Magnetic Flux Rope Identification and Characterization from Observationally-Driven Solar Coronal Models

Abstract

Formed through magnetic field shearing and reconnection in the solar corona, magnetic flux ropes are structures of twisted magnetic field, threaded along an axis. Their evolution and potential eruption are of great importance for space weather. Here we describe a new methodology for the automated detection of flux ropes in simulated magnetic fields, based on fieldline helicity. More robust than previous methods, it also allows the full volume extent of each flux rope structure to be determined. Our Flux Rope Detection and Organization (FRoDO) code is publicly available, and measures the magnetic flux and helicity content of pre-erupting flux ropes over time, as well as detecting eruptions. As a first demonstration the code is applied to the output from a time-dependent magnetofrictional model, spanning 1996 June 15 - 2014 February 10. Over this period, 1561 erupting and 2099 non-erupting magnetic flux ropes are detected, tracked, and characterized. For this particular model data, erupting flux ropes have a mean net helicity magnitude of $(2.66\pm 6.82)\times 10^{43}$ Mx${}^2$, while non-erupting flux ropes have a significantly lower mean of $(4.04\pm 9.25)\times 10^{42}$ Mx${}^2$, although there is overlap between the two distributions. Similarly, the mean unsigned magnetic flux for erupting flux ropes is $(4.04\pm 6.17)\times 10^{21}$ Mx, significantly higher than the mean value of $(7.05\pm 16.8)\times 10^{20}$ Mx for non-erupting ropes. These values for erupting flux ropes are within the broad range expected from observational and theoretical estimates, although the eruption rate in this particular model is lower than that of observed coronal mass ejections. In future the FRoDO code will prove a valuable tool for assessing the performance of different non-potential coronal simulations and comparing them with observations.

arXiv commentAccepted for publication in ApJ (16 pages, 14 figures, 2 tables, 2 animations)

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• Two Classes of Eruptive Events During Solar Minimum
• Relative field line helicity of a large eruptive solar active region
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• On the limitations of magneto-frictional relaxation
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