Westward cross-field motion of negative charge filament activated by gradient-curvature proton drift: A cause of the westward traveling surge

The cross-field interactive dynamics of two azimuthally elongated filaments of negative and positive charge excess which are close to each other is numerically studied. The negative charge filament is assumed to exist in the premidnight sector the plasmasheet, causing a discrete aurora at high latitude in the ionosphere. The positive charge filament responsible for a diffuse aurora is assumed to be caused by injection of the ring current energetic protons and located equatorward of the negative charge filament. In our simulation model using two-fluid approximation, the energetic protons execute the gradient and curvature (westward) drifts in the addition to the E x B drift and the electron motion is approximated by the E x B drift. The spatial and temporal development of the charge filaments is numerically followed in a perpendicular plane to the magnetic field. The simulation results show that the gradient and curvature drift of the positive charge carriers (energetic protons) can significantly increase the westward front-velocity of the negative charge filament is found to be on the order of a kilometer per second as geomagnetically projected on the ionosphere. It is then suggested that this physical process can be a cause of the westward traveling surge. copyright American Geophysical Union 1988