Modeling the Dispersal of an Active Region: Quantifying Energy Input Into the Corona

Mackay, D. H.; Green, Lucie M.; Ballegooijen, A. A. van

doi:10.1088/0004-637x/729/2/97

Cited by 77 publications

(141 citation statements)

References 48 publications

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“…Here we discuss observational results relevant to the decay of ARs. Mackay et al (2011) carried out careful magnetic field measurements over four days spanning the CMP of the AR, tracking short-term evolution of magnetic flux, flux imbalance and separation between the centre of gravity of positive and negative polarities. The latter was determined by a vector S( ) as…”

Section: Fragmentation Of Sunspots and The Re-establishment Of Convecmentioning

confidence: 99%

“…Using the magnetic observational data (61 MDI magnetograms) as lower boundary conditions, Mackay et al (2011) carried out a time-dependent non-linear force-free field (NLFFF) quasi-static modelling in order to study the build-up of free magnetic energy and coronal magnetic helicity resulting from the dispersal of the decaying AR 8005. The novelty of their modelling is that it is data-driven: the successive magnetograms drive the evolution of the coronal magnetic fields between successive force-free equilibria.…”

Section: Fragmentation Of Sunspots and The Re-establishment Of Convecmentioning

confidence: 99%

“…By day 20 of the model evolution, a loss of equilibrium and eruption (CME) ensues (see Figure 16c, d). The rate of build-up of free energy resulting from flux cancellations in a decaying AR was observationally studied by Mackay et al (2011). They found a free energy injection rate of (2.5 -3) × 10 25 erg s −1 , which is sufficient to balance radiative losses of the AR, but it appears to be too slow for an efficient build-up of major eruptive activity (see a more detailed discussion in Section 4.4.1).…”

Section: Modelling the Evolution Of Ars From Emergence Through Decaymentioning

confidence: 99%

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Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

249

131

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The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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Section: Fragmentation Of Sunspots and The Re-establishment Of Convecmentioning

confidence: 99%

Section: Fragmentation Of Sunspots and The Re-establishment Of Convecmentioning

confidence: 99%

Section: Modelling the Evolution Of Ars From Emergence Through Decaymentioning

confidence: 99%

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Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

249

131

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“…For the three-dimensional simulations, the magnetograms are required to be in complete flux balance, so we also correct them for imbalance using same technique as Mackay et al (2011). Data set 1 is already roughly in flux balance; the mean imbalance is 2.3% and the imbalance per pixel is at most 3 G, so is comparable to the noise level.…”

Section: Sdo/hmi Datamentioning

confidence: 99%

THE STORAGE AND DISSIPATION OF MAGNETIC ENERGY IN THE QUIET SUN CORONA DETERMINED FROM SDO /HMI MAGNETOGRAMS

Meyer

Sabol

Mackay

et al. 2013

ApJ

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In recent years, higher cadence, higher resolution observations have revealed the quiet-Sun photosphere to be complex and rapidly evolving. Since magnetic fields anchored in the photosphere extend up into the solar corona, it is expected that the small-scale coronal magnetic field exhibits similar complexity. For the first time, the quiet-Sun coronal magnetic field is continuously evolved through a series of non-potential, quasi-static equilibria, deduced from magnetograms observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, where the photospheric boundary condition which drives the coronal evolution exactly reproduces the observed magnetograms. The build-up, storage, and dissipation of magnetic energy within the simulations is studied. We find that the free magnetic energy built up and stored within the field is sufficient to explain small-scale, impulsive events such as nanoflares. On comparing with coronal images of the same region, the energy storage and dissipation visually reproduces many of the observed features. The results indicate that the complex small-scale magnetic evolution of a large number of magnetic features is a key element in explaining the nature of the solar corona.

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“…This is problematic for studies of magnetic topology because standard techniques (such as potential fields) applied to a sequence of photospheric magnetograms will not give the correct field line topology commensurate with an ideal evolution from one time to the next. To avoid this problem, A&A 539, A1 (2012) a number of studies have used time-dependent 3D simulations to model how topological structure develops in response to simple boundary motions (Milano et al 1999;Galsgaard et al 2003;Aulanier et al 2005;Masson et al 2009) or to boundary motions derived directly from observed magnetograms (Mackay et al 2011). But such time-dependent simulations inevitably suffer from numerical dissipation, leading to inaccuracies in magnetic topology.…”

Section: Introductionmentioning

confidence: 99%

Lagrangian coherent structures in photospheric flows and their implications for coronal magnetic structure

Yeates

Hornig

Welsch

2012

A&A

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Aims. We show how the build-up of magnetic gradients in the Sun's corona may be inferred directly from photospheric velocity data. This enables computation of magnetic connectivity measures such as the squashing factor without recourse to magnetic field extrapolation. Methods. Assuming an ideal evolution in the corona, and an initially uniform magnetic field, the subsequent field line mapping is computed by integrating trajectories of the (time-dependent) horizontal photospheric velocity field. The method is applied to a 12 h high-resolution sequence of photospheric flows derived from Hinode/SOT magnetograms. Results. We find the generation of a network of quasi-separatrix layers in the magnetic field, which correspond to Lagrangian coherent structures in the photospheric velocity. The visual pattern of these structures arises primarily from the diverging part of the photospheric flow, hiding the effect of the rotational flow component: this is demonstrated by a simple analytical model of photospheric convection. We separate the diverging and rotational components from the observed flow and show qualitative agreement with purely diverging and rotational models respectively. Increasing the flow speeds in the model suggests that our observational results are likely to give a lower bound for the rate at which magnetic gradients are built up by real photospheric flows. Finally, we construct a hypothetical magnetic field with the inferred topology, that can be used for future investigations of reconnection and energy release.

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Modeling the Dispersal of an Active Region: Quantifying Energy Input Into the Corona

Cited by 77 publications

References 48 publications

Evolution of Active Regions

Evolution of Active Regions

THE STORAGE AND DISSIPATION OF MAGNETIC ENERGY IN THE QUIET SUN CORONA DETERMINED FROM SDO /HMI MAGNETOGRAMS

Lagrangian coherent structures in photospheric flows and their implications for coronal magnetic structure

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