Mhd Turbulence in the Saturn`s Magnetosheath Downstream of a Quasi Perpendicular and a Quasi Parallel Shock
نویسندگان
چکیده
The magnetosphere of the Earth and the other planets contain a variety of low frequency (f < fp, fp being the proton gyrofrequency) waves. Several sources are known to contribute to these uctuations: (1) Waves present in the solar wind (mainly those occurring in the foreshock) are convected in the magnetosheath and possibly ampli ed passing through the shock front. (2) The bow shock modi es the velocity distribution of the particles crossing its surface, thus producing instabilities, which give origin to di erent types of waves. (3) Plasma instabilities may also arise inside the magnetosheath, where the plasma ow is slowed and diverted, as it approaches the magnetopause. (4) Finally, the magnetopause can be directly responsible of wave generation, e.g. via the Kelvin Helmholtz instability. The last point will not be discussed in this paper. In the outer magnetosheath, the features of the turbulence are mainly controlled by the bow shock structure, which may be quasi perpendicular ( Bn <45 ), where B is the interplanetary magnetic eld and n the shock normal, or quasi parallel ( Bn > 45 ). In the inner subsolar magnetosheath, an important role is played by the magnetic shear across the magnetopause, i.e. by the angle # between the magnetosheath magnetic eld and the geomagnetic eld (Phan et al., 1994). In general, for low values of #, the magnetopause is locally a tangential discontinuity, while, for high values ot #, it becomes a rotational discontinuity, through which magnetic eld reconnection occurs. As a consequence,
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Mhd Turbulence in Saturn's Magnetosheath Downstream of a Quasi Parallel Bow Shock
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