ACE/NOZOMI Multispacecraft Observations of Solar Energetic Particles

Abstract

We report multispacecraft measurements of solar energetic particle (SEP) events using Nozomi and ACE. During July 1998 to April 2002, while Nozomi was cruising toward Mars, instruments on both spacecraft observed many SEP events associated with coronal mass ejections (CMEs) and interplanetary shocks originating from different longitudes. These observations can reveal the longitudinal extent of CME-driven shocks and the accelerated particle populations. We use proton and electron data extending from ~40keV to ~1 MeV measured with the EIS instrument on NOZOMI and the ULEIS and EPAM instruments on ACE. ACE and Nozomi observed a consistent rate of proton events. In spite of their large longitudinal separation many events were simultaneously observed by ACE and NOZOMI. Four examples of individual events have been studied with hourly averaged data. On March 29, 2000, Nozomi observed an event following a CME on the backside of the Sun. In the July 14, 2000 and April 21, 2002 events, both spacecraft observed the same SEP event from different longitudes, resulting in different intensity time profiles.