Global Particle Simulation for a Space Weather Model: Present and Future

The authors report progress in the long-term effort to represent the interaction of the solar wind with the Earth's magnetosphere using a three-dimensional electromagnetic particle model (EMPM) as a space weather model. Magnetohydrodynamic (MHD) simulation models have been refined to establish quantitative global modeling in comparison with observations. The EMPM has become more feasible as the power and speed of supercomputers have improved in recent years. Simulations with southward and dawnward turning IMFs have revealed the fundamental processes which have been confirmed by MHD simulations and observations. After a quasisteady state is established with an unmagnetized solar wind, a southward IMF is switched on, which causes the magnetosphere to stretch with reconnection at the dayside magnetopause. The plasma sheet in the near-Earth magnetotail clearly thins. The cross-field current also thins and intensifies, which excites a kinetic (drift kink) instability along the dawn-dusk direction. As a result of this instability the electron compressibility effect appears to be reduced and to allow the collisionless tearing to grow rapidly with the reduced B/sub z/ component. Later, magnetic reconnection also takes place in the near-Earth magnetotail. In the case where the northward IMF is switched gradually to dawnward, magnetic reconnection takes place at both the dawnside and duskside. The arrival of dawnward IMF at the magnetopause creates a reconnection groove which causes particle entry into the deep region of the magnetosphere via field lines that go near the magnetopause. The flank weak-field region joins onto the plasma sheet and the current sheet to form a geometrical feature called the cross-tail S that structurally integrates the magnetopause and the tail interior.