Space Weather Application Using Projected Velocity Asymmetry of Halo CMEs

Halo coronal mass ejections (HCMEs) originating from regions close to the center of the Sun are likely to be responsible for severe geomagnetic storms. It is important to predict geoeffectiveness of HCMEs by using observations when they are still near the Sun. Unfortunately, coronagraphic observations do not provide true speeds of CMEs because of projection effects. In the present paper, we present a new technique to allow estimates of the space speed and approximate source location using projected speeds measured at different position angles for a given HCME (velocity asymmetry). We apply this technique to HCMEs observed during 2001 – 2002 and find that the improved speeds are better correlated with the travel times of HCMEs to Earth and with the magnitudes of ensuing geomagnetic storms.