Comparison of Two Methods for Calculating Magnetic Helicity in the Solar Corona

Abstract

Duo to the large magnetic Reynolds number, the magnetic helicity originating from the solar interior can be carried away through the photosphere into the corona. However, the relationship between the accumulated magnetic helicity flux through the photosphere and the magnetic helicity in the corona is still unclear. By selecting 36 newly emerging active regions in the 23rd solar cycle, we apply optical flow methods to derive the accumulated magnetic helicity through the photosphere ($H_m^p$) by using the sequential longitudinal magnetograms, use nonlinear force-free field extrapolation to obtain the 3D coronal magnetic field, and adopt finite volume methods to calculate the instantaneous relative magnetic helicity in the corona ($H_m^c$) by using vector magnetograms. It is found that the local correlation tracking (LCT)-based $H_m^p$ is larger than $H_m^c$ in $1"$, and that the Differential Affine Velocity Estimator-based $H_m^p$ is more consistent with $H_m^c$ than the LCT-based $H_m^p$. $H_m^p$ is more consistent with $H_m^c$ in evaluation from $2"$ than from $1"$. Moreover, $H_m^c-H_m^p$ systematically shows consistency with the Hemispheric Helicity Rule (over 55\%), no matter which resolution and method are used. These estimations suggest that the consistency of $H_m^c$ and $H_m^p$ is partly dependent on the resolution of the magnetograms and the calculation methods.

arXiv comment18 pages, 5 figures, 2 tables, accepted for publication in ApJ

References in corpus (18)

• Optimization code with weighting function for the reconstruction of coronal magnetic fields
• Preprocessing of vector magnetograph data for a non-linear force-free magnetic field reconstruction
• Tracking Vector Magnetograms with the Magnetic Induction Equation
• Magnetic Helicity Conservation and Astrophysical Dynamos
• Solar Force-free Magnetic Fields
• The Influence of Spatial Resolution on Nonlinear Force-Free Modeling
• New dynamo pattern revealed by solar helical magnetic fields
• Magnetic Energy and Helicity Budgets in the Active-Region Solar Corona. II. Nonlinear Force-Free Approximation
• Magnetic helicity estimations in models and observations of the solar magnetic field. Part I: Finite volume methods
• On the Connection between Mean Field Dynamo Theory and Flux Tubes
• Accuracy of magnetic energy computations
• Validation and Benchmarking of a Practical Free Magnetic Energy and Relative Magnetic Helicity Budget Calculation in Solar Magnetic Structures
• Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. Part III: Twist Number Method
• Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930
• On the reliability of magnetic energy and helicity computations based on nonlinear force-free coronal magnetic field models
• Evolution of Relative Magnetic Helicity: New Boundary Conditions for the Vector Potential
• Magnetic helicity estimations in models and observations of the solar magnetic field. Part IV: Application to solar observations
• Chirality of Intermediate Filaments and Magnetic Helicity of Active Regions

Cited by in corpus (1)

• The Properties of Non-Potential Magnetic Field Parameters in a Super-Active Region with Complex Structures and Strong Solar Flares