Near-Sun and 1 AU magnetic field of coronal mass ejections: a parametric study

¹ University of Ioannina, Department of Physics, Section of Astrogeophysics, 45110 Ioannina, Greece
e-mail: spatsour@cc.uoi.gr
² Research Center for Astronomy and Applied Mathematics, Academy of Athens, Athens, Greece

Received: 8 February 2016
Accepted: 3 August 2016

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 α_B.

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 α_B = −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.