Coronal mass ejections: The key to major interplanetary and geomagnetic disturbances

Abstract

For years it was thought that solar flares were responsible for major interplanetary (IP) particle events and geomagnetic storms. However, recently we have seen an important paradigm shift such that now coronal mass ejections (CMEs), not flares, are considered the key causal link with solar activity. CMEs are vast structures of plasma and magnetic fields that are expelled from the sun into the heliosphere. We now know that CMEs drive all large geomagnetic storms and their attendant effects, such as auroral displays. Fast CMEs produce transient IP shocks which cause sudden commencements at Earth. The CME‐related shocks also accelerate the solar energetic particle (SEP) events associated with major IP disturbances and with radiation hazards at Earth. This new paradigm has important implications for prioritizing the development of instruments and techniques to predict IP disturbances and geomagnetic activity.