Interaction Between Two CMEs During 14 – 15 February 2011 and Their Unusual Radio Signature

We report a detailed analysis of an interaction between two coronal mass ejections (CMEs) that were observed on 14 – 15 February 2011 and the corresponding radio enhancement, which was similar to the “CME cannibalism” reported by Gopalswamy et al. ( Astrophys. J. 548 , L91, 2001). A primary CME, with a mean field-of-view velocity of 669 km s −1 in the Solar and Heliospheric Observatory (SOHO)/ Large Angle Spectrometric Coronagraph (LASCO), was more than as twice as fast as the slow CME preceding it (326 km s −1 ), which indicates that the two CMEs interacted. A radio-enhancement signature (in the frequency range 1 MHz – 400 kHz) due to the CME interaction was analyzed and interpreted using the CME data from LASCO and from the Solar Terrestrial Relations Observatory (STEREO) HI-1, radio data from Wind / Radio and Plasma Wave Experiment (WAVES), and employing known electron-density models and kinematic modeling. The following results are obtained: i) The CME interaction occurred around 05:00 – 10:00 UT in a height range 20 – 25 R ⊙ . An unusual radio signature is observed during the time of interaction in the Wind /WAVES dynamic radio spectrum. ii) The enhancement duration shows that the interaction segment might be wider than 5 R ⊙ . iii) The shock height estimated using density models for the radio enhancement region is 10 – 30 R ⊙ . iv) Using kinematic modeling and assuming a completely inelastic collision, the decrease of kinetic energy based on speeds from LASCO data is determined to be 0.77×10 23 J, and 3.67×10 23 J if speeds from STEREO data are considered. vi) The acceleration, momentum, and force are found to be a =−168 m s −2 , I =6.1×10 18 kg m s −1 , and F =1.7×10 15 N, respectively, using STEREO data.