Near-Sun and 1 AU magnetic field of coronal mass ejections: a parametric study
Abstract
Aims: The magnetic field of coronal mass ejections (CMEs) determines their structure, evolution, and energetics, as well as their geoeffectiveness. However, we currently lack routine diagnostics of the near-Sun CME magnetic field, which is crucial for determining the subsequent evolution of CMEs.
Methods: We recently presented a method to infer the near-Sun magnetic field magnitude of CMEs and then extrapolate it to 1 AU. This method uses relatively easy to deduce observational estimates of the magnetic helicity in CME-source regions along with geometrical CME fits enabled by coronagraph observations. We hereby perform a parametric study of this method aiming to assess its robustness. We use statistics of active region (AR) helicities and CME geometrical parameters to determine a matrix of plausible near-Sun CME magnetic field magnitudes. In addition, we extrapolate this matrix to 1 AU and determine the anticipated range of CME magnetic fields at 1 AU representing the radial falloff of the magnetic field in the CME out to interplanetary (IP) space by a power law with index αB.
Results: The resulting distribution of the near-Sun (at 10 R⊙) CME magnetic fields varies in the range [0.004, 0.02] G, comparable to, or higher than, a few existing observational inferences of the magnetic field in the quiescent corona at the same distance. We also find that a theoretically and observationally motivated range exists around αB = -1.6 ± 0.2, thereby leading to a ballpark agreement between our estimates and observationally inferred field magnitudes of magnetic clouds (MCs) at L1.
Conclusions: In a statistical sense, our method provides results that are consistent with observations.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- November 2016
- DOI:
- 10.1051/0004-6361/201628277
- arXiv:
- arXiv:1609.00134
- Bibcode:
- 2016A&A...595A.121P
- Keywords:
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- Sun: atmosphere;
- Sun: coronal mass ejections (CMEs);
- Sun: magnetic fields;
- solar-terrestrial relations;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- A&