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    PDG Seminar | Conferences organisation | Past meetings | Participation in Seminars, Conferences | Sheffield Space Initiative Solar Codes


    PDG Seminar


    Every even week Thursday during semester time. Venue - F28 (usually), Hicks Building. Time - 16:00


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    Prof Francisco Guzman
    Universidad Michoacana de San Nicolas de Hidalgo, Mexico



    12.11.2020 at 16:00 via Google Hangouts Meet

    A code that solves the equations of MHD coupled to radiation


    Our code is based on a finite volume discretization, uses high-resolution shock-capturing flux formulae of the HLL class. Concerning the MHD part, we use the divergence cleaning method to preserve the non-monopoles constraint. For radiation, at the moment, we use the M1 closure relation within the gray body approximation. The evolution equations for radiation become stiff for high opacities, for which we use an implicit-explicit evolution method, which allows the use of a standard integration time-step. We present our code's status and mention the solar physics scenarios where we expect to produce some applications.

    Dr Inigo Arregui
    Instituto de Astrofisica de Canarias, Spain



    29.10.2020 at 16:00 via Google Hangouts Meet

    Bayesian coronal seismology


    Coronal seismology is based on the remote diagnostics of physical conditions in the solar corona by comparison between model predictions and observations of wave activity. Our lack of direct access to the physical system of interest makes information incomplete and uncertain so our conclusions are at best probabilities. Bayesian inference is increasingly being employed in the area, following a general trend in solar and astrophysical research. In this seminar, I first justify the use of a Bayesian probabilistic approach to seismology diagnostics and explain its philosophy and methodology. Then, I report on recent results that demonstrate its feasibility and advantage in applications to coronal loops, prominences and extended regions of the corona. To finish, I suggest other areas of current interest where the use of Bayesian methods could contribute to improve our understanding on the structure, dynamics and heating of the corona.

    Prof George Haller
    ETH Zurich, Switzerland



    15.10.2020 at 13:00 via Google Hangouts Meet

    Objective material barriers to the transport of momentum and vorticity


    I discuss a recent theory for material surfaces that maximally inhibit the diffusive transport of a dynamically active (i.e., velocity-dependent) vector field, such as the linear momentum, the angular momentum or the vorticity, in three-dimensional unsteady flows. These diffusion barriers provide physics-based, observer-independent boundaries of dynamically active coherent structures. Instantaneous limits of these Lagrangian diffusion barriers mark objective Eulerian barriers to short-term active transport. I show how active diffusion barriers can be identified with active versions of Lagrangian coherent structure (LCS) diagnostics. In comparison to their passive counterparts, however, active LCS diagnostics require no significant fluid particle separation and hence provide substantially higher-resolved Lagrangian and Eulerian coherent structure boundaries from shorter velocity data sets. I illustrate these results on two-dimensional turbulence and three-dimensional wall-bounded turbulence.


    Dr Rekha Jain
    Sheffield University, UK



    01.10.2020 at 16:00 via Google Hangouts Meet

    Frequency power spectra of Alfvén waves in a solar coronal arcade: Discrete or Continuous?


    In this talk I will present theoretically computed frequency power spectra for shear Alfvén waves excited in a solar coronal arcade. I investigate two separate perturbations, a cosine-modulated Gaussian perturbation and an impulsive driver. The arcade is assumed to consist of potential magnetic field lines embedded in stratified plasma. In principle, the nature of the frequency power spectra can constrain the size and the type of driver.

    Dr Isabell Piantschitsch
    Universitat de les Illes Balears, Spain



    30.07.2020 at 16:00 via Google Hangouts Meet

    A new method for estimating global coronal wave properties from their interaction with solar coronal holes


    Global coronal waves (CWs) and their interaction with coronal holes (CHs) result, among other effects, in the formation of reflected and transmitted waves. Observations of such events provide us with measurements of different CW parameters, such as phase speed and intensity amplitudes. However, several of these parameters are provided with only intermediate observational quality, other parameters, such as the phase speed of transmitted waves, can hardly be observed in general. We present a new method to estimate crucial CW parameters, such as density and phase speed of reflected as well as transmitted waves, Mach numbers and density values of the CH's interior, by using analytical expressions in combination with basic and most accessible observational measurements. The transmission and reflection coefficients are derived from linear theory and subsequently used to calculate estimations for phase speeds of incoming, reflected and transmitted waves. The obtained analytical expressions are validated by performing numerical simulations of CWs interacting with CHs. This new method enables to determine in a fast and straightforward way reliable CW and CH parameters from basic observational measurements which provides a powerful tool to better understand the observed interaction effects between CWs and CHs.

    Dr Jonathan Higham
    University of Liverpool, UK



    23.07.2020 at 16:00 via Google Hangouts Meet

    Modal Decompositions: What are they, why should we use them and how?


    The dynamics of natural systems are often complex and highly non-linear, understanding these procedures is difficult as their dynamics and complexities are usually intertwined and colluded. Whilst we might be able to identify these systems using sets of nonlinear equations, determining the individual process is underlying a complex mechanism are non-trivial. Over the past few decades, there has been much work to develop data driven methods to extract coherent features either in space or in time. Two prominent methods are the proper orthogonal decomposition and the dynamic mode decomposition; in this seminar these two methods will be introduced, the underpinning mathematics and algorithms will be outlined, and variants of the algorithms and methods will also be described. However, much of the seminar will focus on applying these methods, using them at all different scales from idealised small-scale laboratory experiments to large-scale real-world applications. The primary aim of this seminar will be to equip you with an arsenal of spatially and temporally orthogonal tools which you can use to elucidate the complex features from your data sets.

    Dr Nitin Yadav
    Max Planck Institute for Solar System Research, Gottingen, Germany



    02.07.2020 at 16:00 via Google Hangouts Meet

    Vortex Flows in the Solar Atmosphere


    Vortex flows exist over various spatial and temporal scales throughout the solar atmosphere and are of great importance due to their potential in twisting the magnetic field lines and hence facilitating Poynting flux transport. Recent advances in both, observational techniques and numerical simulations, have enabled us to detect a multitude of small-scale vortices in the solar atmosphere. Smaller vortices are suggested to play an important role in the solar atmospheric heating, however, their physical properties remain poorly understood due to limited resolution in observations. Hence, it is crucial to investigate them using high-resolution simulations since they are more abundant and faster rotating flows than the larger vortices. Using MHD simulations, we explored the the relationship between vortex flows at different spatial scales, analyze their physical properties, and investigate their contribution to Poynting flux transport from the lower to the upper layers of the solar atmosphere. We found that a large vortex, as seen at low spatial resolution, consists of a large number of smaller vortices, when seen at high spatial resolution. Statistically, they have higher densities and higher temperatures than the average values at the same geometrical height. Their Poynting flux contribution is more than adequate to compensate for the radiative losses in the chromosphere indicating their possible role in the solar atmospheric heating.

    Dr Matheus Aguiar-Kriginsky Silva
    Universitat de les Illes Balears, Spain



    18.06.2020 at 16:00 via Google Hangouts Meet

    Ubiquituous hundred-Gauss magnetic fields in solar spicules


    Even though they were observed for the first time in the 19th century, the nature of spicules is not well understood because they are are thin and elongated chromospheric jets and therefore their study is limited to the resolution of the instruments used. Every time a step forward in the quality of the observations of the lower chromosphere is taken, the interest in spicules sparks. Most recently, the advent of the Hinode telescope provided high-resolution images of spicules that allowed for a better comprehension of their nature and behavior. Studies regarding their magnetic field have been also undertaken, but most of them did not have the ideal spatial/temporal resolution needed to give definitive results. This study is aimed to provide a step forward in this matter, with observations in the Ca II 854.2 nm line taken with the CRISP instrument at the Swedish 1-meter Solar Telescope in La Palma. The sensitivity of the Ca II 854.2 nm line to the magnetic field is exploited and the Weak Field Approximation (WFA) is used to estimate the line-of-sight component of the magnetic field of spicules both off-limb and on the solar disk. The WFA must be used carefully, since there are conditions that need to be met for it to be applicable. This consideration is assessed in every pixel, and a Bayesian approach is taken to infer the line-of-sight magnetic field component from the WFA equations. It is established that magnetic fields over 100 G are abundant, and the reason for the failure of previous studies to conclude this is carefully studied and is speculated to lie in the poor temporal/spatial resolution of the observations used.

    Dr Suzana de Souza e Almeida Silva



    04.06.2020 at 16:00 via Google Hangouts Meet

    Dynamics of the Vortex Tubes in the Solar Atmosphere


    We use a state of the art vortex detection method, Instantaneous Vorticity Deviation, to define and locate three-dimensional vortices in magneto-convections simulations performed by the MURaM code. The detected vortices extend from the photosphere to the low chromosphere. The dynamics across the vortical flows at different height levels are investigated through radial profiles. We found that the vortices present similar dynamics at all height levels, with nonuniform angular rotational velocity and eddy viscosity effects. The vortices intensify the magnetic field, and in turn, the vortex dynamics are affected by the magnetic field. On the other hand, our findings hint that kinematic vortices need to present high tangential velocities at different height levels to overcome the magnetic tension and generate magnetic vortices.

    Dr José Juan González Avilés



    21.05.2020 at 16:00 via Google Hangouts Meet

    Numerical studies of jet formation in the solar atmosphere

    Using the Newtonian CAFE MHD code to perform 2.5D and 3D resistive MHD simulations in the solar atmosphere, we show that magnetic reconnection may be responsible for the formation of jets with some characteristics of Type II spicules and cool coronal jets. We numerically model the photosphere-corona region using the C7 atmosphere model. The initial magnetic configuration in the 2.5D case consists of two symmetric neighboring loops with opposite polarity, used to support reconnection. In the 3D case, the initial magnetic configuration is extrapolated up to the solar corona region from a dynamic realistic simulation of the solar photospheric magnetoconvection model that mimics the quiet-Sun.
    In the 2.5D simulations, we include the effect of the thermal conduction along the magnetic field lines to study some properties of spicule jets. In this case, we find that thermal conductivity affects morphology, velocity, and temperature of the jets. Also, the heat flux maps indicate the head of the jet and corona interchange energy more efficiently than the body of the jet. In the 3D simulations, we have found that the formation of the jet depends on the Lorentz force, which helps to accelerate the plasma upward. The morphology, the upward velocity covering a range up to 130 km/s, and the timescale formation of the structure between 60 and 90 s, are similar to those expected for Type II spicules. Additionally, we analyze various properties of the jet dynamics, and find that the structure shows rotational and torsional motions which may generate torsional Alfvén waves in the corona region.

    Dr Rahul Sharma



    07.05.2020 at 16:00 via Google Hangouts Meet

    Complex 3D dynamics of solar spicule structures

    Sun’s outer atmosphere is a million degree hotter than it’s visible surface, which is not understood with any of the known laws of thermodynamics and remains an intriguing problem for the astrophysics in general. It is now believed that most of the energy dissipation phenomenon occurs at the interface region in between solar chromosphere and corona, which is a highly dynamic, gravitationally stratified, nonlinear, inhomogeneous environment. Observed dynamics of thin magnetic fluxtube structures in this layer, reflects the confined magnetohydrodynamic (MHD) wave-modes (kink, sausage and torsional Alfven). For the first time, the evolution of the resultant transverse displacement of the observed flux tube structures, estimated from perpendicular velocity components, is analyzed along with cross-sectional width, photometric and azimuthal shear/torsion variations, to accurately identify the confined wave-mode(s). In my talk, I will discuss the observational evidence of pulse-like nonlinear kink wave-mode(s), as indicated by the strong coupling in between kinematic observables, with a frequency-doubling, -tripling aspect, supported by mutual phase relations centered around 0 and +-180 (Sharma et al. 2018). The 3D ensemble of the observed dynamic components revealed complexities pertinent to the accurate identification and interpretation of e.g. linear/nonlinear, coupled/uncoupled MHD wave-modes in the observed waveguides (spicules).

    Mr Abdulaziz Alharbi



    23.04.2020 at 16:00 via Google Hangouts Meet

    Waves in Two-Fluid Gravitationally Stratified Plasmas

    The temperature in the lower part of solar atmosphere is not high enough for a complete ionisation of the plasma. Therefore, this environment region is made up of electrons, positive ions and neutrals that interact through short and long range collisions in the presence of the magnetic field. Due to the low temperature, the gravitational scale-height is also short, meaning that perturbations will be affected by gravity. Here we study the spatial and temporal evolution of slow magnetoacoustics waves propagating in a stratified magnetic flux tube. In the two-fluid plasma the dynamics of neutrals and charged species has to be studied separately. Our analysis shows that the dynamic is described by a system of coupled Klein-Gordon equations that are solved in the strongly ionised limit. For the mentioned two species we study the changes in the cut-off frequency for a range of physical parameters. Asymptotic solutions to the governing equations are obtained for a harmonic driver. Our results reveal that ion-acoustic and neutrals-acoustic slow modes show a different damping scale.

    Mr Yasir Aljohani



    09.04.2020 at 16:00 via Google Hangouts Meet

    Identifying magnetohydrodynamic vortex tubes in the Sun's photosphere

    Vortex flows in the solar photosphere are fundamentally important for the generation of magnetohydrodynamic (MHD) waves which propagate to the upper layers of the solar atmosphere. Vortex tubes are formed as coherent magnetic field structures in the solar atmosphere, e.g. twisted magnetic flux tubes. In this presentation, I will discuss the method of Lagrangian Averaged Vorticity Deviation (LAVD) developed by Haller (2016) to identify vortex flows, namely the center of circulation and their boundary, then I will present the algorithmic technique I have developed to check whether a structure detected by the LAVD method is a true vortex or not and how to determine the rotational direction(clockwise or anticlockwise). In addition, I will apply these methods to MURaM magneto-convection simulation data to detect and track the evolution of both 2D vortices and 3D vortex tubes in the solar photosphere.

    Mr Abdulrahman Albidah



    26.03.2020 at 16:00 via Google Hangouts Meet

    Multi-faceted approach to decomposing and identifying individual magnetohydrodynamic (MHD) wave modes in sunspots and pores

    High resolution observations of pores and sunspots show a rich and complex variety of oscillatory temporal and spatial behaviour. To decompose this data into individual magnetohydrodynamic (MHD) wave modes is non-trivial and requires a multi-faceted approach. Here we take a three-pronged approach of combining Fourier analysis, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The Fourier omega-k power spectrum provides us with a useful overall view of the particular temporal and spatial scales of interest but does not provide any cross-pixel correlation. In this regard, POD classifies modes that are orthogonal in space but places no restrictions on their frequencies. DMD has no such restrictions in space but classifies modes that are orthogonal in time, i.e., identified modes cannot have the same frequency. Each of these complementary techniques have their particular strengths which we will illustrate with synthetic data.

    Dr Viktor Fedun



    12.03.2020 at 16:00 in F28 (Hicks Building)

    Vortex motions in the solar atmosphere

    Solar photosphere vortices have the potential to form coherent magnetic field structures, e.g. twisted magnetic flux tubes and, therefore, may play a key role in the transport of energy and momentum from the lower atmosphere into the upper solar atmosphere. In this talk I will review existing methods for their identification and discuss our approach, which is based on Gamma detection and LAVD of inter-granular photospheric intensity vortices. I will also present new mechanism for the generation of magnetic waveguide from the lower solar atmosphere to the corona. This waveguide appears as the result of interacting perturbations (initially generated by photospheric vortex motions) in neighbouring magnetic flux tubes (modelled in the framework of self-similar approach).


    Dr Ben Snow



    06.03.2020 at 16:00 in F28 (Hicks Building)

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

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

    Dr Sandra Milena Conde Cuellar



    27.02.2020 at 16:00 in F28 (Hicks Building)

    Oscillation of coronal loops associated with flaring events

    Loops are fascinating structures that bring us a lot of information about the exchange of energy in the solar atmosphere. Oscillations and waves represent one of the most fascinating events in the loops, which also plays a key role in the study of coronal seismology. It is not clear how the disturbances are excited, however, there are several candidates, e.g., flares, emerging flux, and eruptions. In this talk, I present a summary of oscillations observed in different active regions in the presence of flares and other events. This analysis has been done with data provided by IRIS, SDO and GOES-15 spacecraft. We have found excitation sources of some disturbances in lower heights of the solar atmosphere. This matches with oscillations found in the top and the footpoints of the coronal loops. We used this information together with semi-empirical models to study the distribution of physical variables in the loops.


    Dr Shahin Jafarzadeh



    13.02.2020 at 16:00 in F28 (Hicks Building)

    Magneto-acoustic Waves in the Lower Solar Atmosphere at High Resolution

    Fibrillar structures of different appearances and/or properties have ubiquitously been observed throughout the Sun's chromosphere. They are often thought to map the magnetic fields, and are likely rooted in small-scale magnetic elements in the solar photosphere. Here, we present properties of magnetohydrodynamic-wave dynamics in various fibrillar structures as well as in small magnetic elements in the low solar atmosphere, at high-spatial resolution, from the SUNRISE balloon-borne observatory as well as the Swedish Solar Telescope. Our analysis reveals the prevalence of kink and sausage waves in both types of magnetic structures, propagating at similar high frequencies. The estimated energy flux carried by the observed waves is marginally enough to heat the chromosphere (and perhaps the corona). Furthermore, such waves are compared with temperature fluctuations in the fibrils from high-temporal resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS) explorer, simultaneously observed at several millimetre and ultraviolet bands of, e.g., ALMA 1.3 mm as well as IRIS Mg II h & k, Si IV, and C II spectral lines, from which, physical properties of the fibrillar structures are also discussed.

    Dr Tom Van Doorsselaere



    05.12.2019 at 16:00 in F28 (Hicks Building)

    Waves and seismology of pores


    In this seminar, I will discuss several aspects of waves in pores. These concentrations of magnetic field similar to miniature sunspots are wave guides for MHD waves. In contrast to waves in coronal loops, they are resolved across the wave guide, but it is harder to know what happens further along the magnetic field. I will discuss mode identification by using wave amplitude ratios, calculation of their energy fluxes as could be used for coronal heating, and resonant absorption of slow waves. An outlook to future work is also included.

    Mr Farhad Allian



    21.11.2019 at 16:00 in F28 (Hicks Building)

    A New Analysis Procedure for Detecting Periodicities within Complex Solar Coronal Arcades


    Coronal loop arcades form the building blocks of the hot and dynamic solar atmosphere. In particular, their oscillations serve as an indispensable tool in estimating the physical properties of the local environment by means of seismology. However, due to the nature of the arcade's complexity, these oscillations can be difficult to analyze. In this talk, I will present a novel image-analysis procedure based on the spatio-temporal autocorrelation function that can be utilized to reveal 'hidden' periodicities within EUV imagery of complex coronal loop systems.

    Dr Norbert Magyar



    07.11.2019 at 16:00 in F28 (Hicks Building)

    Simulations of MHD waves in structured plasmas


    It is well known that in an infinite and homogeneous plasma, there are three types of waves: fast, slow, and Alfven. However, richer dynamics appear in MHD once inhomogeneities are considered.The solar corona and solar wind is often seen to be highly structured, most probably even way below the current resolving capabilities of imaging instruments. The structuring of the plasma gives rise to some well-known phenomena such as surface and body modes, reflection/refraction of waves, phase mixing, resonant absorption and so on. The nonlinear implications of structuring are less well-known, though. In a series of numerical simulations, we will review the basic dynamics of waves supported by structures, and will connect these findings to the generation of turbulence in a structured plasma.

    Mr Yuyang Yuan



    24.10.2019 at 16:00 in F28 (Hicks Building)

    The Solar Spicule Tracking Code


    In this talk I will explain and demonstrate the Solar Spicule Tracking Code (SSTC) that I have developed. This code has the ability to automatically detect and track the motion spicules in imaging data. I will specifically demonstrate the code working with images obtained using the H alpha line from the CRisp Imaging SpectroPolarimeter (CRISP) based at the Swedish Solar Telescope.

    Ms Anwar Aldhafeeri



    10.10.2019 at 16:00 in F28 (Hicks Building)

    Solar atmospheric magnetohydrodynamic wave modes in magnetic flux tubes of elliptical cross-sectional shape


    The approach to understanding and analysing the behaviour of MHD we observed in the solar atmosphere is to find a relevant wave solution for the MHD equations. Therefore many previous studies focused on deriving a dispersion relation equation and solving this equation for a cylindrical tube. We know perfectly well that sunspots and pores do not have an ideal circular cross-section. Therefore, any imbalance in waveguide’s diameters, even if very small, will move the study of the problem from the cylindrical coordinates to elliptical coordinates. Thus the emphasis on knowing the properties and what type of wave modes exist in elliptical waveguides are much more critical than studying them in cylindrical coordinates. In this talk, I will start by deriving the dispersion relation in a compressible flux tube with elliptical cross-sectional shape. I will then solve the dispersion equation and discuss the solution of dispersion equation and how the ellipticity of tube effects the solutions with applications to coronal and photospheric conditions. However, the information we get from the dispersion diagram does not give the full picture of how we can observe a wave, and how much the wave mode changes when the cross-sectional shape of waveguide changes. Therefore I will present some visualisations of eigenfunctions of MHD wave modes and explain how the eccentricity effects each MHD wave mode.

    Dr Dave Jess



    30.05.2019 at 14:00 in LT10 (Hicks Building)

    Resonance Cavities: A wave amplification mechanism above highly magnetic sunspots


    The solar atmosphere provides a unique astrophysical laboratory to study the formation, propagation, and subsequent dissipation of magnetohydrodynamic (MHD) waves across a diverse range of spatial scales. The concentrated magnetic fields synonymous with sunspots allow the examination of guided magnetoacoustic modes as they propagate upwards into the solar corona, where they exist as ubiquitous 3-minute waves readily observed along loops, plumes and fan structures. While cutting-edge observations and simulations are providing insights into the underlying wave generation and damping mechanisms, the in-situ amplification of magnetoacoustic waves as they propagate through the solar chromosphere has proved difficult to explain. Here we provide observational evidence of a resonance cavity existing above a magnetic sunspot, where the intrinsic temperature stratification provides the necessary atmospheric boundaries responsible for the resonant amplification of these waves. Through comparisons with high-resolution numerical MHD simulations, the geometry of the resonance cavity is mapped across the diameter of the underlying sunspot, with the upper boundaries of the chromosphere ranging between 1300–2300 km. This brings forth important implications for next-generation ground-based observing facilities, and provides an unprecedented insight into the MHD wave modelling requirements for laboratory and astrophysical plasmas.

    Dr Peter Wyper



    16.05.2019 at 16:00 Room K14 (Hicks Building)

    Reconnection, Topology and Solar Eruptions


    The majority of free energy in the solar corona is stored within sheared magnetic field structures known as filament channels. Filament channels spend most of their life in force balance before violently erupting. The largest produce powerful solar flares and coronal mass ejections (CMEs), whereby the filament channel is bodily ejected from the Sun. However, a whole range of smaller eruptions and flares also occur throughout the corona. Some are ejective, whilst others are confined. Recently it has been established that coronal jets are also typically the result of a filament channel eruption. The filament channels involved in jets are orders of magnitude smaller than the ones which produce CMEs. In this talk I will start by considering these tiny, jet producing eruptions. I will introduce our MHD simulation model that well describes them and then discuss what jets can tell us about solar eruptions in general. Specifically, I will argue that many different types of eruption can be understood by considering two defining features: the scale of the filament channel and its interaction via reconnection with its surrounding magnetic topology.

    Dr Suzana de Souza e Almeida Silva



    13.05.2019 at 13:00 Room LT9 (Hicks Building)

    Lagrangian Coherent Structures: Overview and applications in solar physics


    Lagrangian coherent structures (LCS) is a newly developed theory which describes the skeleton of turbulent flows. LCS act as barriers in the flow, separating regions with different dynamics and organizing the flow into coherent patterns. This talk will introduce some concepts of LCT techniques as well as recent application to solar physics problems.

    Dr Youra Taroyan



    02.05.2019 at 16:00 Room K14 (Hicks Building)

    Amplification of magnetic twists during prominence formation


    Solar prominences are dense magnetic structures that are anchored to the visible surface known as the photosphere. They extend outwards into the Sun’s upper atmosphere known as the corona. Twists in prominence field lines are believed to play an important role in supporting the dense plasma against gravity as well as in prominence eruptions and coronal mass ejections (CMEs), which may have severe impact on the Earth and its near environment. We will use a simple model to mimic the formation of a prominence thread by plasma condensation. The process of coupling between the inflows and the twists will be discussed. We show that arbitrarily small magnetic twists should be amplified in time during the mass accumulation process. The growth rate of the twists is proportional to the mass condensation rate.

    Prof Philippa Browning



    18.04.2019 at 16:00 Room K14 (Hicks Building)

    Plasma heating and particle acceleration by magnetic reconnection in solar and stellar flares


    In this talk, I will describe recent models of plasma heating and non-thermal particle acceleration in flares, focussing on the role of twisted magnetic flux ropes as reservoirs of free magnetic energy. First, using 2D magnetohydrodynamic simulations coupled with a guiding-centre test-particle code, I will describe magnetic reconnection and particle acceleration in a large-scale flaring current sheet, triggered by an external perturbation – the “forced reconnection” scenario. I will show how reconnection is involved both in creating twisted flux ropes, and in their merger, how this depends on the nature of the driving disturbance, and how particles are accelerated by the different modes of reconnection. Moving to 3D models, showing how fragmented current structures in kink-unstable twisted loops can both heat plasma and accelerate charged particles. Forward modelling of the observational signatures of this process in EUV, hard X-rays and microwaves will be described, and the potential for observational identification of twisted magnetic fields in the solar corona discussed. Then, coronal structure with multiple twisted threads will be considered, showing how instability in a single unstable twisted thread may trigger reconnection with stable neighbours, releasing their stored energy and causing an "avalanche" of heating events, with important implications for solar coronal heating. This avalanche can also accelerate electrons and ions throughout the structure. Many other stars exhibit flares, and I will briefly discuss recent work on modelling radio emission in flares in young stars (T Tauri stars). In particular, the enhanced radio luminosity of these stars relative to scaling laws for the Sun and other Main Sequence stars will be discussed.

    Dr Peter Keys



    21.03.2019

    Small-scale magnetic field evolution with high resolution observations


    Small-scale magnetic fields, ubiquitous across the solar surface, manifest as intensity enhancements in intergranular lanes and, thus, often receive the moniker of magnetic bright point (MBP). MBPs are frequently studied as they are considered as a fundamental building block of magnetism in the solar atmosphere. The theory of convective collapse developed in the late 70’s and early 80’s is often used to explain how kilogauss fields form in MBPs. The dynamic nature of MBPs coupled with these kilogauss fields means that they are frequently posited as a source of wave phenomena in the solar atmosphere.
    Here, with high resolution observations of the quiet Sun with full Stokes spectropolarimetry, we investigate the magnetic properties of MBPs. By analysing the temporal evolution of various physical properties obtained from inversions, we show that kilogauss fields in MBPs can appear due to a variety of reasons, and is not limited to the process of convective collapse. Analysis of MURaM simulations confirms the processes we observe in our data. Also, magnetic field amplification happens on rapid timescales, which has significant implications for many wave studies.

    Dr Patrick Antolin



    07.03.2019

    Transverse MHD Waves and associated dynamic instabilities in the solar atmosphere


    A large amount of recent simulations and analytical work indicate that standing transverse MHD waves in loops should easily lead to the generation of dynamic instabilities at their edges, and in particular of the Kelvin-Helmholtz kind. While a direct observation of these transverse wave-induced Kelvin-Helmholtz rolls (or TWIH rolls) is still lacking, the forward modelling of these simulations give us an indication of what to look for in next generation instrumentation, and which currently observed features could actually be the result of TWIKH rolls. In this talk I will go through some of these results, comparing observations with various instruments with simulations of coronal loops, prominences and spicules.

    Dr. Mark Wrigley



    28.02.2019

    1201 Alarm Project


    The 1201 Alarm Project is the restoration, exhibition and sharing of materials recorded in 1969 of the Apollo moon landings from a domestic television. The talk will review the Apollo flight plan, the recording technologies of the day and the impact that it had on the speaker. The materials will form the basis for an exhibition celebrating the 50th anniversary of moon landings to be held at the National Science and Media Museum in Bradford, Yorkshire.
    Web site: https//1201alarm.org

    Prof. Valery Nakariakov



    31.01.2019 venue LT1, Hicks Building

    The effect of thermal misbalance on compressive oscillations in solar coronal loops


    Fast and slow magnetoacoustic waves are a promising tool for the seismological diagnostics of physical parameters of various plasma structures in the corona of the Sun. In particular, compressive waves can provide us with information about the thermodynamic equilibrium in the coronal plasma, and hence the heating function. Compressive perturbations of the thermodynamic equilibrium by magnetoacoustic waves can cause the misbalance of the radiative cooling and unspecified heating. The effect of the misbalance is determined by the derivatives of the combined heating/cooling function with respect to the plasma density and temperature, and can lead to either enhanced damping of the compressive oscillations or their magnification. Moreover, in the regime of strong misbalance, compressive MHD waves are subject to wave dispersion that can slow down the formation of shocks and can cause the formation of quasi-periodic wave trains.

    Ms. Hope Thackray



    29.11.2018 venue LTD

    Fast MHD modes of a two (and three) shell semi-cylindrical waveguide


    The modelling of coronal loop structures has long been pursued as a means of determining physical properties of the Sun's corona. Here, a 3D semi-cylindrical waveguide is proposed, representing a coronal loop arcade anchored in the photosphere. By considering the eigenfunctions formed at the interface of a sharp density discontinuity (represented by "two-shell" and subsequently "three-shell" density structures), we show that waves are elliptically polarised, and that small changes in density contrast between shells can drastically affect the presence of eigenmodes. Since observational information has restrictions on resolution, the implication is that two similarly determined density structures may produce vastly different estimations of potential eigenmodes.

    Dr. Istvan Ballai



    22.11.2018 venue LT2

    Introduction to multiple scaling methods to solve differential equations with applications to plasma physics. Part II: Nonlinear partial differential equations


    In the second part of my seminar I will focus on nonlinear partial differential equations that can be obtained from the MHD equations. Using the multiple scale technique I will present a method to obtain the Korteweg-de Vries-Burgers equation in a non-ideal plasma in the presence of Hall currents. Using simple methods, I will find solutions to the limiting cases of shock waves and solitons.

    Dr. Istvan Ballai



    15.11.2018 venue K14

    Introduction to multiple scaling methods to solve differential equations with applications to plasma physics. Part I: Ordinary linear differential equations


    Many of the equations we encounter in our research on solar and space plasma physics dynamics contain essential physical constraints (nonlinearity, singularities, complex domains of interest, complex boundary conditions, etc.) that makes difficult to find exact solutions. Therefore, in order to obtain information about solutions of equations, we are forced to use approximative methods, numerical solutions, or both. The most important approximation methods are the perturbation methods, where the solutions are represented by the first few terms of an expansion.

    In this seminar I will review the perturbation methods used to solve ordinary differential equations, highlighting their advantages and shortcomings. The presentation will revolve around simple examples of differential equations, presenting the method of finding approximative solutions of a differential equation we can derive in plasma physics.

    Mr. Samuel Skirvin



    1.11.2018

    Properties of Alfvénic waves in the solar chromosphere


    In the first part of my talk I will discuss the results of investigation of the properties of transverse waves existing in spicules using the automated wave tracking code NUWT. Analysing a distance-time diagram at an altitude of 7 Mm relative to the solar limb produces the measured distribution of properties such as wave amplitude, period and velocity amplitude. In the second part of the talk I will provide an overview of the rescent studies on the effect of initial flow profiles on the dynamics of solar jets.

    Dr. Gary Verth



    18.10.2018

    Introduction to the Sun


    This talk will be an introduction to the science required to understand the Sun and its atmosphere. It is primarily intended for students starting their postgraduate research in plasma, solar, or magnetospheric physics. Due to the introductory nature of the talk, it would also be suitable for any interested non-specialists.


    Conference Organisation

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    Dynamic Sun III





    Past Meetings

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    Dynamic Sun II





    Dynamic Sun I





    Participation in Seminars, Conferences

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    ESPOS, 7.11.2019
    Ms Anwar Aldhafeeri



    MHD wave modes in the solar magnetic flux tubes with elliptical cross-section


    Many previous studies of MHD modes in the magnetic flux tubes were focussed on deriving a dispersion relation for cylindrical waveguides. However, from observations it is well known that, for example, the cross-sectional shape of sunspots and pores are not perfect circles and can often be much better approximated by ellipses. From a theoretical point of view, any imbalance in a waveguide’s diameters, even if very small, will move the study of the problem from cylindrical to elliptical coordinates. In this talk, I will therefore describe a model that predicts the MHD wave modes that can be trapped and propagate in a compressible magnetic flux tube with an elliptical cross-section embedded in a magnetic environment. I will discuss the resultant dispersion relations for body and surface modes, then then I will show how the ellipticity of a magnetic flux tube effects these solutions (with specific applications to the coronal and photospheric conditions). From a practical point of view the information from these dispersion diagrams does not show how these MHD modes will manifest themselves in observational data. Therefore, I will also present several visualisations of the eigenfunctions of these MHD wave modes and explain how the eccentricity effects each wave mode.

    ESPOS, 4.10.2018
    Eleanor Vickers



    Surface waves and instabilities in the presence of an inclined magnetic field


    While surface waves propagating at tangential discontinuities have been studied in great detail, few studies have been dedicated to the investigation of the nature of waves at contact discontinuities, i.e. plasma discontinuity, where the background magnetic field crosses the interface between two media. In this talk, I will show that, by introducing magnetic field inclination, the frequency of waves is rendered complex, where the imaginary part describes wave attenuation, due to lateral energy leakage. We investigate the eigen-value and initial value problem and determine the conditions of transition from contact to tangential discontinuity. Finally, I will present an investigation into the effect of magnetic field inclination on magnetic Rayleigh-Taylor instability.





    Sheffield Space Initiative

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    Sheffield Space Initiative

    Following the fantastic success of the SunbYte mission (2017), the Sheffield Space Initiative (SSI) was founded to further engage University of Sheffield students in the science and engineering challenges involved in the exploration of Space and now consists of four exciting projects, i.e. SunbYte, SunrIde, MoonWorks and ROV Avalon. Working with the world’s largest professional Engineering Institution (IET), UK Students for the Exploration and Development of Space (UKSEDS), National Aeronautics and Space Administration (NASA), European Space Agency (ESA), UK Space Agency (UKSA), Institution of Mechanical Engineers (IMechE), Sheffield Engineering Leadership Academy (SELA), the University of Sheffield Space Society and a number of Faculty of Engineering and Science departments, the SSI aims to inspire the next generation of Space Engineers and Scientists.





    Solar Codes

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    Solar Spicule Tracking Code (SSTC)


    version 1.0

    Solar Spicule Tracking Code version 1.0 (SSTC v1.0, written in MatLab) is designed for automated detection, tracking and analysis of solar spicules properties (also applicable for coronal loop and other curvilinear features detection in the solar atmosphere). The code works best with hi-resolution observational solar imaging data. The choice of either photospheric, chromospheric or coronal spectral lines depends on the particular features to be identified and analysed. As an output, the code provides information on individual spicules/loops detected as well as overall statistics. A gradient contour method is used to constrain identified spicule/loop boundaries as well as their axis (the spicule/loop ``spine''). Detection results may be influenced by quality of current observational data (DKIST data will be tested by the authors when available). The level of accuracy of the code can be improved by adding more points along the spicule/loop ``spine'' (if the detection region has a particularity high density of spicules/loops). This will also provide a more accurate time evolution of the spicules/loops. To improve robustness, Machine Learning (ML) will be implemented in the next version of the code. Data processing time of current version depends on user computing facilities (i.e. number of CPU cores, GPU performance) used.
  • Queries
  • Yuyang Yuan (SoMaS/ACSE), YYuan26 at sheffield.ac.uk
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield for providing the Solar Spicule Tracking Code (SSTC)

    Sheffield Dispersion Diagram Code (SDDC)


    version 1.0

    Sheffield Dispersion Diagram Code version 1.0 (SDDC v1.0, written in Python) is designed to produce the dispersion diagram for magnetoacoustic magnetohydrodynamic (MHD) wave modes within a solar application. The motivation for developing this method comes from the analytical requirement to derive a dispersion relation in order to previously produce a dispersion diagram. In order to do this, simple models or specific case studies are considered so that the mathematics becomes more manageable. Consideration of more complicated models and solving the set of MHD equations result in a differential equation with no known analytic solution. However using the shooting method, the roots of the equation can be found. Therefore more complicated models and plasma structuring can be investigated in more depth using this method than could be conduction through theory alone.
  • Queries
  • Samuel J. Skirvin (ACSE), sjskirvin1 at sheffield.ac.uk
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield and for support provided in the creation of Sheffield Dispersion Diagram Code, SDDC v1.0, 2020. The development of the code was also supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No.824135 (SOLARNET). SJS also thanks STFC for the PhD studentship under which the code was produced and developed.


    version 2.0

    Sheffield Dispersion Diagram Code version 2.0 (SDDC v2.0, written in Python) is designed to produce the dispersion diagram for magnetoacoustic magnetohydrodynamic (MHD) wave modes within a solar application. The version explained in this manual build on the previous v1.0 which was very much the spine of the code. This version is much more streamlined and contains additional features which improve the accuracy of the results and additional files for analysis of results. The improvements made in SDDC v2.0 include:
  • Multiprocessing options - speeding up the elapsed time and optimisation of previous version(s).
  • Analysis Files. These include files which import the output data from the main program to allow for use in plotting and visualisations.
  • Inclusion of physics required to account for background plasma flows, uniform and non-uniform. This file can be provided upon request to the developers.
  • The bulk of the code is still the same as the previous version(s), however may be tweaked for improved optimisation. The same physics is still implemented as described in previous version(s) of the code, for more information on the main functions used in the code see the code manual for SDDC v1.0
  • Queries
  • Samuel J. Skirvin (ACSE), sjskirvin1 at sheffield.ac.uk
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield and for support provided in the creation of Sheffield Dispersion Diagram Code, SDDC v2.0, 2020. The development of the code was also supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No.824135 (SOLARNET). SJS also thanks STFC for the PhD studentship under which the code was produced and developed.

    Wave Mode Analysis Code (WMAC)


    version 1.0

    Wave Mode Analysis Code version 1.0 (WMAC v1.0, written in MatLab 2019a) is prepared to analyse solar data as it is dealing with the techniques of Proper Orthogonal Decomposition (POD), developed by Pearson (1901), and Dynamic Mode Decomposition(DMD), initially developed by Schmid (2010). The POD is a mathematical technique that identifies modes that are orthogonal in space and it provides a clear ranking of the modes in terms of their contribution (Higham et al. 2018). While DMD identities temporal orthogonality and it does not rank the modes in any way. If it is assumed that modes are temporally orthogonal, i.e., different modes cannot have identical frequencies, then DMD with a search criteria offers an optimal methodology to identify coherent mode structure from, for example, intensity snapshots. In this manual we apply the POD and DMD in an intensity time series of a sunspot data to identify MHD wave mode.
  • Queries
  • Abdulrahman B. Albidah (SoMaS), abalbidah1 at sheffield.ac.uk
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
    Istvan Ballai (SoMaS), i.ballai at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield and for support provided in the creation of Sheffield Dispersion Diagram Code, SDDC v1.0, 2020. The development of the code was also supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No.824135 (SOLARNET). SJS also thanks STFC for the PhD studentship under which the code was produced and developed.

    Code for Vortex Flow Analysis (CVFA)


    version 1.1


    CVFA v1.1 code and data, zip (26MB)

    Use the main function "vortex2D.m" to run

    CVFA v1.1 manual (3.4MB)

    Code for Vortex Flow Analysis version 1.1 (CVFA v1.1, written in MatLab 2019a). Vortex flows in the solar photosphere are fundamentally important for the generation of magnetohydrodynamic (MHD) waves which propagate to the upper layers of the solar atmosphere. Vortex tubes are formed as coherent magnetic field structures in the solar atmosphere, e.g. twisted magnetic flux tubes. In this manual, we explain a code of Lagrangian Averaged Vorticity Deviation (LAVD) Haller et al. 2016 adopted to identify vortex flows (the center of circulation and 3D vortex boundary) in the solar atmosphere data, Additional algorithmic technique were developed to check whether a structure detected by the LAVD method is a true vortex or not and how to determine the rotational direction (clockwise or anticlockwise). Also, we applied these methods to the MuRaM magneto-convection simulation data to detect and track the evolution of 2D vortices in the solar photosphere.
  • Queries
  • Yasir Aljohani (SoMaS), yaljohani2 at sheffield.ac.uk
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Istvan Ballai (SoMaS), i.ballai at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield and for support providedin the creation of Code for Vortex Flow Analysis code, CVFA v1.1, 2020. The development of the codewas also supported by the European Union’s Horizon 2020 research and innovation program under grantagreement No.824135 (SOLARNET). YA also thanks Uumm Al Qura University PhD studentship.

    Tool for Analysis of Oscillatory Modes (TAOM)


    version 1.0

    The Tool for Analysis of Oscillatory Modes (TAOM) version 1.0 (TAOM v1.0, written in MatLab) is designed to detect and trace the boundary of binary image of sunspots umbra (or other feature for which boundary can be traced) and then calculate the eigenmodes and eigenfunctions of the shape of the input sunspots image with implies a fixed boundary condition using discrete Laplacian in MatLab. The code scans parameter space for eigenvalues and orthogonal eigenvectors that match the boundary conditions for any given cross-sectional shape. Also this code is designed to find the best elliptical (or other shape) approximation of the sunspot and calculate the eigenmodes/eigenfunctions and provides the comparison between the umbra of the sunspots and elliptical membrane. This code work with binary image only.
  • Queries
  • Anwar Aldhafeeri (SoMaS), aaaldhafeeri1 at sheffield.ac.uk, aaaldhafeeri at kfu.edu.sa
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield and King Faisal University for support provided. The development of the code was also supported by the European Unions Horizon 2020 research and innovation program under grant agreement No.824135 (SOLARNET).



    Vortex Detection Code (VDC)


    version 1.0


    VDC v1.0 zip (30KB)

    Use the main function "gamma_identification_for_vortex_demo.m" to run

    VDC v1.0 manual (4.1MB)

    The Vortex Detection Code (VDC) version 1.0 (VDC v1.0, written in Mat-Lab) is designed to detect and identify the vortex flow motions in the 2D numericalor observational solar data. Code is based on implementation of Gamma func-tions Graftieaux et al. 2001 and new algorithm for more accu-rate tracking of the vortex boundary. The code is fully tested on the numerical datagenerated by SolarBox code.
  • Queries
  • Yuyang Yuan (SoMaS/ACSE), YYuan26 at sheffield.ac.uk
    Viktor Fedun (ACSE), v.fedun at sheffield.ac.uk
    Gary Verth (SoMaS), g.verth at sheffield.ac.uk
  • Citation in the literature
  • We acknowledge the Plasma Dynamics Group at the University of Sheffield and King Faisal University for support provided. The development of the code was also supported by the European Unions Horizon 2020 research and innovation program under grant agreement No.824135 (SOLARNET).