DOCSLIB.ORG

Magnetospheric Interchange Instability in Anisotropic Plasma

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magnetospheric Interchange Instability in Anisotropic Plasma Plunfr. .S;offcfSci.. Vol. 41. No. 3, pp. 245-155. 1993 ~032~633~93 $6.00+ 0.00 Printed in Great Britain. ff 1993 Pergamon Press Ltd Magnetospheric interchange instability in anisotropic plasma Andrew Fazakerley and David Southwood Space and Atmospheric Physics Group. The Blackett Laboratory, Imperial College. London, U.K. Rcceivcd 11 June, 1992 ; revised 22 October. 1992 ; accepred 22 December, 1992 introduction Abstract. We study magnetospheric interchange insta- bility under the assumption that the plasma pressure The idea that the plasma distribution within a planetary distribution is anisotropic. Previous studies of magnetosphere might be maintained in such a way that magnetosphe~c interchange instabihty have only con- plasma motions arise spontaneously was originally pro- sidered the case of isotropic pressure. We also argue posed by Gold (1959) in the context of the terrestrial that, under certain circumstances, substantial particle magnetosphere. Gold recognized that magnetospheric energization can accompany outward interchange plasma. which can usual!y. be described in terms of motions in rapidly rotating magnetic fields. Our studies an MHD fluid. might exhtbtt a form of the well-known of instability treat the plasma as an MHD Ruid and Rayleigh-Taylor fluid instability. in which an adiabatic deal with two special cases in which the plasma pressure exchange of fluid elements results in a reduction of stored evolves anisotropically as the interchange motion pro- energy and the newly released energy is able to fill the ceeds. The first case is that of “fast” interchange role of the kinetic energy associated with the motion. motions, where interchange motions can take place All analyses of magnetospheric interchange instability are rapidly compared with particle bounce times. Our based on this principle. The dominant cause of plasma analysis uses a small perturbation approach and takes circulation in the terrestrial magnetosphere is now known into account the curved magnetic field, and external to be solar-wind-driven convection. though interchange forces such as gravity or an effective gravity arising instability still finds an application in studies of the ter- from rotation of the system. We contrast this with a restrial plasmapause (e.g. Richmond. 1973 : Huang rf al., second case in which the plasma motion conserves the 1990). adiabatic invariants p and J. and in both cases consider The discovery that IO is a strong source of plasma, and the implications for a plasma generated by a satellite that a sheet of logenic plasma exists throughout most of source in the equatorial plane of a rapidly rotating. the rapidly rotating Jovian magnetosphere beyond the lo spin-aligned magnetic field. A consequence of fast inter- torus. led to a number of papers arguing that centrifugally change motions in a corotation-dominated magneto- driven interchange motions are responsible for the radial sphere is that the rapid motions will be accompanied motion of logenic plasma in the Jovian magnetosphere. by motion of ionized material away from (toward) A number of scenarios have been put forward, all involv- the equatorial plane as the material moves outward ing an MHD description of the plasma, ranging from (inward). If an outward (inward) interchange motion large-scale convection patterns (e.g. Hill CI al., 1981) to should be slowed such that it is no longer rapid com- “interchange diffusion” involving ‘-turbulent eddies” (e.g. pared with particle bounce times. particles will resume Siscoe and Summers. 1981). However. there have been bounce motion, but with increased (reduced) parallel difficulties reconciling these models and their later modi- energy. In practice, it is likely that lower energy par- fications (e.g. Pontius ~‘1 ~11.. 1986; Hill and Liu, 1987; ticles in a distribution will violate the longitudinal Summers ct N/., 19X8) with the observed plasma dis- invariant, J, during interchange motion, whereas par- tribution (e.g. Richardson and McNutt. 1987: Vasyliunas, ticles of higher energy wit1 conserve J. Thus our work 1989; Mci and Thorne, 1991). leading to a proposal that implies that the lower the energy of a plasma, the less a pure MHD approach may not be sufbcient to describe likely it is to remain equatorially confined during out- the interchange motions (Southwood and Kivelson, 1989 ; ward interchange motion, whether it is a diffusive or Fazakerley and Southwood. I993 1. steady process. We discuss our results in the context of Despite ail this activity, there have been reiatively few the Jovian magnetosphere. papers in which interch~ln~e stability criteria are studied. The majority of these papers was reviewed by Southwood and Kivelson (1987) who produced a general stability 246 A. Fazakerley and D. Southwood : Magnetospheric interchange instability condition, valid for a plasma with isotropic pressure in a and that the energy, and hence pressure of this plasma curved magnetic field in the presence of gravitational and would become increasingly anisotropic in travelling flux centrifugal forces. The Southwood and Kivelson (1987) tubes. result embodies earlier results (which were usually derived On the basis of these examples and our more general for more specific situations) and. unlike previous results, remarks. we argue that the assumption of isotropic pres- is valid for arbitrary plasma pressure. sure in treatments of interchange instability may often The assumption that the plasma pressure is everywhere result in a poor description of the behaviour of real space isotropic is not generally valid in a collisionless space plasmas. In this paper we do not attempt a general treat- plasma. An isotropic pressure distribution is unlikely to ment for anisotropic plasmas, but concentrate on a special arise unless some non-MHD process (such as scattering) case which we term “fast” interchange, in which the inter- can play the part of collisions and bring about equi- changing plasma moves on a time scale that is short com- partition of energy between parallel and perpendicular pared with a typical bounce period so that J is not con- degrees of freedom, otherwise the parallel and per- served in the plasma. We will show that double adiabatic pendicular pressure (p,, and p_) are free to evolve indepen- theory describes the behaviour of the plasma during a dently. fast interchange motion, which is unsurprising since our The simplest anisotropic pressure scenario assumes definition of “fast” implies that plasma particles do not fluid behaviour both perpendicular and parallel to the have time to travel far along the field during the inter- magnetic field. Localization. the basis for fluid models. is change and that the plasma is thus effectively localized always ensured perpendicular to the magnetic field by the parallel to the field as well as perpendicular to it. There is v x B force, but fluid behaviour parallel to the field is only no possibility of isotropization by scattering effects during possible if the plasma distribution changes sufficiently an interchange motion which occurs on so short a time slowly along the field, and if there is no strong field-aligned scale. current or heat flow. Given localization in both degrees We will also consider the behaviour of individual par- of freedom, the fluid will obey the double adiabatic Chew, ticles associated with a plasma undergoing fast inter- Goldberger and Low (CCL) equations (e.g. see Clemmow change motion in the context of both the MHD picture and Dougherty, 1969) in which separate equations of state of interchange and the recent kinetic picture of Fazakerley apply top,i andp,. Other anisotropic plasma distributions and Southwood (1993). Finally we will consider whether exist in which the plasma behaviour parallel to the field the ideas of fast interchange may be useful in under- cannot be described in terms of a fluid model. Theoretical standing the behaviour of Iogenic plasma in the Jovian studies of the Jovian magnetosphere provide two inter- magnetosphere. esting examples. The Jovian ionosphere is thought to be a source of Jovian magnetospheric plasma, with most of the escaping ionospheric particles entering the magneto- sphere on field lines within the L-shell of IO (90% of the Calculation of stability criteria planet’s surface maps to these field lines). Ions which escape from the ionosphere are expected to have parallel velocities which are at least equal to the local corotation The derivation of instability criteria given here is based velocity, as a consequence of being constrained to move on the small perturbation approach used in Southwood along corotating field lines (Hill et ~1.. 1974). Thus. ions and Kivelson (1987). Additionally. we use a kinetic treat- from opposing hemispheres would form field-aligned ment to describe the independent evolution of parallel beams which are likely to interact. thereby redistributing and perpendicular pressure during a fast interchange some energy into perpendicular degrees of freedom. and motion. giving rise to a trapped. but probably still anisotropic distribution. On L-shells beyond that of the lo torus (L = 6) the magnetospheric plasma is dominated by heavy Unpcrturhed equilibrium ions which originate in the 10 plasma torus and which are thought to be distributed quite differently from magneto- We shall assume in our treatment that if the magneto- spheric ions of ionospheric origin. Observations give sphere is rotating, the planetary--magnetosphere coupling qualitative support to the suggestion of Hill and Michel is strong enough to maintain the magnetospheric plasma (1976) that ions originating at the Jovian satellites would in rigid corotation. In such circumstances Coriolis forces tend to form a sheet of plasma, confined near the spin can be ignored and the sum of the centrifugal and gravi- equatorial plane due to the action of centrifugal force. tational forces can be treated as an “effective” gravity, The idea was expanded upon by Siscoe (1977) who cal- directed away from the planetary rotation axis when the culated how the phase-space distribution of ions picked former force is dominant (e.g.
Load more

Recommended publications
  • Analysis of Plasma Instabilities and Verification of the BOUT Code for The
    Analysis of plasma instabilities and verification of the BOUT code for the Large Plasma Device P. Popovich,1 M.V. Umansky,2 T.A. Carter,1, a) and B. Friedman1 1)Department of Physics and Astronomy and Center for Multiscale Plasma Dynamics, University of California, Los Angeles, CA 90095-1547 2)Lawrence Livermore National Laboratory, Livermore, CA 94550, USA (Dated: 8 August 2018) The properties of linear instabilities in the Large Plasma Device [W. Gekelman et al., Rev. Sci. Inst., 62, 2875 (1991)] are studied both through analytic calculations and solving numerically a system of linearized collisional plasma fluid equations using the 3D fluid code BOUT [M. Umansky et al., Contrib. Plasma Phys. 180, 887 (2009)], which has been successfully modified to treat cylindrical geometry. Instability drive from plasma pressure gradients and flows is considered, focusing on resistive drift waves, the Kelvin-Helmholtz and rotational interchange instabilities. A general linear dispersion relation for partially ionized collisional plasmas including these modes is derived and analyzed. For LAPD relevant profiles including strongly driven flows it is found that all three modes can have comparable growth rates and frequencies. Detailed comparison with solutions of the analytic dispersion relation demonstrates that BOUT accurately reproduces all characteristics of linear modes in this system. PACS numbers: 52.30.Ex, 52.35.Fp, 52.35.Kt, 52.35.Lv, 52.65.Kj arXiv:1004.4674v4 [physics.plasm-ph] 26 Jan 2011 a)Electronic mail: [email protected] 1 I. INTRODUCTION Understanding complex nonlinear phenomena in magnetized plasmas increasingly relies on the use of numerical simulation as an enabling tool.
    [Show full text]
  • Twisted Flux Tube Emergence Creates Solar Active Regions
    Direct evidence: twisted flux tube emergence creates solar active regions MacTaggart D.1, Prior C.2, Raphaldini B.2, Romano, P. 3, Guglielmino, S.L.3 1School of Mathematics and Statistics, University of Glasgow, Glasgow, G12 8QQ, UK 2Department of Mathematical Sciences, Durham University, Durham, DH1 3LE, UK 3INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy The magnetic nature of the formation of solar active regions lies at the heart of understanding solar activity and, in particular, solar eruptions. A widespread model, used in many theoretical studies, simulations and the interpretation of observations1,2,3,4, is that the basic structure of an active region is created by the emergence of a large tube of pre-twisted magnetic field. Despite plausible reasons and the availability of various proxies suggesting the veracity of this model5,6,7, there has not yet been any direct observational evidence of the emergence of large twisted magnetic flux tubes. Thus, the fundamental question, “are active regions formed by large twisted flux tubes?” has remained open. In this work, we answer this question in the affirmative and provide direct evidence to support this. We do this by investigating a robust topological quantity, called magnetic winding8, in solar observations. This quantity, combined with other signatures that are currently available, provides the first direct evidence that large twisted flux tubes do emerge to create active regions. Twisted flux tubes are prominent candidates for the progenitors of solar active regions. Twist allows a flux tube to suffer less deformation in the convection zone compared to untwisted tubes, thus allowing it to survive and reach the photosphere to emerge2,9,10.
    [Show full text]
  • Shear Flow-Interchange Instability in Nightside Magnetotail Causes Auroral Beads As a Signature of Substorm Onset
    manuscript submitted to JGR: Space Physics Shear flow-interchange instability in nightside magnetotail causes auroral beads as a signature of substorm onset Jason Derr1, Wendell Horton1, Richard Wolf2 1Institute for Fusion Studies and Applied Research Laboratories, University of Texas at Austin 2Physics and Astronomy Department, Rice University Key Points: • A wedge model is extended to obtain a MHD magnetospheric wave equation for the near-Earth magnetotail, including velocity shear effects. • Shear flow-interchange instability to replace shear flow-ballooning and interchange in- stabilities as substorm onset cause. • WKB applicability conditions suggest nonlinear analysis is necessary and yields spatial scale of most unstable mode’s variations. arXiv:1904.11056v1 [physics.space-ph] 24 Apr 2019 Corresponding author: Jason Derr, [email protected] –1– manuscript submitted to JGR: Space Physics Abstract A geometric wedge model of the near-earth nightside plasma sheet is used to derive a wave equation for low frequency shear flow-interchange waves which transmit E~ × B~ sheared zonal flows along magnetic flux tubes towards the ionosphere. Discrepancies with the wave equation result used in Kalmoni et al. (2015) for shear flow-ballooning instability are dis- cussed. The shear flow-interchange instability appears to be responsible for substorm onset. The wedge wave equation is used to compute rough expressions for dispersion relations and local growth rates in the midnight region of the nightside magnetotail where the instability develops, forming the auroral beads characteristic of geomagnetic substorm onset. Stability analysis for the shear flow-interchange modes demonstrates that nonlinear analysis is neces- sary for quantitatively accurate results and determines the spatial scale on which the instability varies.
    [Show full text]
  • THEMIS-SOHO-Hinode - 2009 SCIENTIFIC PROPOSAL
    OBSERVING TIME PROPOSAL FORM FOR THEMIS-SOHO-Hinode - 2009 SCIENTIFIC PROPOSAL 1 General Information Principal Investigator: Brigitte Schmieder A±liation: Observatoire de Paris, LESIA Telephone: +33 1 45 07 78 17 Email address: [email protected] Co{Investigators(s): G. Aulanier, E.Pariat, J.M. Malherbe, T. Roudier, Guo Yang, Chandra R., V.Bommier, Lopez Ariste A. PIs of other instruments: E. DeLuca, A. Fludra, L. Golub, P.Heinzel, S. Gunar, P. Kotrc, N. Labrosse, Deng Y.Y., Li Hui, W. Uddin, Y. Kitai, A. Berlicki, T. Berger, Gosain S. A±liation(s): Observatoire de Paris (LESIA, LERMA), THEMIS IAC Spain, Observatoire Midi-Pyr¶enn¶ees,NRL (USA), SAO Harvard (USA), Rutherford Appleton Laboratory (UK), UIO (Norv`ege),HAO (USA), Ondrejov (Czech Rep.), University of Wales Aberystwyth, Huairou Solar Observing Station (China), Purple mountain Observatory (China), ARIES, Nainital (India), Hida Observatory (Kyoto, Japan), Bialkov (Poland) Title of Project: JOP157 Activity of magnetic features in the solar atmosphere (emergence, shear, dispersion) Specify the observation modes: MTR [X] IPM [] MSDP [X] Number of days requested: September 23 to October 10 2009 THEMIS - Observing time 2009 proposal 2 2 Proposed programme A - Scienti¯c rationale Concise scienti¯c background of the project, pertinent references; previous work plus justi¯cations for present proposal. The Scienti¯c Objectives and justi¯cation are the following: Emerging magnetic flux and reconnection Young Active Regions and new emerging magnetic flux produce MMFs associated with Eller- man Bombs (EBs). The models of emerging flux tubes assuming an Omega-shape are commonly accepted (observations of Arch Filament Systems, coronal loops).
    [Show full text]
  • Plasma and Magnetic-Field Structure of the Solar Wind at Inertial-Range Scale Sizes Discerned from Statistical Examinations of the Time-Series Measurements
    REVIEW published: 20 May 2020 doi: 10.3389/fspas.2020.00020 Plasma and Magnetic-Field Structure of the Solar Wind at Inertial-Range Scale Sizes Discerned From Statistical Examinations of the Time-Series Measurements Joseph E. Borovsky* Center for Space Plasma Physics, Space Science Institute, Boulder, CO, United States This paper reviews the properties of the magnetic and plasma structure of the solar wind Edited by: 6 Luca Sorriso-Valvo, in the inertial range of spatial scales (500–5 × 10 km), corresponding to spacecraft National Research Council, Italy timescales from 1s to a few hr. Spacecraft data sets at 1AU have been statistically Reviewed by: analyzed to determine the structure properties. The magnetic structure of the solar wind Bernard Vasquez, often has a flux-tube texture, with the magnetic flux tube walls being strong current sheets University of New Hampshire, United States and the field orientation varying strongly from tube to tube. The magnetic tubes also Yasuhito Narita, exhibit distinct plasma properties (e.g., number density, specific entropy), with variations Austrian Academy of Sciences (OAW), Austria in those properties from tube to tube. The ion composition also varies from tube to Julia E. Stawarz, tube, as does the value of the electron heat flux. When the solar wind is Alfvénic, the Imperial College London, magnetic structure of the solar wind moves outward from the Sun faster than the proton United Kingdom plasma does. In the reference frame moving outward with the structure, there are distinct *Correspondence: Joseph E. Borovsky field-aligned plasma flows within each flux tube. In the frame moving with the magnetic [email protected] structure the velocity component perpendicular to the field is approximately zero; this indicates that there is little or no evolution of the magnetic structure as it moves outward Specialty section: This article was submitted to from the Sun.
    [Show full text]
  • Simultaneous THEMIS Observations in the Near-Tail Portion of the Inner and Outer Plasma Sheet Flux Tubes at Substorm Onset V
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, A00C02, doi:10.1029/2008JA013527, 2008 Click Here for Full Article Simultaneous THEMIS observations in the near-tail portion of the inner and outer plasma sheet flux tubes at substorm onset V. A. Sergeev,1 S. V. Apatenkov,1 V. Angelopoulos,2 J. P. McFadden,3 D. Larson,3 J. W. Bonnell,3 M. Kuznetsova,4 N. Partamies,5 and F. Honary6 Received 23 June 2008; revised 13 August 2008; accepted 22 August 2008; published 19 November 2008. [1] We analyzed the measurements made by two Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes in ideal observational conditions (quiet background, near midnight, inside the substorm current wedge) during two distinct isolated substorm onsets, with probe P2 measuring the inner plasma sheet at 8 Re and P1 near the plasma sheet–lobe interface at 11–12 Re. The earliest onset-related strong perturbations were observed by P1; they include the increase of both Bz (dipolarization) and Ey (a few mV/m) as well as the simultaneous drop in total pressure, indicating the unloading process. This was also accompanied by fast inward plasma motion (up to 100 km/s, toward the neutral sheet) and fast plasma sheet thinning while the poleward auroral expansion was in progress in the conjugate ionosphere. These perturbations were followed after 6–8 min by the rapid expansion of the already heated plasma sheet. While in the adjacent lobe during this thinning phase, probe P1 continued to observe intense flux transfer toward the sheet center plane. The inner probe observed intense dipolarization and inward plasma injection but with a smaller flux transfer and starting 1–2 min after the perturbations at P1, supporting the conclusion that onset instability took place tailward of 12 Re.
    [Show full text]
  • Magnetic Flux Ropes in Space Plasmas
    Magnetic Flux Ropes in Space Plasmas Mark Moldwin UCLA 2007 Heliophysics Summer School With thanks to Mark Linton at NRL Goal of Lecture • Introduce one of the most ubiquitous features in space plasmas • Describe their Origin, Evolution, Structure, and impact • Will present combination of simulations, observations, and synthesis models What is a Flux Tube? • Ideal MHD’s frozen-in flux condition • Equation of motion has the pressure gradient and Lorentz term on RHS • Magnetic force has two components - magnetic pressure term acting perpendicular to field and a tension term along field. • Can think of flux tubes as mutually repulsive rubber bands Pop Quiz • BACKGROUND: Spacecraft X observes a magnetic field change over Y units of time. • How do you know if the observed change in B is due to the relative motion of a boundary past the spacecraft or dynamics/global change/transient in the background configuration? Lesson • Must make models to understand global structure and dynamics • Must use statistics to understand global structure and dynamics • Must make multiple, simultaneous, distributed measurements to understand global structure and dynamics What are Flux Ropes, and Who Cares? • Magnetized plasmas can form structures on various scales - shocks, discontinuities, waves, flux tubes, current sheets etc. • Some are created by magnetic reconnection and can have sharp and clear boundaries • Provide evidence of dynamics AND can give rise to significant energy and momentum flow from one region to another Coronal Mass Ejections are the primary driver of major Geomagnetic storms Their structure determines their geomagnetic effectiveness Pop Quiz • Draw a cartoon model of the structure produced by magnetic reconnection in the lower corona to make a CME.
    [Show full text]
  • Stability Study of the Cylindrical Tokamak--Thomas Scaffidi(2011)
    Ecole´ normale sup erieure´ Princeton Plasma Physics Laboratory Stage long de recherche, FIP M1 Second semestre 2010-2011 Stability study of the cylindrical tokamak Etude´ de stabilit´edu tokamak cylindrique Author: Supervisor: Thomas Scaffidi Prof. Stephen C. Jardin Abstract Une des instabilit´es les plus probl´ematiques dans les plasmas de tokamak est appel´ee tearing mode . Elle est g´en´er´ee par les gradients de courant et de pression et implique une reconfiguration du champ magn´etique et du champ de vitesse localis´ee dans une fine r´egion autour d’une surface magn´etique r´esonante. Alors que les lignes de champ magn´etique sont `al’´equilibre situ´ees sur des surfaces toriques concentriques, l’instabilit´econduit `ala formation d’ˆıles magn´etiques dans lesquelles les lignes de champ passent d’un tube de flux `al’autre, rendant possible un trans- port thermique radial important et donc cr´eant une perte de confinement. Pour qu’il puisse y avoir une reconfiguration du champ magn´etique, il faut inclure la r´esistivit´edu plasma dans le mod`ele, et nous r´esolvons donc les ´equations de la magn´etohydrodynamique (MHD) r´esistive. On s’int´eresse `ala stabilit´ede configurations d’´equilibre vis-`a-vis de ces instabilit´es dans un syst`eme `ala g´eom´etrie simplifi´ee appel´ele tokamak cylindrique. L’´etude est `ala fois analytique et num´erique. La solution analytique est r´ealis´ee par une m´ethode de type “couche limite” qui tire profit de l’´etroitesse de la zone o`ula reconfiguration a lieu.
    [Show full text]
  • Dynamics of Magnetic Flux Tubes in Close Binary Stars
    A&A 405, 303–311 (2003) Astronomy DOI: 10.1051/0004-6361:20030584 & c ESO 2003 Astrophysics Dynamics of magnetic flux tubes in close binary stars II. Nonlinear evolution and surface distributions V. Holzwarth1,2 and M. Sch¨ussler1 1 Max-Planck-Institut f¨ur Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany e-mail: [email protected] 2 School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK Received 28 February 2003 / Accepted 18 April 2003 Abstract. Observations of magnetically active close binaries with orbital periods of a few days reveal the existence of starspots at preferred longitudes (with respect to the direction of the companion star). We numerically investigate the non-linear dynamics and evolution of magnetic flux tubes in the convection zone of a fast-rotating component of a close binary system and explore whether the tidal effects are able to generate non-uniformities in the surface distribution of erupting flux tubes. Assuming a synchronised system with a rotation period of two days and consisting of two solar-type components, both the tidal force and the deviation of the stellar structure from spherical shape are considered in lowest-order perturbation theory. The magnetic field is initially stored in the form of toroidal magnetic flux rings within the stably stratified overshoot region beneath the convection zone. Once the field has grown sufficiently strong, instabilities initiate the formation of rising flux loops, which rise through the convection zone and emerge at the stellar surface. We find that although the magnitude of tidal effects is rather small, they nevertheless lead to the formation of clusters of flux tube eruptions at preferred longitudes on opposite sides of the star, which result from the cumulative and resonant character of the action of tidal effects on rising flux tubes.
    [Show full text]
  • Magnetosheath Flow Near the Subsolar Magnetopause∷ Zwan&Hyphen;Wolf and Southwood&Hyphen;Kivelson Theories
    GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 23, PAGES 3275-3278, DECEMBER 1, 1995 Magnetosheath flow near the subsolar magnetopause- Zwan-Wolf and Southwood-Kivelson theories reconciled DavidJ. Southwood I and Margaret G. Kivelson2 Instituteof Geophysicsand PlanetaryPhysics. University of California.Los Angeles Abstract. We reconcilethe superficiallycontradictory theories the flow upstreamof the magnetopause,the magneticfield should of flow immediately upstreamof the subsolarmagnetopause. decreaseand the gaspressure and plasmadensity should increase We show that the formation of a layer of enhancedfield and whilst Zwan and Wolf [1976] predict a region where the field depresseddensity immediately adjacent to the magnetopauseas increasesand the densityand pressuredecrease. Southwoodand predictedby Zwan and Wolf appearsto requirethe presence Kivelson[1992] acknowledgedthe differencebetween the Zwanand upstreamof a regionof enhancedpressure and field rarel•tction Wo/f[1976]predictions and their own theory. It is thepurpose of aspredicted by Southwoodand Kivelson. We thusargue that the thispaper to link thesetwo apparentlycontradictory notions and to detachedregions of enhanceddensity and the depletion layer arguethat not only do botheffects occur in practicebut they arepart adjacentto the magnetopauseare actually manifestationsof a of one and the same effect. singlephenomenon. The models of the solar wind flow around the Earth's magnetospherein the gas dynamic limit include the field only Introduction kinematically [Spreiter and Alksne, 1969; 1970]. The approach would be entirely adequateif the gas pressurebehind the shock The structureof the magnetosheathfield and flow patternnear everywheregreatly exceededthe magneticpressure. As Zwan and the magnetopauseis of greatinterest in solarterrestrial physics, the Wo/f[1976] point out, it is implicit in Alksne's[1967] calculations region marking as it does the interface between solar wind and that there alwayswill be a regionnear the magnetopausewhere field terrestrialplasma regimes.
    [Show full text]
  • 5 Magnetic Flux Tubes and the Dynamo Problem
    5 Magnetic flux tubes and the dynamo problem Manfred Schüssler and Antonio Ferriz-Mas The observed properties of the magnetic field in the solar photosphere and theoretical studies of magneto-convection in electrically well-conducting fluids suggest that the magnetic field in stellar convection zones is quite inhomogeneous: magnetic flux is concentrated into magnetic flux tubes embedded in significantly less magnetized plasma. Such a state of the magnetic field potentially has strong implications for stellar dynamo theory since the dynamics of an ensemble of flux tubes is rather different from that of a more uniform field and new phenomena like magnetic buoyancy appear. If the diameter of a magnetic flux tube is much smaller than any other relevant length scale, the MHD equations governing its evolution can be considerably simplified in terms of the thin- flux-tube approximation. Studies of thin flux tubes in comparison with observed properties of sunspot groups have led to far-reaching conclusions about the nature of the dynamo-generated magnetic field in the solar interior. The storage of magnetic flux for periods comparable to the amplification time of the dynamo requires the compensation of magnetic buoyancy by a stably stratified medium, a situation realized in a layer of overshooting convection at the bottom of the convection zone. Flux tubes stored in mechanical force equilibrium in this layer become unstable with respect to an undular instability once a critical field strength is exceeded, flux loops rise through the convection zone and erupt as bipolar magnetic regions at the surface. For parameter values relevant for the solar case, the critical field strength is of the order of 105 G.
    [Show full text]
  • Interchange Instability and Transport in Matter-Antimatter Plasmas
    WPEDU-PR(18) 20325 A Kendl et al. Interchange Instability and Transport in Matter-Antimatter Plasmas. Preprint of Paper to be submitted for publication in Physical Review Letters This work has been carried out within the framework of the EUROfusion Con- sortium and has received funding from the Euratom research and training pro- gramme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This document is intended for publication in the open literature. It is made available on the clear under- standing that it may not be further circulated and extracts or references may not be published prior to publication of the original when applicable, or without the consent of the Publications Officer, EUROfu- sion Programme Management Unit, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK or e-mail Publications.Offi[email protected] Enquiries about Copyright and reproduction should be addressed to the Publications Officer, EUROfu- sion Programme Management Unit, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK or e-mail Publications.Offi[email protected] The contents of this preprint and all other EUROfusion Preprints, Reports and Conference Papers are available to view online free at http://www.euro-fusionscipub.org. This site has full search facilities and e-mail alert options. In the JET specific papers the diagrams contained within the PDFs on this site are hyperlinked Interchange instability and transport in matter-antimatter plasmas Alexander Kendl, Gregor Danler, Matthias Wiesenberger, Markus Held Institut f¨ur Ionenphysik und Angewandte Physik, Universit¨at Innsbruck, Technikerstr.
    [Show full text]