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GEOTAIL observations of total pressure and electric field variations in the near and mid‐distant tail associated with substorm onsets
Author(s) -
Miyashita Y.,
Machida S.,
Nishida A.,
Mukai T.,
Saito Y.,
Kokubun S.
Publication year - 1999
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 - 10.1029/1999gl900031
Subject(s) - substorm , physics , electric field , geophysics , astrophysics , magnetic field , magnetosphere , quantum mechanics
Selecting 263 substorm events with Pi 2 pulsation, we have statistically investigated temporal variations in the total pressure and the electric field ( E = − V × B ) in the near‐Earth magnetotail with GEOTAIL data. It was found that a total pressure decrease occurs first in the premidnight region around ( X, Y ) ∼ (−18, 7) R E in the GSM coordinates about 1 or 2 min before onset, and propagates to the surrounding regions successively. The dawn‐to‐dusk electric fields around X ∼ −10 R E and X ∼ −28 R E have the same magnitudes and develop considerably about 1 min after onset, while that around ( X, Y ) ∼ (−20, 5) R E is smaller. These results strongly suggest that the magnetic reconnection takes place at least 2 min earlier than the dipolarization, and that, on the average, the center of the energy release is initially located around the premidnight region of ( X, Y ) ∼ (−19, 6) R E .