Simulating Emission of Coronal Loops with Non-Constant Cross-Section
Abstract
The solar corona is filled with loop-like structures that appear bright against the background when observed in the extreme ultraviolet (EUV). These loops have several remarkable properties. Warm loops (∼ 1 MK) appear to be ∼ 2 - 9 times as dense at their apex as predicted by of hydrostatic atmosphere models. These loops also appear to be of constant cross-section despite the fact that the field strength in a potential magnetic field should decrease in the corona, causing the loops to expand. Why many active region loops appear to be of constant cross-section is not well understood. Theories range from an internal twist of the magnetic field to observational effects. In this work we simulate active region loops with different expansion factors heated by nanoflare storms. We calculate the hydrodynamic properties for each loop as a function of the expansion factor Gamma. We show that even modest tapering ratios can lead to drastic changes in the density profiles of active region loops, and they can also explain the overpressure at the apex of these loops. Synthetic AIA images of each loop are made to show the observable consequences of the expansion of loops near the instrumental resolution. We find that all loops, even those with a large expansion factor, appear to be of near constant cross-section when images are simulated in AIA passbands. Only when the images are simulated for a much higher resolution instrument with 0.1” pixels does the real expansion of the loop become apparent.Abstract (2,250 Maximum Characters): The solar corona is filled with loop-like structures that appear bright against the background when observed in the extreme ultraviolet (EUV). These loops have several remarkable properties. Warm loops (∼ 1 MK) appear to be ∼ 2 - 9 times as dense at their apex as predicted by of hydrostatic atmosphere models. These loops also appear to be of constant cross-section despite the fact that the field strength in a potential magnetic field should decrease in the corona, causing the loops to expand. Why many active region loops appear to be of constant cross-section is not well understood. Theories range from an internal twist of the magnetic field to observational effects. In this work we simulate active region loops with different expansion factors heated by nanoflare storms. We calculate the hydrodynamic properties for each loop as a function of the expansion factor Gamma. We show that even modest tapering ratios can lead to drastic changes in the density profiles of active region loops, and they can also explain the overpressure at the apex of these loops. Synthetic AIA images of each loop are made to show the observable consequences of the expansion of loops near the instrumental resolution. We find that all loops, even those with a large expansion factor, appear to be of near constant cross-section when images are simulated in AIA passbands. Only when the images are simulated for a much higher resolution instrument with 0.1” pixels does the real expansion of the loop become apparent.
- Publication:
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AAS/Solar Physics Division Abstracts #44
- Pub Date:
- July 2013
- Bibcode:
- 2013SPD....44...45W