INTERPLANETARY MAGNETIC-FIELD ORIENTATION FOR TRANSIENT EVENTS IN THEOUTER MAGNETOSPHERE

It is generally believed that flux transfer events (FTEs) in the outer dayside magnetosphere, usually identified by transient (similar to 1 min) bipolar magnetic field perturbations in the direction normal to t he nominal magnetopause, occur when the magnetosheath magnetic field h as a southward component. We compare the results of three methods for determining the magnetosheath magnetic field orientation at the times of previously identified UKS/IRM events: (I) the average magnetosheath magnetic field orientation in the 30-min period adjacent to the neare st magnetopause crossing, (2) the magnetosheath magnetic field orienta tion observed just outside the magnetopause, and (3) the lagged interp lanetary magnetic field (IMF) orientation at the time of the transient events. Whereas the results of method 2 indicate that the events tend to occur for a southward magnetosheath magnetic field, the results of methods 1 and 3 show no such tendency. The fact that the three method s yield significantly different results emphasizes the need for cautio n in future studies.