PARTICLE ENTRY INTO THE MAGNETOSPHERE WITH A SOUTHWARD INTERPLANETARYMAGNETIC-FIELD STUDIED BY A 3-DIMENSIONAL ELECTROMAGNETIC PARTICLE CODE

We report progress in the long-term effort to represent the interactio n of the solar wind with the Earth's magnetosphere using a three-dimen sional electromagnetic particle code, A new run that includes an inter planetary magnetic field yields results that are encouragingly consist ent with established features of the solar wind-magnetosphere interact ion. After a quasi-steady state is established with an unmagnetized so lar wind we switch on a southward interplanetary magnetic field (IMF), which causes the magnetosphere to stretch and allows particles to ent er the cusps and nightside magnetosphere. Analysis of magnetic fields near the Earth confirms a signature of magnetic reconnection at the da yside magnetopause, and the plasma sheet in the near-Earth, magnetotai l clearly thins. Later magnetic reconnection also takes place in the n ear-Earth magnetotail, Arrival of southward IMF near the front of the magnetosphere causes a sunward velocity in the dayside magnetosphere, as required to feed flux tubes into the dayside reconnection process, Sunward flow near the equatorial plane of the magnetosphere implies a dawn-to-dusk electric field. Initially, the velocity in the distant ta il is not much affected by the southward turning. Therefore the dawn-d usk electric field increases in the sunward direction, which causes B- z to decrease with time in the near-Earth magnetotail. The cross-field current also thins and intensifies, which excites a kinetic (drift ki nk) instability along the dawn-dusk direction. As a result of this ins tability the electron compressibility effect appears to be reduced and to allow the collisionless tearing to grow rapidly with the reduced B -z component, At the same time the nightside magnetic fields are dipol arized and a plasmoid is formed tailward, We find that due to the reco nnection particles were injected toward the Earth from the neutral Lin e (X line), Consistent with this dawn-dusk electric field and magnetic reconnection at the dayside magnetopause, both ions and electrons ent er the magnetospheric interior easily, In our simulations, kinetic eff ects self-consistently determine the dissipation rate in the magnetopa use associated with reconnection.