FLUX-TRANSFER EVENTS ON THE MAGNETOPAUSE - SPATIAL-DISTRIBUTION AND CONTROLLING FACTORS

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 to determine the spatial distribution and controlling factors of flux transfer events (FTEs). Owing to the natural evolution of the orbital plane of the spacecraft, the dayside magnetopause region is eventually sampled both above and below the magnetic equator. Two types of magnetic signature in the component normal to the magnetopause are regularly 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, whereas in the southern dusk quadrant the reverse behavior occurs. The dividing line between the two signatures is tilted somewhat with respect to the equator along a south dawn-north dusk direction. However, deviations from this simple pattern are observed in both hemispheres. Examination of simultaneous IMP 8 and ISEE 3 interplanetary data reveals that FTEs occur almost exclusively during southward interplanetary magnetic field (IMF) conditions.