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

Abstract

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 0.77×10²³ J, and 3.67×10²³ J if speeds from STEREO data are considered. vi) The acceleration, momentum, and force are found to be a=−168 m s⁻², I=6.1×10¹⁸ kg m s⁻¹, and F=1.7×10¹⁵ N, respectively, using STEREO data.