Near-Earth Reconnection Confined in the Plasmasheet during the Substorm Growth Phase: A Study of the November 24, 1996, Event

The present study examines a substorm event of November 24, 1996, with an emphasis on magnetic field and plasma flow measurements in the magnetotail during the growth phase. The unique and most intriguing feature of this event is a systematic change of the flow direction from earthward to tailward observed by the Geotail satellite at X = -21 Re. Good correlation between Vx and Bx suggests that observed variations of the flow velocity were spatial rather than temporal and that the earthward and tailward flows lasted at least 9 and 5 min, respectively. The signs of Bz and By variations also changed systematically along with the sign of Vx, which suggests that the observed flow reversal was caused by the earthward movement of a neutral line. This neutral line might be formed in association with a preceding pseudobreakup, and it is inferred that the associated reconnection did not reach the lobe magnetic field. Interestingly, during the interval of the flow reversal, other satellites observed typical growth-phase features. Geosynchronous magnetic field continued to be stretched in the midnight sector. The Interball and IMP-8 satellites observed continuous increase of the lobe field strength at X = -20 and -34 Re, respectively, in the premidnight sector. It is therefore concluded that the tail current intensification during the growth phase is a global process, whereas the near-Earth reconnection is a local process and at its early stage, it can proceed independently from the overall storage of the tail magnetic energy.