G. M. Mason

Spectral Properties of He and Heavy Ions in 3He-rich Solar Flares

Using advanced instrumentation on the ACE spacecraft, we have conducted a survey of solar energetic particle spectra in ^3He-rich events over a broad energy range ~80 keV nucleon^(-1) to 15 MeV nucleon^(-1) during the period 1997 September-2001 March. The spectra of ^4He and heavy ions (C, N, O, Ne, Mg, Si, S, Ca, Fe) were generally similar over this range but often hardened below ~1 MeV nucleon^(-1). In most of the events there was even stronger hardening of the ^3He spectrum below ~1 MeV nucleon^(-1), leading to an energy-dependent ^3He : ^4He ratio. These observations point to unique and distinct properties of ^3He in these events and place new constraints on models that seek to explain enhancements of ^3He and heavy ions using the same mechanisms. In addition to the events with spectra in the form of power laws or double power laws, there is a second class of event in which the low-energy ^3He and Fe spectra are rounded, while the ^4He remains a power law. In these cases ^3He and Fe spectra can be fitted at low energies by a stochastic acceleration model, but this model does not explain the higher energy portions of these spectra, nor the power-law spectral forms of the ^4He. These observations appear to require an additional mechanism, such as acceleration by cascading MHD turbulence. The ^3He enrichment pattern that we observe suggests that all these different spectral features might be due to processes with a common origin but then followed by different acceleration histories.

The isotopic composition of galactic cosmic ray lithium, beryllium and boron

The isotopes of cosmic-ray Li, Be, and B near 100 MeV per nucleon have been measured with cosmic-ray telescopes on board the IMP-7 and IMP-8 satellites during 1973--1974. The measured isotopic abundances provide a stringent test for models of interstellar propagation and solar modulation. It is found that the isotopic abundances can be explained using a steady-state interstellar propagation model with a 5 g cm

Origin, Injection, and Acceleration of CIR Particles: Observations

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New aspects of the cosmic-ray modulation in 1974-1975 near solar minimum

leakage mean free path. These results, taken along with our

Energetic particle abundances at CIR shocks

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Energy dependence of the Si/Fe ratio in the galactic cosmic rays

Be abundance measurements, indicate a longer lifetime for cosmic rays than that predicted by the usual assumption of an average interstellar density of 1 to 3 atoms cm

A new test for solar modulation theory - The 1972 May-July low-energy galactic cosmic-ray proton and helium spectra.

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The anomalous He-4 component in the cosmic-ray spectrum at below approximately 50 MeV per nucleon during 1972-1974

. (AIP)

The age of the galactic cosmic rays derived from the abundance of Be-10

This report emphasizes new observational aspects of CIR ions revealed by advanced instruments launched on the Ulysses, WIND, SOHO, and ACE spacecraft, and by the unique vantage point of Ulysses which carried out the first survey of Corotating Interaction Region (CIR) properties over a very wide range of heliolatitudes. With this more complete observational picture established, this review is the basis to consider the status of theoretical models on origin, injection, and acceleration of CIR particles reported by Scholer, Mann et al. (1999) in this volume.

Energetic proton and helium fluxes associated with interplanetary shocks and their relation to the solar wind composition

Residual cosmic-ray modulation at or near the solar minima of 1965 and 1972-75 is compared on the basis of ground-based and satellite observations of nonrelativistic proton and helium components as well as variations in the relativistic component. It is found that the nonrelativistic fluxes lagged behind the high-energy fluxes to form a hysteresis loop over the period from 1965 to 1973, that the 1975 proton fluxes were about 85% higher than the 1972 level and about 35% higher than the 1965 level, and that the 1975 helium fluxes were about 60% higher than in 1965. Some unique recovery events are discussed, and a time-lag effect dependent on magnetic rigidity is examined which was associated with dynamic changes in the heliosphere. A qualitative explanation is offered for the hysteresis effect.