Interplanetary magnetic field orientation for transient events in the outer magnetosphere

It is generally believed that flux transfer events (FTEs) in the outer dayside magnetosphere, usually identified by transient (∼1 min) bipolar magnetic field perturbations in the direction normal to the nominal magnetopause, occur when the magnetosheath magnetic field has 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: (1) the average magnetosheath magnetic field orientation in the 30‐min period adjacent to the nearest magnetopause crossing, (2) the magnetosheath magnetic field orientation observed just outside the magnetopause, and (3) the lagged interplanetary 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 methods yield significantly different results emphasizes the need for caution in future studies.