Abstract
Abstract. We present an analytical model for the magnetic field perturbations associated with flux transfer events (FTEs) on the dayside magnetopause as a function of the shear between the magnetosheath and magnetospheric magnetic fields and the ratio of their strengths. We assume that the events are produced by component reconnection along subsolar reconnection lines with tilts that depend upon the orientation of the interplanetary magnetic field (IMF), and show that the amplitudes of the perturbations generated during southward IMF greatly exceed those during northward IMF. As a result, even if the distributions of magnetic reconnection burst durations/event dimensions are identical during periods of northward and southward IMF orientation, events occurring for southward IMF orientations must predominate in surveys of dayside events. Two factors may restore the balance between events occurring for northward and southward IMF orientations on the flanks of the magnetosphere. Events generated on the dayside magnetopause during periods of southward IMF move poleward, while those generated during periods of northward IMF slip dawnward or duskward towards the flanks. Due to differing event and magnetospheric magnetic field orientations, events that produce weak signatures on the dayside magnetopause during intervals of northward IMF orientation may produce strong signatures on the flanks.
Highlights
Flux transfer events (FTEs) are common in the vicinity of the dayside magnetopause, where they can be identified on the basis of transient (∼1–2 min) bipolar magnetic field signatures normal to the nominal magnetopause centered on magnetic field strength enhancements (Russell and Elphic, 1978)
To reconcile this finding with an interpretation in terms of magnetic reconnection, Kawano and Russell (1997b) considered three possible explanations: (1) FTEs observed on the flanks originate locally via reconnection between antiparallel magnetosheath and magnetospheric magnetic fields, (2) FTEs observed on the flanks originate via component reconnection on the dayside magnetopause for southward interplanetary magnetic field (IMF) orientations, but via antiparallel reconnection on the high-latitude magnetopause during periods of northward IMF orientation, and (3) FTEs on the flanks originate along component reconnection lines passing through the subsolar magnetopause for all IMF orientations, but some process prevents events generated during periods of northward IMF orientation from being observed on the dayside
We propose that the orientation of FTEs relative to the draped magnetosheath and magnetospheric magnetic fields makes them difficult to observe on the dayside magnetopause during periods of northward IMF orientation
Summary
Flux transfer events (FTEs) are common in the vicinity of the dayside magnetopause, where they can be identified on the basis of transient (∼1–2 min) bipolar magnetic field signatures normal to the nominal magnetopause centered on magnetic field strength enhancements (Russell and Elphic, 1978) Because they tend to occur for southward IMF orientations (Berchem and Russell, 1984) and exhibit a mixture of magnetosheath and magnetospheric plasmas (Paschmann et al, 1982), FTEs are usually interpreted in terms of magnetic reconnection. Sibeck: Occurrence pattern of flux transfer events show no tendency to occur for the strongly antiparallel magnetosheath and magnetospheric magnetic fields that would favor local reconnection They could not rule out a source at high latitudes during intervals of strongly northward IMF orientation, they did demonstrate that events observed on the equatorial flank magnetopause during intervals when the IMF points slightly northward must originate along a dayside reconnection line. We discuss reasons why the same might not be true on the magnetotail flanks
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