On the three-dimensional configuration of coronal mass ejections

Coronal mass ejections (CMEs) are a direct consequence of the dynamic nature of the solar atmosphere. They represent fundamental processes in which energy is transferred from the Sun into interplanetary space, including geospace. Their origin, 3D structure and internal magnetic field configuration are to date not well understood. The SOHO spacecraft, launched by the end of 1995, has provided unprecedented data on CMEs since instruments switched on in 1996. From a detailed investigation of the full set of LASCO (Large Angle Spectroscopic Coronagraph) observations from 1996 to the end of 2002, a set of structured CME events has been identified, which exhibits white-light fine structures likely indicative of their internal magnetic field configuration and possible 3D structure. Their Source regions in the low corona and photosphere have been inferred by means of complementary analyses of data from the Extreme-Ultraviolet Imaging Telescope (EIT) and Michelson Doppler Imager (MDI) on board SOHO, and ground-based Halpha measurements. According to the results of this study, structured CMEs arise in a self-similar manner from pre-existing small scale loop systems, overlying regions of opposite magnetic polarities. From the characteristic pattern of the CMEs' source regions in both solar hemispheres, a generic scheme is presented in which the projected white-light topology of a CME depends primarily on the orientation and position of the source region's neutral line on the solar disk. The paper also provides information about the white-light characteristics of the analysed CMEs, such as angular width and position angle, with respect to their source region properties, such as heliographic location, inclination and length, including the frequency and variation of these parameters over the investigated time period.