DOCSLIB.ORG

Exploring the Sun with ALMA

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exploring the Sun with ALMA Astronomical Science DOI: 10.18727/0722-6691/5065 Exploring the Sun with ALMA Timothy S. Bastian1 18 Space Vehicles Directorate, Air Force and to gain an understanding of how Miroslav Bárta2 Research Laboratory, Albuquerque, mechanical and radiative energy are Roman Brajša3 USA transferred through that atmospheric Bin Chen4 19 National Astronomical Observatories, layer. Bart De Pontieu5, 6 Chinese Academy of Sciences, Beijing, Dale E. Gary4 China Much of what is currently known about Gregory D. Fleishman4 the chromosphere has relied on spectro- Antonio S. Hales1, 7 scopic observations at optical and ultra- Kazumasa Iwai8 The Atacama Large Millimeter/submilli- violet wavelengths using both ground- Hugh Hudson9, 10 meter Array (ALMA) Observatory opens and space-based instrumentation. While Sujin Kim11, 12 a new window onto the Universe. The a lot of progress has been made, the Adam Kobelski13 ability to perform continuum imaging interpretation of such observations is Maria Loukitcheva4, 14, 15 and spectroscopy of astrophysical phe- complex because optical and ultraviolet Masumi Shimojo16, 17 nomena at millimetre and submillimetre lines in the chromosphere form under Ivica Skokić2, 3 wavelengths with unprecedented sen- conditions of non-local thermodynamic Sven Wedemeyer6 sitivity opens up new avenues for the equilibrium. In contrast, emission from Stephen M. White18 study of cosmology and the evolution the Sun’s chromosphere at millimetre Yihua Yan19 of galaxies, the formation of stars and and submillimetre wavelengths is more planets, and astrochemistry. ALMA also straightforward to interpret as the emis- allows fundamentally new observations sion forms under conditions of local 1 National Radio Astronomy Observatory, to be made of objects much closer to thermodynamic equilibrium and the Charlottesville, USA home, including the Sun. The Sun has source function is Planckian. Moreover, 2 Astronomical Institute, Czech Academy long served as a touchstone for our the Rayleigh-Jeans approximation is valid of Sciences, Ondřejov, Czech Republic understanding of astrophysical pro- (hn/kT << 1) and so the observed intensity 3 Hvar Observatory, Faculty of Geodesy, cesses, from the nature of stellar interi- at a given frequency is linearly propor- University of Zagreb, Croatia ors, to magnetic dynamos, non-radiative tional to the temperature of the (optically 4 Center for Solar-Terrestrial Research, heating, stellar mass loss, and ener- thick) emitting material. By tuning across New Jersey Institute of Technology, getic phenomena such as solar flares. the full suite of ALMA’s frequency bands Newark, USA ALMA offers new insights into all of it is possible to probe the entire depth of 5 Lockheed Martin Solar & Astrophysics these processes. the chromosphere. Lab, Palo Alto, USA 6 Rosseland Centre for Solar Physics, Wedemeyer et al. (2016) comprehensively University of Oslo, Norway ALMA solar science discuss the potential of ALMA in this 7 Joint ALMA Observatory (JAO), context. In brief, observations of thermal Santiago, Chile Radiation from the Sun at millimetre and emission from material at chromospheric 8 Institute for Space-Earth Environmental submillimetre wavelengths largely origi- temperatures will be a mainstay of Research, Nagoya University, Japan nates from the chromosphere, the rela- ALMA’s solar physics programme. Multi- 9 School of Physics and Astronomy, tively thin interface between the radia- band, high-resolution, time-resolved University of Glasgow, Scotland, UK tion-dominated photosphere and the observations of the chromosphere at milli- 10 Space Sciences Laboratory, University magnetically dominated corona. The chro- metre and submillimetre wavelengths of California, Berkeley, USA mosphere is highly dynamic in nature as with ALMA will play a key role in con- 11 Korea Astronomy and Space Science magnetohydrodynamic (MHD) waves straining models of chromospheric and Institute, Daejeon, Republic of Korea propagate up from the photosphere below coronal heating. 12 University of Science and Technology, and form shocks that dissipate their Daejeon, Republic of Korea energy (for example, Wedemeyer, 2016). In addition, ALMA will be important for 13 Department of Physics and Astronomy, addressing puzzles associated with West Virginia University, Morgantown, The chromosphere remains an out- solar filaments and prominences that USA standing problem in solar physics and, form along magnetic neutral lines. 14 Max-Planck-Institut für Sonnensystem- by extension, stellar physics. The central Although they are at chromospheric tem- forschung, Göttingen, Germany question is: why does the Sun’s atmos- peratures, they occur at coronal heights 15 Astronomical Institute, St. Petersburg phere increase in temperature above the and are therefore immersed in much University, Russia visible photosphere as one proceeds up hotter plasma. Quiescent prominences 16 National Astronomical Observatory of through the chromosphere and into the can remain stable for days or even weeks Japan (NAOJ), Tokyo, Japan corona? What are the heating mecha- but may then become unstable and 17 Department of Astronomical Science, nisms? How is energy transported? What erupt. ALMA offers new insights into the The Graduate University for Advanced is the role of the magnetic field? ALMA thermal structure and dynamics of Studies (SOKENDAI), Tokyo, Japan is needed to help establish the thermo- prominences, their formation, and their dynamic structure of the chromosphere eventual loss of equilibrium. The Messenger 171 – March 2018 25 Astronomical Science Bastian T. S. et al., Exploring the Sun with ALMA ALMA observations of non-thermal emis- tion, yet considerable work was needed shape and increased side lobes. There- sion will also be of crucial importance. in practice to implement solar observing fore, while solar filters will be needed for Although observations of small flares or modes — work that is still ongoing. Provi- observations of stronger solar flares, small eruptive events may be observed sions were made to ensure that ALMA the second approach was developed for using the existing modes described antennas could safely point at the Sun quiet Sun programmes. below, observations of solar flares are not without damaging the extremely precise yet feasible with ALMA in general. Unlike telescope hardware; in particular, the sur- Yagoubov (2013) pointed out that the quiescent solar emission, solar flares face panels were chemically roughened ALMA superconductor-insulator-super- produce intense non-thermal radiation as in order to scatter optical and infrared conductor (SIS) mixers could be de-tuned a result of energetic electrons interacting radiation and reduce the radiative heating or de-biased to reduce the mixer gain with the local magnetic field. ALMA will of the sub-reflector and other elements and effectively increase the level at which be sensitive to emission from the most to safe levels. However, there are addi- receivers saturate, thereby allowing solar energetic of these electrons. An impor- tional factors to consider when observing observing without the use of the solar tant discovery by Kaufmann et al. (2004) the Sun. While ALMA’s sensitive receivers filters. This idea is illustrated in Figure 1, is that some flares produce a spectral are not damaged by pointing at the Sun, which shows the SIS current gain (left component at millimetre/submillimetre they saturate when such an intense signal axis) and conversion gain (right axis) plot- wavelengths with an inverted spectrum is introduced into the system, resulting in ted against the voltage bias for ALMA — the so-called “sub-terahertz” com- a strongly non-linear performance. Band 3. The normal voltage bias tuning is ponent, which is distinct from the non- on the first photon step where the gain thermal gyrosynchrotron component. There are two approaches to mitigating conversion is a maximum. However, the Krucker et al. (2013) discuss it at length, the problem: attenuate the signal intro- mixer still operates at other voltage bias yet the origin of the sub-terahertz flare duced into the receiver, or increase the settings. These produce lower conver- component remains unknown. ALMA “headroom” of the receiver to ensure that sion gain but, since the dynamic range will play a central role in understanding its response remains linear by reducing scales roughly inversely with gain, these its origin. the receiver gain. Both approaches are settings can handle larger signal levels possible with ALMA. The first approach before saturating. This operational mode Each of these broad science themes was implemented through the use of a is referred to as the mixer de-biased (MD) additionally informs the burgeoning field solar filter on the ALMA Calibration Device. mode. Observing both the source and of “Space Weather”, which is aimed at The solar filter attenuates the incident calibrators in a specific MD mode obviates understanding the drivers of disturbances signal by a frequency-dependent amount the need to explicitly measure the change in the solar corona and wind and their that allows solar observations in a given in system gain introduced by the mode. effects on Earth and the near-Earth frequency band. However, solar filters environment. have a number of undesirable properties Another consideration, however — for mapping the quiet (i.e., non-flaring) regardless of whether the solar filter or Sun: they greatly reduce the sensitivity the MD mode is used — is that the input Enabling solar observing with ALMA with which calibrator
Load more

Recommended publications
  • A Deep Learning Framework for Solar Phenomena Prediction
    FlareNet: A Deep Learning Framework for Solar Phenomena Prediction FDL 2017 Solar Storm Team: Sean McGregor1, Dattaraj Dhuri1,2, Anamaria Berea1,3, and Andrés Muñoz-Jaramillo1,4 1NASA’s 2017 Frontier Development Laboratory 2Tata Institute of Fundamental Research (TIFR), Mumbai, India 3Center for Complexity in Business, University of Maryland, College Park, MD, USA 4SouthWest Research Institute, Boulder, CO, USA Abstract Solar activity can interfere with the normal operation of GPS satellites, the power grid, and space operations, but inadequate predictive models mean we have little warning for the arrival of newly disruptive solar activity. Petabytes of data col- lected from satellite instruments aboard the Solar Dynamics Observatory (SDO) provide a high-cadence, high-resolution, and many-channeled dataset of solar phenomena. Several challenging deep learning problems may be derived from the data, including space weather forecasting (i.e., solar flares, solar energetic particles, and coronal mass ejections). This work introduces a software framework, FlareNet, for experimentation within these problems. FlareNet includes compo- nents for the downloading and management of SDO data, visualization, and rapid experimentation. The system architecture is built to enable collaboration between heliophysicists and machine learning researchers on the topics of image regres- sion, image classification, and image segmentation. We specifically highlight the problem of solar flare prediction and offer insights from preliminary experiments. 1 Introduction The violent release of solar magnetic energy – collectively referred to as “space weather" – is responsible for a variety of phenomena that can disrupt technological assets. In particular, solar flares (sudden brightenings of the solar corona) and coronal mass ejections (CMEs; the violent release of solar plasma) can disrupt long-distance communications, reduce Global Positioning System (GPS) accuracy, degrade satellites, and disrupt the power grid [5].
    [Show full text]
  • Solar and Space Physics: a Science for a Technological Society
    Solar and Space Physics: A Science for a Technological Society The 2013-2022 Decadal Survey in Solar and Space Physics Space Studies Board ∙ Division on Engineering & Physical Sciences ∙ August 2012 From the interior of the Sun, to the upper atmosphere and near-space environment of Earth, and outwards to a region far beyond Pluto where the Sun’s influence wanes, advances during the past decade in space physics and solar physics have yielded spectacular insights into the phenomena that affect our home in space. This report, the final product of a study requested by NASA and the National Science Foundation, presents a prioritized program of basic and applied research for 2013-2022 that will advance scientific understanding of the Sun, Sun- Earth connections and the origins of “space weather,” and the Sun’s interactions with other bodies in the solar system. The report includes recommendations directed for action by the study sponsors and by other federal agencies—especially NOAA, which is responsible for the day-to-day (“operational”) forecast of space weather. Recent Progress: Significant Advances significant progress in understanding the origin from the Past Decade and evolution of the solar wind; striking advances The disciplines of solar and space physics have made in understanding of both explosive solar flares remarkable advances over the last decade—many and the coronal mass ejections that drive space of which have come from the implementation weather; new imaging methods that permit direct of the program recommended in 2003 Solar observations of the space weather-driven changes and Space Physics Decadal Survey. For example, in the particles and magnetic fields surrounding enabled by advances in scientific understanding Earth; new understanding of the ways that space as well as fruitful interagency partnerships, the storms are fueled by oxygen originating from capabilities of models that predict space weather Earth’s own atmosphere; and the surprising impacts on Earth have made rapid gains over discovery that conditions in near-Earth space the past decade.
    [Show full text]
  • Chapter 11 RADIO OBSERVATIONS of CORONAL MASS
    Chapter 11 RADIO OBSERVATIONS OF CORONAL MASS EJECTIONS Angelos Vourlidas Solar Physics Branch, Naval Research Laboratory, Washington, DC [email protected] Abstract In this chapter we review the status of CME observations in radio wavelengths with an emphasis on imaging. It is an area of renewed interest since 1996 due to the upgrade of the Nancay radioheliograph in conjunction with the continu- ous coverage of the solar corona from the EIT and LASCO instruments aboard SOHO. Also covered are analyses of Nobeyama Radioheliograph data and spec- tral data from a plethora of spectrographs around the world. We will point out the shortcomings of the current instrumentation and the ways that FASR could contribute. A summary of the current understanding of the physical processes that are involved in the radio emission from CMEs will be given. Keywords: Sun: Corona, Sun: Coronal Mass Ejections, Sun:Radio 1. Coronal Mass Ejections 1.1 A Brief CME Primer A Coronal Mass Ejection (CME) is, by definition, the expulsion of coronal plasma and magnetic field entrained therein into the heliosphere. The event is detected in white light by Thompson scattering of the photospheric light by the coronal electrons in the ejected mass. The first CME was discovered on December 14, 1971 by the OSO-7 orbiting coronagraph (Tousey 1973) which recorded only a small number of events (Howard et al. 1975). Skylab ob- servations quickly followed and allowed the first study of CME properties ( Gosling et al. 1974). Observations from many thousands of events have been collected since, from a series of space-borne coronagraphs: Solwind (Michels et al.
    [Show full text]
  • Solar Wind Properties and Geospace Impact of Coronal Mass Ejection-Driven Sheath Regions: Variation and Driver Dependence E
    Solar Wind Properties and Geospace Impact of Coronal Mass Ejection-Driven Sheath Regions: Variation and Driver Dependence E. K. J. Kilpua, D. Fontaine, C. Moissard, M. Ala-lahti, E. Palmerio, E. Yordanova, S. Good, M. M. H. Kalliokoski, E. Lumme, A. Osmane, et al. To cite this version: E. K. J. Kilpua, D. Fontaine, C. Moissard, M. Ala-lahti, E. Palmerio, et al.. Solar Wind Properties and Geospace Impact of Coronal Mass Ejection-Driven Sheath Regions: Variation and Driver Dependence. Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2019, 17 (8), pp.1257-1280. 10.1029/2019SW002217. hal-03087107 HAL Id: hal-03087107 https://hal.archives-ouvertes.fr/hal-03087107 Submitted on 23 Dec 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. RESEARCH ARTICLE Solar Wind Properties and Geospace Impact of Coronal 10.1029/2019SW002217 Mass Ejection-Driven Sheath Regions: Variation and Key Points: Driver Dependence • Variation of interplanetary properties and geoeffectiveness of CME-driven sheaths and their dependence on the E. K. J. Kilpua1 , D. Fontaine2 , C. Moissard2 , M. Ala-Lahti1 , E. Palmerio1 , ejecta properties are determined E.
    [Show full text]
  • Solar Modeling and Opacities
    Solar Modeling and Opacities Joyce Ann Guzik Los Alamos National Laboratory Tri-Lab Opacity Workshop August 27, 2020 LA-UR-20-26484 8/28/20 1 The solar abundance problem ® Until 2004, we thought we knew very well the interior structure of the Sun, and how it reached its present state. ® However, new analyses of the Sun’s spectral lines (Asplund et al. 2005) revise downward the mass fraction of elements heavier than H and He, particularly the abundances of O, C, and N. ® Models evolved with the new abundances give worse agreement with helioseismic constraints How can this discrepancy be resolved? Should we adopt the new abundances? 8/28/20 2 Which is the actual problem? ®The solar abundance problem ®The solar opacity problem ®The solar modelling problem 8/28/20 3 Outline for talk ® Standard solar model ® Constraints from helioseismology ® Some attempts to reconcile models and observations ® LLNL OPAL vs. LANL OPLIB opacities 8/28/20 4 Surface composition of the Sun by mass Breakdown for elements 1.8% Other Elements heavier than H and He 25% Helium All other OxygenOxygen elements 73.2% Hydrogen Carbon S Fe Ne Si Mg N 8/28/20 5 Asplund et al. (2005) abundances decreased from previous Grevesse & Sauval (1998) determination Oxygen 48% decrease 8.66±0.05 (cf GS98 8.83±0.06) Carbon 35% decrease 8.39 ± 0.05 (cf GS98 8.52±0.06) Nitrogen 27.5% decrease 7.78±0.06 (cf GS98 7.92±0.06) Neon 74% decrease 7.84 ± 0.06 (cf GS98 8.08 ± 0.06) Argon 66% decrease 6.18 ± 0.08 (cf GS98 6.40 ± 0.06) Na to Ca: lower by 0.05 to 0.1 dex (12 to 25%) Fe: 7.45 ± 0.05
    [Show full text]
  • The Sun As a Guide to Stellar Physics This Page Intentionally Left Blank the Sun As a Guide to Stellar Physics
    The Sun as a Guide to Stellar Physics This page intentionally left blank The Sun as a Guide to Stellar Physics Edited by Oddbjørn Engvold Professor emeritus, Rosseland Centre for Solar Physics, Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway Jean-Claude Vial Emeritus Senior Scientist, Institut d’Astrophysique Spatiale, CNRS-Universite´ Paris-Sud, Orsay, France Andrew Skumanich Emeritus Senior Scientist, High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, United States Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein.
    [Show full text]
  • Coronae, Heliospheres and Astrospheres
    Coronae, Heliospheres and Astrospheres Heliophysics Summer School, Boulder CO, 2018 Outline Part I: I. Solar Vs. stellar physics II. Stellar evolution III. Coronae and winds IV. Stellar environments - astrospheres Part II V.Stellar evolution and magnetized winds VI. Stellar mass-loss rates and stellar spin-down VII. Flares VIII.Exoplanets and planet habitability Material mostly based on Volume IV chapters 2,3,4 Part I The Solar-stellar connection SDO observations of the Sun Photometry - measuring the intensity of the light Spectrometry - measuring the intensity of particular wavelength Transmission spectra - E=hv How many photons with certain energy (thus wavelength) we observe SDO AIA, SDO EVE 9-33 nm <30 nm Fermi JWST 0.6 to 27 micrometer Chandra Kepler systems observed as of Jan 2016 Solar Physics: 1. High-resolution global observations 2. High-cadence observations of temporal evolution 3. Multi-wavelength observations 4. In-situ observations of the interplanetary environment 5. Detailed and constrained models 6. Information only about one star Stellar Astrophysics: 1. Statistical information on many stars 2. Data on different spectral types 3. Data on stellar evolution of each type, including solar analogs 4. Information about planetary systems 5. Limited knowledge about specific parameters 6. Limited knowledge about stellar winds and interplanetary environments 7. Unconstrained models Stellar Evolution Stellar Evolution (yes, some figures are from Wikipedia…) Sun Credit: ESO Star-forming regions - molecular clouds Protoplanetary disk What drives stars? Nuclear Fusion Heavy products sink to the core Main Sequence: H—> He Post-main Sequence: Mid-size stars 1. sub-giant phase - H burning in the H shell 2.
    [Show full text]
  • Physics of Stellar Coronae
    Physics of Stellar Coronae Manuel G¨udel Paul Scherrer Institut, W¨urenlingen and Villigen, CH-5232 Villigen PSI, Switzerland [email protected] 1 Introduction For the plasma physicist, the solar corona offers an outstanding example of a space plasma, and surely one that deserves a lifetime of study. Not only can we observe the solar corona on scales of a few hundred kilometers and monitor its changes in the course of seconds to minutes, we also have a wide range of detailed diagnostics at our disposal that provide immediate access to the prevalent physical processes. Yet, solar physics offers a rich field of unsolved plasma-physical problems. How is the coronal plasma continuously heated to > 106 K? How and where are high-energy particles episodically accelerated? What is the internal dy- namics of plasma in magnetic loops? What is the initial trigger of a coronal flare? How does the corona link to the solar wind, and how and where is the latter accelerated? How is plasma transported into the solar corona? Why, then, study stellar coronae that remain spatially unresolved in X- rays and are only marginally resolved at radio wavelengths, objects that require exposure times of several hours before approximate measurements of the ensemble of plasma structures can be obtained? There are many reasons. In the context of the solar-stellar connection, stellar X-ray astronomy has introduced a range of stellar rotation periods, gravities, masses, and ages into the debate on the magnetic dynamo. Coronal magnetic structures and heating mechanisms may vary together with varia- tions of these parameters.
    [Show full text]
  • The Sun and Heliosphere in Three Dimensions
    The Sun and Heliosphere In Three Dimensions Report of the NASA Science Definition Team for the STEREO Mission Table of Contents Executive Summary ........................................................................................................... 1 1. Introduction ..................................................................................................................3 2. Scientific Objectives ..................................................................................................... 4 Coronal Mass Ejections ....................................................................................................................... 4 CME Onset ..................................................................................................................................... 4 CME Geometry and Onset Signatures............................................................................................ 5 Reconnection .................................................................................................................................. 6 Surface Evolution ........................................................................................................................... 6 The Heliosphere Between the Sun and Earth ...................................................................................... 7 CMEs in the Heliosphere ..................................................................................................................... 9 Tracking Disturbances from the Sun to Earth ..................................................................................
    [Show full text]
  • The New Heliophysics Division Template
    Heliophysics Space Weather at NASA: Research and Small Satellites James Spann, Nicola Fox, Daniel Moses, Roshanak Hakimzadeh - Heliophysics Division COSPAR Symposium: Space Weather and Small Satellites February 11, 2019 1 Overview • Space Weather Science Applications Programs - Research - Infrastructure - International and Interagency Partnerships - New Initiatives - Whole Helio Month campaigns - NASA Science Mission Directorate Rideshare policy - Heliophysics and the Lunar Gateway - Small Satellites - NASA Activities - Heliophysics Small Satellite Missions 2 Space Weather Science Applications Program Establishes an expanded role for NASA in space weather science under single budget element • Consistent with recommendation of the NRC Decadal Survey and the OSTP National Space Weather Strategy Competes ideas and products, leverages existing agency capabilities, collaborates with other national and international agencies, and partners with user communities Three main areas of the Space Weather Science Applications Program are: • Collaboration • Competed Elements • Directed Components Heliophysics Space Weather Science Applications Transition Strategy, first meeting held Nov. 28 3 Space Weather Science Applications Program (1) 3 calls were made between ROSES 2017 and ROSES 2018 in Space Weather Operations-to-Research (SWO2R) • 8 selections made for ROSES 2017 SWO2R - Focus: Improve predictions of background solar wind, solar wind structures, and CMEs • 9 selections made for ROSES 2018 (1) SWO2R - Focus: Improve specifications and forecasts
    [Show full text]
  • Plasma and Solar Physics. the Solar Flare Phenomenon J
    Plasma and solar physics. The solar flare phenomenon J. Heyvaerts To cite this version: J. Heyvaerts. Plasma and solar physics. The solar flare phenomenon. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-37-C7-46. 10.1051/jphyscol:19797427. jpa-00219429 HAL Id: jpa-00219429 https://hal.archives-ouvertes.fr/jpa-00219429 Submitted on 1 Jan 1979 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE Colloque C7, suppldment au no 7, Tome 40, Juillet 1979, page C7-37 Plasma and solar physics. The solar flare phenomenon .I. Heyvaerts Observatolre de Parls-Meudon and UniversitC de Paris VII RCsumB. - Les principaux aspects de la physique solaire ayant trait a la physique des plasmas sont rapidement prtsentts. Le phbnombne d'truption solaire est dCcrit et certaines theories actuelles concernant 1'Ctat prk-truptif et le mtcanisme de dkclenchement passtes en revue, A savoir : la thtorie de I'existence d'un point de retournement dans les Ctats d'kquilibre possible et la thCorie bas6e sur l'analogie avec les instabilitks rtsistives observkes dans les Tokomaks. La microphysique qui, croit-on, permet le confinement turbulent d'un plasma de 100 millions de K dans le plasma coronal est CvoquCe, et on montre enfin qu'une turbulence cyclotron ionique dans la rCgion Cruptive possbde une signature assez caracttristique dans les abondances isotopiques et Ctats de charges des ions acceltrts.
    [Show full text]
  • Solar Flare Physics
    Multi-Wavelength Investigations of Solar Activity Proceedings IAU Symposium No. 223, 2004 c 2004 International Astronomical Union A.V. Stepanov, E.E. Benevolenskaya & A.G. Kosovichev, eds. DOI: 10.1017/S1743921304006349 Solar flare physics Boris V. Somov Solar Physics Department, Astronomical Institute, Moscow State University, Universitetskii Prospekt 13, Moscow 119992, Russia email: [email protected] Abstract. Specific features of magnetic reconnection in solar flares are briefly reviewed and illustrated. In particular, the large-scale structure and dynamics of large flares are interpreted in terms of the rainbow reconnection model. The role of the betatron effect in collapsing magnetic traps is considered. 1. Introduction The potential part of magnetic field in the solar corona determines a large-scale struc- ture of flare-active regions, while the reconnecting current layers (RCLs) at separators, together with other non-potential components of the field, determine energetics and dy- namics of flares (e.g. Somov et al. 2003). The basic properties of magnetic reconnection in solar flares are summarized in § 2. In § 3, the first-order Fermi-type acceleration and betatron effect in the collapsing magnetic traps, that are created by reconnection in the solar atmosphere, are considered. 2. Main features of reconnection in flares 2.1. Collisionless magnetic reconnection Coulomb collisions do not play any role in RCLs of a flare because of very high (super- hot) temperature of a plasma inside a RCL. Hence, this plasma must be considered as essentially collisionless. The concept of collisionless reconnection describes well the fast conversion from magnetic field energy to particle energy. That is what we need, first of all, to explain high power of flares.
    [Show full text]