Magnetic Flux Emergence into the Solar Corona. III. The Role of Magnetic Helicity Conservation

It is well known that coronagraphic observations of halo coronal mass ejections (CMEs) are subject to projection effects. Viewing in the plane of the sky does not allow us to determine the crucial parameters that define the geoeffectiveness of CMEs, such as the space speed, width, or source location. Assuming that halo CMEs have constant velocities, are symmetric, and propagate with constant angular widths, at least in their early phase, we have developed a technique that allows us to obtain the required parameters. This technique requires measurements of sky-plane speeds and the moments of the first appearance of the halo CMEs above opposite limbs. We apply this technique to obtain the parameters of all the halo CMEs observed by the Solar and Heliospheric Observatory (SOHO) missionʹs Large Angle and Spectrometric Coronagraph experiment until the end of 2000. We also present a statistical summary of these derived parameters of the halo CMEs.