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Geotail observations of north‐south plasma velocity enhancements in the lobe near substorm expansion phase onset
Author(s) -
Taguchi S.,
Kiyohara M.,
Mukai T.,
Yamamoto T.,
Nose M.,
Saito Y.,
Kokubun S.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1998gl900132
Subject(s) - substorm , plasma sheet , physics , plasma , lobe , magnetic field , geophysics , perpendicular , magnetic reconnection , magnitude (astronomy) , current sheet , astrophysics , phase velocity , field (mathematics) , magnetosphere , magnetohydrodynamics , optics , geometry , mathematics , quantum mechanics , pure mathematics , anatomy , medicine
This paper reports on the enhancement of the lobe plasma velocity towards the neutral sheet. Analyzing the Geotail plasma and magnetic field data in the lobes earthward of X = −45 R E , we identified 30 events of several‐minute magnetic field increase‐and‐decrease during which the field tilts only southward; that is, the B Z variation is unipolar. For most of these events, we found that the lobe plasma velocity towards the neutral sheet is enhanced and peaked around the most southward tilting of the field. The average of the peak magnitude is about 130 km/s in a plane perpendicular to the magnetic field. For each case, this magnitude is roughly 1–10 % of the lobe Alfven speed. We interpret the velocity enhancement having these characteristics as signatures of the transition from plasma sheet reconnection to lobe reconnection at the near‐Earth neutral line.