Coronal Mass Ejections

Abstract

Sudden expulsions of dense clouds of plasma from the outer atmosphere of the Sun, termed mass ejections (CMEs), are the focus of intense observational and theoretical efforts. CMEs are a type of coronal transient, the general name given the disruption of coronal structure. The mass ejection phenomenon, known for barely a dozen years, is rapidly generating interest within the areas of solar, stellar, and solar-terrestria l physics. Flares, eruptive prominences, and nonequilibrium magnetic field con­ figurations are among the postulated origins of CMEs. Not surprisingly, large-scale magnetic fields are also related to mass ejections. The slowly evolving coronal density structure is now recognized as marking the location of fields and, ultimately, the instantaneous state of the solar dynamo. A new class of CMEs has been found that perhaps shows the continuous renewal of surface fields by interior circulation. Understanding CMEs, the refo re, may lead to insights about flares and other solar phenomena. The CME may be described as an ejection of magnetized plasma out of the gravitational potential well of a central star (56). Thus, phenomena analogous to CMEs should also be occurring in other stars whose magnetic fields and gravitational potentials are Sun-like. Those techniques at radio wavelengths that allow ground-based CME observations at large elon­ , ,. / / ,,' - ..... ..... � � � ; g � ' ,