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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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    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, 4.10.2018





    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.