Solar Energetic Particles and Solar Events - Lessons Learned from Multi-Spacecraft Observations

Abstract

Never before has the heliosphere and the Sun been so carefully monitored by so many spacecraft; in particular, the STEREO spacecraft have allowed simultaneous observations to be made routinely from multiple solar longitudes. The instrumentation on these spacecraft are continually observing solar activity and measuring the characteristics of solar energetic particle (SEP) events, providing a wealth of information on the acceleration and transport of SEPs. In February, 2011 the STEREO spacecraft reached a separation of 180° and since then the entire solar surface has been visible. This unprecedented view has allowed observations of active regions and solar activity to continue after a region has rotated over the limb (as view from Earth) and more importantly, of regions emerging on the solar hemisphere not visible to Earth. The multiple viewpoints afforded by spectrometers and coronagraphs on the STEREO and near-Earth spacecraft has yielded more accurate information regarding the speed, direction, and evolution of coronal mass ejections (CMEs) which drive the interplanetary shocks that generate large SEP events. As is often the case when new capabilities are achieved or new regimes are explored, even while some questions are answered, more emerge. Among the surprises from multi-spacecraft SEP observations is the exceptionally fast longitudinal transport of particles. This paper reviews these multi-spacecraft capabilities, highlights some of the recent observations and surprises, and discusses the impact on the current understanding of energetic particle acceleration and transport.

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