Author name code: hillier ADS astronomy entries on 2022-09-14 author:Hillier, Andrew ------------------------------------------------------------------------ Title: Intermediate shocks in compressible turbulent magnetic reconnection Authors: Snow, Ben; Hillier, Andrew Bibcode: 2022cosp...44.1492S Altcode: Compressible magnetohydrodynamic (MHD) turbulence is a common feature of astrophysical systems such as the solar atmosphere and interstellar medium. Such systems are rife with shock waves that can redistribute and dissipate energy, and hence understanding the role of shocks in compressible turbulence is critical for determining the energy balance of these dynamic systems. However, automated detection and classification of shocks in turbulent systems is inherently difficult due to the highly dynamic medium. Here we present a method for detecting and classifying the full range of MHD shocks (slow, fast and intermediate) applied to the Orszag-Tang vortex. We find that the system is dominated by fast and slow shocks, however we also detect many intermediate shocks (which feature a reversal in the magnetic field) that appear near reconnection sites. We propose that the formation mechanism for these intermediate shocks is related to turbulent reconnection, where slight variations of the inflow parameters allow super-Alfvenic to sub-slow transitions to exist. This acts as an indirect metric for identifying reconnection regions in turbulent simulations and improves our understanding of the structures and dissipation that occurs in such systems. Title: Collisional ionisation and recombination effects on coalescence instability in chromospheric partially ionised plasmas Authors: Murtas, Giulia; Hillier, Andrew; Snow, Ben Bibcode: 2022arXiv220511091M Altcode: Plasmoid-mediated fast magnetic reconnection plays a fundamental role in driving explosive dynamics and heating, but relatively little is known about how it develops in partially ionised plasmas (PIP) of the solar chromosphere. Partial ionisation might largely alter the dynamics of the coalescence instability, which promotes fast reconnection and forms a turbulent reconnecting current sheet through plasmoid interaction, but it is still unclear to what extent PIP effects influence this process. We investigate the role of collisional ionisation and recombination in the development of plasmoid coalescence in PIP through 2.5D simulations of a two-fluid model. The aim is to understand whether these two-fluid coupling processes play a role in accelerating reconnection. We find that in general ionisation-recombination process slow down the coalescence. Unlike the previous models in G. Murtas, A. Hillier \& B. Snow, Physics of Plasmas 28, 032901 (2021) that included thermal collisions only, ionisation and recombination stabilise current sheets and suppress non-linear dynamics, with turbulent reconnection occurring in limited cases: bursts of ionisation lead to the formation of thicker current sheets, even when radiative losses are included to cool the system. Therefore, the coalescence time scale is very sensitive to ionisation-recombination processes. However, reconnection in PIP is still faster than in a fully ionised plasma environment having the same bulk density: the PIP reconnection rate ($M_{_{\operatorname{IRIP}}} = 0.057$) increases by a factor of $\sim 1.2$ with respect to the MHD reconnection rate ($M_{_{\operatorname{MHD}}} = 0.047$). Title: Correction to: The magnetic Rayleigh-Taylor instability in solar prominences Authors: Hillier, Andrew Bibcode: 2021RvMPP...5....5H Altcode: No abstract at ADS Title: Rayleigh-Taylor and Richtmyer-Meshkov instabilities: A journey through scales Authors: Zhou, Ye; Williams, Robin J. R.; Ramaprabhu, Praveen; Groom, Michael; Thornber, Ben; Hillier, Andrew; Mostert, Wouter; Rollin, Bertrand; Balachandar, S.; Powell, Phillip D.; Mahalov, Alex; Attal, N. Bibcode: 2021PhyD..42332838Z Altcode: Hydrodynamic instabilities such as Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities usually appear in conjunction with the Kelvin-Helmholtz (KH) instability and are found in many natural phenomena and engineering applications. They frequently result in turbulent mixing, which has a major impact on the overall flow development and other effective material properties. This can either be a desired outcome, an unwelcome side effect, or just an unavoidable consequence, but must in all cases be characterized in any model. The RT instability occurs at an interface between different fluids, when the light fluid is accelerated into the heavy. The RM instability may be considered a special case of the RT instability, when the acceleration provided is impulsive in nature such as that resulting from a shock wave. In this pedagogical review, we provide an extensive survey of the applications and examples where such instabilities play a central role. First, fundamental aspects of the instabilities are reviewed including the underlying flow physics at different stages of development, followed by an overview of analytical models describing the linear, nonlinear and fully turbulent stages. RT and RM instabilities pose special challenges to numerical modeling, due to the requirement that the sharp interface separating the fluids be captured with fidelity. These challenges are discussed at length here, followed by a summary of the significant progress in recent years in addressing them. Examples of the pivotal roles played by the instabilities in applications are given in the context of solar prominences, ionospheric flows in space, supernovae, inertial fusion and pulsed-power experiments, pulsed detonation engines and Scramjets. Progress in our understanding of special cases of RT/RM instabilities is reviewed, including the effects of material strength, chemical reactions, magnetic fields, as well as the roles the instabilities play in ejecta formation and transport, and explosively expanding flows. The article is addressed to a broad audience, but with particular attention to graduate students and researchers who are interested in the state-of-the-art in our understanding of the instabilities and the unique issues they present in the applications in which they are prominent. Title: Stability of two-fluid partially ionized slow-mode shock fronts Authors: Snow, B.; Hillier, A. Bibcode: 2021MNRAS.506.1334S Altcode: 2021MNRAS.tmp.1714S; 2021arXiv210604199S A magnetohydrodynamic (MHD) shock front can be unstable to the corrugation instability, which causes a perturbed shock front to become increasingly corrugated with time. An ideal MHD parallel shock (where the velocity and magnetic fields are aligned) is unconditionally unstable to the corrugation instability, whereas the ideal hydrodynamic (HD) counterpart is unconditionally stable. For a partially ionized medium (for example, the solar chromosphere), both HD and MHD species coexist and the stability of the system has not been studied. In this paper, we perform numerical simulations of the corrugation instability in two-fluid partially ionized shock fronts to investigate the stability conditions, and compare the results to HD and MHD simulations. Our simulations consist of an initially steady two-dimensional parallel shock encountering a localized upstream density perturbation. In MHD, this perturbation results in an unstable shock front and the corrugation grows with time. We find that for the two-fluid simulation, the neutral species can act to stabilize the shock front. A parameter study is performed to analyse the conditions under which the shock front is stable and unstable. We find that for very weakly coupled or very strongly coupled partially ionized system the shock front is unstable, as the system tends towards MHD. However, for a finite coupling, we find that the neutrals can stabilize the shock front, and produce new features including shock channels in the neutral species. We derive an equation that relates the stable wavelength range to the ion-neutral and neutral-ion coupling frequencies and the Mach number. Applying this relation to umbral flashes gives an estimated range of stable wavelengths between 0.6 and 56 km. Title: Observation of bi-directional jets in a prominence Authors: Hillier, A.; Polito, V. Bibcode: 2021A&A...651A..60H Altcode: Quiescent prominences host a large range of flows, many driven by buoyancy, which lead to velocity shear. The presence of these shear flows could bend and stretch the magnetic field resulting in the formation of current sheets which can lead to magnetic reconnection. Though this has been hypothesised to occur in prominences, with some observations that are suggestive of this process, clear evidence has been lacking. In this paper we present observations performed on June 30, 2015 using the Interface Region Imaging Spectrograph Si IV and Mg II slit-jaw imagers of two bi-directional jets that occur inside the body of the prominence. Such jets are highly consistent with what would be expected from magnetic reconnection theory. Using this observation, we estimate that the prominence under study has an ambient field strength in the range of 4.5−9.2 G with `turbulent' field strengths of 1 G. Our results highlight the ability of gravity-driven flows to stretch and fold the magnetic field of the prominence, implying that locally, the quiescent prominence field can be far from a static, force-free magnetic field.

Movies are available at https://www.aanda.org Title: Dispersion relations for waves in visco-gravitating anisotropic magnetoplasmas Authors: Desta, Ephrem Tesfaye; Hillier, A.; Eritro, Tigistu Haile Bibcode: 2021PhPl...28d2901D Altcode: The effect of Braginskii's full viscosity tensor on an infinite non-conducting, gravitating anisotropic plasma in which the medium is trapped in a strong magnetic field is discussed in the context of Braginskii's magnetohydrodynamic model with Chew-Goldberger-Low double adiabatic approximation and finite Larmor radius (FLR) correction. Through linearization of the perturbed equations, the general dispersion relation is derived for the separate compression, shear, and drift viscosity components as well as the FLR corrections. We investigate the stability for parallel and transverse perturbations with respect to the direction of the magnetic field, and both gravitational and fire-hose instabilities are found. The role of each viscous term is to suppress instability, but each component works in different ways. The FLR acts in a way that is very similar to the drift viscosity. The instability threshold is found to be independent of viscosity for compression and shear viscosity, but both the drift viscosity and FLR corrections can change the critical wavenumber for the instability. The compression viscosity is most effective at reducing the growth rate of the gravitational instability, whereas the shear viscosity works to suppress the fire-hose instability. The result of the present study may be useful for the study of large scale compression, shear, and drift plasma flow in and around clusters of galaxies and galactic disks and for the solar and stellar wind. Title: Coalescence instability in chromospheric partially ionized plasmas Authors: Murtas, Giulia; Hillier, Andrew; Snow, Ben Bibcode: 2021PhPl...28c2901M Altcode: 2021arXiv210201630M Fast magnetic reconnection plays a fundamental role in driving explosive dynamics and heating in the solar chromosphere. The reconnection time scale of traditional models is shortened at the onset of the coalescence instability, which forms a turbulent reconnecting current sheet through plasmoid interaction. In this work, we aim to investigate the role of partial ionization in the development of fast reconnection through the study of the coalescence instability of plasmoids. Unlike the processes occurring in fully ionized coronal plasmas, relatively little is known about how fast reconnection develops in partially ionized plasmas (PIPs) of the chromosphere. We present 2.5D numerical simulations of coalescing plasmoids in a single fluid magnetohydrodynamic (MHD) model and a two-fluid model of a partially ionized plasma (PIP). We find that in the PIP model, which has the same total density as the MHD model but an initial plasma density two orders of magnitude smaller, plasmoid coalescence is faster than the MHD case, following the faster thinning of the current sheet and secondary plasmoid dynamics. Secondary plasmoids form in the PIP model where the effective Lundquist number S = 7.8 × 10 3 , but are absent from the MHD case where S = 9.7 × 10 3 : these are responsible for a more violent reconnection. Secondary plasmoids also form in linearly stable conditions as a consequence of the nonlinear dynamics of the neutrals in the inflow. In the light of these results, we can affirm that two-fluid effects play a major role in the processes occurring in the solar chromosphere. Title: Collisional ionisation, recombination, and ionisation potential in two-fluid slow-mode shocks: Analytical and numerical results Authors: Snow, B.; Hillier, A. Bibcode: 2021A&A...645A..81S Altcode: 2020arXiv201006303S Context. Shocks are a universal feature of warm plasma environments, such as the lower solar atmosphere and molecular clouds, which consist of both ionised and neutral species. Including partial ionisation leads to the existence of a finite width for shocks, where the ionised and neutral species decouple and recouple. As such, drift velocities exist within the shock that lead to frictional heating between the two species, in addition to adiabatic temperature changes across the shock. The local temperature enhancements within the shock alter the recombination and ionisation rates and hence change the composition of the plasma.
Aims: We study the role of collisional ionisation and recombination in slow-mode partially ionised shocks. In particular, we incorporate the ionisation potential energy loss and analyse the consequences of having a non-conservative energy equation.
Methods: A semi-analytical approach is used to determine the possible equilibrium shock jumps for a two-fluid model with ionisation, recombination, ionisation potential, and arbitrary heating. Two-fluid numerical simulations are performed using the (P<underline>I</underline>P) code. Results are compared to the magnetohydrodynamic (MHD) model and the semi-analytic solution.
Results: Accounting for ionisation, recombination, and ionisation potential significantly alters the behaviour of shocks in both substructure and post-shock regions. In particular, for a given temperature, equilibrium can only exist for specific densities due to the radiative losses needing to be balanced by the heating function. A consequence of the ionisation potential is that a compressional shock will lead to a reduction in temperature in the post-shock region, rather than the increase seen for MHD. The numerical simulations pair well with the derived analytic model for shock velocities. Conclusion. Multi-fluid effects can lead to a significant departure from MHD results. The results in this paper are applicable to a wide range of partially ionised plasmas, including the solar chromosphere and molecular clouds.

The simulation data from this study are available from BS upon reasonable request. The (P<underline>http://I</underline>http://P) code is available at https://github.com/AstroSnow/PIP. Title: Estimating the Energy Dissipation from Kelvin-Helmholtz Instability Induced Turbulence in Oscillating Coronal Loops Authors: Hillier, Andrew; Van Doorsselaere, Tom; Karampelas, Konstantinos Bibcode: 2020ApJ...897L..13H Altcode: 2020arXiv200709068H Kelvin-Helmholtz instability induced turbulence is one promising mechanism by which loops in the solar corona can be heated by MHD waves. In this Letter we present an analytical model of the dissipation rate of Kelvin-Helmholtz instability induced turbulence ɛD, finding it scales as the wave amplitude (d) to the third power (ɛD ∝ d3). Based on the concept of steady-state turbulence, we expect the turbulence heating throughout the volume of the loop to match the total energy injected through its footpoints. In situations where this holds, the wave amplitude has to vary as the cube-root of the injected energy. Comparing the analytic results with those of simulations shows that our analytic formulation captures the key aspects of the turbulent dissipation from the numerical work. Applying this model to the observed characteristics of decayless kink waves we predict that the amplitudes of these observed waves are insufficient to turbulently heat the solar corona. Title: Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere Authors: Snow, B.; Hillier, A. Bibcode: 2020A&A...637A..97S Altcode: 2020arXiv200402550S Context. The plasma of the lower solar atmosphere consists of mostly neutral particles, whereas the upper solar atmosphere is mostly made up of 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. The way the energy is distributed between the two modes depends on the angle of magnetic field.
Aims: We aim to investigate the separation of neutral and ionised species in a gravitationally stratified atmosphere. 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 were performed using the (P<underline>I</underline>P) code of a wave steepening into a shock in an isothermal, partially-ionised atmosphere. The collisional coefficient was 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 and, 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 impacts 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, which may lead to a new potential observable of two-fluid effects in the lower solar atmosphere. Title: Coronal Cooling as a Result of Mixing by the Nonlinear Kelvin-Helmholtz Instability Authors: Hillier, Andrew; Arregui, Iñigo Bibcode: 2019ApJ...885..101H Altcode: 2019arXiv190911351H Recent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain the observed temperature evolution is that the threads were heated by turbulence driven by the Kelvin-Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin-Helmholtz instability is an instability that works to mix the two fluids on either side of the velocity shear layer, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In this paper, we develop a simple phenomenological model of nonlinear Kelvin-Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer. For the case under study, with constant pressure across the two fluids, these quantities are {ρ }mixed}=\sqrt{{ρ }1{ρ }2} and {T}mixed}=\sqrt{{T}1{T}2}. One result from the model is that it provides an accurate—as determined by comparison with simulation results—determination of the kinetic energy in the mean velocity field. A consequence of this is that the magnitude of turbulence—and with it, the energy that can be dissipated on fast timescales—as driven by this instability can be determined. For the prominence-corona system, the mean temperature rise possible from turbulent heating is estimated to be less than 1% of the characteristic temperature (which is found to be T mixed = 105 K). These results highlight that mixing, and not heating, is likely to be the cause of the observed transition between cool to warm material. One consequence of this result is that the mixing creates a region with higher radiative loss rates on average than either of the original fluids, meaning that this instability could contribute a net loss of thermal energy from the corona, i.e., coronal cooling. Title: Achievements of Hinode in the first eleven years Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick; Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks, David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio; Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra, Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.; Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao, Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota, Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu, Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin; Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young, Peter R. Bibcode: 2019PASJ...71R...1H Altcode: Hinode is Japan's third solar mission following Hinotori (1981-1982) and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in operation currently. Hinode carries three instruments: the Solar Optical Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These instruments were built under international collaboration with the National Aeronautics and Space Administration and the UK Science and Technology Facilities Council, and its operation has been contributed to by the European Space Agency and the Norwegian Space Center. After describing the satellite operations and giving a performance evaluation of the three instruments, reviews are presented on major scientific discoveries by Hinode in the first eleven years (one solar cycle long) of its operation. This review article concludes with future prospects for solar physics research based on the achievements of Hinode. Title: Dynamic Evolution of Current Sheets, Ideal Tearing, Plasmoid Formation and Generalized Fractal Reconnection Scaling Relations Authors: Singh, K. A. P.; Pucci, Fulvia; Tenerani, Anna; Shibata, Kazunari; Hillier, Andrew; Velli, Marco Bibcode: 2019ApJ...881...52S Altcode: 2019arXiv190400755S Magnetic reconnection may be the fundamental process allowing energy stored in magnetic fields to be released abruptly, with solar flares and coronal mass ejection being archetypal natural plasma examples. Magnetic reconnection is much too slow of a process to be efficient on the large scales, but accelerates once small enough scales are formed in the system. For this reason, the fractal reconnection scenario was introduced to explain explosive events in the solar atmosphere; it was based on the recursive triggering and collapse via tearing instability of a current sheet originally thinned during the rise of a filament in the solar corona. Here we compare the different fractal reconnection scenarios that have been proposed, and derive generalized scaling relations for the recursive triggering of fast, “ideal” —i.e., Lundquist number independent—tearing in collapsing current sheet configurations with arbitrary current profile shapes. An important result is that the Sweet-Parker scaling with Lundquist number, if interpreted as the aspect ratio of the singular layer in an ideally unstable sheet, is universal and does not depend on the details of the current profile in the sheet. Such a scaling, however, must not be interpreted in terms of stationary reconnection, rather it defines a step in the accelerating sequence of events of the ideal tearing mediated fractal cascade. We calculate scalings for the expected number of plasmoids for such generic profiles and realistic Lundquist numbers, showing that in ideal tearing scenarios a smaller number of plasmoids, by orders of magnitude, is generated compared to the original fractal model. Title: Ion-neutral decoupling in the nonlinear Kelvin-Helmholtz instability: Case of field-aligned flow Authors: Hillier, A. Bibcode: 2019PhPl...26h2902H Altcode: 2019arXiv190712507H Nonlinear magnetic Kelvin-Helmholtz instability (KHI), and the turbulence it creates appear in many astrophysical systems. This includes those systems where the local plasma conditions are such that the plasma is not fully ionized, for example in the lower solar atmosphere and molecular clouds. In a partially ionized system, the fluids couple via collisions which occur at characteristic frequencies, therefore neutral and plasma species become decoupled for sufficiently high-frequency dynamics. Here, we present high-resolution 2D two-fluid simulations of the nonlinear KHI for a system that traverses the dynamic scales between decoupled fluids and coupled dynamics. We discover some interesting phenomena, including the presence of a density coupling that is independent of the velocity coupling. Using these simulations, we analyze the heating rate, and two regimes appear. The first is a regime where the neutral flow is decoupled from the magnetic field that is characterized by a constant heating rate, then at larger scales, the strong coupling approximation holds the heating rate with the KHI layer width to the power of -2. There is an energy cascade in the simulation, but the nature of the frictional heating means the heating rate is determined by the largest scale of turbulent motions, a fact that has consequences for understanding turbulent dissipation in multifluid systems. Title: Intermediate shock sub-structures within a slow-mode shock occurring in partially ionised plasma Authors: Snow, B.; Hillier, A. Bibcode: 2019A&A...626A..46S Altcode: 2019arXiv190412518S Context. Slow-mode shocks are important in understanding fast magnetic reconnection, jet formation and heating in the solar atmosphere, and other astrophysical systems. The atmospheric conditions in the solar chromosphere allow both ionised and neutral particles to exist and interact. Under such conditions, fine sub-structures exist within slow-mode shocks due to the decoupling and recoupling of the plasma and neutral species.
Aims: We study numerically the fine sub-structure within slow-mode shocks in a partially ionised plasma, in particular, analysing the formation of an intermediate transition within the slow-mode shock.
Methods: High-resolution 1D numerical simulations were performed using the (P<underline>I</underline>P) code using a two-fluid approach.
Results: We discover that long-lived intermediate (Alfvén) shocks can form within the slow-mode shock, where there is a shock transition from above to below the Alfvén speed and a reversal of the magnetic field across the shock front. The collisional coupling provides frictional heating to the neutral fluid, resulting in a Sedov-Taylor-like expansion with overshoots in the neutral velocity and neutral density. The increase in density results in a decrease of the Alfvén speed and with this the plasma inflow is accelerated to above the Alfvén speed within the finite width of the shock leading to the intermediate transition. This process occurs for a wide range of physical parameters and an intermediate shock is present for all investigated values of plasma-β, neutral fraction, and magnetic angle. As time advances the magnitude of the magnetic field reversal decreases since the neutral pressure cannot balance the Lorentz force. The intermediate shock is long-lived enough to be considered a physical structure, independent of the initial conditions.
Conclusions: Intermediate shocks are a physical feature that can exist as shock sub-structure for long periods of time in partially ionised plasma due to collisional coupling between species. Title: On Kelvin-Helmholtz and parametric instabilities driven by coronal waves Authors: Hillier, Andrew; Barker, Adrian; Arregui, Iñigo; Latter, Henrik Bibcode: 2019MNRAS.482.1143H Altcode: 2018MNRAS.tmp.2618H; 2018arXiv181002773H The Kelvin-Helmholtz instability has been proposed as a mechanism to extract energy from magnetohydrodynamic (MHD) kink waves in flux tubes, and to drive dissipation of this wave energy through turbulence. It is therefore a potentially important process in heating the solar corona. However, it is unclear how the instability is influenced by the oscillatory shear flow associated with an MHD wave. We investigate the linear stability of a discontinuous oscillatory shear flow in the presence of a horizontal magnetic field within a Cartesian framework that captures the essential features of MHD oscillations in flux tubes. We derive a Mathieu equation for the Lagrangian displacement of the interface and analyse its properties, identifying two different instabilities: a Kelvin-Helmholtz instability and a parametric instability involving resonance between the oscillatory shear flow and two surface Alfvén waves. The latter occurs when the system is Kelvin-Helmholtz stable, thus favouring modes that vary along the flux tube, and as a consequence provides an important and additional mechanism to extract energy. When applied to flows with the characteristic properties of kink waves in the solar corona, both instabilities can grow, with the parametric instability capable of generating smaller scale disturbances along the magnetic field than possible via the Kelvin-Helmholtz instability. The characteristic time-scale for these instabilities is ∼100 s, for wavelengths of 200 km. The parametric instability is more likely to occur for smaller density contrasts and larger velocity shears, making its development more likely on coronal loops than on prominence threads. Title: The magnetic Rayleigh-Taylor instability in solar prominences Authors: Hillier, Andrew Bibcode: 2018RvMPP...2....1H Altcode: The magnetic Rayleigh-Taylor instability is a fundamental instability of many astrophysical systems, and recent observations are consistent with this instability developing in solar prominences. Prominences are cool, dense clouds of plasma that form in the solar corona that display a wide range of dynamics of a multitude of spatial and temporal scales, and two different phenomena that have been discovered to occur in prominences can be understood as resulting from the Rayleigh-Taylor instability. The first is that of plumes that rise through quiescent prominences from low density bubbles that form below them. The second is that of a prominence eruption that fragments as the material falls back to the solar surface. To identify these events as the magnetic Rayleigh-Taylor instability, a wide range of theoretical work, both numerical and analytical has been performed, though alternative explanations do exist. For both of these sets of observations, determining that they are created by the magnetic Rayleigh-Taylor instability has meant that the linear instability conditions and nonlinear dynamics can be used to make estimates of the magnetic field strength. There are strong connections between these phenomena and those in a number of other astro, space and plasma systems, making these observations very important for our understanding of the role of the Rayleigh-Taylor instability in magnetised systems. Title: Observations of the Kelvin-Helmholtz Instability Driven by Dynamic Motions in a Solar Prominence Authors: Hillier, Andrew; Polito, Vanessa Bibcode: 2018ApJ...864L..10H Altcode: 2018arXiv180802286H Prominences are incredibly dynamic across the whole range of their observable spatial scales, with observations revealing gravity-driven fluid instabilities, waves, and turbulence. With all of these complex motions, it would be expected that instabilities driven by shear in the internal fluid motions would develop. However, evidence of these have been lacking. Here we present the discovery in a prominence, using observations from the Interface Region Imaging Spectrograph, of a shear flow instability, the Kelvin-Helmholtz sinusoidal-mode of a fluid channel, driven by flows in the prominence body. This finding presents a new mechanism through which we can create turbulent motions from the flows observed in quiescent prominences. The observation of this instability in a prominence highlights their great value as a laboratory for understanding the complex interplay between magnetic fields and fluid flows that play a crucial role in a vast range of astrophysical systems. Title: Three-dimensional Velocity Measurements in Solar Prominence Bubbles and Combined Kelvin-Helmholtz/Rayleigh-Taylor Instability Authors: Berger, Thomas; Hillier, Andrew; Liu, Wei Bibcode: 2018cosp...42E.293B Altcode: We present measurements of flow velocities in solar prominences that display so-called "prominence bubble" events. Prominence bubbles are large-scale buoyant intrusions into prominences that rise from below and penetrate into the overlying plasma. They are believed to be due to magnetic flux emergence below prominences and can trigger Rayleigh-Taylor and Kelvin-Helmholtz instability flows as they interact with the overlying prominence. Prominence bubbles frequently result in the formation of plumes that rise into, or entirely through, the overlying prominence. This presents a mechanism for increasing magnetic flux and helicity in the associated coronal magnetic flux tubes, which are key for their eventual loss of equilibrium and eruptions as coronal mass ejections (CMEs). In this presentation, Hinode/Solar Optical Telescope (SOT) and Interface Region Imaging Spectrograph (IRIS) observations are analyzed to infer three-dimensional flow vectors in the "boundary layer" above several prominence bubble events. IRIS Doppler velocity measurements indicate flow speeds of 50-100 km/sec perpendicular to the sky plane, consistent with flow speeds inferred from combined Kelvin-Helmholtz/Rayleigh-Taylor instability analysis using typical quiescent prominence density and magnetic flux density values. With these typical values, flow speeds and magnetic flux densities within the bubbles can be inferred to be on the order of 100 km/sec and 10 Gauss, respectively. We discuss the implications of these novel results, and in particular, the potential for strong shear flows at the bubble boundary to trigger Kelvin-Helmholtz instability waves that develop into large-scale Rayleigh-Taylor instability plumes. Title: Observations of a shear-flow instability driven by dynamic prominence motions Authors: Hillier, Andrew; Polito, . V. Bibcode: 2018cosp...42E1460H Altcode: Prominences are incredibly dynamic across the whole range of their observable spatial scales, with observations revealing gravity-driven fluid instabilities, waves, and turbulence. With all these complex motions, it would be expected that instabilities driven by shear in the fluid motions contained in the prominence body would develop. However, evidence of these have been lacking. Here we present the discovery in a prominence, using observations from the Interface Region Imaging Spectrograph (IRIS), of a shear flow instability, a mode of the Kelvin-Helmholtz instability that makes streams of fluid develop serpentine patterns, driven by transonic motions in the prominence body. This finding presents a new mechanism through which we can create turbulence from the flows observed in quiescent prominences. The observation of this instability in a prominence highlights their great value as a laboratory for understanding the complex interplay between magnetic fields and fluid flows that play a crucial role in a vast range of astrophysical systems. Title: Onset of 2D magnetic reconnection in the solar photosphere, chromosphere, and corona Authors: Snow, B.; Botha, G. J. J.; McLaughlin, J. A.; Hillier, A. Bibcode: 2018A&A...609A.100S Altcode: 2017arXiv171100683S
Aims: We aim to investigate the onset of 2D time-dependent magnetic reconnection that is triggered using an external (non-local) velocity driver located away from, and perpendicular to, an equilibrium Harris current sheet. Previous studies have typically utilised an internal trigger to initiate reconnection, for example initial conditions centred on the current sheet. Here, an external driver allows for a more naturalistic trigger as well as the study of the earlier stages of the reconnection start-up process.
Methods: Numerical simulations solving the compressible, resistive magnetohydrodynamic (MHD) equations were performed to investigate the reconnection onset within different atmospheric layers of the Sun, namely the corona, chromosphere and photosphere.
Results: A reconnecting state is reached for all atmospheric heights considered, with the dominant physics being highly dependent on atmospheric conditions. The coronal case achieves a sharp rise in electric field (indicative of reconnection) for a range of velocity drivers. For the chromosphere, we find a larger velocity amplitude is required to trigger reconnection (compared to the corona). For the photospheric environment, the electric field is highly dependent on the inflow speed; a sharp increase in electric field is obtained only as the velocity entering the reconnection region approaches the Alfvén speed. Additionally, the role of ambipolar diffusion is investigated for the chromospheric case and we find that the ambipolar diffusion alters the structure of the current density in the inflow region.
Conclusions: The rate at which flux enters the reconnection region is controlled by the inflow velocity. This determines all aspects of the reconnection start-up process, that is, the early onset of reconnection is dominated by the advection term in Ohm's law in all atmospheric layers. A lower plasma-β enhances reconnection and creates a large change in the electric field. A high plasma-β hinders the reconnection, yielding a sharp rise in the electric field only when the velocity flowing into the reconnection region approaches the local Alfvén speed. Title: Quiescent Prominence Dynamics Observed with the Hinode Solar Optical Telescope. II. Prominence Bubble Boundary Layer Characteristics and the Onset of a Coupled Kelvin-Helmholtz Rayleigh-Taylor Instability Authors: Berger, Thomas; Hillier, Andrew; Liu, Wei Bibcode: 2017ApJ...850...60B Altcode: 2017arXiv170705265B We analyze solar quiescent prominence bubble characteristics and instability dynamics using Hinode/Solar Optical Telescope data. We measure the bubble expansion rate, prominence downflows, and the profile of the boundary layer brightness and thickness as a function of time. The largest bubble analyzed rises into the prominence with a speed of about 1.3 {km} {{{s}}}-1 until it is destabilized by a localized shear flow on the boundary. Boundary layer thickness grows gradually as prominence downflows deposit plasma onto the bubble with characteristic speeds of 20{--}35 {km} {{{s}}}-1. Lateral downflows initiate from the thickened boundary layer with characteristic speeds of 25{--}50 {km} {{{s}}}-1, “draining” the layer of plasma. Strong shear flow across one bubble boundary leads to an apparent coupled Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) instability. We measure shear flow speeds above the bubble of 10 {km} {{{s}}}-1 and infer interior bubble flow speeds on the order of 100 {km} {{{s}}}-1. Comparing the measured growth rate of the instability to analytic expressions, we infer a magnetic flux density across the bubble boundary of ∼10-3 T (10 Gauss) at an angle of ∼ 70^\circ to the prominence plane. The results are consistent with the hypothesis that prominence bubbles are caused by magnetic flux that emerges below a prominence, setting up the conditions for RT, or combined KH-RT, instability flows that transport flux, helicity, and hot plasma upward into the overlying coronal magnetic flux rope. Title: The non-linear growth of the magnetic Rayleigh-Taylor instability Authors: Carlyle, Jack; Hillier, Andrew Bibcode: 2017A&A...605A.101C Altcode: 2017arXiv170707987C This work examines the effect of the embedded magnetic field strength on the non-linear development of the magnetic Rayleigh-Taylor instability (RTI) (with a field-aligned interface) in an ideal gas close to the incompressible limit in three dimensions. Numerical experiments are conducted in a domain sufficiently large so as to allow the predicted critical modes to develop in a physically realistic manner. The ratio between gravity, which drives the instability in this case (as well as in several of the corresponding observations), and magnetic field strength is taken up to a ratio which accurately reflects that of observed astrophysical plasma, in order to allow comparison between the results of the simulations and the observational data which served as inspiration for this work. This study finds reduced non-linear growth of the rising bubbles of the RTI for stronger magnetic fields, and that this is directly due to the change in magnetic field strength, rather than the indirect effect of altering characteristic length scales with respect to domain size. By examining the growth of the falling spikes, the growth rate appears to be enhanced for the strongest magnetic field strengths, suggesting that rather than affecting the development of the system as a whole, increased magnetic field strengths in fact introduce an asymmetry to the system. Further investigation of this effect also revealed that the greater this asymmetry, the less efficiently the gravitational energy is released. By better understanding the under-studied regime of such a major phenomenon in astrophysics, deeper explanations for observations may be sought, and this work illustrates that the strength of magnetic fields in astrophysical plasmas influences observed RTI in subtle and complex ways. Title: Prominence Bubble Shear Flows and the Coupled Kelvin-Helmholtz — Rayleigh-Taylor Instability Authors: Berger, Thomas; Hillier, Andrew Bibcode: 2017SPD....4820103B Altcode: Prominence bubbles are large arched structures that rise from below into quiescent prominences, often growing to heights on the order of 10 Mm before going unstable and generating plume upflows. While there is general agreement that emerging flux below pre-existing prominences causes the structures, there is lack of agreement on the nature of the bubbles and the cause of the instability flows. One hypothesis is that the bubbles contain coronal temperature plasma and rise into the prominence above due to both magnetic and thermal buoyancy, eventually breaking down via a magnetic Rayleigh-Taylor (RT) instability to release hot plasma and magnetic flux and helicity into the overlying coronal flux rope. Another posits that the bubbles are actually just “arcades” in the prominence indicating a magnetic separator line between the bipole and the prominence fields with the observed upflows and downflows caused by reconnection along the separator. We analyze Hinode/SOT, SDO/AIA, and IRIS observations of prominence bubbles, focusing on characteristics of the bubble boundary layers that may discriminate between the two hypotheses. We find speeds on the order of 10 km/s in prominence plasma downflows and lateral shear flows along the bubble boundary. Inflows to the boundary gradually increase the thickness and brightness of the layer until plasma drains from there, apparently around the dome-like bubble domain. In one case, shear flow across the bubble boundary develops Kelvin-Helmholtz (KH) vortices that we use to infer flow speeds in the low-density bubble on the order of 100 km/sec. IRIS spectra indicate that plasma flows on the bubble boundary at transition region temperatures achieve Doppler speeds on the order of 50 km/s, consistent with this inference. Combined magnetic KH-RT instability analysis leads to flux density estimates of 10 G with a field angle of 30° to the prominence, consistent with vector magnetic field measurements. In contrast, we find no evidence of the impulsive brightening or bi-directional jets that are expected from reconnection driven flows at bubble boundaries. We conclude that observations to date are consistent with the hot bubble/Rayleigh-Taylor instability hypothesis. Title: Differences between Doppler velocities of ions and neutral atoms in a solar prominence Authors: Anan, T.; Ichimoto, K.; Hillier, A. Bibcode: 2017A&A...601A.103A Altcode: 2017arXiv170302132A Context. In astrophysical systems with partially ionized plasma, the motion of ions is governed by the magnetic field while the neutral particles can only feel the magnetic field's Lorentz force indirectly through collisions with ions. The drift in the velocity between ionized and neutral species plays a key role in modifying important physical processes such as magnetic reconnection, damping of magnetohydrodynamic waves, transport of angular momentum in plasma through the magnetic field, and heating.
Aims: This paper aims to investigate the differences between Doppler velocities of calcium ions and neutral hydrogen in a solar prominence to look for velocity differences between the neutral and ionized species.
Methods: We simultaneously observed spectra of a prominence over an active region in H I 397 nm, H I 434 nm, Ca II 397 nm, and Ca II 854 nm using a high dispersion spectrograph of the Domeless Solar Telescope at Hida observatory. We compared the Doppler velocities, derived from the shift of the peak of the spectral lines presumably emitted from optically-thin plasma.
Results: There are instances when the difference in velocities between neutral atoms and ions is significant, for example 1433 events ( 3% of sets of compared profiles) with a difference in velocity between neutral hydrogen atoms and calcium ions greater than 3σ of the measurement error. However, we also found significant differences between the Doppler velocities of two spectral lines emitted from the same species, and the probability density functions of velocity difference between the same species is not significantly different from those between neutral atoms and ions.
Conclusions: We interpreted the difference of Doppler velocities as being a result of the motions of different components in the prominence along the line of sight, rather than the decoupling of neutral atoms from plasma.

The movie attached to Fig. 1 is available at http://www.aanda.org Title: Investigating prominence turbulence with Hinode SOT Dopplergrams Authors: Hillier, A.; Matsumoto, T.; Ichimoto, K. Bibcode: 2017A&A...597A.111H Altcode: 2016arXiv161008281H Quiescent prominences host a diverse range of flows, including Rayleigh-Taylor instability driven upflows and impulsive downflows, and so it is no surprise that turbulent motions also exist. As prominences are believed to have a mean horizontal guide field, investigating any turbulence they host could shed light on the nature of magnetohydrodynamic (MHD) turbulence in a wide range of astrophysical systems. In this paper we have investigated the nature of the turbulent prominence motions using structure function analysis on the velocity increments estimated from Hα Dopplergrams constructed with observational data from Hinode Solar Optical Telescope (SOT). The probability density function of the velocity increments shows that as we look at increasingly small spatial separations the distribution displays greater departure from a reference Gaussian distribution, hinting at intermittency in the velocity field. Analysis of the even order structure functions for both the horizontal and vertical separations showed the existence of two distinct regions displaying different exponents of the power law with the break in the power law at approximately 2000 km. We hypothesise this to be a result of internal turbulence excited in the prominence by the dynamic flows of the system found at this spatial scale. We found that the scaling exponents of the pth order structure functions for these two regions generally followed the p/ 2 (smaller scales) and p/ 4 (larger scales) laws that are the same as those predicted for weak MHD turbulence and Kraichnan-Iroshnikov turbulence respectively. However, the existence of the p/ 4 scaling at larger scales than the p/ 2 scaling is inconsistent with the increasing nonlinearity expected in MHD turbulence. We also found that as we went to higher order structure functions, the dependence of the scaling exponent on the order p is nonlinear implying that intermittency may be playing an important role in the turbulent cascade. Estimating the heating from the turbulent energy dissipation showed that this turbulence would be very inefficient at heating the prominence plasma, but that the mass diffusion through turbulence driven reconnection was of the order of 1010 cm2 s-1. This is of similar order to that of the expected value of the ambipolar diffusion and a few orders of magnitude greater than Ohmic diffusion for a quiescent prominence.

The movie associated to Fig. 4 is available at http://www.aanda.org Title: On the nature of the magnetic Rayleigh-Taylor instability in astrophysical plasma: the case of uniform magnetic field strength Authors: Hillier, Andrew S. Bibcode: 2016MNRAS.462.2256H Altcode: 2016arXiv161008317H The magnetic Rayleigh-Taylor instability has been shown to play a key role in many astrophysical systems. The equation for the growth rate of this instability in the incompressible limit, and the most-unstable mode that can be derived from it, are often used to estimate the strength of the magnetic field that is associated with the observed dynamics. However, there are some issues with the interpretations given. Here, we show that the class of most unstable modes ku for a given θ, the class of modes often used to estimate the strength of the magnetic field from observations, for the system leads to the instability growing as σ2 = 1/2Agku, a growth rate which is independent of the strength of the magnetic field and which highlights that small scales are preferred by the system, but not does not give the fastest growing mode for that given k. We also highlight that outside of the interchange (k ṡ B = 0) and undular (k parallel to B) modes, all the other modes have a perturbation pair of the same wavenumber and growth rate that when excited in the linear regime can result in an interference pattern that gives field aligned filamentary structure often seen in 3D simulations. The analysis was extended to a sheared magnetic field, where it was found that it was possible to extend the results for a non-sheared field to this case. We suggest that without magnetic shear it is too simplistic to be used to infer magnetic field strengths in astrophysical systems. Title: The formation and evolution of reconnection-driven, slow-mode shocks in a partially ionised plasma Authors: Hillier, A.; Takasao, S.; Nakamura, N. Bibcode: 2016A&A...591A.112H Altcode: 2016arXiv160201112H The role of slow-mode magnetohydrodynamic (MHD) shocks in magnetic reconnection is of great importance for energy conversion and transport, but in many astrophysical plasmas the plasma is not fully ionised. In this paper, we use numerical simulations to investigate the role of collisional coupling between a proton-electron, charge-neutral fluid and a neutral hydrogen fluid for the one-dimensional (1D) Riemann problem initiated in a constant pressure and density background state by a discontinuity in the magnetic field. This system, in the MHD limit, is characterised by two waves. The first is a fast-mode rarefaction wave that drives a flow towards a slow-mode MHD shock wave. The system evolves through four stages: initiation, weak coupling, intermediate coupling, and a quasi-steady state. The initial stages are characterised by an over-pressured neutral region that expands with characteristics of a blast wave. In the later stages, the system tends towards a self-similar solution where the main drift velocity is concentrated in the thin region of the shock front. Because of the nature of the system, the neutral fluid is overpressured by the shock when compared to a purely hydrodynamic shock, which results in the neutral fluid expanding to form the shock precursor. Once it has formed, the thickness of the shock front is proportional to ξ I-1.2 , which is a smaller exponent than would be naively expected from simple scaling arguments. One interesting result is that the shock front is a continuous transition of the physical variables of subsonic velocity upstream of the shock front (a c-shock) to a sharp jump in the physical variables followed by a relaxation to the downstream values for supersonic upstream velocity (a j-shock). The frictional heating that results from the velocity drift across the shock front can amount to ~2 per cent of the reference magnetic energy. Title: Nonlinear instability and intermittent nature of magnetic reconnection in solar chromosphere Authors: Singh, K. A. P.; Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari Bibcode: 2015PASJ...67...96S Altcode: 2016arXiv160201999S; 2015PASJ..tmp..234S The recent observations of Singh et al. (2012, ApJ, 759, 33) have shown multiple plasma ejections and the intermittent nature of magnetic reconnection in the solar chromosphere, highlighting the need for fast reconnection to occur in highly collisional plasma. However, the physical process through which fast magnetic reconnection occurs in partially ionized plasma, like the solar chromosphere, is still poorly understood. It has been shown that for sufficiently high magnetic Reynolds numbers, Sweet-Parker current sheets can become unstable leading to tearing mode instability and plasmoid formation, but when dealing with a partially ionized plasma the strength of coupling between the ions and neutrals plays a fundamental role in determining the dynamics of the system. We propose that as the reconnecting current sheet thins and the tearing instability develops, plasmoid formation passes through strongly, intermediately, and weakly coupled (or decoupled) regimes, with the time scale for the tearing mode instability depending on the frictional coupling between ions and neutrals. We present calculations for the relevant time scales for fractal tearing in all three regimes. We show that as a result of the tearing mode instability and the subsequent non-linear instability due to the plasmoid-dominated reconnection, the Sweet-Parker current sheet tends to have a fractal-like structure, and when the chromospheric magnetic field is sufficiently strong the tearing instability can reach down to kinetic scales, which are hypothesized to be necessary for fast reconnection. Title: Superflare Occurrence and Energies on G-, K-, and M-type Dwarfs Authors: Candelaresi, S.; Hillier, A.; Maehara, H.; Brandenburg, A.; Shibata, K. Bibcode: 2014ApJ...792...67C Altcode: 2014arXiv1405.1453C Kepler data from G-, K-, and M-type stars are used to study conditions that lead to superflares with energies above 1034 erg. From the 117,661 stars included, 380 show superflares with a total of 1690 such events. We study whether parameters, like effective temperature or rotation rate, have any effect on the superflare occurrence rate or energy. With increasing effective temperature we observe a decrease in the superflare rate, which is analogous to the previous findings of a decrease in dynamo activity with increasing effective temperature. For slowly rotating stars, we find a quadratic increase of the mean occurrence rate with the rotation rate up to a critical point, after which the rate decreases linearly. Motivated by standard dynamo theory, we study the behavior of the relative starspot coverage, approximated as the relative brightness variation. For faster rotating stars, an increased fraction of stars shows higher spot coverage, which leads to higher superflare rates. A turbulent dynamo is used to study the dependence of the Ohmic dissipation as a proxy of the flare energy on the differential rotation or shear rate. The resulting statistics of the dissipation energy as a function of dynamo number is similar to the observed flare statistics as a function of the inverse Rossby number and shows similarly strong fluctuations. This supports the idea that superflares might well be possible for solar-type G stars. Title: The Rayleigh-Taylor Instability and the role of Prominences in the Chromosphere-Corona Mass Cycle Authors: Berger, Thomas; Liu, Wei; Hillier, Andrew; Scullion, Eamon; Low, Boon Chye Bibcode: 2014AAS...22421201B Altcode: We review recent results in the study of so-called "prominence bubbles", a buoyant instability discovered in quiescent solar prominences by the Hinode/SOT instrument in 2007. Analysis of the plasma flows along the boundary of the bubbles indicates that shear flows leading to Kelvin-Helmholtz instability waves can develop into the seed perturbations triggering the Rayleigh-Taylor instability. The non-linear phase of the RT instability leads to the formation of large turbulent plumes that transport the bubble plasma (and presumably magnetic flux) into the overlying coronal flux rope. We propose that the upward turbulent transport of hot bubble plasma and the downflows of cooler chromospheric plasma in the prominence are related aspects of a large-scale "chromosphere-corona mass cycle" in which hot plasma and magnetic flux and helicity from the chromosphere are transported upwards while the cooler prominence plasma downflows, which decouple from the magnetic field they are originally frozen-into, represent the condensation return flows of the cycle. This cycling enables a mechanism by which magnetic flux and helicity build up in the coronal flux rope while mass drains out of the flux rope, eventually triggering a "loss of confinement" eruption in the form of a CME. Title: The Generation and Damping of Propagating MHD Kink Waves in the Solar Atmosphere Authors: Morton, R. J.; Verth, G.; Hillier, A.; Erdélyi, R. Bibcode: 2014ApJ...784...29M Altcode: 2013arXiv1310.4650M The source of the non-thermal energy required for the heating of the upper solar atmosphere to temperatures in excess of a million degrees and the acceleration of the solar wind to hundreds of kilometers per second is still unclear. One such mechanism for providing the required energy flux is incompressible torsional Alfvén and kink magnetohydrodynamic (MHD) waves, which are magnetically dominated waves supported by the Sun's pervasive and complex magnetic field. In particular, propagating MHD kink waves have recently been observed to be ubiquitous throughout the solar atmosphere, but, until now, critical details of the transport of the kink wave energy throughout the Sun's atmosphere were lacking. Here, the ubiquity of the waves is exploited for statistical studies in the highly dynamic solar chromosphere. This large-scale investigation allows for the determination of the chromospheric kink wave velocity power spectra, a missing link necessary for determining the energy transport between the photosphere and corona. Crucially, the power spectra contain evidence for horizontal photospheric motions being an important mechanism for kink wave generation in the quiescent Sun. In addition, a comparison with measured coronal power spectra is provided for the first time, revealing frequency-dependent transmission profiles, suggesting that there is enhanced damping of kink waves in the lower corona. Title: Within the International Collaboration CHAIN: a Summary of Events Observed with Flare Monitoring Telescope (FMT) in Peru Authors: Ishitsuka, J.; Asai, A.; Morita, S.; Terrazas, R.; Cabezas, D.; Gutierrez, V.; Martinez, L.; Buleje, Y.; Loayza, R.; Nakamura, N.; Takasao, S.; Yoshinaga, Y.; Hillier, A.; Otsuji, K.; Shibata, K.; Ishitsuka, M.; Ueno, S.; Kitai, R.; Ishii, T.; Ichimoto, K.; Nagata, S.; Narukage, N. Bibcode: 2014SunGe...9...85I Altcode: In 2008 we inaugurated the new Solar Observatory in collaboration with Faculty of Sciences of San Luis Gonzaga de Ica National University, 300 km south of Lima. In March of 2010 a Flare Monitoring Telescope of Hida Observatory of Kyoto University arrived to Ica, part of CHAIN Project (Continuous H-alpha Imaging Network). In October of the same year we hosted the First FMT Workshop in Ica, then in July of 2011 the Second FMT Workshop was opened. Since that we are focused on two events registered by FMT in Peru to publish results. FMT is a good tool to introduce young people from universities into scientific knowledge; it is good also for education in Solar Physics and outreach. Details of this successful collaboration will be explained in this presentation. Title: Investigating the Dynamics and Density Evolution of Returning Plasma Blobs from the 2011 June 7 Eruption Authors: Carlyle, Jack; Williams, David R.; van Driel-Gesztelyi, Lidia; Innes, Davina; Hillier, Andrew; Matthews, Sarah Bibcode: 2014ApJ...782...87C Altcode: 2014arXiv1401.4824C This work examines in-falling matter following an enormous coronal mass ejection on 2011 June 7. The material formed discrete concentrations, or blobs, in the corona and fell back to the surface, appearing as dark clouds against the bright corona. In this work we examined the density and dynamic evolution of these blobs in order to formally assess the intriguing morphology displayed throughout their descent. The blobs were studied in five wavelengths (94, 131, 171, 193, and 211 Å) using the Solar Dynamics Observatory Atmospheric Imaging Assembly, comparing background emission to attenuated emission as a function of wavelength to calculate column densities across the descent of four separate blobs. We found the material to have a column density of hydrogen of approximately 2 × 1019 cm-2, which is comparable with typical pre-eruption filament column densities. Repeated splitting of the returning material is seen in a manner consistent with the Rayleigh-Taylor instability. Furthermore, the observed distribution of density and its evolution is also a signature of this instability. By approximating the three-dimensional geometry (with data from STEREO-A), volumetric densities were found to be approximately 2 × 10-14 g cm-3, and this, along with observed dominant length scales of the instability, was used to infer a magnetic field of the order 1 G associated with the descending blobs. Title: Determination of Prominence Plasma β from the Dynamics of Rising Plumes Authors: Hillier, Andrew; Hillier, Richard; Tripathi, Durgesh Bibcode: 2014IAUS..300...94H Altcode: Observations of quiescent prominences show rising plumes, dark in chromospheric lines, that propagate from large bubbles. In this paper we present a method that may be used to determine the plasma β (ratio of gas pressure to magnetic pressure) from the rising plumes. Using the classic fluid dynamic solution for flow around a circular cylinder, the compression of the prominence material can be estimated. Application to a prominence gave an estimate of the plasma β as β=0.47-1.13 for a ratio of specific heats of γ=1.4-1.7. Title: A Statistical Study of Transverse Oscillations in a Quiescent Prominence Authors: Hillier, A.; Morton, R. J.; Erdélyi, R. Bibcode: 2013ApJ...779L..16H Altcode: 2013arXiv1310.8009H The launch of the Hinode satellite has allowed for seeing-free observations at high-resolution and high-cadence making it well suited to study the dynamics of quiescent prominences. In recent years it has become clear that quiescent prominences support small-amplitude transverse oscillations, however, sample sizes are usually too small for general conclusions to be drawn. We remedy this by providing a statistical study of transverse oscillations in vertical prominence threads. Over a 4 hr period of observations it was possible to measure the properties of 3436 waves, finding periods from 50 to 6000 s with typical velocity amplitudes ranging between 0.2 and 23 km s-1. The large number of observed waves allows the determination of the frequency dependence of the wave properties and derivation of the velocity power spectrum for the transverse waves. For frequencies less than 7 mHz, the frequency dependence of the velocity power is consistent with the velocity power spectra generated from observations of the horizontal motions of magnetic elements in the photosphere, suggesting that the prominence transverse waves are driven by photospheric motions. However, at higher frequencies the two distributions significantly diverge, with relatively more power found at higher frequencies in the prominence oscillations. These results highlight that waves over a large frequency range are ubiquitous in prominences, and that a significant amount of the wave energy is found at higher frequency. Title: Can Superflares Occur on Our Sun? Authors: Shibata, Kazunari; Isobe, Hiroaki; Hillier, Andrew; Choudhuri, Arnab Rai; Maehara, Hiroyuki; Ishii, Takako T.; Shibayama, Takuya; Notsu, Shota; Notsu, Yuta; Nagao, Takashi; Honda, Satoshi; Nogami, Daisaku Bibcode: 2013PASJ...65...49S Altcode: 2012arXiv1212.1361S Recent observations of Sun-like stars, similar to our Sun in their surface temperature (5600-6000 K) and slow rotation (rotational period > 10 d), using the Kepler satellite by Maehara et al. (2012, Nature, 485, 478) have revealed the existence of superflares (with energy of 1033-1035 erg). From statistical analyses of these superflares, it was found that superflares with energy of 1034 erg occur once in 800 yr, and superflares with 1035 erg occur once in 5000 yr. In this paper, we examine whether superflares with energy of 1033-1035 erg could occur on the present Sun through the use of simple order-of-magnitude estimates based on current ideas related to the mechanisms of the solar dynamo. If magnetic flux is generated by differential rotation at the base of the convection zone, as assumed in typical dynamo models, it is possible that the present Sun would generate a large sunspot with a total magnetic flux of ∼2 × 1023 Mx (= G cm2) within one solar cycle period, and lead to superflares with an energy of 1034 erg. To store a total magnetic flux of ∼1024 Mx, necessary for generating 1035 erg superflares, it would take ∼40 yr. Hot Jupiters have often been argued to be a necessary ingredient for the generation of superflares, but we found that they do not play any essential role in the generation of magnetic flux in the star itself, if we consider only the magnetic interaction between the star and the hot Jupiter. This seems to be consistent with Maehara et al.'s finding of 148 superflare-generating solar-type stars that do not have a hot Jupiter-like companion. Altogether, our simple calculations, combined with Maehara et al.'s analysis of superflares on Sun-like stars, show that there is a possibility that superflares of 1034 erg would occur once in 800 yr on our present Sun. Title: On the Support of Solar Prominence Material by the Dips of a Coronal Flux Tube Authors: Hillier, Andrew; van Ballegooijen, Adriaan Bibcode: 2013ApJ...766..126H Altcode: 2013arXiv1303.4130H The dense prominence material is believed to be supported against gravity through the magnetic tension of dipped coronal magnetic field. For quiescent prominences, which exhibit many gravity-driven flows, hydrodynamic forces are likely to play an important role in the determination of both the large- and small-scale magnetic field distributions. In this study, we present the first steps toward creating a three-dimensional magneto-hydrostatic prominence model where the prominence is formed in the dips of a coronal flux tube. Here 2.5D equilibria are created by adding mass to an initially force-free magnetic field, then performing a secondary magnetohydrodynamic relaxation. Two inverse polarity magnetic field configurations are studied in detail, a simple o-point configuration with a ratio of the horizontal field (Bx ) to the axial field (By ) of 1:2 and a more complex model that also has an x-point with a ratio of 1:11. The models show that support against gravity is either by total pressure or tension, with only tension support resembling observed quiescent prominences. The o-point of the coronal flux tube was pulled down by the prominence material, leading to compression of the magnetic field at the base of the prominence. Therefore, tension support comes from the small curvature of the compressed magnetic field at the bottom and the larger curvature of the stretched magnetic field at the top of the prominence. It was found that this method does not guarantee convergence to a prominence-like equilibrium in the case where an x-point exists below the prominence flux tube. The results imply that a plasma β of ~0.1 is necessary to support prominences through magnetic tension. Title: Simulations of the Dynamics of the Magnetic Rayleigh-Taylor Instability in Solar Prominences Authors: Hillier, A.; Berger, T.; Shibata, K.; Isobe, H. Bibcode: 2013ASPC..474..147H Altcode: The magnetic Rayleigh-Taylor instability plays an important role in the mass and magnetic flux transport in many astrophysical bodies. Solar prominences also display this instability and recent observations using the Solar Optical Telescope onboard the Hinode satellite have revealed these dynamics in amazing detail. The observations show rising plumes, approximately 1 Mm in width, that propagate through the dense prominence material from low-density bubbles, i.e. the situation expected when the magnetic Rayleigh-Taylor instability occurs. To study this phenomenon, we performed 3D simulations of the magnetic Rayleigh-Taylor instability in the Kippenhahn-Schlüter prominence model. The plumes formed in these simulations are filamentary structures that are aligned with the magnetic field created as 3D modes of the magnetic Rayleigh-Taylor instability. The plumes rise, developing large structures from smaller structures through an inverse cascade process driven by nonlinear interaction. The results suggest that the plumes observed in the prominence may be used to study the conditions inside the prominence. Title: Determination of Prominence Plasma β from the Dynamics of Rising Plumes Authors: Hillier, Andrew; Hillier, Richard; Tripathi, Durgesh Bibcode: 2012ApJ...761..106H Altcode: 2012arXiv1211.0742H Observations by the Hinode satellite show in great detail the dynamics of rising plumes, dark in chromospheric lines, in quiescent prominences that propagate from large (~10 Mm) bubbles that form at the base of the prominences. These plumes present a very interesting opportunity to study magnetohydrodynamic (MHD) phenomena in quiescent prominences, but obstacles still remain. One of the biggest issues is that of the magnetic field strength, which is not easily measurable in prominences. In this paper we present a method that may be used to determine a prominence's plasma β when rising plumes are observed. Using the classic fluid dynamic solution for flow around a circular cylinder with an MHD correction, the compression of the prominence material can be estimated. This has been successfully confirmed through simulations; application to a prominence gave an estimate of the plasma β as β = 0.47 ± 0.079 to 1.13 ± 0.080 for the range γ = 1.4-1.7. Using this method it may be possible to estimate the plasma β of observed prominences, therefore helping our understanding of a prominence's dynamics in terms of MHD phenomena. Title: Numerical Simulations of the Magnetic Rayleigh-Taylor Instability in the Kippenhahn-Schlüter Prominence Model. II. Reconnection-triggered Downflows Authors: Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari; Berger, Thomas Bibcode: 2012ApJ...756..110H Altcode: 2011arXiv1106.2613H The launch of the Hinode satellite has allowed high-resolution observations of supersonic bright downflows in quiescent prominences, known as prominence knots. We present observations in the Ca II H spectral line using the Solar Optical Telescope on board the Hinode satellite of a descending plasma knot of size ~900 km. The knot initially undergoes ballistic motion before undergoing impulsive accelerations at the same time as experiencing increases in intensity. We also present a subset of our three-dimensional magnetohydrodynamic simulations, performed to investigate the nonlinear stability of the Kippenhahn-Shlüter prominence model to the magnetic Rayleigh-Taylor instability in which interchange reconnection occurs. The interchange reconnection in the model breaks the force balance along the field lines which initiates the downflows. The downflows propagate with a downward fluid velocity of ~15 km s-1 and a characteristic size of ~700 km. We conclude that the observed plasma blob and the simulated downflow are driven by the breaking of the force balance along the magnetic field as a result of a change in magnetic topology caused by reconnection of the magnetic field. Title: Spicule Dynamics over Plage Region Authors: Anan, T.; Kitai, R.; Hillier, A.; Kawate, T.; Ichimoto, K.; Shibata, K. Bibcode: 2012ASPC..454...91A Altcode: We have studied spicular jets over a plage region and derived their dynamic characteristics using Hinode Solar Optical Telescope (SOT) high-resolution Ca II H images. We have identified 169 spicules over the target plage. This sample size permits us to derive statistically reliable results regarding spicular dynamics. The properties of plage spicules can be summarized as follows: (1) In a plage area, we clearly identify spicular jet features. (2) They are shorter in length than the quiet-region limb spicules, and follow ballistic motion under constant deceleration. (3) The majority (80%) of the plage spicules show a full rise and retreat (which we call ‘parabolic’ spicules), while 10% of them fade out without a complete retreat phase(which we call ‘fade out’ spicules). (4) The deceleration of the spicule is proportional to the velocity of ejection (i.e. the initial velocity). Title: Simulations of the Magnetic Rayleigh-Taylor Instability in the Kippenhahn-Schlüter Prominence Model Authors: Hillier, A.; Berger, T.; Shibata, K.; Isobe, H. Bibcode: 2012ASPC..456..157H Altcode: The launch of the Hinode satellite, with the Solar Optical Telescope, allowed for high resolution, high time cadence observations of prominences to be performed in the seeing free environment of space. The most striking discovery from these observations is of plumes, approximately 1 Mm in width, that propagate through the prominence material. The plumes initiate from underdense bubbles that form beneath prominences, rise at constant speeds of approximately 20 km s-1 and are formed in the conditions required for the magnetic Rayleigh-Taylor instability to occur. To study this phenomenon, we performed 3D simulations of the magnetic Rayleigh-Taylor instability in the Kippenhahn-Schlüter prominence model. The plumes formed in these simulations are filamentary structures that are aligned with the magnetic field created as 3D modes of the magnetic Rayleigh-Taylor instability. The plumes rise, developing large structures from smaller structures through an inverse cascade process driven by nonlinear interaction. The results suggest that the plumes observed in the prominence may be used to study the conditions inside the prominence. Title: Numerical Simulations of the Magnetic Rayleigh-Taylor Instability in the Kippenhahn-Schlüter Prominence Model. I. Formation of Upflows Authors: Hillier, Andrew; Berger, Thomas; Isobe, Hiroaki; Shibata, Kazunari Bibcode: 2012ApJ...746..120H Altcode: The launch of the Hinode satellite led to the discovery of rising plumes, dark in chromospheric lines, that propagate from large (~10 Mm) bubbles that form at the base of quiescent prominences. The plumes move through a height of approximately 10 Mm while developing highly turbulent profiles. The magnetic Rayleigh-Taylor instability was hypothesized to be the mechanism that drives these flows. In this study, using three-dimensional (3D) MHD simulations, we investigate the nonlinear stability of the Kippenhahn-Schlüter prominence model for the interchange mode of the magnetic Rayleigh-Taylor instability. The model simulates the rise of a buoyant tube inside the quiescent prominence model, where the interchange of magnetic field lines becomes possible at the boundary between the buoyant tube and the prominence. Hillier et al. presented the initial results of this study, where upflows of constant velocity (maximum found 6 km s-1) and a maximum plume width ≈1.5 Mm which propagate through a height of approximately 6 Mm were found. Nonlinear interaction between plumes was found to be important for determining the plume dynamics. In this paper, using the results of ideal MHD simulations, we determine how the initial parameters for the model and buoyant tube affect the evolution of instability. We find that the 3D mode of the magnetic Rayleigh-Taylor instability grows, creating upflows aligned with the magnetic field of constant velocity (maximum found 7.3 km s-1). The width of the upflows is dependent on the initial conditions, with a range of 0.5-4 Mm which propagate through heights of 3-6 Mm. These results are in general agreement with the observations of the rising plumes. Title: Simulations of the magnetic Rayleigh-Taylor instability in a quiescent prominence model to study the dark upflows observed in prominences Authors: Hillier, A. S.; Berger, T. E.; Shibata, K.; Isobe, H. Bibcode: 2011AGUFMSH33A2033H Altcode: Observations of quiescent prominences by the Solar Optical Telescope (SOT) on board the Hinode satellite show plumes of hot, underdense material rising through the prominence. These plumes form at the boundary between the prominence and low density bubbles, approximately 10 Mm in size, that appear beneath the prominence, and then rise through the prominence material at speeds of approximately 20 km/s and widths of approximately 1.5 Mm. The plume profile ranges from highly turbulent to smooth, suggesting that the prominence conditions, as well as those of the bubble, are important in determining the dynamics. To investigate this phenomenon, we perform simulations of the magnetic Rayleigh-Taylor instability in a local prominence model. The instability creates rising plumes of hot, underdense material that propagate through the prominence material at a velocity of approximately 6-7 km/s and widths of approximately 1.5 Mm, in rough agreement with the Hinode observations. Nonlinear effects, in which the interaction between plumes drives an inverse cascade process creating large plumes from smaller plumes, are found to be important. Increasing the magnetic field strength creates smoother plume structures. The addition of a strong guide field, which is suggested in some prominence models, does not hinder plume formation but does change the dynamic scaling. The Rayleigh-Taylor instability drives an upward flow of magnetic energy and a downward flow of mass. The results from the simulations well match the characteristics of the observed plumes, suggesting that the magnetic Rayleigh-Taylor instability could be important in determining prominence structure as well as changing the magnetic energy distribution in overlying coronal cavities which ultimately erupt as coronal mass ejections. Title: Numerical Simulations of the Magnetic Rayleigh-Taylor Instability in the Kippenhahn-Schlüter Prominence Model Authors: Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari; Berger, Thomas Bibcode: 2011ApJ...736L...1H Altcode: 2011arXiv1107.4882A The launch of the Hinode satellite has allowed unprecedented high-resolution, stable images of solar quiescent prominences to be taken over extended periods of time. These new images led to the discovery of dark upflows that propagated from the base of prominences, developing highly turbulent profiles. As yet, how these flows are driven is not fully understood. To study the physics behind these phenomena, we use three-dimensional magnetohydrodynamic simulations to investigate the nonlinear stability of the Kippenhahn-Shlüter prominence model to the magnetic Rayleigh-Taylor instability. The model simulates the rise of a buoyant tube inside a quiescent prominence, where the upper boundary between the tube and prominence model is perturbed to excite the interchange of magnetic field lines. We found upflows of constant velocity (maximum found 6 km s-1) and a maximum plume width ≈1500 km which propagate through a height of approximately 6 Mm in the no guide field case. The case with the strong guide field (initially By = 2Bx ) results in a large plume that rises through the prominence model at ~5 km s-1 with width ~900 km (resulting in width of 2400 km when viewed along the axis of the prominence), reaching a height of ~3.1 Mm. In both cases, nonlinear processes were important for determining plume dynamics. Title: Observations of Plasma Blob Ejection from a Quiescent Prominence by Hinode Solar Optical Telescope Authors: Hillier, Andrew; Isobe, Hiroaki; Watanabe, Hiroko Bibcode: 2011PASJ...63L..19H Altcode: 2011arXiv1103.3750H We report findings from 0''.2 resolution observations of the 2007 October 03 quiescent prominence observed with the Solar Optical Telescope on the Hinode satellite. The observations show clear ejections from the top of the quiescent prominence of plasma blobs. The ejections, originating from the top of prominence threads, are impulsively accelerated to approximately Alfvén velocities and then undergo ballistic motion. The ejections have a characteristic size between ∼ 1000-2000 km. These characteristics are similar to downwardly propagating knots (typical size ∼ 700 km) that have been observed in prominence threads, we suggest that the plasma blob ejections could be the upward moving counterpart to the downwardly propagating knots. We discuss the tearing instability as a possible mechanism to explain the ejections. Title: Magneto-thermal convection in solar prominences Authors: Berger, Thomas; Testa, Paola; Hillier, Andrew; Boerner, Paul; Low, Boon Chye; Shibata, Kazunari; Schrijver, Carolus; Tarbell, Ted; Title, Alan Bibcode: 2011Natur.472..197B Altcode: Coronal cavities are large low-density regions formed by hemispheric-scale magnetic flux ropes suspended in the Sun's outer atmosphere. They evolve over time, eventually erupting as the dark cores of coronal mass ejections. Although coronal mass ejections are common and can significantly affect planetary magnetospheres, the mechanisms by which cavities evolve to an eruptive state remain poorly understood. Recent optical observations of high-latitude `polar crown' prominences within coronal cavities reveal dark, low-density `bubbles' that undergo Rayleigh-Taylor instabilities to form dark plumes rising into overlying coronal cavities. These observations offered a possible mechanism for coronal cavity evolution, although the nature of the bubbles, particularly their buoyancy, was hitherto unclear. Here we report simultaneous optical and extreme-ultraviolet observations of polar crown prominences that show that these bubbles contain plasma at temperatures in the range (2.5-12)×105 kelvin, which is 25-120 times hotter than the overlying prominence. This identifies a source of the buoyancy, and suggests that the coronal cavity-prominence system supports a novel form of magneto-thermal convection in the solar atmosphere, challenging current hydromagnetic concepts of prominences and their relation to coronal cavities. Title: MHD simulations of quiescent prominence upflows in the Kippenhahn-Schlüter prominence model Authors: Hillier, A. S.; Isobe, H.; Shibata, K.; Berger, T. E. Bibcode: 2011ASInC...2..331H Altcode: Images from the Hinode satellite have led to the discovery of dark upflows that propagate from the base of prominences, developing highly turbulent profiles. The magnetic Rayleigh-Taylor instability has been hypothesized as the mechanism to create these plumes. To study the physics behind this phenomenon we use 3D magnetohydrodynamic simulations to investigate the nonlinear stability of the Kippenhahn-Shlüter prominence model to the magnetic Rayleigh-Taylor instability. The model simulates the rise of a buoyant tube inside a quiescent prominence, where the upper boundary between the tube and prominence model is perturbed to excite the interchange of magnetic field lines. We find upflows of constant velocity (maximum found 6 km s^{-1}) and a maximum plume width ≈ 1500 km which propagate through a height of approximately 6 Mm, in general agreement with the Hinode observations. Title: Evolution of the Kippenhahn-Schlüter Prominence Model Magnetic Field under Cowling Resistivity Authors: Hillier, Andrew; Shibata, Kazunari; Isobe, Hiroaki Bibcode: 2010PASJ...62.1231H Altcode: 2010arXiv1007.1909H We present the results from 1.5D diffusion simulations of the Kippenhahn-Schlüter prominence model magnetic field evolution under the influence of the ambipolar terms of Cowling resistivity. We show that initially the evolution is determined by the ratio of the horizontal and vertical magnetic fields, which gives current sheet thinning (thickening) when this ratio is small (large) and a marginal case where a new characteristic current sheet length scale is formed. After a timespan greater than the Cowling resistivity time, the current sheet thickens as a power law of t independent of the ratio of the field strengths. These results imply that when Cowling resistivity is included in the model, the tearing instability time scale is reduced by more than one order of magnitude when the ratio of the horizontal field to the vertical field is 20% or less. These results imply that, over the course of its lifetime, the structure of the prominence can be significantly altered by Cowling resistivity, and in some cases will allow the tearing instability to occur. Title: Spicule Dynamics over a Plage Region Authors: Anan, Tetsu; Kitai, Reizaburo; Kawate, Tomoko; Matsumoto, Takuma; Ichimoto, Kiyoshi; Shibata, Kazunari; Hillier, Andrew; Otsuji, Kenichi; Watanabe, Hiroko; Ueno, Satoru; Nagata, Shin'ichi; Ishii, Takako T.; Komori, Hiroyuki; Nishida, Keisuke; Nakamura, Tahei; Isobe, Hiroaki; Hagino, Masaoki Bibcode: 2010PASJ...62..871A Altcode: 2010arXiv1002.2288A We studied spicular jets over a plage area and derived their dynamic characteristics using Hinode Solar Optical Telescope (SOT) high-resolution images. A target plage region was near to the west limb of the solar disk. This location permitted us to study the dynamics of spicular jets without any overlapping effect of spicular structures along the line of sight. In this work, to increase the ease with which we could identify spicules on the disk, we applied the image processing method `MadMax' developed by Koutchmy et al. (1989). It enhances fine, slender structures (like jets), over a diffuse background. We identified 169 spicules over the target plage. This sample permited us to derive statistically reliable results regarding spicular dynamics. The properties of plage spicules can be summarized as follows: (1) In a plage area, we clearly identified spicular jet features. (2) They were shorter in length than the quiet region limb spicules, and followed a ballistic motion under constant deceleration. (3) The majority (80%) of the plage spicules showed a cycle of rise and retreat, while 10% of them faded out without a complete retreat phase. (4) The deceleration of the spicule was proportional to the velocity of ejection (i.e., the initial velocity). Title: MHD simulations of upflows in the Kippenhahn-Schlueter prominence model Authors: Hillier, Andrew; Shibata, Kazunari; Isobe, Hiroaki; Berger, Thomas Bibcode: 2010cosp...38.2914H Altcode: 2010cosp.meet.2914H The launch of SOT on the Hinode satellite, with it's previously unprecedented high resolution, high cadence images of solar prominences, led to the discovery of small scale, highly dynamic flows in quiescent prominences. Berger et al. (2008) reported dark upflows that propagated from the base of the prominence through a height of approximately 10 Mm before ballooning into the familiar mushroom shape often associated with the Rayleigh-Taylor instability. Whether such phenomena can be driven by instabilities and, if so, how the instability evolve is yet to be fully investigated. In this study, we use the Kippenhahn-Schlueter (K-S) prominence model as the base for 3D numerical MHD simulations. The K-S prominence model is linearly stable for ideal MHD perturbationss, but can be made unstable through nonlinear perturbations, which we impose through inserting a low density (high temperature) tube through the centre of the prominence. Our simulations follow the linear and nonlinear evolution of upflows propagating from the hot tube through the K-S prominence model. We excited Rayleigh-Taylor like modes inside the K-S model with a wave along the contact discontinuity created between the hot tube and the K-S prominence, and solved the pertur-bations of this system. For such a complex setting, the linear evolution of the instability has 0.7 not been studied, and we found the growth rate to be ∼ ( ρ+ -ρ- - 0.05)k 0.22 . The most ρ+ +ρ- unstable wavelength was ∼ 100 km which, through the inverse cascade process, created upflows of ∼ 300 km. The rising plumes obtained a constant rise velocity in the nonlinear stage due to the creation of adverse magnetic and gas pressure gradients at the top of the plume. Title: Preservation of Lantern Slides for Use in Today's Technology Authors: Hillier, A. S. Bibcode: 2007ASPC..377..308H Altcode: 2007lisa.conf..308H Lantern slides will keep a long time, which is a good quality for preservation. However, as I have found, they break. Unless there is a lantern slide projector available, there is no way to show these valuable assets to others. This poster will explain my project to bring these pictures to life, to use them in education projects, and to simply show a bit of history to an attentive audience. With today's technology they can be placed on computers and stored more easily and be a joy to all.