Coronal mass ejection geoeffectiveness depending on field orientation and interplanetary coronal mass ejection classification

Abstract

In this study, we have examined the coronal mass ejection (CME) geoeffectiveness characterized by Dst ≤ −50 nT according to the field orientation (N or S) in a CME source region and its dependence on interplanetary CME (ICME) classification (magnetic clouds or ejecta). We first considered 133 CME‐ICME pairs (1996 to 2001) whose CME source locations are identified by SOHO Large‐Angle Spectrometric Coronograph (SOHO/LASCO) and extreme ultraviolet imaging telescope (SOHO/EIT) data. Then we identified the shapes (S or Inverse‐S) of the X‐ray sigmoids associated with 63 of these CMEs using Yohkoh/Soft X‐Ray Telescope (SXT) data. To determine the field orientation in the sigmoids, we applied the coronal flux rope (CFR) model and the force‐free field (FFF) model to these 63 sigmoids using SOHO/Michelson Doppler Imager (MDI) images. We present the results in contingency tables, classified according to solar field orientation and geomagnetic storm strength/occurrence. We found that (1) the prediction of geomagnetic storms (Dst ≤ −50 nT) based on the CFR model is much better than that on the FFF model, (2) the prediction for magnetic clouds (MCs) is much better than that for ejecta (EJ), which implies that the field orientation of the MCs is well conserved through the heliosphere, and (3) for about 86% of the magnetic clouds, the directions of their leading fields are consistent with those in the CME source regions. Our results support the findings that the southward orientations of the magnetic field in the CME source regions plays an important role in the production of geomagnetic storms.