities observed.
Electron and proton streams caused by long-lived solar events
Long lived streams of low energy solar electrons and protons and association with bright flares or solar active regions
The solar particle events of 18 November 1968, 25 February 1969, and 30 March 1969 were studied using data from the detector system aboard the lunar orbiting satellite Explorer 35. Protons, alpha particles, and Z or = 3 nuclei were registered in the solid state detector of the system. Interplanetary propagation, particle anisotropy, and the intensity ratios of protons to alpha particles and of alpha particles to C, N, and O nuclei above a common specific energy of 0.5 MeV/nucleon were studied. Diffusion coefficients and decay constants for the three events are given, as well as magnitudes and directions of anisotropies.
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The intensity-time behavior for protons and helium, as well as for carbon, oxygen and iron ions was measured following the 1974 September 19 solar flare for energies between 0.5 and approximately 5 MeV per nucleon. The profiles displayed a time dispersion which is inversely proportional to velocity for each individual species. In addition, at a given velocity the time dispersion also depended on the charge to mass ratio of the ion. Based on this latter dependence, it was concluded that while carbon and oxygen are essentially fully stripped, iron nuclei are not, having an effective charge Q = 10 + or - 5. The observed dispersion cannot be explained by purely rigidity dependent diffusive propagation.
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The intensity-time behavior for protons and alpha-particles, as well as for carbon, oxygen, and iron ions, has been measured following the solar flare of September 19, 1974, for energies between 0.5 and about 5 MeV per nucleon. The profiles display a time dispersion which is inversely proportional to velocity for each individual species. In addition, at a given velocity the time dispersion also depends on the charge-to-mass ratio of the ion. Based on this latter dependence, it is concluded that while carbon and oxygen are essentially fully stripped, iron nuclei are not, having an effective charge of 10 plus or minus 5. The observed dispersion cannot be explained by purely rigidity-dependent diffusive propagation.
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Some new results concerning coronal and interplanetary propagation of energetic particles are discussed in the context of previous and current observations and interpretations. Evidence is presented that the bulk of protons of approximately 1 MeV can be preferentially injected onto interplanetary field lines at coronal longitudes and latitudes well-removed (approximately 60 deg) from the site of the associated active region. For these protons, interplanetary propagation parallel and transverse to the interplanetary field evidently involves little scattering near 1 AU, so that parallel propagation is approximately 'scatter free' and transverse propagation is primarily that due to the E x B drift. Upstream of the earth's bow shock, both intensities and anisotropies of approximately 1-MeV protons and electrons are significantly modified by the magnetosphere, and these effects may provide a probe of the structure of the bow shock and magnetosheath in regions not readily accessible to spacecraft.
Observations of particle events associated with type II radio bursts as recorded on the ISEE-3 spacecraft are reported. Data on burst events following flares of Sept. 23,1978 and Aug. 18, 1979 yield time histories of the particle fluxes, which exceeded 25 MeV energy. The profiles of the Category-1 type II bursts display a continuous release of particles, which was concluded by no decrease in the fluxes until after the passage of the shock. The continuous nature of the recorded events suggests that the secondary acceleration process associated with the type II bursts is maintained as the flare shock propagates through interplanetary space, and may be the source of the energetic particles which propagate with the shock.