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The Sun’s Non-Potential Corona over Solar Cycle 24 (2024)
Journal Article
Yeates, A. R. (2024). The Sun’s Non-Potential Corona over Solar Cycle 24. Solar Physics, 299(6), Article 83. https://doi.org/10.1007/s11207-024-02328-5

The global magnetic field in the solar corona is known to contain free magnetic energy and magnetic helicity above that of a current-free (potential) state. But the strength of this non-potentiality and its evolution over the solar cycle remain uncer... Read More about The Sun’s Non-Potential Corona over Solar Cycle 24.

Transition to a weaker Sun: Changes in the solar atmosphere during the decay of the Modern Maximum (2024)
Journal Article
Mursula, K., Pevtsov, A. A., Asikainen, T., Tähtinen, I., & Yeates, A. R. (2024). Transition to a weaker Sun: Changes in the solar atmosphere during the decay of the Modern Maximum. Astronomy & Astrophysics, 685, Article A170. https://doi.org/10.1051/0004-6361/202449231

Context. The Sun experienced a period of unprecedented activity during the 20th century, now called the Modern Maximum (MM). The decay of the MM after its maximum in cycle 19 has changed the Sun, the heliosphere, and the planetary environments in man... Read More about Transition to a weaker Sun: Changes in the solar atmosphere during the decay of the Modern Maximum.

A Near-half-century Simulation of the Solar Corona (2024)
Journal Article
Aslanyan, V., Meyer, K. A., Scott, R. B., & Yeates, A. R. (2024). A Near-half-century Simulation of the Solar Corona. Astrophysical Journal Letters, 961(1), Article L3. https://doi.org/10.3847/2041-8213/ad1934

We present an overview of results from a magnetofrictional model of the entire solar corona over a period of 47 yr. The simulation self-consistently reproduces decades of solar phenomena, varying in duration between rapid eruptions and the long-term... Read More about A Near-half-century Simulation of the Solar Corona.

Computation of Winding-Based Magnetic Helicity and Magnetic Winding Density for SHARP Magnetograms in Spherical Coordinates (2023)
Journal Article
Xiao, D., Prior, C. B., & Yeates, A. R. (2023). Computation of Winding-Based Magnetic Helicity and Magnetic Winding Density for SHARP Magnetograms in Spherical Coordinates. Solar Physics, 298(10), Article 116. https://doi.org/10.1007/s11207-023-02211-9

Magnetic helicity has been used widely in the analysis and modelling of solar active regions. However, it is difficult to evaluate and interpret helicity in spherical geometry since coronal magnetic fields are rooted in the photosphere and helicity i... Read More about Computation of Winding-Based Magnetic Helicity and Magnetic Winding Density for SHARP Magnetograms in Spherical Coordinates.

Eruptivity Criteria for Solar Coronal Flux Ropes in Magnetohydrodynamic and Magnetofrictional Models (2023)
Journal Article
Rice, O. E. K., & Yeates, A. R. (2023). Eruptivity Criteria for Solar Coronal Flux Ropes in Magnetohydrodynamic and Magnetofrictional Models. Astrophysical Journal, 955(2), Article 114. https://doi.org/10.3847/1538-4357/acefc1

We investigate which scalar quantity or quantities can best predict the loss of equilibrium and subsequent eruption of magnetic flux ropes in the solar corona. Our models are initialized with a potential magnetic arcade, which is then evolved by mean... Read More about Eruptivity Criteria for Solar Coronal Flux Ropes in Magnetohydrodynamic and Magnetofrictional Models.

Spherical winding and helicity (2023)
Journal Article
Xiao, D., Prior, C., & Yeates, A. (2023). Spherical winding and helicity. Journal of Physics A: Mathematical and Theoretical, 56(20), Article 205201. https://doi.org/10.1088/1751-8121/accc17

In ideal magnetohydrodynamics, magnetic helicity is a conserved dynamical quantity and a topological invariant closely related to Gauss linking numbers. However, for open magnetic fields with non-zero boundary components, the latter geometrical inter... Read More about Spherical winding and helicity.

Surface Flux Transport on the Sun (2023)
Journal Article
Yeates, A., Cheung, M., Jiang, J., Petrovay, K., & Wang, Y. (2023). Surface Flux Transport on the Sun. Space Science Reviews, https://doi.org/10.1007/s11214-023-00978-8

We review the surface flux transport model for the evolution of magnetic flux patterns on the Sun’s surface. Our underlying motivation is to understand the model’s prediction of the polar field (or axial dipole) strength at the end of the solar cycle... Read More about Surface Flux Transport on the Sun.

Automated driving for global non-potential simulations of the solar corona (2022)
Journal Article
Yeates, A., & Bhowmik, P. (2022). Automated driving for global non-potential simulations of the solar corona. Astrophysical Journal, 935(1), Article 13. https://doi.org/10.3847/1538-4357/ac7de4

We describe a new automated technique for active region emergence in coronal magnetic field models, based on the inversion of the electric field locally from a single line-of-sight magnetogram for each region. The technique preserves the arbitrary sh... Read More about Automated driving for global non-potential simulations of the solar corona.

Eruptivity Criteria for Two-dimensional Magnetic Flux Ropes in the Solar Corona (2022)
Journal Article
Rice, O. E., & Yeates, A. R. (2022). Eruptivity Criteria for Two-dimensional Magnetic Flux Ropes in the Solar Corona. Frontiers in Astronomy and Space Sciences, 9, Article 849135. https://doi.org/10.3389/fspas.2022.849135

We apply the magneto-frictional approach to investigate which quantity or quantities can best predict the loss of equilibrium of a translationally-invariant magnetic flux rope. The flux rope is produced self-consistently by flux cancellation combined... Read More about Eruptivity Criteria for Two-dimensional Magnetic Flux Ropes in the Solar Corona.

Exploring the Origin of Stealth Coronal Mass Ejections with Magnetofrictional Simulations (2022)
Journal Article
Bhowmik, P., Yeates, A., & Rice, O. (2022). Exploring the Origin of Stealth Coronal Mass Ejections with Magnetofrictional Simulations. Solar Physics, 297(3), Article 41. https://doi.org/10.1007/s11207-022-01974-x

Coronal mass ejections (CMEs) – among the most energetic events originating from the Sun – can cause significant and sudden disruption to the magnetic and particulate environment of the heliosphere. Thus, in the current era of space-based technologie... Read More about Exploring the Origin of Stealth Coronal Mass Ejections with Magnetofrictional Simulations.

On the limitations of magneto-frictional relaxation (2022)
Journal Article
Yeates, A. (2022). On the limitations of magneto-frictional relaxation. Geophysical and Astrophysical Fluid Dynamics, 116(4), 305-320. https://doi.org/10.1080/03091929.2021.2021197

The magneto-frictional method is used in solar physics to compute both static and quasi-static models of the Sun’s coronal magnetic field. Here, we examine how accurately magneto-friction (without fluid pressure) is able to predict the relaxed state... Read More about On the limitations of magneto-frictional relaxation.

Global Coronal Equilibria with Solar Wind Outflow (2021)
Journal Article
Rice, O. E., & Yeates, A. R. (2021). Global Coronal Equilibria with Solar Wind Outflow. Astrophysical Journal, 923(1), Article 57. https://doi.org/10.3847/1538-4357/ac2c71

Given a known radial magnetic field distribution on the Sun’s photospheric surface, there exist wellestablished methods for computing a potential magnetic field in the corona above. Such potential fields are routinely used as input to solar wind mode... Read More about Global Coronal Equilibria with Solar Wind Outflow.

A Comparison of Sparse and Non-sparse Techniques for Electric-Field Inversion from Normal-Component Magnetograms (2021)
Journal Article
Mackay, D., & Yeates, A. (2021). A Comparison of Sparse and Non-sparse Techniques for Electric-Field Inversion from Normal-Component Magnetograms. Solar Physics, 296(12), Article 178. https://doi.org/10.1007/s11207-021-01924-z

An important element of 3D data-driven simulations of solar magnetic fields is the determination of the horizontal electric field at the solar photosphere. This electric field is used to drive the 3D simulations and inject energy and helicity into th... Read More about A Comparison of Sparse and Non-sparse Techniques for Electric-Field Inversion from Normal-Component Magnetograms.

Intrinsic winding of braided vector fields in tubular subdomains (2021)
Journal Article
Prior, C. B., & Yeates, A. R. (2021). Intrinsic winding of braided vector fields in tubular subdomains. Journal of Physics A: Mathematical and Theoretical, 54(46), Article 465701. https://doi.org/10.1088/1751-8121/ac2ea3

Braided vector fields on spatial subdomains which are homeomorphic to the cylinder play a crucial role in applications such as solar and plasma physics, relativistic astrophysics, fluid and vortex dynamics, elasticity, and bio-elasticity. Often the v... Read More about Intrinsic winding of braided vector fields in tubular subdomains.

Evolution of Field Line Helicity in Magnetic Relaxation (2021)
Journal Article
Yeates, A., Russell, A., & Hornig, G. (2021). Evolution of Field Line Helicity in Magnetic Relaxation. Physics of Plasmas, 28(8), Article 082904. https://doi.org/10.1063/5.0059756

Plasma relaxation in the presence of an initially braided magnetic field can lead to self-organization into relaxed states that retain non-trivial magnetic structure. These relaxed states may be in conflict with the linear force-free fields predicted... Read More about Evolution of Field Line Helicity in Magnetic Relaxation.

Two Classes of Eruptive Events During Solar Minimum (2021)
Journal Article
Bhowmik, P., & Yeates, A. (2021). Two Classes of Eruptive Events During Solar Minimum. Solar Physics, 296(7), Article 109. https://doi.org/10.1007/s11207-021-01845-x

During solar minimum, the Sun is relatively inactive with few sunspots observed on the solar surface. Consequently, we observe a smaller number of highly energetic events such as solar flares or coronal mass ejections (CMEs), which are often associat... Read More about Two Classes of Eruptive Events During Solar Minimum.

Additivity of relative magnetic helicity in finite volumes (2020)
Journal Article
Valori, G., Démoulin, P., Pariat, E., Yeates, A., Moraitis, K., & Linan, L. (2020). Additivity of relative magnetic helicity in finite volumes. Astronomy & Astrophysics, 643, Article A26. https://doi.org/10.1051/0004-6361/202038533

Context. Relative magnetic helicity is conserved by magneto-hydrodynamic evolution even in the presence of moderate resistivity. For that reason, it is often invoked as the most relevant constraint on the dynamical evolution of plasmas in complex sys... Read More about Additivity of relative magnetic helicity in finite volumes.

Towards an algebraic method of solar cycle prediction (2020)
Journal Article
Petrovay, K., Nagy, M., & Yeates, A. R. (2020). Towards an algebraic method of solar cycle prediction. Journal of Space Weather and Space Climate, 10, Article 50. https://doi.org/10.1051/swsc/2020050

We discuss the potential use of an algebraic method to compute the value of the solar axial dipole moment at solar minimum, widely considered to be the most reliable precursor of the activity level in the next solar cycle. The method consists of summ... Read More about Towards an algebraic method of solar cycle prediction.

How good is the bipolar approximation of active regions for surface flux transport? (2020)
Journal Article
Yeates, A. (2020). How good is the bipolar approximation of active regions for surface flux transport?. Solar Physics, 295(9), Article 119. https://doi.org/10.1007/s11207-020-01688-y

We investigate how representing active regions with bipolar magnetic regions (BMRs) affects the end-of-cycle polar field predicted by the surface flux transport model. Our study is based on a new database of BMRs derived from the SDO/HMI active regio... Read More about How good is the bipolar approximation of active regions for surface flux transport?.

The Minimal Helicity of Solar Coronal Magnetic Fields (2020)
Journal Article
Yeates, A. (2020). The Minimal Helicity of Solar Coronal Magnetic Fields. Astrophysical Journal Letters, 898(2), Article L49. https://doi.org/10.3847/2041-8213/aba762

Potential field extrapolations are widely used as minimum-energy models for the Sun's coronal magnetic field. As the reference to which other magnetic fields are compared, they have—by any reasonable definition—no global (signed) magnetic helicity. H... Read More about The Minimal Helicity of Solar Coronal Magnetic Fields.

Impact of Inner Heliospheric Boundary Conditions on Solar Wind Predictions at Earth (2020)
Journal Article
Gonzi, S., Weinzierl, M., Bocquet, F., Bisi, M., Odstrcil, D., Jackson, B., …Nikolos Arge, C. (2021). Impact of Inner Heliospheric Boundary Conditions on Solar Wind Predictions at Earth. Space Weather, 19(1), https://doi.org/10.1029/2020sw002499

Predictions of the physical parameters of the solar wind at Earth are at the core of operational space weather forecasts. Such predictions typically use line-of-sight observations of the photospheric magnetic field to drive a heliospheric model. The... Read More about Impact of Inner Heliospheric Boundary Conditions on Solar Wind Predictions at Earth.

Hemispheric injection of magnetic helicity by surface flux transport (2019)
Journal Article
Hawkes, G., & Yeates, A. (2019). Hemispheric injection of magnetic helicity by surface flux transport. Astronomy & Astrophysics, 631, Article A138. https://doi.org/10.1051/0004-6361/201936475

Aims. We estimate the injection of relative magnetic helicity into the solar atmosphere by surface flux transport over 27 solar cycles (1700–2009). Methods. We determine the radial magnetic field evolution using two separate surface flux transport mo... Read More about Hemispheric injection of magnetic helicity by surface flux transport.

The need for active region disconnection in 3D kinematic dynamo simulations (2019)
Journal Article
Whitbread, T., Yeates, A., & Munoz-Jaramillo, A. (2019). The need for active region disconnection in 3D kinematic dynamo simulations. Astronomy & Astrophysics, 627, Article A168. https://doi.org/10.1051/0004-6361/201935986

In this paper we address a discrepancy between the surface flux evolution in a 3D kinematic dynamo model and a 2D surface flux transport model that has been closely calibrated to the real Sun. We demonstrate that the difference is due to the connecti... Read More about The need for active region disconnection in 3D kinematic dynamo simulations.

Reconstructing solar magnetic fields from historical observations : IV. Testing the reconstruction method (2019)
Journal Article
Virtanen, I., Virtanen, I., Pevtsov, A., Bertello, L., Yeates, A., & Mursula, K. (2019). Reconstructing solar magnetic fields from historical observations : IV. Testing the reconstruction method. Astronomy & Astrophysics, 627(A11), Article A11. https://doi.org/10.1051/0004-6361/201935606

Abstract Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especial... Read More about Reconstructing solar magnetic fields from historical observations : IV. Testing the reconstruction method.

Magnetic Helicity Condensation and the Solar Cycle (2018)
Journal Article
Mackay, D. H., DeVore, C. R., Antiochos, S. K., & Yeates, A. R. (2018). Magnetic Helicity Condensation and the Solar Cycle. Astrophysical Journal, 869(1), Article 62. https://doi.org/10.3847/1538-4357/aaec7c

Solar filaments exhibit a global chirality pattern where dextral/sinistral filaments, corresponding to negative/positive magnetic helicity, are dominant in the northern/southern hemisphere. This pattern is opposite to the sign of magnetic helicity in... Read More about Magnetic Helicity Condensation and the Solar Cycle.

Magnetic Structures at the Boundary of the Closed Corona: Interpretation of S-Web Arcs (2018)
Journal Article
Scott, R. B., Pontin, D. I., Yeates, A. R., Wyper, P. F., & Higginson, A. K. (2018). Magnetic Structures at the Boundary of the Closed Corona: Interpretation of S-Web Arcs. Astrophysical Journal, 869(1), Article 60. https://doi.org/10.3847/1538-4357/aaed2b

The topology of coronal magnetic fields near the open-closed magnetic flux boundary is important to the the process of interchange reconnection, whereby plasma is exchanged between open and closed flux domains. Maps of the magnetic squashing factor i... Read More about Magnetic Structures at the Boundary of the Closed Corona: Interpretation of S-Web Arcs.

Relative field-line helicity in bounded domains (2018)
Journal Article
Yeates, A., & Page, M. (2018). Relative field-line helicity in bounded domains. Journal of Plasma Physics, 84(6), Article 775840602. https://doi.org/10.1017/s0022377818001204

Models for astrophysical plasmas often have magnetic field lines that leave the boundary rather than closing within the computational domain. Thus, the relative magnetic helicity is frequently used in place of the usual magnetic helicity, so as to re... Read More about Relative field-line helicity in bounded domains.

Estimating the Rate of Field Line Braiding in the Solar Corona by Photospheric Flows (2018)
Journal Article
Candelaresi, S., Pontin, D., Yeates, A., Bushby, P., & Hornig, G. (2018). Estimating the Rate of Field Line Braiding in the Solar Corona by Photospheric Flows. Astrophysical Journal, 864(2), Article 157. https://doi.org/10.3847/1538-4357/aad8bc

In this paper, we seek to understand the timescale in which the photospheric motions on the Sun braid coronal magnetic field lines. This is a crucial ingredient for determining the viability of the braiding mechanism for explaining the high temperatu... Read More about Estimating the Rate of Field Line Braiding in the Solar Corona by Photospheric Flows.

Global Non-Potential Magnetic Models of the Solar Corona During the March 2015 Eclipse (2018)
Journal Article
Yeates, A., Amari, T., Contopoulos, I., Feng, X., Mackay, D., Mikic, Z., …Torok, T. (2018). Global Non-Potential Magnetic Models of the Solar Corona During the March 2015 Eclipse. Space Science Reviews, 214, Article 99. https://doi.org/10.1007/s11214-018-0534-1

Seven different models are applied to the same problem of simulating the Sun’s coronal magnetic field during the solar eclipse on 2015 March 20. All of the models are non-potential, allowing for free magnetic energy, but the associated electric curre... Read More about Global Non-Potential Magnetic Models of the Solar Corona During the March 2015 Eclipse.

Quantifying reconnective activity in braided vector fields (2018)
Journal Article
Prior, C., & Yeates, A. (2018). Quantifying reconnective activity in braided vector fields. Physical Review E, 98(1), Article 013204. https://doi.org/10.1103/physreve.98.013204

We introduce a technique for evaluating the changing connectivity of a vector field whose integral curves (field lines) form tangled tubular bundles. Applications of such fields include magnetic flux ropes, relativistic plasma jets, stirred two-dimen... Read More about Quantifying reconnective activity in braided vector fields.

A new technique for observationally derived boundary conditions for space weather (2018)
Journal Article
Pagano, P., Mackay, D. H., & Yeates, A. R. (2018). A new technique for observationally derived boundary conditions for space weather. Journal of Space Weather and Space Climate, 8, Article A26. https://doi.org/10.1051/swsc/2018012

Context. In recent years, space weather research has focused on developing modelling techniques to predict the arrival time and properties of coronal mass ejections (CMEs) at the Earth. The aim of this paper is to propose a new modelling technique su... Read More about A new technique for observationally derived boundary conditions for space weather.

The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations (2018)
Journal Article
Nandy, D., Bhowmik, P., Yeates, A. R., Panda, S., Tarafder, R., & Dash, S. (2018). The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations. Astrophysical Journal, 853(1), Article 72. https://doi.org/10.3847/1538-4357/aaa1eb

On 2017 August 21, a total solar eclipse swept across the contiguous United States, providing excellent opportunities for diagnostics of the Sun's corona. The Sun's coronal structure is notoriously difficult to observe except during solar eclipses; t... Read More about The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations.

Parameter optimization for surface flux transport models (2017)
Journal Article
Whitbread, T., Yeates, A., Muñoz-Jaramillo, A., & Petrie, G. (2017). Parameter optimization for surface flux transport models. Astronomy & Astrophysics, 607, Article A76. https://doi.org/10.1051/0004-6361/201730689

Accurate prediction of solar activity calls for precise calibration of solar cycle models. Consequently we aim to find optimal parameters for models which describe the physical processes on the solar surface, which in turn act as proxies for what occ... Read More about Parameter optimization for surface flux transport models.

The Open Flux Problem (2017)
Journal Article
Linker, J., Caplan, R., Downs, C., Riley, P., Mikic, Z., Lionello, R., …Owens, M. (2017). The Open Flux Problem. Astrophysical Journal, 848(1), Article 70. https://doi.org/10.3847/1538-4357/aa8a70

The heliospheric magnetic field is of pivotal importance in solar and space physics. The field is rooted in the Sun's photosphere, where it has been observed for many years. Global maps of the solar magnetic field based on full-disk magnetograms are... Read More about The Open Flux Problem.

Magnetic Flux Rope Identification and Characterization from Observationally Driven Solar Coronal Models (2017)
Journal Article
Lowder, C., & Yeates, A. (2017). Magnetic Flux Rope Identification and Characterization from Observationally Driven Solar Coronal Models. Astrophysical Journal, 846(2), Article 106. https://doi.org/10.3847/1538-4357/aa86b1

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... Read More about Magnetic Flux Rope Identification and Characterization from Observationally Driven Solar Coronal Models.

Reconstructing solar magnetic fields from historical observations (2017)
Journal Article
Virtanen, I., Virtanen, I., Pevtsov, A., Yeates, A., & Mursula, K. (2017). Reconstructing solar magnetic fields from historical observations. Astronomy & Astrophysics, 604, Article A8. https://doi.org/10.1051/0004-6361/201730415

Aims. We aim to use the surface flux transport model to simulate the long-term evolution of the photospheric magnetic field from historical observations. In this work we study the accuracy of the model and its sensitivity to uncertainties in its main... Read More about Reconstructing solar magnetic fields from historical observations.

Sparse reconstruction of electric fields from radial magnetic data (2017)
Journal Article
Yeates, A. (2017). Sparse reconstruction of electric fields from radial magnetic data. Astrophysical Journal, 836(1), Article 131. https://doi.org/10.3847/1538-4357/aa5c84

Accurate estimates of the horizontal electric field on the Sun's visible surface are important not only for estimating the Poynting flux of magnetic energy into the corona but also for driving time-dependent magnetohydrodynamic models of the corona.... Read More about Sparse reconstruction of electric fields from radial magnetic data.

The global distribution of magnetic helicity in the solar corona (2016)
Journal Article
Yeates, A., & Hornig, G. (2016). The global distribution of magnetic helicity in the solar corona. Astronomy & Astrophysics, 594, Article A98. https://doi.org/10.1051/0004-6361/201629122

By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningf... Read More about The global distribution of magnetic helicity in the solar corona.

The Possible Impact of L5 Magnetograms on Non-Potential Solar Coronal Magnetic Field Simulations (2016)
Journal Article
Weinzierl, M., Mackay, D. H., Yeates, A. R., & Pevtsov, A. A. (2016). The Possible Impact of L5 Magnetograms on Non-Potential Solar Coronal Magnetic Field Simulations. Astrophysical Journal, 828(2), Article 102. https://doi.org/10.3847/0004-637x/828/2/102

The proposed Carrington-L5 mission would bring instruments to the L5 Lagrange point to provide us with crucial data for space weather prediction. To assess the importance of including a magnetograph, we consider the possible differences in non-potent... Read More about The Possible Impact of L5 Magnetograms on Non-Potential Solar Coronal Magnetic Field Simulations.

A New Technique for the Photospheric Driving of Non-Potential Solar Coronal Magnetic Field Simulations (2016)
Journal Article
Weinzierl, M., Yeates, A. R., Mackay, D. H., Henney, C. J., & Arge, C. N. (2016). A New Technique for the Photospheric Driving of Non-Potential Solar Coronal Magnetic Field Simulations. Astrophysical Journal, 823(1), Article 55. https://doi.org/10.3847/0004-637x/823/1/55

In this paper, we develop a new technique for driving global non-potential simulations of the Sun's coronal magnetic field solely from sequences of radial magnetic maps of the solar photosphere. A primary challenge to driving such global simulations... Read More about A New Technique for the Photospheric Driving of Non-Potential Solar Coronal Magnetic Field Simulations.

Stellar coronal response to differential rotation and flux emergence (2016)
Journal Article
Gibb, G., Mackay, D., Jardine, M., & Yeates, A. (2016). Stellar coronal response to differential rotation and flux emergence. Monthly Notices of the Royal Astronomical Society, 456(4), 3624-3637. https://doi.org/10.1093/mnras/stv2920

We perform a numerical parameter study to determine what effect varying differential rotation and flux emergence has on a star's non-potential coronal magnetic field. In particular we consider the effects on the star's surface magnetic flux, open mag... Read More about Stellar coronal response to differential rotation and flux emergence.

Influence of Non-Potential Coronal Magnetic Topology on Solar-Wind Models (2015)
Journal Article
Edwards, S., Yeates, A., Bocquet, F., & Mackay, D. (2015). Influence of Non-Potential Coronal Magnetic Topology on Solar-Wind Models. Solar Physics, 290(10), 2791-2808. https://doi.org/10.1007/s11207-015-0795-8

By comparing a magneto-frictional model of the low-coronal magnetic-field to a potential-field source-surface model, we investigate the possible impact of non-potential magnetic structure on empirical solar-wind models. These empirical models (such a... Read More about Influence of Non-Potential Coronal Magnetic Topology on Solar-Wind Models.

Physical role of topological constraints in localized magnetic relaxation (2015)
Journal Article
Yeates, A., Russell, A., & Hornig, G. (2015). Physical role of topological constraints in localized magnetic relaxation. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 471(2178), Article 20150012. https://doi.org/10.1098/rspa.2015.0012

Predicting the final state of turbulent plasma relaxation is an important challenge, both in astro-physical plasmas such as the Sun's corona and in controlled thermonuclear fusion. Recent numerical simulations of plasma relaxation with braided magnet... Read More about Physical role of topological constraints in localized magnetic relaxation.

Evolution of field line helicity during magnetic reconnection (2015)
Journal Article
Russell, A., Yeates, A., Hornig, G., & Wilmot-Smith, A. (2015). Evolution of field line helicity during magnetic reconnection. Physics of Plasmas, 22(3), Article 032106. https://doi.org/10.1063/1.4913489

We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an importa... Read More about Evolution of field line helicity during magnetic reconnection.

Source of a Prominent Poleward Surge During Solar Cycle 24 (2015)
Journal Article
Yeates, A., Baker, D., & van Driel-Gesztelyi, L. (2015). Source of a Prominent Poleward Surge During Solar Cycle 24. Solar Physics, 290(11), 3189-3201. https://doi.org/10.1007/s11207-015-0660-9

As an observational case study, we consider the origin of a prominent poleward surge of leading polarity, visible in the magnetic butterfly diagram during Solar Cycle 24. A new technique is developed for assimilating individual regions of strong magn... Read More about Source of a Prominent Poleward Surge During Solar Cycle 24.

Small-scale and global dynamos and the area and flux distributions of active regions, sunspot groups, and sunspots : a multi-database study (2015)
Journal Article
Muñoz-Jaramillo, A., Senkpeil, R., Windmueller, J., Amouzou, E., Longcope, D., Tlatov, A., …Martens, P. (2015). Small-scale and global dynamos and the area and flux distributions of active regions, sunspot groups, and sunspots : a multi-database study. Astrophysical Journal, 800(1), Article 48. https://doi.org/10.1088/0004-637x/800/1/48

In this work, we take advantage of 11 different sunspot group, sunspot, and active region databases to characterize the area and flux distributions of photospheric magnetic structures. We find that, when taken separately, different databases are bett... Read More about Small-scale and global dynamos and the area and flux distributions of active regions, sunspot groups, and sunspots : a multi-database study.

A complete topological invariant for braided magnetic fields (2014)
Journal Article
Yeates, A., & Hornig, G. (2014). A complete topological invariant for braided magnetic fields. Journal of Physics: Conference Series, 544(1), Article 012002. https://doi.org/10.1088/1742-6596/544/1/012002

A topological flux function is introduced to quantify the topology of magnetic braids: non-zero line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of t... Read More about A complete topological invariant for braided magnetic fields.

Observations of a hybrid double-streamer/pseudostreamer in the solar corona (2014)
Journal Article
Rachmeler, L., Platten, S., Bethge, C., Seaton, D., & Yeates, A. (2014). Observations of a hybrid double-streamer/pseudostreamer in the solar corona. Astrophysical Journal Letters, 787(1), https://doi.org/10.1088/2041-8205/787/1/l3

We report on the first observation of a single hybrid magnetic structure that contains both a pseudostreamer and a double streamer. This structure was originally observed by the SWAP instrument on board the PROBA2 satellite between 2013 May 5 and 10.... Read More about Observations of a hybrid double-streamer/pseudostreamer in the solar corona.

On the helicity of open magnetic fields (2014)
Journal Article
Prior, C., & Yeates, A. (2014). On the helicity of open magnetic fields. Astrophysical Journal, 787(2), Article 100. https://doi.org/10.1088/0004-637x/787/2/100

We reconsider the topological interpretation of magnetic helicity for magnetic fields in open domains, and relate this to the relative helicity. Specifically, our domains stretch between two parallel planes, and each of these ends may be magnetically... Read More about On the helicity of open magnetic fields.

The coronal energy input from magnetic braiding (2014)
Journal Article
Yeates, A., Bianchi, F., Welsh, B., & Bushby, P. (2014). The coronal energy input from magnetic braiding. Astronomy & Astrophysics, 564, Article A131. https://doi.org/10.1051/0004-6361/201323276

We estimate the energy input into the solar corona from photospheric footpoint motions, using observations of a plage region by the Hinode Solar Optical Telescope. Assuming a perfectly ideal coronal evolution, two alternative lower bounds for the Poy... Read More about The coronal energy input from magnetic braiding.

Detection of coherent structures in photospheric turbulent flows (2014)
Journal Article
Chian, A., Rempel, E., Aulanier, G., Schmieder, B., Shadden, S., Welsch, B., & Yeates, A. (2014). Detection of coherent structures in photospheric turbulent flows. Astrophysical Journal, 786(1), https://doi.org/10.1088/0004-637x/786/1/51

We study coherent structures in solar photospheric flows in a plage in the vicinity of the active region AR 10930 using the horizontal velocity data derived from Hinode/Solar Optical Telescope magnetograms. Eulerian and Lagrangian coherent structures... Read More about Detection of coherent structures in photospheric turbulent flows.

Kinematic active region formation in a three-dimensional solar dynamo model (2013)
Journal Article
Yeates, A., & Munoz-Jaramillo, A. (2013). Kinematic active region formation in a three-dimensional solar dynamo model. Monthly Notices of the Royal Astronomical Society, 436(4), 3366-3379. https://doi.org/10.1093/mnras/stt1818

We propose a phenomenological technique for modelling the emergence of active regions within a three-dimensional, kinematic dynamo framework. By imposing localized velocity perturbations, we create emergent flux tubes out of toroidal magnetic field a... Read More about Kinematic active region formation in a three-dimensional solar dynamo model.

Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-potential Simulations (2013)
Journal Article
Yeates, A. (2014). Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-potential Simulations. Solar Physics, 289(2), 631-648. https://doi.org/10.1007/s11207-013-0301-0

Coupled flux transport and magneto-frictional simulations are extended to simulate the continuous magnetic-field evolution in the global solar corona for over 15 years, from the start of Solar Cycle 23 in 1996. By simplifying the dynamics, our model... Read More about Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-potential Simulations.

Pathways of Large-scale Magnetic Couplings Between Solar Coronal Events (2013)
Journal Article
Schrijver, C., Title, A., Yeates, A., & DeRosa, M. (2013). Pathways of Large-scale Magnetic Couplings Between Solar Coronal Events. Astrophysical Journal, 773(2), https://doi.org/10.1088/0004-637x/773/2/93

The high-cadence, comprehensive view of the solar corona by SDO/AIA shows many events that are widely separated in space while occurring close together in time. In some cases, sets of coronal events are evidently causally related, while in many other... Read More about Pathways of Large-scale Magnetic Couplings Between Solar Coronal Events.

Unique topological characterization of braided magnetic fields (2013)
Journal Article
Yeates, A., & Hornig, G. (2013). Unique topological characterization of braided magnetic fields. Physics of Plasmas, 20(1), Article 012102. https://doi.org/10.1063/1.4773903

We introduce a topological flux function to quantify the topology of magnetic braids: non-zero, line-tied magnetic fields whose field lines all connect between two boundaries. This scalar function is an ideal invariant defined on a cross-section of t... Read More about Unique topological characterization of braided magnetic fields.

The Sun's Global Photospheric and Coronal Magnetic Fields: Observations and Models (2012)
Journal Article
Mackay, D., & Yeates, A. (2012). The Sun's Global Photospheric and Coronal Magnetic Fields: Observations and Models. Living Reviews in Solar Physics, 9, Article 6. https://doi.org/10.12942/lrsp-2012-6

In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are descri... Read More about The Sun's Global Photospheric and Coronal Magnetic Fields: Observations and Models.

Lagrangian coherent structures in photospheric flows and their implications for coronal magnetic structure (2012)
Journal Article
Yeates, A., Hornig, G., & Welsch, B. (2012). Lagrangian coherent structures in photospheric flows and their implications for coronal magnetic structure. Astronomy & Astrophysics, 539, https://doi.org/10.1051/0004-6361/201118278

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 fi... Read More about Lagrangian coherent structures in photospheric flows and their implications for coronal magnetic structure.

Chirality of high-latitude filaments over Solar Cycle 23 (2012)
Journal Article
Yeates, A., & Mackay, D. (2012). Chirality of high-latitude filaments over Solar Cycle 23. Astrophysical Journal Letters, 753(2), https://doi.org/10.1088/2041-8205/753/2/l34

A non-potential quasi-static evolution model coupling the Sun's photospheric and coronal magnetic fields is applied to the problem of filament chirality at high latitudes. For the first time, we run a continuous 15 year simulation, using bipolar acti... Read More about Chirality of high-latitude filaments over Solar Cycle 23.

Heating of Braided Coronal Loops (2011)
Journal Article
Wilmot-Smith, A., Pontin, D., Yeates, A., & Hornig, G. (2011). Heating of Braided Coronal Loops. Astronomy & Astrophysics, 536, https://doi.org/10.1051/0004-6361/201117942

Aims. We investigate the relaxation of braided magnetic loops in order to find out how the type of braiding via footpoint motions affects resultant heating of the loop. Methods. Two magnetic loops, braided in different ways, are used as initial condi... Read More about Heating of Braided Coronal Loops.

A Generalized Flux Function for Three-dimensional Magnetic Reconnection (2011)
Journal Article
Yeates, A., & Hornig, G. (2011). A Generalized Flux Function for Three-dimensional Magnetic Reconnection. Physics of Plasmas, 18(10), Article 102118. https://doi.org/10.1063/1.3657424

The definition and measurement of magnetic reconnection in three-dimensional magnetic fields with multiple reconnection sites is a challenging problem, particularly in fields lacking null points. We propose a generalization of the familiar two-dimens... Read More about A Generalized Flux Function for Three-dimensional Magnetic Reconnection.

Dynamical constraints from field line topology in magnetic flux tubes (2011)
Journal Article
Yeates, A., & Hornig, G. (2011). Dynamical constraints from field line topology in magnetic flux tubes. Journal of Physics A: Mathematical and Theoretical, 44(26), https://doi.org/10.1088/1751-8113/44/26/265501

A topological constraint on the dynamics of a magnetic field in a flux tube arises from the fixed point indices of its field line mapping. This can explain unexpected behaviour in recent resistive-magnetohydrodynamic simulations of magnetic relaxatio... Read More about Dynamical constraints from field line topology in magnetic flux tubes.

A nonpotential model for the Sun's open magnetic flux (2010)
Journal Article
Yeates, A., Mackay, D., van Ballegooijen, A., & Constable, J. (2010). A nonpotential model for the Sun's open magnetic flux. Journal of Geophysical Research: Space Physics, 115(A9), https://doi.org/10.1029/2010ja015611

[1] Measurements of the interplanetary magnetic field (IMF) over several solar cycles do not agree with computed values of open magnetic flux from potential field extrapolations. The discrepancy becomes greater around solar maximum in each cycle when... Read More about A nonpotential model for the Sun's open magnetic flux.

A double-ring algorithm for modeling solar active regions: Unifying kinematic dynamo models and surface flux-transport simulations (2010)
Journal Article
Muñoz-Jaramillo, A., Nandy, D., Martens, P., & Yeates, A. (2010). A double-ring algorithm for modeling solar active regions: Unifying kinematic dynamo models and surface flux-transport simulations. Astrophysical Journal, 720(1), https://doi.org/10.1088/2041-8205/720/1/l20

The emergence of tilted bipolar active regions (ARs) and the dispersal of their flux, mediated via processes such as diffusion, differential rotation, and meridional circulation, is believed to be responsible for the reversal of the Sun's polar field... Read More about A double-ring algorithm for modeling solar active regions: Unifying kinematic dynamo models and surface flux-transport simulations.

Solar cycle variation of magnetic flux ropes in a quasi-static coronal evolution model (2010)
Journal Article
Yeates, A., Constable, J., & Martens, P. (2010). Solar cycle variation of magnetic flux ropes in a quasi-static coronal evolution model. Solar Physics, 263(1-2), 121-134. https://doi.org/10.1007/s11207-010-9546-z

The structure of electric current and magnetic helicity in the solar corona is closely linked to solar activity over the 11-year cycle, yet is poorly understood. As an alternative to traditional current-free “potential-field” extrapolations, we inves... Read More about Solar cycle variation of magnetic flux ropes in a quasi-static coronal evolution model.

Comparison of a global magnetic evolution model with observations of coronal mass ejections (2010)
Journal Article
Yeates, A., Attrill, G., Nandy, D., Mackay, D., Martens, P., & van Ballegooijen, A. (2010). Comparison of a global magnetic evolution model with observations of coronal mass ejections. Astrophysical Journal, 709(2), https://doi.org/10.1088/0004-637x/709/2/1238

The relative importance of different initiation mechanisms for coronal mass ejections (CMEs) on the Sun is uncertain. One possible mechanism is the loss of equilibrium of coronal magnetic flux ropes formed gradually by large-scale surface motions. In... Read More about Comparison of a global magnetic evolution model with observations of coronal mass ejections.

Initiation of coronal mass ejections in a global evolution model (2009)
Journal Article
Yeates, A., & Mackay, D. (2009). Initiation of coronal mass ejections in a global evolution model. Astrophysical Journal, 699(2), Article 1024-1037. https://doi.org/10.1088/0004-637x/699/2/1024

Loss of equilibrium of magnetic flux ropes is a leading candidate for the origin of solar coronal mass ejections (CMEs). The aim of this paper is to explore to what extent this mechanism can account for the initiation of CMEs in the global context. A... Read More about Initiation of coronal mass ejections in a global evolution model.

Modelling the global solar corona III: Origin of the hemispheric pattern of filaments (2009)
Journal Article
Yeates, A., & Mackay, D. (2009). Modelling the global solar corona III: Origin of the hemispheric pattern of filaments. Solar Physics, 254(1), 77-88. https://doi.org/10.1007/s11207-008-9276-7

We consider the physical origin of the hemispheric pattern of filament chirality on the Sun. Our 3D simulations of the coronal field evolution over a period of six months, based on photospheric magnetic measurements, were previously shown to be highl... Read More about Modelling the global solar corona III: Origin of the hemispheric pattern of filaments.

Evolution and distribution of current helicity in full-Sun simulations (2008)
Journal Article
Yeates, A., Mackay, D., & van Ballegooijen, A. (2008). Evolution and distribution of current helicity in full-Sun simulations. Astrophysical Journal Letters, 680(2), L165-L168. https://doi.org/10.1086/590057

Current helicity quantifies the location of twisted and sheared nonpotential structures in a magnetic field. We simulate the evolution of magnetic fields in the solar atmosphere in response to flux emergence and shearing by photospheric motions. In o... Read More about Evolution and distribution of current helicity in full-Sun simulations.

Where do solar filaments form? Consequences for theoretical models. (2008)
Journal Article
Mackay, D., Gaizauskas, V., & Yeates, A. (2008). Where do solar filaments form? Consequences for theoretical models. Solar Physics, 248(1), 51-65. https://doi.org/10.1007/s11207-008-9127-6

This paper examines the locations where large, stable solar filaments form relative to magnetic bipoles lying underneath them. The study extends the earlier work of F. Tang to include two additional classification categories for stable filaments and... Read More about Where do solar filaments form? Consequences for theoretical models..

Exploring the physical basis of solar cycle predictions: Flux transport dynamics and persistence of memory in advection versus diffusion-dominated solar convection zones (2008)
Journal Article
Yeates, A., Nandy, D., & Mackay, D. (2008). Exploring the physical basis of solar cycle predictions: Flux transport dynamics and persistence of memory in advection versus diffusion-dominated solar convection zones. Astrophysical Journal, 673(1), 544-556. https://doi.org/10.1086/524352

The predictability, or lack thereof, of the solar cycle is governed by numerous separate physical processes that act in unison in the interior of the Sun. Magnetic flux transport and the finite time delay that it introduces, specifically in the so-ca... Read More about Exploring the physical basis of solar cycle predictions: Flux transport dynamics and persistence of memory in advection versus diffusion-dominated solar convection zones.

Modelling the global solar corona II: Coronal evolution and filament chirality comparison (2008)
Journal Article
Yeates, A., Mackay, D., & van Ballegooijen, A. (2008). Modelling the global solar corona II: Coronal evolution and filament chirality comparison. Solar Physics, 247(1), 103-121. https://doi.org/10.1007/s11207-007-9097-0

This paper considers the hemispheric pattern of solar filaments using newly developed simulations of the real photospheric and 3D coronal magnetic fields over a six-month period, on a global scale. The magnetic field direction in the simulation is co... Read More about Modelling the global solar corona II: Coronal evolution and filament chirality comparison.

Modelling the global solar corona : filament chirality observations and surface simulations (2007)
Journal Article
Yeates, A., Mackay, D., & van Ballegooijen, A. (2007). Modelling the global solar corona : filament chirality observations and surface simulations. Solar Physics, 245(1), 87-107. https://doi.org/10.1007/s11207-007-9013-7

The hemispheric pattern of solar filaments is considered in the context of the global magnetic field of the solar corona. In recent work Mackay and van Ballegooijen have shown how, for a pair of interacting magnetic bipoles, the observed chirality pa... Read More about Modelling the global solar corona : filament chirality observations and surface simulations.