Intermediate shock sub-structures within a slow-mode shock occurring in partially ionised plasma

Snow, Ben; Hillier, Andrew

doi:10.1051/0004-6361/201935326

Cited by 26 publications

(33 citation statements)

References 21 publications

(32 reference statements)

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“…Snow & Hillier (2019) have suggested that such shock behavior has the potential to occur in a wide range of phenomena in the solar atmosphere in which partial ionization effects are impor-tant, including magnetic reconnection (e.g., Ellerman bombs, spicules) and wave steepening (e.g., umbral flashes). Snow & Hillier (2019) highlight that the shock effects are likely to be most significant in the lower chromospheric regions, which is consistent with what we demonstrate in the present study. The plethora of possible Alfvén shock environments implies that these events may provide a significant contribution to the overall heating requirements of the chromosphere, consistent with the ideas put forward by Matsumoto & Suzuki (2014).…”

Section: Rankine-hugoniot Classificationmentioning

confidence: 99%

Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

Houston

Jess

Keppens

et al. 2020

ApJ

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The formation of shocks within the solar atmosphere remains one of the few observable signatures of energy dissipation arising from the plethora of magnetohydrodynamic waves generated close to the solar surface. Active region observations offer exceptional views of wave behavior and its impact on the surrounding atmosphere. The stratified plasma gradients present in the lower solar atmosphere allow for the potential formation of many theorized shock phenomena. In this study, using chromospheric Ca II 8542Å line spectropolarimetric data of a large sunspot, we examine fluctuations in the plasma parameters in the aftermath of powerful shock events that demonstrate polarimetric reversals during their evolution. Modern inversion techniques are employed to uncover perturbations in the temperatures, line-of-sight velocities, and vector magnetic fields occurring across a range of optical depths synonymous with the shock formation. Classification of these non-linear signatures is carried out by comparing the observationally-derived slow, fast, and Alfvén shock solutions to the theoretical Rankine-Hugoniot relations. Employing over 200 000 independent measurements, we reveal that the Alfvén (intermediate) shock solution provides the closest match between theory and observations at optical depths of log 10 τ = −4, consistent with a geometric height at the boundary between the upper photosphere and lower chromosphere. This work uncovers first-time evidence of the manifestation of chromospheric intermediate shocks in sunspot umbrae, providing a new method for the potential thermalization of wave energy in a range of magnetic structures, including pores, magnetic flux ropes, and magnetic bright points.

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Section: Rankine-hugoniot Classificationmentioning

confidence: 99%

Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

Houston

Jess

Keppens

et al. 2020

ApJ

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“…for density ρ, velocity v, pressure P , internal energy e, magnetic field B, the collisional coupling term α c , and gravity g. Note that the thermal component of the collisional term in Equations (3) and (7) is different from in previous papers using the (PIP) code by a factor of 1/2 (Hillier et al 2016;Snow & Hillier 2019). The corrected term was found to have no significant changes for the reconnection driven shock considered in previous works.…”

Section: Methodsmentioning

confidence: 97%

“…In addition, previous studies have shown that another potential observable of two-fluid effects is the electric field felt by the neutrals (Anan et al 2014;Snow & Hillier 2019). The large drift velocities lead to polarisation of the neutrals as they flow past the magnetic field, and hence have an associated electric field term of the form E n = (v n − v p ) × B.…”

Section: Observational Consequencesmentioning

confidence: 99%

“…Fast-mode shocks propagate perpendicular to the magnetic field and are also important for magnetic reconnection (Yokoyama & Shibata 1996). There in also a class of intermediate shocks which have a transition from above to below the Alfvén speed, which can arise due to two-fluid effects in slow-mode shocks (Snow & Hillier 2019).…”

Section: Introductionmentioning

confidence: 99%

“…As such, shocks are a promising area for the two-fluid effects to have a significant impact on the physics of the system. Previous work has shown that additional shocks can form within the finite width of a reconnection-driven slow-mode shock, (Snow & Hillier 2019).…”

Section: Introductionmentioning

confidence: 99%

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Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

Snow

Hillier

2020

A&A

Self Cite

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Context. The plasma of the lower solar atmosphere consists of mostly neutral particles, whereas the upper solar atmosphere is mostly ionised particles and electrons. A shock that propagates upwards in the solar atmosphere therefore undergoes a transition where the dominant fluid is either neutral or ionised. An upwards propagating shock also passes a point where the sound and Alfvén speed are equal. At this point the energy of the acoustic shock can separated into fast and slow components. How the energy is distributed between the two modes depends on the angle of magnetic field. Aims. The separation of neutral and ionised species in a gravitationally stratified atmosphere is investigated. The role of two-fluid effects on the structure of the shocks post-mode-conversion and the frictional heating is quantified for different levels of collisional coupling. Methods. Two-fluid numerical simulations are performed using the (PIP) code of a wave steepening into a shock in an isothermal, partially-ionised atmosphere. The collisional coefficient is varied to investigate the regimes where the plasma and neutral species are weakly, strongly and finitely coupled. Results. The propagation speeds of the compressional waves hosted by neutral and ionised species vary, therefore velocity drift between the two species is produced as the plasma attempts to propagate faster than the neutrals. This is most extreme for a fast-mode shock. We find that the collisional coefficient drastically changes the features present in the system, specifically the mode conversion height, type of shocks present, and the finite shock widths created by the two-fluid effects. In the finitely-coupled regime fast-mode shock widths can exceed the pressure scale height leading to a new potential observable of two-fluid effects in the lower solar atmosphere.

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Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes

Jess

Jafarzadeh

Keys

et al. 2023

Living Rev Sol Phys

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Waves and oscillations have been observed in the Sun’s atmosphere for over half a century. While such phenomena have readily been observed across the entire electromagnetic spectrum, spanning radio to gamma-ray sources, the underlying role of waves in the supply of energy to the outermost extremities of the Sun’s corona has yet to be uncovered. Of particular interest is the lower solar atmosphere, including the photosphere and chromosphere, since these regions harbor the footpoints of powerful magnetic flux bundles that are able to guide oscillatory motion upwards from the solar surface. As a result, many of the current- and next-generation ground-based and space-borne observing facilities are focusing their attention on these tenuous layers of the lower solar atmosphere in an attempt to study, at the highest spatial and temporal scales possible, the mechanisms responsible for the generation, propagation, and ultimate dissipation of energetic wave phenomena. Here, we present a two-fold review that is designed to overview both the wave analyses techniques the solar physics community currently have at their disposal, as well as highlight scientific advancements made over the last decade. Importantly, while many ground-breaking studies will address and answer key problems in solar physics, the cutting-edge nature of their investigations will naturally pose yet more outstanding observational and/or theoretical questions that require subsequent follow-up work. This is not only to be expected, but should be embraced as a reminder of the era of rapid discovery we currently find ourselves in. We will highlight these open questions and suggest ways in which the solar physics community can address these in the years and decades to come.

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Intermediate shock sub-structures within a slow-mode shock occurring in partially ionised plasma

Cited by 26 publications

References 21 publications

Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes

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