Anomalous cosmic rays and solar energetic particle composition

Abstract

This is a rapporteur paper for the 26th International Cosmic Ray Conference covering the sessions on anomalous cosmic rays (SH 4.1-SH 4.4) and on energetic charged particle composition, spectra, and charge states (SH 1.4). The ACR sessions covered the topics anomalous cosmic ray elemental and isotopic composition and energy spectra, anomalous cosmic ray sources, preacceleration and acceleration, ACR transport, modulation and time variation, the observation of ACRs trapped in the Earth’s magnetic field, and energetic neutral atoms of ACR origin from the outer heliosphere. Among the highlights of the ACR sessions were the discovery of new ACR elements of possibly heliospheric origin, the new high resolution measurements of ACR elemental and isotopic composition with instrumentation onboard ACE, and the first report on energetic neutral hydrogen atoms of ACR origin observed onboard SOHO. Session SH 1.4 covered the elemental and isotopic composition, the energy spectra, and the ionic charge composition of energetic charged particles in gradual and impulsive solar energetic particle events and the signature of a quiet-time interplanetary low-energy component. This brief report will concentrate on compositional variations during individual gradual events and their simulation, on new observations of the event-to event variability of elemental and isotopic composition, and on the determination of the ionic charge composition, using a variety of indirect methods and direct observations. Among the highlights of the SEP session were the new high-resolution measurements of elemental, isotopic, and ionic charge composition with unprecedented sensitivity providing new insight into the characteristic differences between gradual and impulsive events.