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Magnetic Clouds: Solar Cycle Dependence, Sources, and Geomagnetic Impacts
Y Li1, J G Luhmann1, B J Lynch1
1Space Sciences Laboratory, University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94804 USA.
Solar Physics
|November 6, 2018
Summary
Magnetic clouds (MCs) with southward magnetic fields (Bz south) are key drivers of space weather. This study analyzes MCs from 1995-2017, finding most contain Bz south and originate closer to the solar disk center, impacting space weather.
Area of Science:
- Space Physics
- Solar Physics
- Astrophysics
Background:
- Magnetic clouds (MCs) are transient solar wind structures characterized by strong magnetic fields.
- Southward magnetic fields (Bz south) within MCs and their sheath regions are primary drivers of space weather disturbances.
- Understanding MCs is crucial for predicting and mitigating space weather impacts.
Purpose of the Study:
- To conduct a comprehensive analysis of magnetic clouds (MCs) and their associated southward magnetic field (Bz south) components.
- To investigate the relationship between MC characteristics, solar cycle phase, and occurrence frequency.
- To determine the origin of MCs and their contribution to major space weather events like Dst storms.
Main Methods:
- Analysis of magnetic cloud (MC) and sheath region data from 1995 to 2017.
- Quantification of southward magnetic field (Bz south) components within MCs and their sheaths.
- Correlation analysis between MC properties (speed, magnitude, Bz polarity) and solar cycle phase.
- Investigation of MC origins and their association with solar disk center proximity and active regions.
Main Results:
- 85% of 303 analyzed MCs exhibited a southward magnetic field (Bz south) up to 50 nT.
- Strongest magnetic magnitudes and Bz south in MCs occurred during the declining phase of the solar cycle.
- Bipolar MCs showed solar-cycle dependence in polarity, while unipolar MCs showed dependence in occurrence frequency.
- MCs with highest speeds and sheath Bz south originated from regions closer to the solar disk center.
- Approximately 80% of large Dst storms were attributed to MC events, with combined sheath and MC southward fields causing the most significant storms.
Conclusions:
- The solar-cycle dependence of bipolar MC polarity, linked to quiescent filaments and weak MCs, spans 42 years.
- MCs originating from active region flares exhibit mixed Bz polarity, lacking solar-cycle dependence and posing forecasting challenges.
- Southward magnetic fields in MCs and their sheaths are critical for understanding and predicting space weather events.
- Proximity of MC source regions to the solar disk center influences their speed and magnetic field strength.
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