Understanding the Nature of Collision of CMEs in the Heliosphere

Understanding the propagation of coronal mass ejections (CMEs) in the heliosphere is important to estimate their arrival time at Earth. The kinematics of CMEs can change when they interact or collide with each other as they propagate in the heliosphere. The knowledge about nature of collision of CMEs can be utilized to predict their post-collision kinematics and relatively accurate arrival time at the Earth. To calculate the coefficient of restitution for the colliding CMEs, we need to estimate the propagation and expansion speeds, impact direction and the masses of the CMEs. Although, these parameters could be derived from heliospheric imaging observations, but have large uncertainties. In the present study, we have thoroughly discussed the uncertainties involved in the calculation of coefficient of restitution. Our results suggest that calculated value of coefficient of restitution, from mere use of kinematics from STEREO/COR and HI observations, should also be validated with simulation before making a reliable conclusion for nature of collision for the CMEs. We also highlight the significance of HI observations in studying CME-CME collision for the purpose of improved space weather forecasting.