Magnetic Field Strength in the Upper Solar Corona Using White-Light Shock Structures Surrounding Coronal Mass Ejections

Kim, Rok‐Soon; Gopalswamy, N.; Moon, Yong‐Jae; Cho, Kyung-Suk; Yashiro, S.

doi:10.1088/0004-637x/746/2/118

Cited by 40 publications

(82 citation statements)

References 50 publications

(72 reference statements)

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“…They rely on techniques such as Faraday rotation and CME-shock stand-off distance and give magnetic field strengths in the range [0.009-0.02] G (e.g., Bemporad & Mancuso 2010;Gopalswamy & Yashiro 2011;Kim et al 2012;Fig. 4.…”

Section: Parametric Studymentioning

confidence: 99%

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

Patsourakos¹,

Georgoulis²

2016

A&A

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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.

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Section: Parametric Studymentioning

confidence: 99%

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

Patsourakos¹,

Georgoulis²

2016

A&A

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“…Several researchers investigated the CME-driven shock signatures and measured CME stand-off distances D ( ) CME , which are defined as the distances between CME fronts and their associated shock fronts, in order to estimate the strengths and radial profiles of coronal magnetic fields (Gopalswamy & Yahiro 2011;Kim et al 2012). Recently, Kwon et al (2014) found that the CME-driven shock signatures observed near CME leading edges could be associated with a bow shock by comparing 3D speeds between the leading edge of a CME and its associated shock front derived from the graduated cylindrical shell (GCS) and ellipsoid models.…”

Section: Introductionmentioning

confidence: 99%

Which Bow Shock Theory, Gasdynamic or Magnetohydrodynamic, Better Explains CME Stand-off Distance Ratios from LASCO-C2 Observations ?

Lee

Moon

Lee

et al. 2017

ApJ

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It is generally believed that fast coronal mass ejections (CMEs) can generate their associated shocks, which are characterized by faint structures ahead of CMEs in white-light coronagraph images. In this study, we examine whether the observational stand-off distance ratio, defined as the CME stand-off distance divided by its radius, can be explained by bow shock theories. Of 535 SOHO/LASCO CMEs (from 1996 to 2015) with speeds greater than 1000 km s −1 and angular widths wider than 60°, we select 18 limb CMEs with the following conditions: (1) their Alfvénic Mach numbers are greater than one under Mann's magnetic field and Saito's density distributions; and (2) the shock structures ahead of the CMEs are well identified. We determine observational CME stand-off distance ratios by using brightness profiles from LASCO-C2 observations. We compare our estimates with theoretical stand-off distance ratios from gasdynamic (GD) and magnetohydrodynamic (MHD) theories. The main results are as follows. Under the GD theory, 39% (7/18) of the CMEs are explained in the acceptable ranges of adiabatic gamma (γ) and CME geometry. Under the MHD theory, all the events are well explained when we consider quasiparallel MHD shocks with γ=5/3. When we use polarized brightness (pB) measurements for coronal density distributions, we also find similar results: 8% (1/12) under GD theory and 100% (12/12) under MHD theory. Our results demonstrate that the bow shock relationships based on MHD theory are more suitable than those based on GD theory for analyzing CME-driven shock signatures.

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“…Over the last decade, many works focused on the signatures of CME-driven shocks in white-light (WL) observations, namely from the Solar and Heliospheric Observatory (SOHO)/LASCO C2 and C3 coronagraphs and the STEREO/ COR1 and COR2 telescopes (Sheeley et al 2000;Vourlidas et al 2003Vourlidas et al , 2013Gopalswamy et al 2009;Ontiveros & Vourlidas 2009;Gopalswamy & Yashiro 2011;Kim et al 2012;Lee et al 2014). WL data have proven to contain much more information than previously thought, and were used with various techniques to derive shock speeds, shock compression ratios X d u r r = (i.e., the ratio between the upstream u r and the downstream d r plasma densities), geometrical properties of the shock fronts, as well as the strength of the coronal magnetic field encountered by the shocks, and also allowed studies on the correlation between the SEP fluxes and associated CME speeds (e.g., Kahler 2001).…”

Section: Introductionmentioning

confidence: 99%

Plasma Physical Parameters Along Cme-Driven Shocks. Ii. Observation–simulation Comparison

Bacchini

Susino

Бемпорад

et al. 2015

ApJ

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In this work, we compare the spatial distribution of the plasma parameters along the 1999 June 11 coronal mass ejection (CME)-driven shock front with the results obtained from a CME-like event simulated with the FLIPMHD3D code, based on the FLIP-MHD particle-in-cell method. The observational data are retrieved from the combination of white-light coronagraphic data (for the upstream values) and the application of the RankineHugoniot equations (for the downstream values). The comparison shows a higher compression ratio X and Alfvénic Mach number M A at the shock nose, and a stronger magnetic field deflection d toward the flanks, in agreement with observations. Then, we compare the spatial distribution of M A with the profiles obtained from the solutions of the shock adiabatic equation relating M A , X, and Bn q (the angle between the upstream magnetic field and the shock front normal) for the special cases of parallel and perpendicular shock, and with a semi-empirical expression for a generically oblique shock. The semi-empirical curve approximates the actual values of M A very well, if the effects of a non-negligible shock thickness sh d and plasma-to magnetic pressure ratio u b are taken into account throughout the computation. Moreover, the simulated shock turns out to be supercritical at the nose and sub-critical at the flanks. Finally, we develop a new one-dimensional Lagrangian ideal MHD method based on the GrAALE code, to simulate the ion-electron temperature decoupling due to the shock transit. Two models are used, a simple solar wind model and a variable-γ model. Both produce results in agreement with observations, the second one being capable of introducing the physics responsible for the additional electron heating due to secondary effects (collisions, Alfvén waves, etc.).

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Magnetic Field Strength in the Upper Solar Corona Using White-Light Shock Structures Surrounding Coronal Mass Ejections

Cited by 40 publications

References 50 publications

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

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

Which Bow Shock Theory, Gasdynamic or Magnetohydrodynamic, Better Explains CME Stand-off Distance Ratios from LASCO-C2 Observations ?

Plasma Physical Parameters Along Cme-Driven Shocks. Ii. Observation–simulation Comparison

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