Kinematics of Interacting ICMEs and Related Forbush Decrease: Case Study
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We study heliospheric propagation and some space weather aspects of three Earth-directed interplanetary coronal mass ejections (ICMEs), successively launched from the active region AR 11158 in the period 13 – 15 February 2011. From the analysis of the ICME kinematics, morphological evolution, and in situ observations, we infer that the three ICMEs interacted on their way to Earth, arriving together at 1 AU as a single interplanetary disturbance. Detailed analysis of the in situ data reveals complex internal structure of the disturbance, where signatures of the three initially independent ICMEs could be recognized. The analysis also reveals compression and heating of the middle ICME, as well as ongoing magnetic reconnection between the leading and the middle ICME. We present evidence showing that the propagation of these two, initially slower ICMEs, was boosted by the fastest, third ICME. Finally, we employ the ground-based cosmic ray observations, to show that this complex disturbance produced a single cosmic ray event, i.e., a simple Forbush decrease (FD). The results presented provide a better understanding of the ICME interactions and reveal effects that should be taken into account in forecasting of the arrival of such compound structures.
KeywordsCosmic rays Interplanetary coronal mass ejections Solar wind, disturbances
The authors are grateful to the STEREO/SECCHI team (Goddard Space Flight Center, Naval Research Laboratory), the SOHO/LASCO team (Naval Research Laboratory, Max Planck Institute for Solar System Research), the Wind team, the Moscow neutron monitor team, SEVAN Cosmic Ray Division for providing the data and MT gratefully acknowledges the Austrian Science Fund (FWF): V195-N16. The research leading to these results has received funding from the European Commission’s Seventh Framework Programme (FP7/2007–2013) under the grant agreements n∘ 263252 [COMESEP] and n∘ 284461 [eHEROES].
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