Properties and geoeffectiveness of magnetic clouds in the rising, maximum and early declining phases of solar cycle 23
By K. Huttunen, R. Schwenn, V. Bothmer, H. Koskinen. 2005
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The magnetic structure and geomagnetic response of 73 magnetic clouds (MC) observed by the WIND and ACE satellites in solar cycle 23 are examined. The results have been compared with the surveys from the previous solar cy- cles. The preselected candidate MC events were investigated using the minimum variance analysis to determine if they have a flux-rope structure and to obtain the estimation for the axial orientation ( C, C ). Depending on the calculated inclination relative to the ecliptic we divided MCs into "bipo- lar" ( C 45 ). The number of ob- served MCs was largest in the early rising phase, although the halo CME rate was still low. It is likely that near solar maximum we did not identify all MCs at 1 AU, as they were crossed far from the axis or they had interacted strongly with the ambient solar wind or with other CMEs. The occurrence rate of MCs at 1 AU is also modified by the migration of the filament sites on the Sun towards the poles near solar maxi- mum and by the deflection of CMEs towards the equator due to the fast solar wind flow from large polar coronal holes near solar minimum. In the rising phase nearly all bipolar MCs were associated with the rotation of the magnetic field from the south at the leading edge to the north at the trailing edge. The results for solar cycles 21-22 showed that the direction of the magnetic field in the leading portion of the MC starts to reverse at solar maximum. At solar maximum and in the declining phase (2000-2003) we observed several MCs with the rotation from the north to the south. We observed unipo- lar (i.e. highly inclined) MCs frequently during the whole investigated period. For solar cycles 21-22 the majority of MCs identified in the rising phase were bipolar while in the declining phase most MCs were unipolar. The geomagnetic response of a given MC depends greatly on its magnetic structure and the orientation of the sheath fields. For each event we distinguished the effect of the sheath fields and the MC fields. All unipolar MCs with magnetic field southward at the axis were geoeffective (Dst< 50 nT) while those with the field pointing northward did not cause magnetic storms at all. About half of the all identified MCs were not geoffective or the sheath fields preceding the MC caused the storm. MCs caused more intense magnetic storms (Dst< 100 nT) than moderate magnetic storms ( 50 nT Dst 100 nT).
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/659bce0bdfea9013c16709c20352389f8ff16b7a
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Citations in the corpus
- Interplanetary conditions causing intense geomagnetic storms (Dst ≤ −100 nT) during solar cycle 23 (1996–2006) (2008, result): “Note that other authors used slightly different criteria for MCs [e.g., Huttunen et al., 2005; Zhang et al., 2007].”
- The association of coronal mass ejections with their effects near the Earth (2005, background): “For the set of magnetic clouds that occurred between 1997 and 2002, Huttunen et al. (2004) found that the majority of magnetic clouds with perpendicular axis orientation occurred in 1997 and 1998, i.e. during the early Figure 3.”
- Interplanetary conditions leading to superintense geomagnetic storms (Dst ≤ −250 nT) during solar cycle 23 (2008, background): “[9] Figure 2 shows the interplanetary and Dst data for the largest geomagnetic storm of solar cycle 23, the event during November 20 2003 [Gopalswamy et al., 2005; Huttunen et al., 2005; Gonzalez et al., 2007].”
- Geoeffective Properties of Solar Transients and Stream Interaction Regions (2017, background): “The occurrence of bipolar MCs has a clear trend with the 22-year solar magnetic cycle (e.g., Bothmer and Schwenn 1998; Huttunen et al. 2005; Li et al. 2011).”