2D PIC simulations of a curved supercritical shock: dynamics of the whistler precursor
Résumé
The whistler precursor emitted from the curved terrestrial shock front plays an important role in pre-decelerating and heating the incoming solar wind. Most previous works have mainly analyzed the features of the whistler precursor emission for a 1D planar shock where it is forced to propagate along the shock normal (Liewer and al, 1991) or to propagate obliquely with respect to a fixed shock normal direction in 2D planar shock simulation (Krauss-Varban et al., 1995). In the present case, the dynamics of the precursor is analyzed for a full curved shock with the help of a 2D full particle simulation where full curvature effects and both electrons and ions dynamics are described by a self consistent approach. Curvature effects continously cover all shock normal directions within the angular range 90° <= thetaBn <= 45° where thetaBn is the angle between the shock normal and the upstream magnetostatic field. This approach allows a free accessibility of the whistler precursor to a large angular range without any constraint. Preliminary results show that : (i) the whistler precursor strongly extends far from the shock front mainly along the magnetostatic field (projected on the simulation plane) but this extension is progressively reduced outside this privileged direction; (ii) wave fronts of the whistler precursor have a curvature similar to that of the main curved shock front but the width of these curved wave fronts strongly decreases when moving far from the shock front; (iii) near the shock front, the precursor is emitted within an angular range much larger than that predicted by linear theory; (iv) the critical angle of occurrence of the precursor fits with the theoretical value expected from Krasnoselskikh et al. (2002) model but this angle is not associated to a transition between stationary and non-stationary shocks in contrast with a statement announced by this theoretical model; and (v) the damping rate of the whistler precursor is analyzed for different directions of the shock normal and compared with previous modes (Gary et Mellott, 1985). These results will be discussed and compared with previous 1D and 2D simulations of planar shocks. References: Gary S. P. and M.M.Mellott, Whistler Damping at oblique propagation: Laminar Shock Precursors, J. Geophys .Res., 1985. Liewer J., K. Decyk, J.M. Dawson and B. Lembege, Numerical Studies of Electron Dynamics in Oblique Quasi-Perpendicular Collisionless Shock Waves, J. Geophys.Res. ,96, 9455, 1991. Krauss-Varban D., F. Pantellini et D. Burgess, Electron dynamics and whistler waves at quasi-perpendicular shocks , G. Res. Lett., 22, 16, 2091, 1995 Krasnoselskikh V. , B. Lembège, P. Savoini and V.V. Lobzin, Nonstationarity of strong Collisionless quasiperpendicular shocks: theory and full particle simulations, Phys. Plasma, 9, 4, 1192, 2002.