Determining the 3D Structure of the Corona Using Vertical Height Constraints on Observed Active Region Loops

Abstract

The corona associated with an active region is structured by hightemperature, magnetically-dominated closed and open loops. The projected 2D geometry of these loops is captured in EUV filtergrams. In this study using SDO/AIA 171Å filtergrams, we expand our previous method to derive the 3D structure of these loops, independent of heliostereoscopy. We employ an automated loop recognition scheme (Occult-2) and fit the extracted loops with 2D cubic Bézier splines. Utilizing SDO HMI magnetograms, we extrapolate the magnetic field to obtain simple field models within a rectangular cuboid. Using these models, we minimize the misalignment angle with respect to Bézier control points to extend the splines to 3D (Gary, Hu, and Lee, 2013). The derived Bézier control points give the 3D structure of the fitted loops. We demonstrate the process by deriving the position of 3D coronal loops in three active regions (AR 11117, AR 11158, and AR 11283). The numerical minimization process converges and produces 3D curves which are consistent with the height of the loop structures when the active region is seen on the limb. From this we conclude that the method can be important in both determining estimates of the 3D magnetic field structure and determining the best magnetic model among competing advanced magnetohydrodynamics or force-free-magnetic-field computer simulations.

Comparison of Two Coronal Magnetic Field Models to Reconstruct a Sigmoidal Solar Active Region with Coronal Loops

“…Here we briefly review the procedures of tracing and fitting the coronal loops developed by Gary et al (2014b). First, an automated loop recognition scheme (the code OCCULT-2) is employed to trace the loop structures from the EUV images taken by SDO/AIA in 171 Å.…”

“…Recently, Gary et al (2014b) developed a new method of deriving the 3D structure of observed 2D coronal loops independent of heliostereoscopy, and suggested that it can determine the matching of extrapolated magnetic fields with coro-nal loops. In that method, an automated loop recognition scheme (OCCULT-2, Aschwanden et al 2013) is first used to extract 2D loop structures from EUV images and then the extracted loops are fitted with 2D cubic Bézier splines that are based on 4 control points (Gary et al 2014a).…”

“…In this paper, we will evaluate our extrapolation results from the NLFFF (CESE-MHD-NLFFF) and the NFFF codes, by introducing a critical comparison of the modelled magnetic field lines with the coronal loop geometry. In particular, we will employ Gary et al (2014b)'s method to compute the misalignment angles of the model field lines and identified loops. The target region used in this examination is AR 12158 prior to its major eruption on 2014 September 10, which exhibits a well-shaped sigmoid that indicates a non-potential field.…”

“…We first briefly describe the CESE-MHD-NLFFF code and the NFFF code in Sections 2 and 3, respectively. Then in Section 4 we give a short review of the coronal loop tracing and fitting method developed by Gary et al (2014b). The results of assessing the extrapolated coronal magnetic fields for AR 12158 are given in Section 5, and finally discussions appear in Section 6.…”

Evolution of flare ribbons, electric currents, and quasi-separatrix layers during an X-class flare

“…It occurred near disk center at position N14W18. Because of its intensity and its location, the flare has been the object of many studies (Petrie 2012;Wang et al 2012;Feng et al 2013;Jiang et al , 2014aZharkov et al 2013;Gary et al 2014;Liu et al 2014;Yang et al 2014;Xu et al 2014). The flare, as recorded by the Geostationary Orbiting Environmental Satellites (GOES), started at 22:12 UT, peaking around 22:20 UT.…”