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Sciences de la Terre et de l'Univers
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The radial flux of charged particles from the sun called the solar wind is responsible of the existence of a cavity where the Earth’s magnetic field is confined, the magnetosphere. Inside the magnetosphere, the dynamics of the ionised gas (plasma) results from the interaction of the solar wind with the magnetosphere at its outer boundary. Because magnetic field lines in plasma are highly conducting, processes occurring at the magnetopause and in the outer magnetosphere map down along the Earth’s magnetic field lines, to the high-latitude ionosphere where their signatures can be observed by radars.
At high frequencies (HF), a radar signal transmitted to the ionosphere is refracted and partly backscattered by the small-scale electron density irregularities. The Doppler shift of the backscattered signal is a measure of the radial velocity of the plasma. SuperDARN (Dual Auroral Radar Network) radars can thus monitor the plasma convection over large areas (53° in azimuth and 3500 km in range). In order to determine a velocity vector from two independent components, two radars on different sites share a common field of view. SuperDARN is an international consortium and consists of a total of 35 radars operating in the Northern and Southern hemispheres. The French contribution to SuperDARN consists of the radar in Kerguelen.
Several coupling mechanisms occur at the boundary between the solar wind and the magnetosphere. The primary response of the magnetosphere to this interaction is plasma convection at various spatial and temporal scales and constitutes the main objective of SuperDARN. Global oscillations of the magnetosphere, magnetic conjugacy between hemispheres, reconnection in the tail and magnetospheric substorms, estimation of ionospheric electron density belong also to the scientific objectives of SuperDARN. The processes by which the energy from the Sun is transferred to the ionosphere and ultimately to lower altitudes in the atmosphere can thus be studied. Because of its global coverage and realtime data analysis, SuperDARN is also included in major magnetospheric research and space weather programs.