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Accueil > Recherche > Plasmas Spatiaux > Thématiques scientifiques > The Magnetopause of the Earth

The Magnetopause of the Earth

  LPP team

G. Belmont, N. Cornilleau-Wehrlin, A. Retinò, L. Rezeau

 Selection of publications

  • Dorville N., Belmont G., Rezeau L., Grappin R., Retinò A., Rotational/compressional nature of the magnetopause : Application of the BV technique on a magnetopause case study, Journal of Geophysical Research Space Physics 119 1898-1908 (2014)
  • Rossi C., Califano F., Retinò, A., Sorriso Valvo L., Henri P., Valentini F.,
    Servidio S.,Chasapis A.,and Rezeau L., Two dimensional turbulence inside Kelvin-Helmholtz vortices at the terrestrial magnetopause, Physics of Plasmas, 22 (12), 2303, doi : 10.1063/1.4936795, (2015)

 What is a magnetopause ?

Earth, like other planets or satellites of the solar system, has an intrinsic magnetic field, mainly generated by a dynamo effect due to convection in the Earth’s core, composed of 90% of liquid iron. Close to Earth, this field is mostly dipolar. However, at greater distances, of the order of several Earth radii, it is compressed and deformed by the effect of its interaction with the solar wind. The area dominated by the Earth’s magnetic field, called the magnetosphere, thus has a flattened shape towards the sun (nose of the magnetosphere) and stretched on the other side (magnetotail).

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The Magnetosphere of the Earth
Schematics of the solar wind-magnetosphere interaction. The Sun is far left. The magnetic field lines of the magnetosphere (in violet) are calculated by the Tsyganenko model. The solar wind speed is shown by the yellow arrows.
Credit. P. Robert, LPP

When the supersonic wind of charged particles emitted by the Sun meets the magnetic obstacle, it is slowed down and compressed by a shock, forming around the Earth’s magnetosphere, the region called magnetosheath. This region surrounds the magnetosphere, which appears as a "bubble" in the interior of it, with a density ten times lower and a temperature ten times higher. The magnetic field of the magnetosheath essentially representative of that carried by the solar wind, is very different, especially for his direction of that generated by the Earth’s dynamo.
The boundary called terrestrial magnetopause is the thin boundary that exists between magnetosheath and magnetosphere, that is to say between two regions of different magnetic fields, as well as of different densities and temperatures. The magnetopause does not have a regular shape or a constant position, but is continupislmy in movement and in deformation, due to solar wind variations, local development of instabilities and in particular the existence of surface waves. Its relatively low distance from the Earth makes it an ideal place for the in-situ study of interfaces such fine transition between two different plasmas and magnetic fields. His study is of general interest in astrophysics and plasma physics. It is the place of universal processes such as magnetic reconnection or instability Kelvin-Helmholtz.

 Space exploration

Some of the scientific missions to which LPP participates have among their objectives a better understanding of the structure of this bondaryr and of the physical phenomena that prevail there. This is the case of missions like Cluster, THEMIS , or MMS. A number of more distant exploration missions, such as the mission Cassini or Juice, in the future, are also used to study magnetopauses of other solar system objects.

  Questions studied at LPP

Studies at LPP concern the determination of the boundary structure when it is at rest and how it is perturbed. At rest, there is to understand how the solar wind plasma and the magnetospheric one do interpenetrate. Can this boundary be simply described using discontinuities theories in plasmas ? How to experimentally characterize this structure and how can we understand it with the help of the theory (kinetic equilibrium) and of numerical simulations ? This is actually a complex boundary, far from being stationary and impenetrable, but which is perturbed by the inhomogeneities of the incoming solar wind plasma and by local instabilities, especially the Kelvin-Helmholtz instability and the tearing instability. From an experimental point of view, it raises delicate issues of data processing : Is it flat ? What is the normal direction ? How to characterize its motion ? How to diagnosis the presence of instabilities ?

CNRS Ecole Polytechnique Sorbonne Université Université Paris-Saclay Observatoire de Paris
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Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Dominique Fontaine (Directrice)