Geotail observations of FTE velocities

Abstract. We discuss the plasma velocity signatures expected in association with flux transfer events (FTEs). Events moving faster than or opposite the ambient media should generate bipolar inward/outward (outward/inward) flow perturbations normal to the nominal magnetopause in the magnetosphere (magnetosheath). Flow perturbations directly upstream and downstream from the events should be in the direction of event motion. Flows on the flanks should be in the direction opposite the motion of events moving at subsonic and subAlfvénic speeds relative to the ambient plasma. Events moving with the ambient flow should generate no flow perturbations in the ambient plasma. Alfvén waves propagating parallel (antiparallel) to the axial magnetic field of FTEs may generate anticorrelated (correlated) magnetic field and flow perturbations within the core region of FTEs. We present case studies illustrating many of these signatures. In the examples considered, Alfvén waves propagate along event axes away from the inferred reconnection site. A statistical study of FTEs observed by Geotail over a 3.5-year period reveals that FTEs within the magnetosphere invariably move faster than the ambient flow, while those in the magnetosheath move both faster and slower than the ambient flow.