Abstract
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.
Highlights
Magnetic reconnection dominates the solar windmagnetosphere interaction
If a portion of this flow occurred within the core region of the event, the anticorrelated field and flow perturbations normal to the nominal magnetopause indicate an Alfven wave propagating parallel to the southward and duskward magnetosheath magnetic field, i.e. away from the postulated reconnection site at higher northern latitudes
To determine which flux transfer events (FTEs) flow velocity signatures are most prevalent, we identified 365 Geotail FTEs satisfying the magnetic field criteria described in Sect. 3 during the interval from February 1994 to June 1997
Summary
Magnetic reconnection dominates the solar windmagnetosphere interaction. During periods of southward interplanetary magnetic field (IMF) orientation, reconnection removes magnetic flux from the dayside magnetosphere, advects it across the polar cap, and deposits it in the Earth’s. Spacecraft entering the core region must observe intermediate densities and temperatures as well as a mixture of magnetosheath and magnetospheric plasmas, since the events contain interconnected magnetic field lines. Observations in the vicinity of the dayside magnetopause during periods of southward IMF orientation indicate that events marked by bipolar magnetic field signatures normal to the nominal magnetopause and enhanced (Russell and Elphic, 1978) or crater-like (Rijnbeek et al, 1987) magnetic field strength variations are common. Features with these characteristics are called flux transfer events (FTEs). We present case studies illustrating the range of signatures observed and a statistical survey describing the occurrence patterns of these signatures on the surface of the magnetopause
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