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Solar pores are intense concentrations of magnetic flux that emerge through the Sun's photosphere. When compared to sunspots, they are much smaller in diameter and hence can be impacted and buffeted by neighbouring granular activity to generate significant magnetohydrodynamic (MHD) wave energy flux within their confines. However, observations of solar pores from ground-based telescope facilities may struggle to capture subtle motions synonymous with higher-order MHD wave signatures due to seeing effects produced in the Earth's atmosphere. Hence, we have exploited timely seeing-free and high-quality observations of four small magnetic pores from the Polarimetric and Helioseismic Imager (PHI) on board the Solar Orbiter spacecraft. Through acquisition of data under stable observing conditions, we have been able to measure the area fluctuations and horizontal displacements of the solar pores. Cross correlations between perturbations in intensity, area, line-of-sight velocity, and magnetic fields, coupled with the first-time application of novel Proper Orthogonal Decomposition (POD) techniques on the boundary oscillations, provide a comprehensive diagnosis of the embedded MHD waves as sausage and kink modes. Additionally, the previously elusive m = 2 fluting mode is identified in the most magnetically isolated of the four pores. An important consideration lies in how the identified wave modes contribute towards the transfer of energy into the upper solar atmosphere. We find that the four pores examined have approximately 56%, 72%, 52%, and 34% of their total wave energy associated with the identified sausage modes, and around 23%, 17%, 39%, and 49% to their kink modes, respectively, while the first pore also has around an 11% contribution linked to the fluting mode. This study marks the first-time identification of concurrent sausage, kink, and fluting MHD wave modes in solar magnetic pores., Comment: Accepted for publication in Astronomy & Astrophysics

The solar atmosphere is known to be replete with magneto-hydrodynamic wave modes, and there has been significant investment in understanding how these waves propagate through the Sun's atmopshere and deposit their energy into the plasma. The waves' journey is made interesting by the vertical variation in plasma quantities that define the solar atmosphere. In addition to this large-scale inhomogeneity, a wealth of fine-scale structure through the chromosphere and corona has been brought to light by high-resolution observations over the last couple of decades. This fine-scale sturcture represents inhomogeneity that is thought to be perpendicular to the local magnetic fields. The implications of this form of inhomogeneity on wave propagation is still being uncovered, but is known to fundamentally change the nature of MHD wave modes. It also enables interesting physics to arise including resonances, turbulence and instabilities. Here we review some of the key insights into how the inhomogeneity influences Alfv\'enic wave propagation through the Sun's atmosphere, discussing both inhomogeneities parallel and perpendicular to the magnetic field., Comment: Accepted in Journal of Modern Plasma Physics

Sunspots have played a key role in aiding our understanding of magnetohydrodynamic (MHD) wave phenomenon in the Sun's atmosphere, and it is well known they demonstrate a number of wave phenomenon associated with slow MHD modes. Recent studies have shown that transverse wave modes are present throughout the majority of the chromosphere. Using high-resolution Ca II 8542 {\AA} observations from the Swedish Solar Telescope, we provide the first demonstration that the chromospheric super-penumbral fibrils, which span out from the sunspot, also show ubiquitous transverse motions. We interpret these motions as transverse waves, in particular the MHD kink mode. We compile the statistical properties of over 2000 transverse motions to find distributions for periods and amplitudes, finding they are broadly consistent with previous observations of chromospheric transverse waves in quiet Sun fibrils. The very presence of the waves in super-penumbral fibrils raises important questions about how they are generated, and could have implications for our understanding of how MHD wave energy is transferred through the atmosphere of a sunspot., Comment: To be published in a Special Issue of the Philosophical Transactions of the Royal Society A

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate? (2) How do solar transients drive heliospheric variability? (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere? (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans (SOOPs), resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime., Comment: 20 pages, 1 figure, accepted by Astronomy & Astrophysics

The design of a primary electron beam facility at CERN is described. The study has been carried out within the framework of the wider Physics Beyond Colliders study. It re-enables the Super Proton Synchrotron (SPS) as an electron accelerator, and leverages the development invested in Compact Linear Collider (CLIC) technology for its injector and as an accelerator research and development infrastructure. The facility would be relevant for several of the key priorities in the 2020 update of the European Strategy for Particle Physics, such as an electron-positron Higgs factory, accelerator R\&D, dark sector physics, and neutrino physics. In addition, it could serve experiments in nuclear physics. The electron beam delivered by this facility would provide access to light dark matter production significantly beyond the targets predicted by a thermal dark matter origin, and for natures of dark matter particles that are not accessible by direct detection experiments. It would also enable electro-nuclear measurements crucial for precise modelling the energy dependence of neutrino-nucleus interactions, which is needed to precisely measure neutrino oscillations as a function of energy. The implementation of the facility is the natural next step in the development of X-band high-gradient acceleration technology, a key technology for compact and cost-effective electron/positron linacs. It would also become the only facility with multi-GeV drive bunches and truly independent electron witness bunches for plasma wakefield acceleration. A second phase capable to deliver positron witness bunches would make it a complete facility for plasma wakefield collider studies. [...]

The mechanism behind coronal heating still elude direct observation and modelling of viable theoretical processes and the subsequent effect on coronal structures is one of the key tools available to assess possible heating mechanisms. Wave-heating via phase-mixing of Magnetohydrodynamics (MHD) transverse waves has been proposed as a possible way to convert magnetic energy into thermal energy but increasingly, MHD models suggest this is not a sufficiently efficient mechanism. We model heating by phase-mixing of transverse MHD waves in various configurations, to investigate whether certain circumstances can enhance the heating sufficiently to sustain the million degree solar corona and to assess the impact of the propagation and phase-mixing of transverse MHD waves on the structure of the boundary shell of coronal loops. We use 3D MHD simulations of a pre-existing density enhancement in magnetised medium and a boundary driver to trigger the propagation of transverse waves with the same power spectrum as measured by the COmP. We consider different density structures, boundary conditions at the non-drive footpoint, characteristics of the driver, and different forms of magnetic resistivity. We find that different initial density structures affect the evolution of the boundary shell and some driver configurations enhance the heating generated from the dissipation of the MHD waves. In particular, drivers coherent on a larger spatial scale and higher dissipation coefficients generate significant heating, although it is still insufficient. We conclude that while phase-mixing of transverse MHD waves is unlikely to sustain the thermal structure of the corona, there are configurations that allow for an enhanced efficiency of this mechanism. We provide possible signatures to identify the presence of such configurations, such as the location of where the heating is deposited along the coronal loop

The proposed Beam Dump Facility (BDF) is foreseen to be located at the North Area of the SPS. It is designed to be able to serve both beam dump like and fixed target experiments. The SPS and the new facility would offer unique possibilities to enter a new era of exploration at the intensity frontier. Possible options include searches for very weakly interacting particles predicted by Hidden Sector models, and flavour physics measurements. In the first instance, exploitation of the facility, in beam dump mode, is envisaged to be for the Search for Hidden Particle (SHiP) experiment. Following the first evaluation of the BDF in 2014-2016, CERN management launched a Comprehensive Design Study over three years for the facility. The BDF study team has since executed an in-depth feasibility study of proton delivery to target, the target complex, and the underground experimental area, including prototyping of key sub-systems and evaluations of the radiological aspects and safety. A first iteration of detailed integration and civil engineering studies have been performed in order to produce a realistic schedule and cost. This document gives a detailed overview of the proposed facility together with the results of the studies, and draws up a possible road map for a three-year Technical Design Report phase, followed by a 5 to 6 year construction phase., Comment: 589 pages

Many cool stars possess complex magnetic fields [1] that are considered to undertake a central role in the structuring and energising of their atmospheres [2]. Alfv\'enic waves are thought to make a critical contribution to energy transfer along these magnetic fields, with the potential to heat plasma and accelerate stellar winds [3] [4] [5]. Despite Alfv\'enic waves having been identified in the Sun's atmosphere, the nature of the basal wave energy flux is poorly understood. It is generally assumed that the associated Poynting flux is generated solely in the photosphere and propagates into the corona, typically through the continuous buffeting of magnetic fields by turbulent convective cells [4] [6] [7]. Here we provide evidence that the Sun's internal acoustic modes also contribute to the basal flux of Alfv\'enic waves, delivering a spatially ubiquitous input to the coronal energy balance that is sustained over the solar cycle. Alfv\'enic waves are thus a fundamental feature of the Sun's corona. Acknowledging that internal acoustic modes have a key role in injecting additional Poynting flux into the upper atmospheres of Sun-like stars has potentially significant consequences for the modelling of stellar coronae and winds., Comment: 22 pages, 4 figures

High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase-difference spectra reveal a cutoff frequency near 3 mHz, up to which the oscillations are evanescent, while those with higher frequencies propagate upwards. The power-law index appears to increase with atmospheric height. Also, shorter damping lengths are observed for oscillations with higher frequencies suggesting frequency-dependent damping. Using the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we estimate the energy flux at different heights, which seems to decay gradually from the photosphere, in agreement with recent numerical simulations. Furthermore, a comparison of power spectra across the umbral radius highlights an enhancement of high-frequency waves near the umbral center, which does not seem to be related to magnetic field inclination angle effects., Comment: Accepted for publication in ApJ

Using the spectroscopic imaging capabilities of the Swedish Solar Telescope, we aim to provide the first investigation on the nature and dynamics of elongated absorption features (fibrils) observed in H$\alpha$ in the internetwork. We observe and identify a number of internetwork fibrils, which form away from the kilogauss, network magnetic flux, and we provide a synoptic view on their behaviour. The internetwork fibrils are found to support wave-like behaviour, which we interpret as Magnetohydrodynamic (MHD) kink waves. The properties of these waves, that is, amplitude, period, and propagation speed, are measured from time-distance diagrams and we attempt to exploit them via magneto-seismology in order to probe the variation of plasma properties along the wave-guides. We found that the Internetwork (IN) fibrils appear, disappear, and re-appear on timescales of tens of minutes, suggesting that they are subject to repeated heating. No clear photospheric footpoints for the fibrils are found in photospheric magnetograms or H$\alpha$ wing images. However, we suggest that they are magnetised features as the majority of them show evidence of supporting propagating MHD kink waves, with a modal period of $120$~s. Additionally, one IN fibril is seen to support a flow directed along its elongated axis, suggesting a guiding field. The wave motions are found to propagate at speeds significantly greater than estimates for typical chromospheric sound speeds. Through their interpretation as kink waves, the measured speeds provide an estimate for local average Alfv\'en speeds. Furthermore, the amplitudes of the waves are also found to vary as a function of distance along the fibrils, which can be interpreted as evidence of stratification of the plasma in the neighbourhood of the IN fibril., Comment: Accepted Astronomy & Astrophysics

Determining the mechanisms responsible for the heating of the coronal plasma and maintaining and accelerating the solar wind are long standing goals in solar physics. There is a clear need to constrain the energy, mass and momentum flux through the solar corona and advance our knowledge of the physical process contributing to these fluxes. Furthermore, the accurate forecasting of Space Weather conditions at the near-Earth environment and, more generally, the plasma conditions of the solar wind throughout the heliosphere, require detailed knowledge of these fluxes in the near-Sun corona. Here we present a short case for a space-based imaging-spectrometer coronagraph, which will have the ability to provide synoptic information on the coronal environment and provide strict constraints on the mass, energy, and momentum flux through the corona. The instrument would ideally achieve cadences of $\sim10$~s, spatial resolution of 1" and observe the corona out to 2~$R_{\sun}$. Such an instrument will enable significant progress in our understanding of MHD waves throughout complex plasmas, as well as potentially providing routine data products to aid Space Weather forecasting., Comment: 4 pages, 1 figure

The Coronal Multi-channel Polarimeter (CoMP) has previously demonstrated the presence of Doppler velocity fluctuations in the solar corona. The observed fluctuations are thought to be transverse waves, i.e. highly incompressible motions whose restoring force is dominated by the magnetic tension, some of which demonstrate clear periodicity. We aim to exploit CoMP's ability to provide high cadence observations of the off-limb corona to investigate the properties of velocity fluctuations in a range of coronal features, providing insight into how(if) the properties of the waves are influenced by the varying magnetic topology in active regions, quiet Sun and open fields regions. An analysis of Doppler velocity time-series of the solar corona from the $10,747$~{\AA} Iron XIII line is performed, determining the velocity power spectra and using it as a tool to probe wave behaviour. Further, the average phase speed and density for each region are estimated and used to compute the spectra for energy density and energy flux. In addition, we assess the noise levels associated with the CoMP data, deriving analytic formulae for the uncertainty on Doppler velocity measurements and providing a comparison by estimating the noise from the data. It is found that the entire corona is replete with transverse wave behaviour. The corresponding power spectra indicates that the observed velocity fluctuations are predominately generated by stochastic processes, with the spectral slope of the power varying between the different magnetic regions. Most strikingly, all power spectra reveal the presence of enhanced power occurring at $ \sim3$~mHz, potentially implying that the excitation of coronal transverse waves by $p$-modes is a global phenomenon., Comment: Accepted in ApJ

{Observations of the solar atmosphere have shown that magnetohydrodynamic waves are ubiquitous throughout. Improvements in instrumentation and the techniques used for measurement of the waves now enables subtleties of competing theoretical models to be compared with the observed waves behaviour. Some studies have already begun to undertake this process. However, the techniques employed for model comparison have generally been unsuitable and can lead to erroneous conclusions about the best model. The aim here is to introduce some robust statistical techniques for model comparison to the solar waves community, drawing on the experiences from other areas of astrophysics. In the process, we also aim to investigate the physics of coronal loop oscillations. } {The methodology exploits least-squares fitting to compare models to observational data. We demonstrate that the residuals between the model and observations contain significant information about the ability for the model to describe the observations, and show how they can be assessed using various statistical tests. In particular we discuss the Kolmogorov-Smirnoff one and two sample tests, as well as the runs test. We also highlight the importance of including any observational trend line in the model-fitting process.} {To demonstrate the methodology, an observation of an oscillating coronal loop undergoing standing kink motion is used. The model comparison techniques provide evidence that a Gaussian damping profile provides a better description of the observed wave attenuation than the often used exponential profile. This supports previous analysis from Pascoe et al. (2016). Further, we use the model comparison to provide evidence of time-dependent wave properties of a kink oscillation, attributing the behaviour to the thermodynamic evolution of the local plasma.}, Comment: Accepted in Astronomy & Astrophysics http://dx.doi.org/10.1051/0004-6361/201628613

The presence of magneto-acoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magneto-acoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope (DOT) and Rapid Oscillations in the Solar Atmosphere (ROSA) instruments, we captured two series of high-resolution intensity images with short cadence of two isolated magnetic pores. Combining wavelet analysis and empirical mode decomposition (EMD), we determined characteristic periods within the cross-sectional (i.e., area) and intensity time series. Then, by applying the theory of linear magnetohydrodynamics (MHD), we identified the mode of these oscillations within the MHD framework. Several oscillations have been detected within these two magnetic pores. Their periods range from 3 to 20 minutes. Combining wavelet analysis and EMD enables us to confidently find the phase difference between the area and intensity oscillations. From these observed features, we concluded that the detected oscillations can be classified as slow sausage MHD waves. Further, we determined several key properties of these oscillations such as the radial velocity perturbation, magnetic field perturbation and vertical wavenumber using solar magnetoseismology. The estimated range of the related wavenumbers reveals that these oscillations are trapped within these magnetic structures. Our results suggest that the detected oscillations are standing harmonics, and, this allows us to estimate the expansion factor of the waveguides by employing SMS. The calculated expansion factor ranges from 4-12., Comment: 10 pages, 4 figures. Accepted into ApJ

We present observational evidence of compressible magnetohydrodynamic wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four wavelength bands using the Dunn Solar Telescope. Employing Fourier and wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181-412s, with an average period ~290s, consistent with the global p-mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out-of-phase with one another, displaying phase angles of 6.12 degrees, 5.82 degrees and 15.97 degrees between 4170 Angstrom continuum - G-band, G-band - Na I D1 and Na I D1 - Ca II K heights, respectively, reiterating the presence of upwardly-propagating sausage-mode waves. A phase relationship of ~0 degrees between same-bandpass emission and area perturbations of the pore best categorises the waves as belonging to the `slow' regime of a dispersion diagram. Theoretical calculations reveal that the waves are surface modes, with initial photospheric energies in excess of 35000 W/m^2. The wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport waves that exhibit appreciable energy damping, which may release considerable energy into the local chromospheric plasma., Comment: 14 pages, 5 figures, accepted into ApJ

The chromosphere is a thin layer of the solar atmosphere that bridges the relatively cool photosphere and the intensely heated transition region and corona. Compressible and incompressible waves propagating through the chromosphere can supply significant amounts of energy to the interface region and corona. In recent years an abundance of high-resolution observations from state-of-the-art facilities have provided new and exciting ways of disentangling the characteristics of oscillatory phenomena propagating through the dynamic chromosphere. Coupled with rapid advancements in magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly investigate the role waves play in supplying energy to sustain chromospheric and coronal heating. Here, we review the recent progress made in characterising, categorising and interpreting oscillations manifesting in the solar chromosphere, with an impetus placed on their intrinsic energetics., Comment: 48 pages, 25 figures, accepted into Space Science Reviews

There is intense interest in determining the precise contribution of Alfv\'enic waves propagating along solar structures to the problems of coronal heating and solar wind acceleration. Since the launch of SDO/AIA, it has been possible to resolve transverse oscillations in off-limb solar polar plumes and recently McIntosh et al. (2011, Nature, 475, 477) concluded that such waves are energetic enough to play a role in heating the corona and accelerating the fast solar wind. However, this result is based on comparisons to Monte Carlo simulations and confirmation via direct measurements is still outstanding. Thus, this letter reports on the first direct measurements of transverse wave motions in solar polar plumes. Over a 4 hour period, we measure the transverse displacements, periods and velocity amplitudes of 596 distinct oscillations observed in the 171 \AA channel of SDO/AIA. We find a broad range of non-uniformly distributed parameter values which are well described by log-normal distributions with peaks at $234$ km, $121$ s and $8$ km s$^{-1}$, and mean and standard deviations of $407\pm297$ km, $173\pm118$ s and $14\pm10$ km s$^{-1}$. Within standard deviations, our direct measurements are broadly consistent with previous results. However, accounting for the whole of our observed non-uniform parameter distribution we calculate an energy flux of $9-24$ W m$^{-2}$, which is $4-10$ times below the energy requirement for solar wind acceleration. Hence, our results indicate that transverse MHD waves as resolved by SDO/AIA cannot be the dominant energy source for fast solar wind acceleration in the open-field corona., Comment: 16 pages, 4 figures, 1 table

The \textit{High resolution Coronal Imager (Hi-C)} has provided the sharpest view of the EUV corona to date. In this paper we exploit its impressive resolving power to provide the first analysis of the fine-scale structure of moss in an active region. The data reveal that the moss is made up of a collection of fine threads, that have widths with a mean and standard deviation of $440\pm190$~km (Full Width Half Maximum). {The brightest moss emission is located at the visible head of the fine-scale structure and the fine structure appears to extend into the lower solar atmosphere.} The emission decreases along the features implying the lower sections are most likely dominated by cooler transition region plasma. These threads appear to be the cool, lower legs of the hot loops. In addition, the increased resolution allows for the first direct observation {of physical displacements of the moss fine-structure in a direction transverse to its central axis. Some of these transverse displacements demonstrate periodic behaviour, which we interpret as a signature of kink (Alfv\'enic) waves. Measurements of the properties of the transverse motions are made and the wave motions have} means and standard deviations of $55\pm37$~km for the transverse displacement amplitude, $77\pm33$~s for the period and $4.7\pm2.5$~km/s for the velocity amplitude. The presence of waves in the transition region of hot loops could have important implications for the heating of active regions., Comment: 34 Pages, 10 Figures, 1 Table - accepted in ApJ

The observation of propagating magneto-hydrodynamic kink waves in magnetic structures and measurement of their properties (amplitude, phase speed) can be used to diagnose the plasma conditions in the neighbourhood of the magnetic structure via magneto-seismology (MS). We aim to reveal properties of the chromosphere/Transition Region above the sunspot penumbra using this technique. Hinode observed a sunspot as it was crossing the limb, providing a unique side on view of the sunspot atmosphere. The presence of large spicule-like jets is evident in \ion{Ca}{II} H images. The jets are found to support transverse wave motions that displace the central axis, which can be interpreted as a kink wave. The properties of a wave event are measured and used to determine the magnetic and density stratification along the structure. We also measure the width of the spicule and the intensity profile along the structure. The measured wave properties reveal an initial rapid increase in amplitude with height above the solar surface, followed by a decrease in amplitude. The MS inversion suggests this initial increase corresponds to large changes in density and magnetic field strength. In addition, we provide the first measurements of spicule width with height, which confirm that the spicule under goes rapid expansion. The measured expansion shows good agreement with the results from the MS. The observed variations in plasma parameters are suggested to be partly due to the presence of a gravitational stratified, ambient atmosphere. Combining width measurements with phase speed measurements implies the observed decrease in wave amplitude at greater heights can be explained by wave damping. Hence, we provide the first direct evidence of wave damping in chromospheric spicules and the quality factor of the damping is found to be significantly smaller than estimated coronal values., Comment: 13 pages, 10 figures - Accepted in A&A

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 three-hour 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 to 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., Comment: 6 pages, 5 figures, accepted for publication in ApJ letters

EUV jets situated in coronal holes are thought to play an important role in supplying heated material to the corona and solar wind. The multi-wavelength capabilities and high signal-to-noise of detectors on-board SDO allows for detailed study of these jet's evolution. We aim to exploit SDO's capabilities to reveal information on the jet dynamics and obtain estimates for plasma properties associated with the jet. We study the dynamics an EUV jet with AIA/SDO at a coronal hole boundary. The details of the jet evolution are discussed and measurements of the jet's parameters, e.g. length, width, life time, outward speed, are obtained. Further, automated emission measure analysis is exploited to determine estimates for the temperature and density of the jet. A propagating transverse wave supported by the jet spire is also observed. Measurement of the wave properties are exploited for magneto-seismology and are used in conjunction with the emission measure results to estimate the magnetic field strength of the jet. We present a detailed description of the jet's evolution, with new evidence for plasma flows, prior to the jet's initiation, along the loops at the base of the jet and also find further evidence that flows along the jet spire consist of multiple, quasi-periodic small-scale plasma ejection events. In addition, DEM analysis suggests that the jet has temperatures of $\log{5.89\pm0.08}$ K and electron densities of $\log{8.75\pm0.05}$ cm$^{-3}$. Measured properties of the transverse wave suggest the wave is heavily damped as it propagates along the jet spire with speeds of $\sim110$ km/s. The magneto-seismological inversion of the wave parameters provides values of $B=1.21\pm0.2$ G along the jet spire, which is in line with previous estimates for open fields in coronal holes.}, Comment: Accepted Astronomy and Astrophysics

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 kilometres per second is still unclear. One such mechanism for providing the required energy flux is incompressible torsional Alfv\'en 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 unclear. 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 contains evidence for horizontal photospheric motions being the main mechanism for kink wave generation in the quiescent Sun. In addition, a comparison to measured coronal power spectra is provided, revealing frequency-dependent transmission profiles suggesting there is enhanced damping of kink waves in the lower corona., Comment: In Press ApJ - March 2014

Using data obtained by the high temporal and spatial resolution Rapid Oscillations in the Solar Atmosphere (ROSA) instrument on the Dunn Solar Telescope, we investigate at an unprecedented level of detail transverse oscillations in chromospheric fine structures near the solar disk center. The oscillations are interpreted in terms of propagating and standing magnetohydrodynamic kink waves. Wave characteristics including the maximum transverse velocity amplitude and the phase speed are measured as a function of distance along the structure's length. Solar magneto-seismology is applied to these measured parameters to obtain diagnostic information on key plasma parameters (e.g., magnetic field, density, temperature, flow speed) of these localised waveguides. The magnetic field strength of the mottle along the $\sim$2 Mm length is found to decrease by a factor of 12, while the local plasma density scale height is $\sim280\pm$80 km., Comment: 8 pages, 7 figures, accepted in ApJ

The details of the mechanism(s) responsible for the observed heating and dynamics of the solar atmosphere still remain a mystery. Magnetohydrodynamic (MHD) waves are thought to play a vital role in this process. Although it has been shown that incompressible waves are ubiquitous in off-limb solar atmospheric observations their energy cannot be readily dissipated. We provide here, for the first time, on-disk observation and identification of concurrent MHD wave modes, both compressible and incompressible, in the solar chromosphere. The observed ubiquity and estimated energy flux associated with the detected MHD waves suggest the chromosphere is a vast reservoir of wave energy with the potential to meet chromospheric and coronal heating requirements. We are also able to propose an upper bound on the flux of the observed wave energy that is able to reach the corona based on observational constraints, which has important implications for the suggested mechanism(s) for quiescent coronal heating., Comment: Published in Nature Communications, 3, 1315 (2012)

The recent launch of the High resolution Coronal imager (Hi-C) provided a unique opportunity to study the EUV corona with unprecedented spatial resolution. We utilize these observations to investigate the properties of low frequency (50-200 s) active region transverse waves, whose omnipresence had been suggested previously. The five-fold improvement in spatial resolution over SDO/AIA reveals coronal loops with widths 150-310 km and that these loops support transverse waves with displacement amplitudes <50 km. However, the results suggest that wave activity in the coronal loops is of low energy, with typical velocity amplitudes <3 km/s. An extended time-series of SDO data suggest low-energy wave behaviour is typical of the coronal structures both before and after the Hi-C observations., Comment: 8 pages,4 figures - published in Astronomy and Astrophysics Letters

Observing the excitation mechanisms of incompressible transverse waves is vital for determining how energy propagates through the lower solar atmosphere. We aim to show the connection between convectively driven photospheric flows and incompressible chromospheric waves. The observations presented here show the propagation of incompressible motion through the quiet lower solar atmosphere, from the photosphere to the chromosphere. We determine photospheric flow vectors to search for signatures of vortex motion and compare results to {photospheric flows present in} convective simulations. Further, we search for the chromospheric response to vortex motions. Evidence is presented that suggests incompressible waves can be excited by the vortex motions of a strong magnetic flux concentration in the photosphere. A chromospheric counterpart to the photospheric vortex motion is also observed, presenting itself as a quasi-periodic torsional motion. Fine-scale, fibril structures that emanate from the chromospheric counterpart support transverse waves that are driven by the observed torsional motion. A new technique for obtaining details of transverse waves from time-distance diagrams is presented and the properties of transverse waves (e.g., amplitudes and periods) excited by the chromospheric torsional motion are measured., Comment: 12 pages, 6 figures, Accepted ApJ

Evidence is beginning to be put forward that demonstrates the role of the chromosphere in supplying energy and mass to the corona. We aim to assess the role of chromospheric jets in active region dynamics. Using a combination of the Hinode/SOT Ca II H and TRACE 1550 {\AA} and 1600 {\AA} filters we examine chromospheric jets situated at the edge of a sunspot. Analysis reveals a near continuous series of jets, that raise chromospheric material into the low corona above a sunspot. The jets have average rise speeds of 30 km\,s^{-1} and a range of 10-100km\,s^{-1}. Enhanced emission observed at the jets leading edge suggests the formation of a shock front. Increased emission in TRACE bandpasses above the sunspot and the disappearance of the jets from the Ca II filter suggests that some of the chromospheric jet material is at least heated to \sim0.1MK. The evidence suggests that the jets could be a mechanism which provides a steady, low-level heating for active region features., Comment: A&A, In press 2012

A variety of periodic phenomena have been observed in conjunction with large solar jets. We aim to find further evidence for {(quasi-)}periodic behaviour in solar jets and determine what the periodic behaviour can tell us about the excitation mechanism and formation process of the large solar jet. Using the 304 {\AA} (He-II), 171 {\AA} (Fe IX), 193 {\AA} (Fe XII/XXIV) and 131 {\AA} (Fe VIII/XXI) filters on-board the Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA), we investigate the intensity oscillations associated with a solar jet. Evidence is provided for multiple magnetic reconnection events occurring between a pre-twisted, closed field and open field lines. Components of the jet are seen in multiple SDO/AIA filters covering a wide range of temperatures, suggesting the jet can be classified as a blowout jet. Two bright, elongated features are observed to be co-spatial with the large jet, appearing at the jet's footpoints. Investigation of these features reveal they are defined by multiple plasma ejections. The ejecta display (quasi-)periodic behaviour on timescales of 50 s and have rise velocities of 40-150 km\,s$^{-1}$ along the open field lines. Due to the suggestion that the large jet is reconnection-driven and the observed properties of the ejecta, we further propose that these ejecta events are similar to type-II spicules. The bright features also display (quasi)-periodic intensity perturbations on the timescale of 300 s. Possible explanations for the existence of the (quasi-)periodic perturbations in terms of jet dynamics and the response of the transition region are discussed., Comment: Astronomy and Astrophysics - In Print

A number of recent investigations have revealed that transverse waves are ubiquitous in the solar chromosphere. The vast majority of these have been reported in limb spicules and active region fibrils. We investigate long-lived, quiet Sun, on-disk features such as chromospheric mottles (jet-like features located at the boundaries of supergranular cells) and their transverse motions. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument at the Dunn Solar Telescope. The dataset comprises simultaneous imaging in the H$\alpha$ core, Ca II K, and G band of an on-disk quiet Sun region. Time-distance techniques are used to study the characteristics of the transverse oscillations. We detect over 40 transverse oscillations in both bright and dark mottles, with periods ranging from 70 to 280 s, with the most frequent occurrence at ~ 165 s. The velocity amplitudes and transverse displacements exhibit characteristics similar to limb spicules. Neighbouring mottles oscillating in-phase are also observed. The transverse oscillations of individual mottles are interpreted in terms of magnetohydrodynamic kink waves. Their estimated periods and damping times are consistent with phase mixing and resonant mode conversion., Comment: 5 pages, 5 figures, accepted in ApJ

A thin dark thread is observed in a UV/EUV solar jet in the 171A, 193A and 211A and partially in 304A. The dark thread appears to originate in the chromosphere but its temperature does not appear to lie within the passbands of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We therefore implement solar magnetoseismology to estimate the plasma parameters of the dark thread. A propagating fast kink (transverse) wave is observed to travel along the dark thread. The wave is tracked over a range of ~7000km by placing multiple slits along the axis of the dark thread. The phase speed and amplitude of the wave are estimated and magnetoseismological theory is employed to determine the plasma parameters. We are able to estimate the plasma temperature, density gradient, magnetic field gradient and sub-resolution expansion of the dark thread. The dark thread is found to be cool, T~3x10^4$ with both strong density and magnetic field gradients. The expansion of the flux tube along its length is ~300-400km., Comment: Accepted ApJ, Publication expected Novemember 2011

We investigate the propagation of MHD waves in a homogenous, magnetized plasma in a weakly stratified atmosphere, representing hot coronal loops. In most of earlier studies a time-independent equilibrium is considered. Here we abandon this restriction and allow the equilibrium to develop as function of time. In particular, the background plasma is assumed to be cooling due to thermal conduction. The cooling is assumed to be on a time scale greater than the characteristic travel times of the perturbations. We investigate the influence of cooling of the background plasma on the properties of magneto-acoustic waves. The MHD equations are reduced to a 1-D system modelling magneto-acoustic modes progressing along a dynamically cooling coronal loop. A time dependent dispersion relation which describes the propagation of the magneto-acoustic waves is derived by using the WKB theory. An analytic solution for the time-dependent amplitude of waves is obtained and the method of characteristics is used to find an approximate analytical solution. Numerical calculations are applied to the analytically derived solutions to obtain further insight into the behavior of the MHD waves in a system with variable, time-dependent background. The results show that there is a strong damping of MHD waves that can be linked to the widely observed damping of hot coronal loop oscillations. The damping also appears to be independent of position along the loop. Studies of MHD wave behaviour in time-dependent background seem to be a fundamental and very important next step in developing MHD wave theory applicable to a wide range in solar physics., Comment: 14 pages; 5 figures

We study non-axisymmetric oscillations of a straight magnetic tube with an elliptic cross-section and density varying along the tube. The governing equations for kink and fluting modes in the thin tube approximation are derived. We found that there are two kink modes, polarised along the large and small axes of the elliptic cross-section. We have shown that the ratio of frequencies of the first overtone and fundamental harmonic is the same for both kink modes and independent of the ratio of the ellipse axes. On the basis of this result we concluded that the estimates of the atmospheric scale height obtained using simultaneous observations of the fundamental harmonic and first overtone of the coronal loop kink oscillations are independent of the ellipticity of the loop cross-section.

We present here evidence for the observation of the magneto-hydrodynamic (MHD) sausage modes in magnetic pores in the solar photosphere. Further evidence for the omnipresent nature of acoustic global modes is also found. The empirical decomposition method of wave analysis is used to identify the oscillations detected through a 4170 {\AA} 'blue continuum' filter observed with the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument. Out of phase, periodic behavior in pore size and intensity is used as an indicator of the presence of magneto-acoustic sausage oscillations. Multiple signatures of the magneto-acoustic sausage mode are found in a number of pores. The periods range from as short as 30 s up to 450 s. A number of the magneto-acoustic sausage mode oscillations found have periods of 3 and 5 minutes, similar to the acoustic global modes of the solar interior. It is proposed that these global oscillations could be the driver of the sausage type magneto-acoustic MHD wave modes in pores., Comment: 11 pages, 2 figures