Comparison of CME and ICME Structures Derived from Remote-Sensing and In Situ Observations

Abstract

We present results from the comparison of the near-Sun and in situ analysis of two Earth-directed coronal mass ejections (CMEs) with different 3D orientations and solar source region characteristics. The CME on 14 July 2000, the so-called Bastille Day storm, a well-studied event, was observed from a single-point perspective by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). It caused a major geomagnetic storm with a peak Kp of 9. The CME originated from a magnetic bipolar photospheric source region with the polarity inversion line being oriented rather parallel to the heliographic equator. In contrast, the CME on 29 September 2013, which caused a geomagnetic storm with a peak Kp intensity of 8-, originated from a magnetic quadrupolar photospheric source region with the polarity inversion line between the two bipoles almost vertically oriented with respect to the heliographic equator. The results of a graduated cylindrical shell (GCS) analysis of the CMEs near the Sun are compared with the minimum variance analysis (MVA) of the magnetic field structure of the interplanetary CME (ICME) measured in situ near Earth’s orbit. The results are in good agreement for the September 2013 CME and ICME, whereas the July 2000 ICME appears substantially inclined near Earth’s orbit. The discrepancy can likely be explained taking into account kinks in the CME’s near-Sun structure of the CME that expands into the interplanetary medium.