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A study of solar proton events with well‐identified sources has been carried out using data from Goddard particle experiments on IMPs 4, 5, 7, and 8 and ISEE 3. The experiments cover the energy range from about 1 to 300 MeV. The 235 events of our study represent approximately 70% of all increases above 10−3 particles cm−2 sr−1 s−1 MeVminus;1 at energies > 20 MeV detected in a 19.7‐year period commencing mid‐May 1967. It is shown that intensity‐time profiles of solar proton events display an organization with respect to heliolongitude. Whilst it has been known for many years that the profile of a proton event depends on the longitude of the solar event relative to the observer, we suggest that the major controlling agent is the existence of an interplanetary (IP) shock. Furthermore, we explain the change in shape as a function of heliolongitude within the framework of a recently derived model for the large‐scale structure of IP shocks. In particular, the long delay to maximum intensity for far eastern events (a property previously ascribed to coronal processes) and the overall extended duration can be accounted for by IP shock acceleration and continued magnetic connection to the shock even after it has propagated beyond 1 AU.

Abstract. The Advanced Composition Explorer was launched August 25, 1997 carrying six high resolution spectrometers that measure the elemental, isotopic, and ionic charge state composition of nuclei from H to Ni (1 Z 28) from solar wind energies (1 keV/nuc) to galactic cosmic ray energies (500 MeV/nuc). Data from these instruments is being used to measure and compare the elemental and isotopic composition of the solar corona, the nearby interstellar medium, and the Galaxy, and to study particle acceleration processes that occur in a wide range of environments. ACE also carries three instruments that provide the heliospheric context for ion composition studies by monitoring the state of the interplanetary medium. From its orbit about the Sun-Earth libration point 1.5 million km sunward of Earth, ACE also provides real-time solar wind measurements to NOAA for use in forecasting space weather. This paper provides an introduction to the ACE mission, including overviews of the scientific goals and objectives, the instrument payload, and the spacecraft and ground systems.

[1] We examined the properties and associations of 280 solar proton events that extended above 25 MeV and occurred in the years 1997-2006. The properties include early peak intensities of five species over several energy ranges and the intensity-time profiles. Solar event associations were made for as many events as possible. The solar parameters determined include coronal mass ejection and flare properties and radio emissions from a wavelength range of meters to kilometers. The events were divided into five representative types based on the relative abundances and particle profiles to more easily illustrate how particle characteristics vary with the solar parameters. We find a continuum of event properties with no indication of specific parameters that clearly separate out groups of events. There is, however, a reasonable separation of events based on the timing of the associated type III emissions relative to the H a flare. Type III bursts indicate the presence of flare particles that escape to the interplanetary medium. The least intense, relatively short-lived, proton events that are electron-rich (and generally Fe-rich and He-rich) have associated type III bursts that occur at the start of the flare (i.e., in the impulsive phase), indicating rapid acceleration and escape of particles. In the largest events the type III emissions occur after the impulsive phase. It is likely that this late acceleration and/or release of particles results in a composition different from that of impulsive acceleration and release. A scenario in which concomitant flare processes contribute particles in the majority of solar energetic particle events is consistent with the observations.

We report on abundance measurements of 10Be, 26Al, 36Cl, and 54Mn in the Galactic cosmic rays (GCRs) using the Cosmic-Ray Isotope Spectrometer (CRIS) instrument aboard the Advanced Composition Explorer spacecraft at energies from D70 to D400 MeV nucleon~1. We also report an upper limit on the abundance of GCR 14C. The high statistical signiÐcance of these measurements allows the energy dependence of their relative abundances to be studied. A steady-state, leaky-box propagation model, incorporating observations of the local interstellar medium (ISM) composition and density and recent partial fragmentation cross section measurements, is used to interpret these abundances. Using this model, the individual galactic conÐnement times derived using data for each species are consistent with a unique conÐnement time value of Myr. The CRIS abundance measurements are consis-q esc \ 15.0^1.6 tent with propagation through an average ISM hydrogen number density H atoms n H \ 0.34^0.04 cm~3. The surviving fractions, f, for each radioactive species have been calculated. From predictions of the di †usion models of Ptuskin & Soutoul, the values of f indicate an interstellar cosmic-ray di †usion coefficient of D \ (3.5^2.0) ] 1028 cm2 s~1.