Relation between CME Speed and Magnetic Helicity in Solar Source Regions

Coronal mass ejections (CMEs) are thought to be powered by the free energy in the solar source regions. The magnetic helicity in the source regions is one of the indicators of this free energy. In order to see the relationship between the magnetic helicity of CME source regions and CME energy, we considered a set of 41 solar source regions (from solar cycle 23) from which CMEs erupted and ended up as magnetic clouds near Earth. Using EUV and magnetogram data from the Solar and Heliospheric Observatory (SOHO) mission, we determined the most probable linear force-free magnetic structure and its magnetic helicity for each CME source region. The magnetograms taken just prior to the CME eruption were used to compute the magnetic helicity. The CME speeds were obtained from the SOHO/LASCO CME catalog (http://cdaw.gsfc.nasa.gov). We found that the magnetic helicity is positively correlated with the speed of CMEs. This result suggests that the magnetic helicity of CME source regions maybe useful for predicting CME speed.