Deriving the Interaction Point between a Coronal Mass Ejection and High-speed Stream: A Case Study

We analyze the interaction between an interplanetary coronal mass ejection (ICME) detected in situ at the L1 Lagrange point on 2016 October 12 with a trailing high-speed stream (HSS). We aim to estimate the region in the interplanetary (IP) space where the interaction happened/started using a combined observational-modeling approach. We use minimum variance analysis (MVA) and the Walen test to analyze possible reconnection exhaust at the interface of ICME and HSS. We perform a graduated cylindrical shell reconstruction of the CME to estimate the geometry and source location of the CME. Finally, we use a two-step drag-based model (DBM) model to estimate the region in IP space where the interaction took place. The magnetic obstacle observed in situ shows a fairly symmetric and undisturbed structure and shows the magnetic flux, helicity, and expansion profile/speed of a typical ICME. The MVA together with the Walen test, however, confirms reconnection exhaust at the ICME–HSS boundary. Thus, in situ signatures are in favor of a scenario where the interaction is fairly recent. The trailing HSS shows a distinct velocity profile which first reaches a semi-saturated plateau with an average velocity of 500 km s −1 and then saturates at a maximum speed of 710 km s −1 . We find that the HSS's interaction with the ICME is influenced only by this initial plateau. The results of the two-step DBM suggest that the ICME has started interacting with the HSS close to Earth (∼0.81 au), which compares well with the deductions from in situ signatures.