DOCSLIB.ORG

PDF Version Roberts & Nakariakov 2003

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
PDF Version Roberts & Nakariakov 2003 feature Coronal activity captured Vibrating magnetic by the SOHO spacecraft structures in the solar Studies so far seem to atmosphere are indicate that the key to opening up a new way understanding the corona lies in its complex magnetic structure. to study the Sun The corona is dominated by a magnetic field. That field is rooted in the dense layers of the photosphere, where it is influenced by the churning and convective upwelling of material from the layers beneath, interacting with localised magnetic fields that are in the form of magnetic tubes. The tubes range in diameter from a few hundred kilometres up to tens of thousands of kilometres, the larger structures being visible as sunspots. High above the photosphere, in the corona, magnetic fields expand to fill the plasma. There, they control much of what we see – be it the dramatic solar flares with loops of material ejected violently into space, or the quieter long-lived events that generate the numerous wispy structures seen in the CBernard Robertso and Valeryr Nakariakovonal corona, including the coronal loops. he Sun’s corona is remarkable for its beauty. First revealed in photographs of total solar eclipses,T the corona is now routinely studied seismology from spacecraft, which have exposed in dramatic detail a stunning pattern of – a new science streamers and loops in the thin ionised gas, or plasma, constituting it. This complexity is physicists. They are important not only for Magnetic vibrations nowhere more evident than in the our understanding of fundamental aspects Recently, observations from TRACE and remarkable data gathered daily by the of plasma astrophysics but also for the SOHO began revealing a new phenomenon NASA solar space mission – the Transition new branch of applied space physics known which may provide the answers we are Region And Coronal Explorer (TRACE), as space weather (which discusses how seeking. Magnetic fields embedded in a and the ESA-NASA mission – Solar and the solar wind affects our near-space plasma like the corona are elastic, and this Heliospheric Observatory (SOHO). environment). Plasmas are ubiquitous in the means they can oscillate, creating ‘magnetic Nevertheless, the corona presents an Universe and play significant roles in, for waves’. We can describe the waves using the enigma. It is much hotter than the example, the generation of magnetic fields theory of magnetohydrodynamics (MHD) photosphere (the apparent surface of Sun within a star’s interior and the production – a subject that is a marriage of fluid as we see it in the sky) that lies below, of activity in its atmosphere, including its mechanics and electromagnetism. This reaching one million degrees or more ability to produce and emit X-rays. In any theoretical approach gives rise to three (compared with about 6000 degrees for the case, a full understanding of the physical kinds of MHD wave, which are in fact 12 surface). The corona also releases into space processes operating in the Sun’s corona – analogous to the more familiar sound waves a stream of accelerated charged particles, and by implication in the coronae of many in an ordinary gas such as air and the the solar wind. The mechanisms behind stars – is likely to involve a mixture of new vibrations of a guitar string (the magnetic these phenomena have long intrigued solar observations and theory. field playing the role of the elastic string). Researchers have long thought that MHD helioseismology which tends to look at the rapidly! This is in marked contrast to sound waves would occur in the corona but there solar interior as a whole (though it is also waves in the solar interior. We do not know were few observations to support this idea. beginning to probe local features). what is responsible for this dramatic coronal Now, TRACE and SOHO have provided We have already made progress in this effect, though very recent theoretical work unequivocal evidence that the magnetic direction. One major uncertainty is the carried out at the Universities of Sheffield loop structures seen in the corona do in fact magnetic field strength in localised and St Andrews reveal a promising vibrate, the vibration perhaps following a possibility connected with the flare or similar event. In fact, the key to inhomogeneity of the corona. But they oscillate in distinctive whatever is responsible for the decay, this ways that may be interpreted understanding the corona too carries distinct information in terms of MHD wave theory about the coronal plasma. All this – the basis of which our research group at lies in its complex encourages us to believe that the University of St Andrews developed magnetic structure coronal seismology will develop almost two decades ago! fruitfully in the near future. ✦ The presence of these waves in the corona is perhaps not surprising, given its structures such as coronal loops. We can Professor B. Roberts is an applied magnetic nature. What is exciting is that determine magnetic field strengths at the mathematician and Professor of Solar such magnetic waves, long thought to play solar surface from spectra (a magnetic field Magnetohydrodynamics at the University of a part in explaining coronal heating, have splits the spectral lines, producing the St Andrews. Dr V. Nakariakov is a senior now been detected and their properties so-called Zeeman splittings). This reveals lecturer in physics at Warwick University. measured, even though their role in coronal fields of 3000 gauss in sunspots, to be E-mails: [email protected]; heating remains unclear. compared with the Earth’s magnetic field of [email protected] less than a gauss. But we cannot apply this A new source of information method in the almost vacuum-like medium The first observational example of ‘kink’ oscillations (waving from side to side) of coronal loops taken Waves have another role: they carry of the corona. However, by fitting the by the TRACE satellite in 1998. These were first information about the medium through observed oscillations with MHD wave predicted by Bernie Roberts 20 years ago. The which they pass. This means that detecting theory, we can determine that the field diagram shows a possible mechanism for excitation of kink oscillations of coronal loops by a solar flare magnetic waves in the corona offers the strength in a coronal loop is about 13 gauss. possibility of obtaining information about These studies, which were carried out at the coronal plasma that is otherwise Warwick University and elsewhere, are unavailable. This is by no means a new still at an early stage, but they suggest approach. Just as geophysicists have used that coronal seismology using MHD waves elastic waves to find out about the Earth’s will be a useful tool in studying the outer interior (seismology), so solar physicists solar structure. have exploited sound waves to learn about There is another feature of the coronal the solar interior (helioseismology). Sound oscillations seen by TRACE and SOHO that waves trapped in the Sun are measured, in is worth mentioning: the oscillations decay the surface oscillations they produce, by ground-based observatories such as BISON (operated by Birmingham University) and spacecraft such as SOHO. The data can then Flare epicentre be used to determine, for example, how the various layers in the Sun rotate or how the Kink oscillations sound speed increases with depth beneath the surface of the Sun. Helioseismology has proved a great Loop success and we hope to repeat this success for the corona. Observing coronal oscillations, coupled with magnetic wave theory, offers the prospect of developing a new method for studying the Sun – coronal 13 seismology. Because magnetic fields control Blast wave Footpoint (fast magnetoacoustic) the structure of the corona it is likely that the technique will be able to investigate Footpoint localised phenomena – in contrast to.
Load more

Recommended publications
  • 1 Introduction
    1 1 Introduction Uchida [1], who suggested the idea of plasma and magnetic field diagnostics in the solar corona on the basis of waves and oscillations in 1970, and Rosenberg [2], who first explained the pulsations in type IV solar radio bursts in terms of the loop magnetohydrodynamic (MHD) oscillations, can be considered to be pioneers of coronal seismology. Various approaches have been used to describe physical processes in stellar coronal structures: kinetic, MHD, and electric circuit models are among them. Two main models are presently very popular in coronal seismology. The first considers magnetic flux tubes and loops as wave guides and resonators for MHD waves and oscillations, whereas the second describes a loop in terms of an equivalent electric (RLC) circuit. Several detailed reviews are devoted to problems of coronal seismology (see, i.e., [3–7]). Recent achievements in the solar coronal seismology are also referred in Space Sci. Rev. vol. 149, No. 1–4 (2009). Nevertheless, some important issues related to diagnostics of physical processes and plasma parameters in solar and stellar flares are still insufficiently presented in the literature. The main goal of the book is the successive description and analysis of the main achievements and problems of coronal seismology. There is much in common between flares on the Sun and on late-type stars, especially red dwarfs [8]. Indeed, the timescales, the Neupert effect, the fine structure of the optical, radio, and X-ray emission, and the pulsations are similar for both solar and stellar flares. Studies of many hundreds of stellar flares have indicated that the latter display a power–law radiation energy distribution, similar to that found for solar flares.
    [Show full text]
  • “Oscillatory Processes in Solar and Stellar Coronae”
    www.issibj.ac.cn ISSI-BJ WORKSHOP “OSCILLATORY PROCESSES IN SOLAR AND STELLAR CORONAE” Topics I. Sergey Anfinogentov, et al. "Novel techniques in coronal seismology data analysis" II. Valery Nakariakov, et al. "Kink oscillations and waves in the corona" III. Tongjiang Wang, et al. "Slow waves in coronal loops" IV. Dipankar Banerjee, et al. "MHD waves in open coronal structures" V. Ivan Zimovets, et al. "Quasi-periodic pulsations in solar and stellar flares" VI. Bo Li, et al. "Sausage oscillations and waves in the corona" VII. Tom Van Doorsselaere, et al. "Coronal heating by MHD waves” VIII. Other I. Sergey Anfinogentov, et al. "Novel techniques in coronal seismology data analysis" David Pascoe High-resolution Diagnostic Techniques for the Solar Corona The high spatial and temporal resolution provided by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory has inspired the development of advanced observational techniques to probe the solar atmosphere. For example, forward modelling of the EUV intensity of coronal structures and the seismological analysis of kink oscillations provide powerful diagnostics to constrain properties such as the plasma density and magnetic field strength. We also increasingly employ Bayesian analysis and Markov chain Monte Carlo sampling in our analysis to increase the robustness and accuracy of our modelling. These techniques are now also being applied to study quasi-periodic pulsations associated with solar and stellar flares. [email protected] www.issibj.ac.cn Inigo Arregui Recent results in Bayesian coronal and prominence seismology We report on recent results from the application of Bayesian analysis techniques to seismology of coronal loops and prominence fine structures.
    [Show full text]
  • Temporal Evolution of Mhd Waves in Solar Coronal Arcades
    DOCTORAL THESIS 2019 TEMPORAL EVOLUTION OF MHD WAVES IN SOLAR CORONAL ARCADES Samuel Rial Lesaga palabra DOCTORAL THESIS 2019 Doctoral Programe of Physics TEMPORAL EVOLUTION OF MHD WAVES IN SOLAR CORONAL ARCADES. Samuel Rial Lesaga Thesis supervisor: I~nigoArregui Uribe-Echevarria Thesis supervisor: Ram´onOliver Herrero Thesis Tutor: Alicia Sintes Olives Doctor by the university of the Balearic islands Supervisor letter Supervisor letter v Supervisor letter Supervisor letter Dr. I˜nigo Arregui Uribe-Echebarria of the Instituto de Astrof´ısica de Canarias. DECLARE: That the thesis entitled “Temporal evolution of magnetohydrodynamic waves in solar coronal arcades”, presented by Samuel Rial Lesaga to obtain the PhD degree, has been completed under my supervision. For all intents and purposes, I hereby sign this document. Signature Firmado por ARREGUI URIBE- ECHEVARRIA IÑIGO - 15392542E el día 20/05/2019 con un certificado emitido por AC FNMT Usuarios Dr. I˜nigo Arregui Uribe-Echebarria La Laguna, 17 May 2019 vi Acknowledgments En primer lugar me gustar´ıaagradecer al Dr. Ramon Oliver la amistad, la con- fianza y el apoyo incondicional que me siempre me ha ofrecido. El siempre ha sabido animarme y motivarme en los m´ultiplesmomentos dif´ıcilesque ha tenido esta tesis y estoy plenamente convencido de que si no hubiera sido por ´elesta tesis no existir´ıa. Gracias Al Dr. I~nigoArregui por su paciencia y su confianza en mi trabajo y en mi. Gracias motivarme cuando no lo estaba y por hacerme ver que este esfuerzo merece la pena. Al Dr. Jos´eLuis Ballester y a todo el grupo de personas que forman o han formado parte el grupo de f´ısicasolar de la Universitat de les Illes Balears y con los que he compartido alg´uncongreso, desayuno o cena.
    [Show full text]
  • Coronal Seismology Through Wavelet Analysis
    A&A 381, 311–323 (2002) Astronomy DOI: 10.1051/0004-6361:20011659 & c ESO 2002 Astrophysics Coronal seismology through wavelet analysis I. De Moortel1,A.W.Hood1, and J. Ireland2 1 School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK 2 Osservatorio Astronomica de Capodimonte, via Moiariello 16, 80131 Napoli, Italy Received 10 September 2001 / Accepted 18 October 2001 Abstract. This paper expands on the suggestion of De Moortel & Hood (2000) that it will be possible to infer coronal plasma properties by making a detailed study of the wavelet transform of observed oscillations. TRACE observations, taken on 14 July 1998, of a flare-excited, decaying coronal loop oscillation are used to illustrate the possible applications of wavelet analysis. It is found that a decay exponent n ≈ 2 gives the best fit to the 2 double logarithm of the wavelet power, thus suggesting an e−εt damping profile for the observed oscillation. Additional examples of transversal loop oscillations, observed by TRACE on 25 October 1999 and 21 March 2001, n are analysed and a damping profile of the form e−εt ,withn ≈ 0.5andn ≈ 3 respectively, is suggested. It is n demonstrated that an e−εt damping profile of a decaying oscillation survives the wavelet transform, and that the value of both the decay coefficient ε and the exponent n can be extracted by taking a double logarithm of the normalised wavelet power at a given scale. By calculating the wavelet power analytically, it is shown that a sufficient number of oscillations have to be present in the analysed time series to be able to extract the period of the time series and to determine correct values for both the damping coefficient and the decay exponent from the wavelet transform.
    [Show full text]
  • Coronal Magnetic Field Measurement Using Loop Oscillations Observed by Hinode/EIS
    A&A 487, L17–L20 (2008) Astronomy DOI: 10.1051/0004-6361:200810186 & c ESO 2008 Astrophysics Letter to the Editor Coronal magnetic field measurement using loop oscillations observed by Hinode/EIS T. Van Doorsselaere1,V.M.Nakariakov1, P. R. Young2, and E. Verwichte1 1 Centre for Fusion, Space and Astrophysics, Physics Department, University of Warwick, Coventry CV4 7AL, UK e-mail: [t.van-doorsselaere;v.nakariakov;erwin.verwichte]@warwick.ac.uk 2 STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK e-mail: [email protected] Received 13 May 2008 / Accepted 12 June 2008 ABSTRACT We report the first spectroscopic detection of a kink MHD oscillation of a solar coronal structure by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Japanese Hinode satellite. The detected oscillation has an amplitude of 1 km s−1 in the Doppler shift of the FeXII 195 Å spectral line (1.3 MK), and a period of 296 s. The unique combination of EIS’s spectroscopic and imaging abilities enables us to measure simultaneously the mass density and length of the oscillating loop. This enables us to measure directly the magnitude of the local magnetic field, the fundamental coronal plasma parameter, as 39 ± 8 G, with unprecedented accuracy. This proof of concept makes EIS an exclusive instrument for the full scale implementation of the MHD coronal seismological technique. Key words. instrumentation: spectrographs – Sun: corona – Sun: oscillations – Sun: magnetic fields 1. Introduction oscillating structure. In the case of standing waves, the phase speed can be estimated by the period of the observed oscilla- Coronal seismology utilises observed waves and oscillations in tions and the wavelength given by the size of the resonator.
    [Show full text]
  • Coronal Loop Seismology - State-Of-The-Art Models
    2292-24 School and Conference on Analytical and Computational Astrophysics 14 - 25 November, 2011 Coronal Loop Seismology - State-of-the-art Models Malgorzata Selwa Katholic University of Leuven, Centre for Plasma Astrophysics Belgium Coronal Loop Seismology - State-of-the-art Models Mag Selwa ICTP School and Conference on Analytical and Computational Astrophysics, Trieste, 23.11.2011 Outline 9 Observations of coronal loops oscillations as an input for coronal seismology: ¾Scale height ¾Damping mechanisms 9Recent observations (STEREO) 9Alfvén waves 9Other structures: ¾EIT waves ¾QPP ¾streamers ¾prominences B from kink oscillations transverse oscillations in an off-limb arcade observed with TRACE: J tn §·2S Best fit [I(tAe ) cos¨¸ t ©¹P 1/2 B |u7.9 1013 nd001/ nne 0 P Verwichte et al. (2004) B from kink oscillations P1 P2 First identification of kink second harmonics P2 ≈ P1/2, the mode has a node at loop apex. Here P1/P2 = 0.55 and 0.61 Verwichte et al. (2004) Scale height from kink oscillations Scale height (for planetary atmospheres) is the vertical distance over which the pressure of the atmosphere changes by a factor of e (decreasing upward). The scale height remains constant for a particular temperature. 9exponentially stratified atmosphere UU ()h 0 exp(h/) H 9stratification function projected on a semicircular loop of length L UU ()z expL>@ sinSS z// L H 0 A tool for independent 9P1/P2≠2 (no node at the loop apex) estimation of stratification P2 /P1 ~ H (scale height) Andries et al. (2005) Multiple periodicities–scale height 9O’Shea et al. (2007): wave harmonics in cool loops (OV observation, TR line).
    [Show full text]
  • Periodicities in an Active Region Correlated with Type III Radio Bursts Observed by Parker Solar Probe
    A&A 650, A6 (2021) Astronomy https://doi.org/10.1051/0004-6361/202039510 & © C. Cattell et al. 2021 Astrophysics Parker Solar Probe: Ushering a new frontier in space exploration Special issue Periodicities in an active region correlated with Type III radio bursts observed by Parker Solar Probe Cynthia Cattell1, Lindsay Glesener1, Benjamin Leiran1, John Dombeck1, Keith Goetz1, Juan Carlos Martínez Oliveros2, Samuel T. Badman2,3, Marc Pulupa2, and Stuart D. Bale2,3 1 School of Physics and Astronomy, University of Minnesota, 116 Church St. SE Minneapolis, MN 55455, USA e-mail: [email protected] 2 Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94709, USA 3 Department of Physics, University of California, Berkeley, Berkeley, CA 94709, USA Received 23 September 2020 / Accepted 26 January 2021 ABSTRACT Context. Periodicities have frequently been reported across many wavelengths in the solar corona. Correlated periods of 5 min, comparable to solar p-modes, are suggestive of coupling between the photosphere and the corona. ∼ Aims. Our study investigates whether there are correlations in the periodic behavior of Type III radio bursts which are indicative of nonthermal electron acceleration processes, and coronal extreme ultraviolet (EUV) emission used to assess heating and cooling in an active region when there are no large flares. Methods. We used coordinated observations of Type III radio bursts from the FIELDS instrument on Parker Solar Probe (PSP), of EUV emissions by the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and white light observations by SDO Helioseismic and Magnetic Image (HMI), and of solar flare X-rays by Nuclear Spectroscopic Telescope Array (NuSTAR) on April 12, 2019.
    [Show full text]
  • Magnetohydrodynamic Oscillations in the Solar Corona and Earth’S Magnetosphere: Towards Consolidated Understanding
    Noname manuscript No. (will be inserted by the editor) Magnetohydrodynamic Oscillations in the Solar Corona and Earth's Magnetosphere: Towards Consolidated Understanding V. M. Nakariakov · V. Pilipenko · B. Heilig · P. Jel´ınek · M. Karlick´y · D.Y. Klimushkin · D.Y. Kolotkov · D.-H. Lee · G. Nistic`o · T. Van Doorsselaere · G. Verth · I.V. Zimovets Received: date / Accepted: date V. M. Nakariakov Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry CV4 7AL, UK, School of Space Research, Kyung Hee University, Yongin, 446-701, Gyeonggi, Korea, Central Astronomical Observatory at Pulkovo, St Petersburg 196140, Russia, E-mail: [email protected] V.A. Pilipenko Space Research Institute, Moscow 117997, Russia B. Heilig Tihany Geophysical Observatory, Geological and Geophysical Institute of Hungary, Tihany, Hungary P. Jel´ınek Institute of Physics and Biophysics, Faculty of Science, University of South Bohemia, CZ - 370 05 Cesk´eBudˇejovice,ˇ Czech Republic M. Karlick´y Astronomical Institute of the Academy of Sciences of the Czech Republic, 25165, Ondˇrejov, Czech Republic D.Y. Klimushkin Institute of Solar-Terrestrial Physics, Lermontov St. 126A, Irkutsk 664033, Russia D.Y. Kolotkov Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry CV4 7AL, UK, D.-H. Lee School of Space Research, Kyung Hee University, Yongin, 446-701, Gyeonggi, Korea G. Nistic`o Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry CV4 7AL, UK T. Van Doorsselaere Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, B- 3001 Leuven, Belgium G. Verth Solar Physics and Space Plasma Research Centre (SP2RC), University of Sheffield, Sheffield S3 7RH, UK I.V.
    [Show full text]
  • Progress in Coronal Seismology B
    Waves & Oscillations in the Solar Atmosphere: Heating and Magneto-Seismology Proceedings IAU Symposium No. 247, 2007 c 2008 International Astronomical Union R. Erd´elyi & C. A. Mendoza-Bricen˜o, eds. doi:10.1017/S1743921308014609 Progress in coronal seismology B. Roberts Mathematical Institute, University of St Andrews, St Andrews, Fife KY16 9SS, Scotland, UK email: [email protected] Abstract. Coronal seismology is now a well developed area of solar physics, even though many questions remain for resolution. Here we take stock of the progress made since the first direct imaging of oscillating loops was achieved through TRACE spacecraft observations in 1999. Keywords. Sun: oscillations, MHD waves, coronal seismology 1. Introduction Coronal seismology is a marriage of theory and observations with the aim of producing a detailed knowledge of physical parameters in the corona. It aims to estimate such quantities as the magnetic field strength in a coronal loop, the width of the loop and the steepness of its density or magnetic field profile across the loop, or the longitudinal density scale height along the loop. Also, it offers the prospect of determining the thermal, viscous or ohmic damping coefficients of the coronal plasma. All these quantities are difficult to obtain by direct measurement, so coronal seismology offers an important way of progressing in their determination. The subject exploits observations of coronal oscillations by matching such observations to predicted theoretical results derived for a model loop. The same ideas may be applied elsewhere in the solar atmosphere, including the photosphere or chromosphere and in prominences, and indeed in stellar atmospheres.
    [Show full text]
  • Agenda and Abstracts
    Agenda and Abstracts Day 1: April 27, 2021 Allotted Time Title Speakers Time (EDT) (min.) Welcome, Logistics, & Meeting Opening Nour E. Raouafi Heliophysics Division: Early Career Scientists and Nicola J. Fox – NASA HPD, Diversity Support Director 30 10:00–10:30 Space Exploration at APL Jason Kalirai – Mission Area Executive for Civil Space Chairs: Kristoff Paulson & Vamsee Krishna Fast Electrostatic Waves with Frequency Lily Kromyda 10:30–10:50 Shifts in the Solar Wind Sunward of 1/3 CU Boulder - LASP 20 AU [email protected] New Insights into Small-scale Alfvénic Lloyd Woodham Turbulence from Near-Sun Solar Wind Imperial College London 20 10:50–11:10 Observations [email protected] Relative heating of ions and electrons in Niranjana Shankarappa the young solar wind due to turbulent University of Arizona 20 11:10–11:30 dissipation mediated through Landau [email protected] damping BREAK 10 11:30–11:40 Chairs: Robert Allen & Clara Froment Wave Composition, Propagation, and Xingyu Zhu Polarization of Magnetohydrodynamic Peking University 20 11:40–12:00 Turbulence within 0.3 au as Observed by [email protected] Parker Solar Probe Daniele Telloni Evolution of Solar Wind Turbulence from Particle Dynamics (Turbulence & Heating) & Particle(Turbulence Dynamics INAF – Astrophysical - 0.1 to 1 au during the First Parker Solar 20 12:00–12:20 Observatory of Torino Probe – Solar Orbiter Radial Alignment [email protected] Wave On the Scaling Properties of Magnetic- Tommaso Alberti field Fluctuations through the Inner INAF-IAPS, Rome, Italy 20 12:20–12:30 Heliosphere [email protected] BREAK – Breakout Rooms 25 12:30–12:55 Chairs: Jamie Rankin & Claire Gasque Probing the ambipolar electric field and Laura Bercic potential in the solar wind through in situ MSSL/UCL 20 12:55–13:15 measured electron velocity distribution [email protected] functions J.
    [Show full text]
  • Coronal Loop Seismology Using Damping of Standing Kink Oscillations by Mode Coupling D
    A&A 589, A136 (2016) Astronomy DOI: 10.1051/0004-6361/201628255 & c ESO 2016 Astrophysics Coronal loop seismology using damping of standing kink oscillations by mode coupling D. J. Pascoe, C. R. Goddard, G. Nisticò, S. Anfinogentov, and V. M. Nakariakov Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, CV4 7AL, UK e-mail: [email protected] Received 4 February 2016 / Accepted 23 March 2016 ABSTRACT Context. Kink oscillations of solar coronal loops are frequently observed to be strongly damped. The damping can be explained by mode coupling on the condition that loops have a finite inhomogeneous layer between the higher density core and lower density background. The damping rate depends on the loop density contrast ratio and inhomogeneous layer width. Aims. The theoretical description for mode coupling of kink waves has been extended to include the initial Gaussian damping regime in addition to the exponential asymptotic state. Observation of these damping regimes would provide information about the structuring of the coronal loop and so provide a seismological tool. Methods. We consider three examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) for which the general damping profile (Gaussian and exponential regimes) can be fitted. Deter- mining the Gaussian and exponential damping times allows us to perform seismological inversions for the loop density contrast ratio and the inhomogeneous layer width normalised to the loop radius. The layer width and loop minor radius are found separately by comparing the observed loop intensity profile with forward modelling based on our seismological results.
    [Show full text]
  • Seismology of the Corona of The
    Coronal seismology n Sunday 1 November 1755 a strong earthquake accompanied by a tsunami Odevastated the city of Lisbon and left 70 000 inhabitants dead. This dramatic event Seismology of the triggered a new approach in understanding the forces of the Earth: seismology. In more general terms, seismology is the remote diagnostics of media by means of waves. Seismology has corona of the Sun become a well-developed technique in various applications; as well as seismology of the Earth’s interior, there are ultrasound scans of V M Nakariakov and E Verwichte put seismology to work in the study the human body and marine acoustics (sonars), of the solar corona, the hot atmosphere of the Sun. and a less familiar but important application in laboratory plasma spectroscopy. The first Abstract implementation of this technique in solar flare epicentre physics – helioseismology – is connected with Seismology now includes study of the kink oscillations solar surface oscillations, discovered by Robert Sun’s corona, a promising research target loop Leighton in the early 1960s. These oscillations both in its own right and for its role in were interpreted in terms of acoustic-gravita- the relationship between the Sun and the tional waves and now provide unique informa- Earth and its links to the solar magnetic tion about the solar interior, its structure and blast wave footpoint field. In addition, the corona, as a natural (fast magnetoacoustic) differential rotation – and even about the far plasma, is itself an objective for footpoint side of the Sun (see discussion by Thompson, fundamental physics. Observations using this issue p4.21–4.25).
    [Show full text]