Geography
Magnetosphere
The magnetosphere is the region surrounding a planet where its magnetic field interacts with the solar wind, a stream of charged particles emitted by the sun. This interaction creates a protective shield that deflects most of the solar wind, preventing it from reaching the planet's surface. Earth's magnetosphere plays a crucial role in protecting the planet from harmful solar radiation and cosmic rays.
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11 Key excerpts on "Magnetosphere"
- A.K. Oppenheim(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
It is expected that the International Magnetospheric Study 1976-78 will solve many of the problems involved, particularly those related to the timing of dynamical changes during substorms, the identification of spatial locations for these changes, the nature of magnetospheric boundaries and the energy budget in the solar wind-Magnetosphere-iono: phere system. 1. Introduction THE Magnetosphere is defined as the region of near-earth space that is threaded by magnetic field lines linked to the earth, and in which ionized gas predominates over the neutral atmosphere. It represents the outer limits of man's environment, and is populated with ions and electrons of the earth's upper atmosphere, with plasma captured from the impinging solar wind, and with high-energy particles trapped in the radiation belt. Using instrumented satellites, we have learned over the last decade or more that the particle and field structure surrounding the earth is extremely complex. However, it may in fact be one of the simpler of the natural systems found throughout the universe that have the capability to confine plasmas and accelerate particles to high energies. The surface and the atmosphere of the sun, and similarly the atmospheres of other stars, may contain a vast complex of electromagnetic-field systems that in many aspects are analogous to our earth's rnagnetosphere. We now know that the understanding of the stability of such field systems is fundamental to plasma-confinement problems, the solutions to which are being actively pursued in laboratory research. Thus the study of the earth's rnagnetosphere is important to our better understanding of the universe in which we live as well as to the solution of physical problems for the benefit of mankind. But the rnagnetosphere is also relevant in other, perhaps more practical or 1
eBook - PDFGeomagnetism
Volume 4
- John A. Jacobs(Author)
- 2016(Publication Date)
- Academic Press(Publisher)
The Magnetosphere MICHAEL SCHULZ 1 I N T R O D U C T I O N The Earth is, among other things, a large magnet (Gilbert, 1600). The Earth's magnetic field is subjected continuously to a plasma flow, known as the solar wind, that is directed outward from the Sun (Parker, 1958). The interaction between solar wind and geomagnetic field results in the for-mation of an electrical current layer, known as the magnetopause, behind which the Earth's magnetic field is (in first approximation) entirely confined (Chapman and Per raro, 1931). The region enclosed by the magnetopause is known as the Magnetosphere. It was deep within the Magnetosphere that the Earth's radiation belts, consisting of energetic charged particles trapped by the geomagnetic field, were discovered (Van Allen etaL, 1958; Vernov etaL, 1959a,b) at the beginning of the satellite era. However, the Magnetosphere is far more than a container for charged particles; it is a dynamical entity in its own right. The visible aurora, for example, is a major manifestation of magnetospheric dynamics observable from the Earth's surface as well as from orbiting spacecraft (see Fig. 1). The magnetic signatures of magnetospheric electrical currents are another. Interhemispheric propagation of radio signals, either transmitted from ground stations or generated by lightning discharges, is profoundly affected by the spatial distribution of magnetospheric plasma. Numerous additional manifestations of magnetospheric activity have become evident at rocket and satellite altitudes. Radiation-belt particle intensities, for example, are found to vary with time in a manner that suggests impulsive enhancement followed by exponential decay. A similar pattern of temporal variation is typical of the magnetospheric currents mentioned above. Moreover, the GEOMAGNETISM VOL. 4 Copyright © 1991 Academic Press Limited ISBN 0-12-378674-6 All rights of reproduction in any form reserved 2 Figure 1.
eBook - PDF- Jennifer A. Grier Ph.D., Andrew S. Rivkin(Authors)
- 2009(Publication Date)
- Greenwood(Publisher)
This was strong evidence in favor of new crust coming up from the ridge and being forced outward to either side, spreading the sea floor. And it allowed for an estimation of the timing of the formation of the new crust, as well. Plate tectonics and sea floor spreading are, of course, processes that con- tinue today. A PLANETARY Magnetosphere Just as with defining the atmosphere for a planet, defining Magnetosphere can be a challenge. It is sometimes used synonymously with ‘‘planetary magnetic field’’ or ‘‘region under the influence of a dipole,’’ but this is not quite accurate. The Magnetosphere of a planet results from the inter- actions between its magnetic field and the solar wind, including the potential involvement of a planetary atmosphere as well as the larger Interplanetary Magnetic Field (IMF) that is always in play throughout the solar system. There is a region around the Earth, a sphere of influence (not actually shaped like a sphere), where the Earth’s magnetic field has a dramatic effect on the movement of charged particles. Charged particles are impinging on this field at all times, most of them a part of the solar wind streaming from the Sun. Where the solar wind and the magnetic field meet forms the boun- dary of the planetary Magnetosphere. So a Magnetosphere is that area around a planet or other body where phenomena, like particle interactions, are dominated by the body’s magnetic field. The shape isn’t an actual Planetary Shield: Magnetospheric Processes • 113 sphere because the solar wind pushes on the Magnetosphere and forces it into a teardrop shape, with its tail ‘‘downwind’’ of the solar wind. And as one would expect from our previous discussion, the sort of particles that can be diverted by a planetary magnetic field are ones that have charge. Something like an electron, but also atoms, if the atoms have been ionized. An ion is an atom that is missing one or more electrons.
eBook - ePub- Lucy-Ann McFadden, Torrence Johnson, Paul Weissman(Authors)
- 2006(Publication Date)
- Academic Press(Publisher)
CHAPTER 28 Planetary Magnetospheres Margaret Galland Kivelson University of California, Los Angeles, California Fran Bagenal University of Colorado, Boulder Boulder, Colorado 1. What is a Magnetosphere? 2. Types of Magnetospheres 3. Planetary Magnetic Fields 4. Magnetospheric Plasmas 5. Dynamics 6. Interaction with Moons 7. Conclusions 1. What is a Magnetosphere? The term Magnetosphere was coined by T. Gold in 1959 to describe the region above the ionosphere in which the magnetic field of the Earth controls the motions of charged particles. The magnetic field traps low-energy plasma and forms the Van Allen belts, torus-shaped regions in which high-energy ions and electrons (tens of keV and higher) drift around the Earth. The control of charged particles by the planetary magnetic field extends many Earth radii into space but finally terminates near 10 Earth radii in the direction toward the Sun. At this distance, the Magnetosphere is confined by a low-density, magnetized plasma called the solar wind that flows radially outward from the Sun at supersonic speeds. Qualitatively, a planetary Magnetosphere is the volume of space from which the solar wind is excluded by a planet’s magnetic field. (A schematic illustration of the terrestrial Magnetosphere is given in Fig. 1, which shows how the solar wind is diverted around the magnetopause, a surface that surrounds the volume containing the Earth, its distorted magnetic field, and the plasma trapped within that field.) This qualitative definition is far from precise. Most of the time, solar wind plasma is not totally excluded from the region that we call the Magnetosphere. Some solar wind plasma finds its way in and indeed many important dynamical phenomena give clear evidence of intermittent direct links between the solar wind and the plasmas governed by a planet’s magnetic field
eBook - PDF- Minaketan Behara, Rudolf Fritsch, Rubens G. Lintz, Minaketan Behara, Rudolf Fritsch, Rubens G. Lintz(Authors)
- 2011(Publication Date)
- De Gruyter(Publisher)
It enlarges the cross section of the Earth by a large factor of the order of 400 and serves as a shield for energetic cosmic rays which are deflected in the strong external field configuration from reaching the Earth's surface. Similar Magnetospheres exist in various other astrophysical objects asplanets, magnetized stars, pulsars, and even galaxies. The Magnetosphere is a very complicated dynamic region exhibiting many vari-ational modes and spatial structures. The most important of these variations is the substorm. It is caused by magnetic energy release in the tail plasma of the Magnetosphere and leads to violent distortions of the external magnetic field and magnetospheric field configuration of time scales of the order of tens of minutes which are accompanied by reconfigurations of the Magnetosphere, particle accel-eration, and aurorae in the polar ionosphere. The magnetic variations resulting from ionospheric equivalent currents can be measured on the ground. During such 712 Section 11: R.A. TYeumann INJECTION of ELECTRONS ACCELERATED •TRAPPED CONICS Figure 12. Equipotential line configuration (left) in the upper ionosphere in the region where the auroral acceleration process takes place [23]. Shear motions lead to curved electric potential lines which result in parallel potential drops of U-like shape (right). These structures are electrostatic shocks, if turbulent, or double layers, if laminar, and are responsible for auroral electrons [24]. disturbances a variety of fast variations is excited, of electrical, magnetic, and elec-tromagnetic nature which result from the interaction of the plasma components in the Magnetosphere. Their investigation is carried out by the help of spacecraft and has opened the field of experimental and theoretical plasma physics and has found wide application in astrophysics. Acknowledgment This paper is based on an invited lecture given at the 2nd Gauss Symposium in Munich. The author ackowledges the hospitality of Professors R.
eBook - ePubMagnetohydrodynamic Waves in Geospace
The Theory of ULF Waves and their Interaction with Energetic Particles in the Solar-Terrestrial Environment
- A.D.M. Walker(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
PART 2THE SOLAR–TERRESTRIAL ENVIRONMENT
Passage contains an image
Chapter 12
The Sun, the solar wind, and the Magnetosphere
12.1 IntroductionSolar-terrestrial physics deals with the interaction between matter emitted from the Sun and the geospace environment. The region of interest extends from the Sun’s surface to the Earth’s ionosphere. In this region all matter is in the plasma state. Many of the processes occurring in the region are MHD processes.The dynamics of the Geospace region are governed by the interaction between the Earth’s magnetic field and the solar wind. The region over which the geomagnetic field is a dominant influence is called the Magnetosphere. In this chapter, we set the stage with a brief descriptive account of solar wind processes and the formation and structure of the Magnetosphere. This is to provide a context for our discussion of MHD waves and their interaction with the solar–terrestrial environment. MHD processes associated with the Sun are described in detail by Priest [160 ]. Discussions of magnetospheric structure and processes can be found in the books by Lyons and Williams [127 ], Baumjohann and Treumann [26 ], and Kivelson and Russell [112 ].12.2 The SunThe Sun is a medium-sized star, consisting largely of hydrogen with a significant fraction of helium. To a first approximation, it can be regarded a plasma in gravitational and magnetohydrostatic equilibrium. It is heated from within by a fusion reaction. Energy is conducted outwards from the core through the conduction region. At about two-thirds of the radius, convection becomes the dominant process. Its MHD behaviour is discussed by Priest [160 ]. Observational evidence for wide variety of phenomena outlined here are given by many authors [72 ,156 ,160 ]. Some major properties of the Sun are listed in table 12.1 .Table 12.1. Properties of the Sun.12.2.1 The visible outer regionsThe visible surface of the Sun is called the photosphere. Its position defines the solar radius. Visually, it has a changing granular structure as a consequence of the convection processes going on below it. It may be disturbed by violent phenomena occurring in active regions. These are consequences of MHD processes, driven by the energy source in the core. Immediately above the photosphere is a thin (~20 000 km) region called the chromosphere. Originally observed during solar eclipses, it can be seen on the sun’s limb at totality as having a pink colour. It is characterized by a rapid temperature rise through its thickness and a great deal of fine structure. It is not in thermal equilibrium with the interior and is probably heated by acoustic shock dissipation.
eBook - PDFSpace Physics
An Introduction
- C. T. Russell, J. G. Luhmann, R. J. Strangeway(Authors)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
10 The terrestrial Magnetosphere 10.1 INTRODUCTION Beginning in Chapter 4 , we examined the energy fl ow starting in the nuclear fi res of the Sun that both powers the optical emissions of the photosphere and heats the solar atmosphere producing the solar wind. When it reaches 1 AU, the momentum fl ux of the solar wind couples to the Earth ’ s Magnetosphere. Much of this coupling arises through the process known as magnetic reconnection. Just before the solar wind reaches the Earth ’ s Magnetosphere, its properties change dramatically as the solar wind crosses the bow shock that slows, heats, and compresses the solar wind, as discussed in Chapter 6 . This alteration, which is controlled by the Mach number of the bow shock, affects its ability to couple the solar-wind momentum to the stationary Magnetosphere, as we discussed in Chapter 9 . In the present chapter, we discuss the processes that occur within the magneto-sphere that result from the boundary conditions that the solar wind and reconnection have imposed upon the magnetopause. These processes stir the magneto-sphere, energize the ring current and the radiation belts, and control the loss processes therein. We begin by reviewing the structure of the magneto-sphere, including the polar cusp, the plasma mantle, the near-Earth plasma sheet, the ring current, and the plasmasphere. We follow with a discussion of the radiation belts, and close the chapter with a discus-sion of the waves in the Magnetosphere that interact with the radiation belts and the other particle popula-tions in the Magnetosphere. 10.2 THE STRUCTURE OF THE Magnetosphere The magnetic con fi guration of the Earth ’ s magneto-sphere is captured very simply in Figure 10.1 , which shows how the Earth ’ s magnetic fi eld (in the noon – midnight meridian) is con fi ned by the shocked solar-wind fl ow.
eBook - PDFAtmosphere, Ocean and Climate Dynamics
An Introductory Text
- John Marshall, R. Alan Plumb(Authors)
- 1969(Publication Date)
- Academic Press(Publisher)
Unfortunately, it is extremely difficult to measure the electric field in situ. The field is of order 1mV m -1 , whereas a variable field typically 100 times greater is developed around space vehicles by their motion across the geomagnetic field, and by photoemission from their surfaces, and other causes. However, the motions of barium clouds-if interpreted as electromagnetic drifts-do possess the expected order of magnitude, and may give a measure of ionospheric electric fields (Haerendel et al., 1967). 7.5 The Magnetosphere 7.5 THE Magnetosphere 241 7.51 THE EXTENT OF THE Magnetosphere Our picture of the Magnetosphere has evolved enormously since the launching of the first space probes. In this book, we are interested in its possible relationships with the ionosphere. The following brief account is based on contemporary ideas; we have drawn on the review papers of the 1966 Belgrade Symposium (King and Newman, 1967), especially the papers of Ness, Dungey, Obayashi, and O'Brien. In Fig. 61 we present a rough sketch of the Magnetosphere, viewed from the equatorial plane. The main geomagnetic field extends, in roughly dipole fashion, to dis-tances of a few earth radii. Beyond this it is influenced by the flow of charged particles known as the solar wind (see Parker, 1967), which causes the geo-Fig,61. Rough sketch of the earth's Magnetosphere, viewed from the equatorial plane. Solar wind flow is supersonic where shown by full arrows, but it is subsonic and disturbed in the apex of the sheath, where shown by dashed arrows. Some typical geomagnetic field lines are shown, though the extent to which they merge with the neutral sheet is ill defined. Black spots indicate two positions where neutral points may exist on the magnetopause. The domain of auroral particles is stippled, and the domain of stably trapped particles is shaded. 242 VII. GEOMAGNETISM AND THE IONOSPHERE magnetic field to be confined within a boundary called the magnetopause.
- Romain Maggiolo, Nicolas André, Hiroshi Hasegawa, Daniel T. Welling(Authors)
- 2021(Publication Date)
- American Geophysical Union(Publisher)
Part I The Earth Magnetosphere Passage contains an image
1 A Brief History of the Magnetosphere
David J. SouthwoodSpace and Atmospheric Physics, Imperial College, London, UKABSTRACT
The early history of the Magnetosphere is taken from the earliest suggestions of a material transport between Sun and Earth by Sabine in the nineteenth century, through the work of both Birkeland and Chapman and coworkers in the early twentieth century to the naming of the Magnetosphere, the proposal of the open Magnetosphere, and the discoveries of the first decade and a half of the space age.1.1 INTRODUCTION
One could begin a history of the Magnetosphere as early as 1600 when Gilbert published his “De Magnete,” which first treated the magnetism of the Earth as having an embedded planetary dipole. Alternatively, one could start with the coining of the term by Thomas Gold in the early space age in 1959. As neither Gilbert nor Gold really understood what turned out to be the most sensitive and basic scientific issues, it is probably a good compromise to start with Edward Sabine in 1852 (Sabine, 1852 ). In his report to the Royal Society of London, Sabine was the first to glimpse dimly the nature of the electromagnetic coupling between the Sun and Earth that is fundamental to both the formation of the Magnetosphere and also its activity.1.2 BRITISH WORK IN THE NINETEENTH CENTURY
Edward Sabine was a both scientist and a soldier, in the latter capacity seeing service in North America in the War of 1812. His interest in geophysics stemmed initially from working in geodesy. He moved from measuring terrestrial gravity to the study of the terrestrial magnetic field, which he realized needed to be surveyed globally. No doubt after pointing out to his superiors in a maritime nation with a global empire the relevance of understanding the magnetic field for navigational purposes, Colonel Sabine set up magnetic observatories across the globe. His 1852 paper reports results on the variation of the field with time at the widely separated locations of Toronto and Hobarton (now Hobart, Tasmania). Diurnal variations are seen but also there are disturbances detected at both sites widely separated in longitude and latitude. The most important comment he makes for our purpose is to relate his results to those of a German astronomer, Heinrich Schwabe, who had proposed from a long record of solar observations that sunspots exhibited a regular 11 year cycle. Sabine noted that the variation in global magnetic activity appeared to match Schwabe’s sunspot period. He further noted that Schwabe had failed to detect any change in terrestrial climate on the same scale. He then goes on to make the prescient remark “But it is quite conceivable that affections of the gaseous envelope of the Sun, or causes occasioning those affections, may give rise to sensible magnetical effects at the surface of our planet, without producing sensible thermic effects
eBook - PDF- Paul Weissman, Lucy-Ann McFadden, Torrence Johnson(Authors)
- 1998(Publication Date)
- Academic Press(Publisher)
Sometimes, as for a spring stretched beyond its breaking point, the Magnetosphere responds in a very nonlinear manner, with both field and plasma experiencing large-scale, abrupt changes. These changes can be identified readily in records of magne-tometers (a magnetometer is an instrument that mea- P L A N E T A R Y M A G N E T O S P H E R E S 491 sures the magnitude and direction of the magnetic field), in scattering of radio waves by the ionosphere or emissions of such waves from the ionosphere, and in the magnetic field configuration, plasma conditions and flows, and energetic particle fluxes measured by a spacecraft moving through the Magnetosphere itself. Auroral activity is the most dramatic signature of magnetospheric dynamics. Records from ancient days include accounts of the aurora (the lights flickering in the night sky that inspired fear and awe), but the oldest scientific records of magnetospheric dynamics are the measurements of fluctuating magnetic fields at the sur-face of the Earth. Consequently, the term geomagnetic activity is used to refer to magnetospheric dynamics of all sorts. Fluctuating magnetic signatures with timescales from seconds to days are typical. For exam-ple, periodic fluctuations at frequencies between 1 mHz and 1 Hz are called magnetic pulsations. In addition, impulsive decreases in the horizontal north– south component of the surface magnetic field (re-ferred to as the H-component) with timescales of tens of minutes occur intermittently at latitudes between 65 and 75 often several times a day. The field returns to its previous value typically in a few hours. These events are referred to as substorms. A signature of a substorm at an 70 latitude magnetic observatory is shown in Fig.
eBook - PDFGeomagnetism, Aeronomy and Space Weather
A Journey from the Earth's Core to the Sun
- Mioara Mandea, Monika Korte, Andrew Yau, Eduard Petrovsky(Authors)
- 2019(Publication Date)
- Cambridge University Press(Publisher)
and Boteler, D. (2016) A colorful blackout. IEEE Power Energy Mag., 14, 59–71. Prescott, G. B. (1866) History, Theory, and Practice of the Electric Telegraph. Ticnor and Fields, Boston. Sabine, E. (1852) On periodical laws discoverable in the mean effects of the larger magnetic disturbances – No. II. Philos. Trans. R. Soc. London, 142, 103–24. Turner, G. (2011) North Pole, South Pole: The Epic Quest to Solve the Great Mystery of Earth’s Magnetism. The Experiment, New York. 2.7 Geomagnetic Field and Biosphere Jean-Pierre Valet Magnetism has fascinated since the early discovery of the magnet. Despite its relatively weak strength, the Earth’s magnetic field does not escape this rule. It is generated by somehow mysterious motions within the Earth’s liquid core and interacts with Sun activity yielding amazing and splen- did events like aurorae. It is also remarkable that the geo- magnetic field history has been punctuated by large and puzzling convulsions that reach their apogee with the Geomagnetic Field and Biosphere 27 polarity reversals. These extraordinary phenomena incite to speculate on the existence of causal links between the Earth’s magnetic field and the biosphere. The geomagnetic field strength and its geometry impose the shape of the Magnetosphere surrounding the planet that is usually regarded as a shield which protects us against penetration of highly energetic cosmic and solar particles. The possibility of links between the geo- magnetic field and the biosphere has always generated a large interest which has been recently reactivated by the acquisition of long and detailed time series. The first studies emerged after two major discoveries. The first one was the observation of radiation belts (Van Allen and Franck, 1959), while the second one was the existence of geomagnetic reversals that were rapidly seen as events associated with weak field periods and therefore poor protection against harmful radiations that could affect the biosphere.
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