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Modeling of AR 12760 with GX Simulator and Evidence for the Extended Transition Region in Peripheral Active Region Loops

Therese A. Kucera, Gelu M. Nita, James A. Klimchuk, Gregory D. Fleishman

Abstract

In order to understand solar atmospheric heating it is important to test heating models against spatially resolved data from solar active regions. Here we model a small active region, AR~12760 observed on 2020 April 28, with the GX Simulator package by fitting the EUV intensities in wavebands observed by Solar Dynamics Observatory's Atmospheric Imaging Assembly. We assume the temporally and spatially averaged heating rate along a loop has a power-law dependence on loop length, $L$ and average magnetic field strength along the loop, $B_{avg}$. We find that the best fit heating model for the 211~Å band is $<\!\!Q\!\!>\approx 7\times 10^{-3} (B_{avg}/{100 \mbox{G}})^{1.5}(L/{10^9\mbox{cm}})^{-1}$ erg cm$^{-3}$ s$^{-1}$ but that there is a range of parameters that give qualitatively reasonable fits, which we conclude is due to a correlation between $B_{avg}$ and $L$. In addition, we find that the models of the bands including cooler emission (131 and 171~Å) greatly underestimate the extent of the emission in the legs of the longer loops at the peripheries of the active region that are the strongest contributors of the emission in those bands. We conclude that this is because the modeling assumes that all transition region emission is confined to the loop foot points, but in reality the upper transition region of longer loops extends significantly farther into the loop. It is important to consider this aspect of the transition region in future efforts to model EUV emission.

Modeling of AR 12760 with GX Simulator and Evidence for the Extended Transition Region in Peripheral Active Region Loops

Abstract

In order to understand solar atmospheric heating it is important to test heating models against spatially resolved data from solar active regions. Here we model a small active region, AR~12760 observed on 2020 April 28, with the GX Simulator package by fitting the EUV intensities in wavebands observed by Solar Dynamics Observatory's Atmospheric Imaging Assembly. We assume the temporally and spatially averaged heating rate along a loop has a power-law dependence on loop length, and average magnetic field strength along the loop, . We find that the best fit heating model for the 211~Å band is erg cm s but that there is a range of parameters that give qualitatively reasonable fits, which we conclude is due to a correlation between and . In addition, we find that the models of the bands including cooler emission (131 and 171~Å) greatly underestimate the extent of the emission in the legs of the longer loops at the peripheries of the active region that are the strongest contributors of the emission in those bands. We conclude that this is because the modeling assumes that all transition region emission is confined to the loop foot points, but in reality the upper transition region of longer loops extends significantly farther into the loop. It is important to consider this aspect of the transition region in future efforts to model EUV emission.

Paper Structure

This paper contains 19 sections, 4 equations, 21 figures, 1 table.

Table of Contents

  1. Introduction
  2. Modeling Process
  3. Overview
  4. EUV Data
  5. Magnetic Field Model
  6. Loop Plasma
  7. Fitting of the Model
  8. Fit Results
  9. Fit to the 211 Å band
  10. Fit to the 171 Å band
  11. Fits to other AIA bands
  12. Discussion
  13. Heating Parameters
  14. Transition-Region Emission
  15. Loop Expansion
  16. ...and 4 more sections

Figures (21)

  • Figure 1: Flowchart showing the overall process used to fit EUV data with GX Simulator
  • Figure 2: (a)-(f) averages of SDO/AIA intensity for the 94, 131, 171, 193, 211, and 335 Å bands from 9:15-13:15 UT shown with linear scaling. (g) HMI intensity and (h) longitudinal magnetic field data at 11:11 UT.
  • Figure 3: The 171 and 211 Å images at 11:15 UT (left) compared with the average images made using one image every five minutes from 09:15-13:15 UT (right). The on line-version of this paper includes an animation with the equivalent frame showing each image (one every 5 minutes from 09:15-13:15 UT) used to calculate the average. The video is 4 s long.
  • Figure 4: Magnetic field lines from (a) Magnetic Model 1 and (b) Magnetic Model 2 superimposed on a map of the radial photospheric field. Field lines closing within the model box are shown in green while ones that do not close are shown in yellow.
  • Figure 5: Contours show regions in which it was assumed there was transition-region emission using Magnetic Model 1 (top row) and Magnetic Model 2 (bottom row) superimposed on a HMI longitudinal magnetogram (left) and AIA 171 Å image (right).
  • ...and 16 more figures