The magnetic and plasma structure of flux transfer events

Flux transfer events have been interpreted to be manifestations of transien t reconnection of the magnetospheric and magnetosheath magnetic fields at t he Earth's magnetopause. In this study we determine the interior structure of flux transfer events by examining high-resolution magnetic field and pla sma distribution functions from the ISEE 2 spacecraft. The sampling time an d cadence of these data are more than adequate tb resolve the rapidly chang ing plasma regimes and to avoid spatial aliasing. From these data we have c onfirmed the existence of two distinct legions within a flux transfer event (FTE), a central core and a field-draping region, and these two regions ha ve been found within FTEs observed both on the magnetosheath side and the m agnetospheric side of the magnetopause. The boundaries between the two regi ons are apparent in both the field and the plasma data. In the field-drapin g region the plasma distribution functions show little difference from thos e in the neighboring magnetosheath or magnetosphere, and the magnetic field consistently exhibits signatures expected from field-line draping around a flux tube. Within the central core region, plasma appears to be a mixture of the magnetosheath and magnetospheric components. In FTEs observed in the magnetosphere, we find transmitted magnetosheath plasma and a strong deple tion of hot magnetospheric plasma. In FTEs observed in the magnetosheath, w e find an outflow of magnetospheric plasma mixed with the magnetosheath pla sma. These signatures unambiguously show the reconnection of the interplane tary magnetic field and the Earth's magnetic field. Thus our observations i ndicate that the magnetic field lines within the central core region are op en allowing the inflow of cold magnetosheath plasma and the outflow of hot magnetospheric plasma through the open flux tube. The reconnection picture is further supported by the observation of separate electron and ion edges at the trailing boundary of a northward moving flux tube, expected as time- of-flight effects on newly reconnected field lines. Thus our observations a re consistent with the reconnected open flux tube interpretation for FTEs.