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Magnetohydrodynamic Oscillations in the Solar Corona and Earth’S Magnetosphere: Towards Consolidated Understanding

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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. Zimovets Space Research Institute, Moscow 117997, Russia. 2 Abstract Magnetohydrodynamic (MHD) oscillatory processes in different plasma sys- tems, such as the corona of the Sun and the Earth's magnetosphere show interesting similarities and differences, which so far received little attention and remain under- exploited. The successful commissioning within the past ten years of SDO, Hinode, STEREO and THEMIS spacecraft, in combination with matured analysis of data from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI) makes it very timely to survey the breadth of observations giving evidence for MHD oscillatory pro- cesses in solar and space plasmas, and state-of-the-art theoretical modelling. The paper reviews several important topics, such as Alfv´enicresonances and mode conversion; MHD waveguides, such as the magnetotail, coronal loops, coronal streamers; mecha- nisms for periodicities produced in energy releases during substorms and solar flares, possibility of Alfv´enicresonators along open field lines; possible drivers of MHD waves; diagnostics of plasmas with MHD waves; interaction of MHD waves with partly-ionised boundaries (ionosphere and chromosphere). The review is mainly oriented to special- ists in magnetospheric physics and solar physics, but not familiar with specifics of the adjacent research fields. PACS 52.35.Bj · 94.30.cq · 94.30.Ms · 96.60.P- · 96.60.Q- · 96.60.qe Contents 1 Introduction . .4 1.1 What is the solar corona? . .5 1.2 What is the Earth's magnetosphere? . .9 1.2.1 Outline of the Earth's magnetosphere . .9 1.2.2 The magnetosphere as a zoo for MHD wave species . 11 1.2.3 Magnetosphere as a particle trap and accelerator . 13 2 Global propagating waves in solar corona . 15 2.1 Observations of global coronal waves . 15 2.2 Theoretical modelling of global coronal waves . 18 3 Magnetospheric MHD waveguides and resonators . 21 3.1 MHD waves in a cold plasma . 21 3.2 Magnetospheric cavities and waveguides for the fast magnetoacoustic mode . 23 3.3 Magnetospheric Alfv´enresonator . 25 3.4 Alfv´enwaves in a finite-pressure plasma . 26 3.5 Alfv´enicresonators on open field lines . 28 3.6 Alfv´enicfield line resonators in a warm plasma . 30 3.7 Alfv´enresonators across the field lines . 31 3.8 Resonators and waveguides in the Earth's ionosphere and atmosphere . 32 3.8.1 Ionospheric Alfv´enicresonator and fast magnetoacoustic waveguide . 33 4 Coronal plasma non-uniformities as magnetoacoustic waveguides and resonators . 35 5 MHD mode conversion . 40 5.1 The box model . 40 5.2 MHD wave conversion in the terrestrial magnetosphere . 42 5.3 MHD wave coupling on open field lines in the magnetosphere . 44 5.4 Ground monitoring of the magnetospheric plasma density with the use of ULF waves ......................................... 46 5.4.1 Gradient method of the magnetospheric plasma diagnostics . 48 5.4.2 Travel time magnetoseismology . 49 5.5 Effect of resonant conversion/absorption in coronal loops . 50 6 Standing modes of coronal plasma structures . 54 6.1 Standing kink modes . 55 6.2 Sausage modes . 58 6.3 Longitudinal modes . 60 7 Propagating MHD waves in coronal plasma structures . 63 3 7.1 Propagating longitudinal waves . 63 7.2 Propagating kink waves . 64 7.3 Transverse waves in coronal streamers . 66 7.4 Rapidly-propagating wave trains . 67 8 Flapping oscillations of current sheets . 69 9 Sources of MHD waves . 73 9.1 External generation mechanisms in the magnetosphere . 73 9.1.1 Shear flow instabilities . 73 9.1.2 Solar wind fluctuations . 76 9.1.3 Waves generated by the interaction between the solar wind and the mag- netosphere . 77 9.2 Internal generation mechanisms . 80 9.2.1 Kinetic Alfv´enicinstabilities . 81 9.2.2 Moving sources . 83 9.3 Excitation of kink oscillations of solar coronal loops . 86 10 Interaction of MHD waves with partly-ionised boundaries . 89 10.1 Interaction of long-period MHD waves with the thin ionosphere . 89 10.2 Short-period Alfv´enwave interaction with a realistic ionosphere . 91 10.3 The role of partially ionised plasma in coronal MHD oscillations . 93 11 Quasi-periodic pulsations in solar flares . 96 11.1 Standard model of a solar flare . 96 11.2 Observational manifestation of QPPs . 98 11.3 Modulation of flaring emission by MHD waves . 99 11.4 Periodic triggering of energy releases by external MHD oscillations . 102 11.5 Spontaneous mechanisms for QPPs . 104 12 Beyond MHD . 107 12.1 Dispersive Alfv´enwaves in the magnetosphere . 108 12.2 Field-aligned potential drop, turbulent layer, and Alfv´enwaves . 108 12.3 Interaction of Alfv´enwaves with a turbulent layer . 111 12.4 Kinetic description of compressive ULF modes . 114 12.4.1 Slow modes . 114 12.4.2 Drift compressive modes. 116 12.4.3 Drift mirror modes. 117 12.5 High-frequency effects on coronal MHD waves . 117 13 Is the direct impact of solar MHD oscillations on the magnetosphere possible? . 119 14 Conclusions and perspectives . 121 4 1 Introduction The solar corona and the Earth's magnetosphere are undoubtedly the most studied nat- ural plasma systems. Both consist of highly ionised plasmas penetrated by a magnetic field, that plays the decisive role in the structure, short-term dynamics and long-term evolution of these plasmas. The solar corona and the Earth's magnetosphere are the key elements of the solar-terrestrial connections and hence attract growing interest in the context of space weather and climate. Moreover, both the corona and the magneto- sphere are natural plasma laboratories, where one can find the combinations of physical conditions of broad interest. In particular, there are conditions directly relevant to the efforts in controlled fusion. Also, the corona and magnetosphere are priceless for the investigation of fundamental physical processes operating in natural and laboratory plasmas (e.g. magnetic reconnection, wave-particle interaction, macroscopic and mi- croscopic instabilities, charged particle acceleration, turbulence). One of these basic physical processes is magnetohydrodynamic (MHD) waves. In both the Earth's mag- netosphere and the solar corona MHD waves are well observed with satisfactory time and spatial resolution, mainly because of the recently commissioned new generation of space-borne and ground-based observational tools. MHD waves are propagating or standing perturbations of macroscopic parame- ters of the plasma (see Alfv´en1942, who was eventually awarded the Nobel prize in 1970). More specifically, MHD waves can perturb the magnitude and direction of the magnetic field, the plasma mass density and associated concentrations of individual species (e.g. electrons and positive ions), plasma temperature and gas pressure. In addition, MHD waves include perturbations of the electric field, electric current, and macroscopic (or bulk) flows of the plasma. Essentially, the presence of MHD waves is connected with MHD restoring forces associated with the magnetic tension and total (gas plus magnetic) pressure, and with the plasma inertia, caused by the frozen-in con- dition (perpendicular motions of the plasma lead to the change of the magnetic field geometry, and the other way around). MHD waves have been intensively studied in the Earth's magnetosphere for several decades. In the solar corona, the main interest in MHD waves appeared more recently, in the late 90s, with the first observations of these waves with high-resolution EUV imagers on the space missions SOHO and TRACE. Both coronal and magnetospheric observations provide us with abundant information about MHD waves. In both the fields, there is a number of elaborated theoretical models addressing specific observational properties of MHD waves. Responding to the intensive research activity in the MHD wave studies, there are a number of compre- hensive reviews of different aspects of the topic, see, e.g. Zaitsev and Stepanov (2008); Petrosyan et al. (2010); Banerjee et al. (2011); Patsourakos and Vourlidas (2012a); De Moortel and Nakariakov (2012); Stepanov et al. (2012); Mathioudakis et al. (2013); Liu and Ofman (2014) for most recent \solar" reviews, and Guglielmi and Pokhotelov (1996); Walker (2005); Alperovich and Fedorov (2007) for \magnetospheric" reviews. Regrettably, in the majority of cases MHD wave phenomena in the solar corona and the Earth's magnetosphere are studied separately.
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