STRUCTURE AND DYNAMICS OF THE MAGNETOPAUSE CURRENT LAYER (FLUX TRANSFER EVENTS, RECONNECTION, ROTATIONAL DISCONTINUITY)

Magnetic field profiles across the dayside magnetopause, obtained during the first five years (1977-1981) of the ISEE mission have been examined in boundary normal coordinates. Only a small fraction of the hodograms of the magnetic field perturbation inside the current layer, show the circular rotation expected for magnetopause of the rotational discontinuity type. However, observed senses of rotation are not consistent with the electron polarization predicted by the linear theory. Rotations greater than 180 degrees are not observed for quiescent magnetopauses. Our study suggests that the rotation is in fact controlled by the relative orientation between magnetosheath and magnetospheric fields. The magnetopause assumes the polarization needed to minimize the angular shear between both directions.;Spatial distribution and controlling factors of flux transfer events (FTE's) are also investigated. Two types of magnetic signature in the component normal to the magnetopause are observed when an FTE passes the spacecraft. In the northern dawn quadrant the perturbation along the normal direction is usually first outward and then inward; in the southern dusk quadrant the reverse behavior occurs. Deviations from this sample pattern are observed in both hemispheres. Simultaneous interplanetary data reveal that FTE's occur almost exclusively during southward interplanetary magnetic field (IMF) conditions. FTE's occur about 45% of the time when the IMF has a southward component, with greatest occurrence for due southward IMF. The east-west polarity of the IMF does not control the rate of FTE occurrence.;Several periods of a limited number of orbits of close separation between the dual ISEE 1 and 2 spacecraft allow us to reliably measure of the velocity and thickness of the current layer. In almost 50% of the cases the velocity varies between a few km/s to 45 km/s and the thickness between 600 to 1000 km. Velocities about 200 km/s, and thicknesses of the order of 2000 km are occasionally measured. The ion gyroradius does not appear to scale the variation observed and the thickness is better ordered by magnetic dipole latitude. The magnetopause is thinnest at the magnetic equator (about 500km), suggesting that reconnection is initiated in the equatorial region rather than in the polar cusps.