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Preface in Solar Eruptions and Energetic Particles

  • Editors: Gopalswamy, N.; Mewaldt, R.; Torsti, J.
  • Publication: Geophysical Monograph 165, p. ix, 2006
  • Preface
  • ADS link
  • Abstract: Research over the last three decades identifies coronal mass ejections (CMEs) as the most energetic events in the heliosphere. Although studies of solar energetic particle (SEP) events and nonthermal radio bursts have a longer history, the close connection between CMEs and energetic particles has become much clearer thanks to the large armada of spacecraft observing these phenomena since the mid-1990s. Indeed, understanding the most violent forms of solar eruptions — CMEs, flares, and SEPs — is of fundamental importance to the physics involved and our ability to predict and mitigate disruptive space weather episodes. Questions, of course, remain: We do not fully understand how CMEs and SEPs are accelerated but we do know that they affect space weather in several significant ways. The magnetized plasma of CMEs impacts Earth's magnetosphere, causing large geomagnetic storms. Energetic CMEs also drive shocks that accelerate electrons (observed as type II radio bursts) and ions (detected by spaceborne instruments). SEPs ionize the upper atmosphere, disrupting communications, driving atmospheric chemistry, while presenting a radiation hazard to humans and hardware in space.

This volume reviews extensive observations of solar eruptions and SEPs by instruments on board a number of spacecraft, including the Solar and Heliospheric Observatory (SOHO), Wind, the Advanced Composition Explorer (ACE), the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and the Transition Region and Coronal Explorer (TRACE). Highly sensitive coronagraphs on board SOHO image CMEs with unprecedented sensitivity. Several thousand CMEs have been observed, measured and cataloged for the current solar cycle, but only about 1% of these are associated with SEPs. Radio instruments on the Wind spacecraft obtain signatures of solar energetic electrons injected into the heliosphere within minutes of their release near the Sun and also track MHD shocks driven by CMEs. A majority of space instruments detect SEPs in situ and measure their elemental, ionic charge state, and isotopic compositions. Thus, it has become possible to link the evolution of SEP events to CME-driven shocks as they propagate from the Sun to geospace and beyond. In early 2002, RHESSI began complementing these observations with high-resolution imaging of x-rays and gamma rays from flares associated with these events. These multi-spacecraft, multi-instrument and multi-wavelength observations have raised more pointed questions about the origin, acceleration, and interplanetary propagation of SEPs. This volume records advances made in the understanding of solar eruptions with significant consequences in the heliosphere.

The volume is organized into five topical areas, with an introductory review of the early development and current state of CME and energetic particle studies. Topical areas include: CMEs, SEPs, connection to flares, associated phenomena, and space weather. In-depth reviews on solar eruptions and energetic particles also contain observational studies, discussion of theoretical developments, and modeling results. The papers on associated phenomena deal with flares, type II radio bursts, and shock waves. After considering the interplanetary propagation of CMEs and energetic particles, space weather implications are discussed, including the arrival of energetic particles at geospace and their impact on Earth's radiation belts. The review papers cover all important aspects of CMEs and energetic particles making the volume largely self-contained.

Most of the papers in this volume were presented at an AGU Chapman Conference, entitled "Solar Energetic Plasmas and Particles," held at the University of Turku, Finland, August 2-6, 2004. Several additional papers were solicited to make the volume as complete a survey of the subject as possible. Two experts provided peer review for each paper. The editors appreciate the constructive and timely reviews by many members of the international space weather, and Living with a Star, communities that have greatly enhanced the quality of this volume. Finally, the editors are very grateful for the excellent conference arrangements made by the local organizing committee headed by Eino Valtonen from the University of Turku.

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