Abstract
Solar eruptive phenomena embrace a variety of eruptions, including flares, solar energetic particles, and radio bursts. Since the vast majority of these are associated with the eruption, development, and evolution of coronal mass ejections (CMEs), we focus on CME observations in this review. CMEs are a key aspect of coronal and interplanetary dynamics. They inject large quantities of mass and magnetic flux into the heliosphere, causing major transient disturbances. CMEs can drive interplanetary shocks, a key source of solar energetic particles and are known to be the major contributor to severe space weather at the Earth. Studies over the past decade using the data sets from (among others) the SOHO, TRACE, Wind, ACE, STEREO, and SDO spacecraft, along with ground-based instruments, have improved our knowledge of the origins and development of CMEs at the Sun and how they contribute to space weather at Earth. SOHO, launched in 1995, has provided us with almost continuous coverage of the solar corona over more than a complete solar cycle, and the heliospheric imagers SMEI (2003–2011) and the HIs (operating since early 2007) have provided us with the capability to image and track CMEs continually across the inner heliosphere. We review some key coronal properties of CMEs, their source regions and their propagation through the solar wind. The LASCO coronagraphs routinely observe CMEs launched along the Sun-Earth line as halo-like brightenings. STEREO also permits observing Earth-directed CMEs from three different viewpoints of increasing azimuthal separation, thereby enabling the estimation of their three-dimensional properties. These are important not only for space weather prediction purposes, but also for understanding the development and internal structure of CMEs since we view their source regions on the solar disk and can measure their in-situ characteristics along their axes. Included in our discussion of the recent developments in CME-related phenomena are the latest developments from the STEREO and LASCO coronagraphs and the SMEI and HI heliospheric imagers.
Highlights
Coronal mass ejections (CMEs) consist of large structures containing plasma and magnetic fields that are expelled from the Sun into the heliosphere
This paper reviews the best-determined coronal properties of CMEs and what we know about their source regions, and some key signatures of CMEs in the solar wind
Hundhausen (1993) first noted that this CME latitude variation more closely parallels that of streamers and prominences than of active regions or sunspots. This pattern is closely linked to the variation of the global solar magnetic field, as exemplified by the tilt angle of the heliospheric current sheet (HCS) when the Sun makes its transition from solar minimum to maximum. This pattern including the match between CMEs, prominence eruptions and the HCS has been confirmed with the LASCO data (Figure 11 – Gopalswamy, 2004; Gopalswamy et al, 2010a)
Summary
Page 9: Replaced erroneous Solwind values from Vourlidas et al (2010, 2011b) with values from Howard et al (1985). Page 27: Added paragraph on initial CME formation and references to Dere et al (1997) and Vourlidas et al (2012). Page 29: Revised two sentences and added reference to Hudson et al (1995). Page 43: Removed sentence: “ such observations were part of the evidence concluding the Solar Flare Myth, evidence that had been accumulated with many datasets through the 1970s and 1980s.”. Page 43: Revised sentence on “stealth CMEs” Page 43: Removed sentence: “ such observations were part of the evidence concluding the Solar Flare Myth, evidence that had been accumulated with many datasets through the 1970s and 1980s.” Page 43: Revised sentence on “stealth CMEs”
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