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.

Magnetic helicity and energy of emerging solar active regions and their erruptivity

“…The helicity threshold we derived is consistent with that derived by Tziotziou et al (2012), which was 2 × 10 42 Mx 2 . Furthermore, our inferred threshold for magnetic helicity is broadly consistent with the maximum likelihood value of the helicity distribution of magnetic clouds, which is 6.3 × 10 42 Mx 2 , according to Patsourakos & Georgoulis (2016), who compiled calculations published by Lynch et al (2003) and Lepping et al (2006). Due to the conserved nature of helicity, the magnetic cloud helicity is considered as a proxy to the helicity carried away by its parent CME.…”

The sun as a significant agent provoking earthquakes

“…Despite the fact that dramatic solar flares or large CMEs-associated geomagnetic storms are known to drive spectacular effects in the Earth's near-space environment ( [87] and references therein), the importance of the CH-driven high speed streams (HSSs) for geomagnetic activity has also become increasingly accepted across the space community over the past few years. Various aspects of the physics of solar wind streams and their influence on the Earth's environment can be found in the AGU collection of papers in Geophysical Monograph #167 edited by Tsurutani et al [123] and in several specialized books and papers [1,2,25,26,38,62,86,[100][101][102][103][121][122][123]131], as well as in references therein).…”

Predicting the geoeffective properties of coronal mass ejections: current status, open issues and path forward

“…The model has been applied to a single event study [46]. Parametric studies of H-CME taking into account the statistical distributions of its input parameters applied to various analytical models showed that it could reproduce the statistical distributions of ICME observed magnetic field magnitudes at 1 AU, for a narrow range of α B values [94,95]. The estimated near-Sun CME magnetic fields are difficult to validate but they were higher than the background coronal magnetic fields derived from radio observations at the same heights.…”