Coronal mass ejections and geomagnetic storms: Seasonal variations
The well-established semiannual geomagnetic cycle, with peak activity near the equinoxes, has been attributed to the angle between the solar rotation axis and the geomagnetic dipole, which modulates the GSM Bz component in the interplanetary magnetic field (MF). This effect is predicted to be accentuated in the shocked plasma ahead of fast coronal mass ejections (CMESs); its relevance to the internal fields of the ejecta is unclear. CMEs, particularly fast events driving interplanetary shocks, are the cause of almost all large geomagnetic storms near solar maximum. We use a set of CMEs identified by ISEE-3 observations of bidirectional electron streaming, plus IMF and geomagnetic data, to investigate the semiannual geomagnetic variation and its relation to CMEs. We find that the geomagnetic effectiveness of CMEs and post-shock solar wind is well-ordered by speed and by the southward component of the IMF in GSM coordinates, as well as by preexisting geomagnetic conditions. The post-shock seasonal effect, with geomagnetic effectiveness maximizing near April 5 for negative GSEQ By and near October 5 for positive GSEQ By, is identifiable in shock and shock/CME events, but not for CME events without leading shocks. When used to complement the more fundamental causal parameter of CME speed, the seasonal effect appears to have value for prediction of geomagnetic storms.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Department of Defense, Washington, DC (United States); National Aeronautics and Space Administration, Washington, DC (United States)
- OSTI ID:
- 10153209
- Report Number(s):
- LA-UR-92-1616; CONF-9205201-1; ON: DE92015141
- Resource Relation:
- Conference: Solar-terrestrial predictions workshop,Ottawa (Canada),18-22 May 1992; Other Information: PBD: [1992]
- Country of Publication:
- United States
- Language:
- English
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