Topic/Type: 1. Plasma Simulation, Poster
D. Cai, B. Lembege, K-I Nishikawa
University of Tsukuba, LATMOS-UVSQ-IPSL-CNRS, NSSTC/NASA
Three-dimensional PIC (Particle-In-Cell) simulations are used to analyze the dynamics of the terrestrial magnetosphere under the impact of a varying IMF. The distance between the dayside magnetopause subsolar point and the \'Earth\' center, Rmp , is measured, as the intensity of southward IMF |Bz | is slowly varying. Based on the bifurcation theory, one analyzes the variation of ?Rmp as a reference index of the dynamics of this interaction, when IMF |Bz | successively increases and decreases to its original value. Striking results are: (i) as the IMF |Bz |increases above a critical value, the variation of Rmp ?suddenly changes (so called \'bifurcation\' process in field topology); ?(ii) the subsolar point recovers its original location by following different paths as the IMF |Bz | value successively ?increases (from zero to a maximum fixed value) and decreases (from this maximum to zero) passing through some critical values. These different paths are the signature of an \'hysteresis\' effect, and are characteristic of the so-called \'subcritical-type bifurcation\'. This hysteresis signature indicates that dissipation processes take place via an energy transfer from the solar wind to the magnetosphere by some irreversible way, which leads to a drastic change in the magnetospheric field topology. This hysteresis is interpreted herein as a consequence of the magnetic reconnection taking ?place at the dayside magnetopause. Based on the field topology theory, Rmp can be replaced by the some topological function, for example, the distance between bifurcated negative and positive nulls or the strength of the magnetic field connecting these two nulls. ?The positive or negative nulls on the magnetosphere can bifurcate in pairs one on dawn and one on dusk side or vice versa. ?The choice of positive or negative null on either dawn or dusk side is the ?bifurcated topology? which the magnetospheric system decided. The critical topology can appear before the bifurcation in order to let the magnetic reconnection occurs structurally in 3D.