Solar Energetic Particle Anisotropies from the ACE Solar Isotope Spectrometer

Although not specifically designed for it, the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer spacecraft is sensitive to particle anisotropies of heavy ions at energies of tens of MeV/nucleon. Using the arrival time of each particle (to the nearest second) and the trajectory measured with the instrument's position sensing detector, the arrival direction of each particle may be determined to ˜30° in azimuth about the spacecraft spin axis and to better than 1° in zenith angle from the axis. This allows the angular distribution of particles to be measured within the ˜145° wide field of view of the instrument, from which the intensities both along the field and perpendicular to it can usually be determined. We describe how anisotropies are obtained from SIS and present examples demonstrating some of the capabilities of SIS in studying anisotropies. With further analysis, SIS can contribute to studies exploring the dependence of particle angular distributions on energy and species.