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Influence of coronal mass ejection orientation on dynamics in interplanetary space

Coronal mass ejections (CMEs) are generally considered magnetic structures in which the magnetic field spirals around a central axis (flux rope, FR). The FR axis can be oriented at any angle to the ecliptic. The dynamics of the CME in interplanetary (IP) space is determined primarily by the magnetohydrodynamic (MHD) drag force, i.e., the interaction of the CME with the interplanetary magnetic field (IMF) and the ambient solar wind (SW). The configuration of IMF and SW is neither homogeneous nor isotropic in IP space. For this very reason, we expect the occurrence of variations in the dynamics of the CME with respect to the orientation of its FR axis. In other words, we expect some difference in the propagation of CMEs with a FR axis parallel to the ecliptic plane (CMEs with low inclination) and CMEs with a FR axis perpendicular to the ecliptic plane (CMEs with high inclination). We study isolated Earth-directed CMEs during 1997- 2018. We obtain the inclination of the CME in the "near-Sun" environment by applying the ellipse fitting technique to the outer front of the CME determined with the SOHO /LASCO coronagraph. In the "near-Earth" environment, we determined the orientation of the corresponding ICME using in situ plasma and magnetic field data. We also investigate the non-radial flows (NRFs) in the sheath region of ICME. Most of the CME-ICME associations studied have low inclination. For most CME-ICME pairs, we have obtained consistent estimates of the dominant inclination from remote sensing and in situ data. The observed NRFs in the sheath region show a larger ratio between y- and z-directions for high inclination events, suggesting that the orientation of the CME likely has an impact on its propagation. In addition, we discuss the effects of CME orientation on MHD drag in IP space. These results provide new insights into CME dynamics, the understanding of which is critical for improving space weather forecasting.

Sun, Heliosphere, coronal mass ejections

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