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ABSTRACT
We present THEMIS observations of a substorm
on March 1, 2008 to substantiate the global M-I coupling substorm model
that initiates dipolarization by the Cowling electrojet current loop
(CECL). The Cowling electrojet is intensified by the induced equatorward
E-field measured by Mozer (1971) driven by the earthward convection that
is enhanced by the NEXL observed at X ~ −15 RE. Divergence of the
Cowling electrojet launches Alfvén waves to form the time-dependent
CECL, which then initiates the dipolarization as proposed by Kan (2007).
Predictions of the CECL model include: (I) Brightening of the substorm
onset preceded the dipolarization onset by ~80 ± 3 sec. This is
consistent with the Alfvén travel time from the ionospheric footprint
to the THEMIS-D in the neutral sheet estimated at ~80.3 sec based on
the AM02 field model (Kubyshkina et al., 2009). (II) The substorm onset
arcs are imbedded in the Cowling electrojet channel and connected by
field lines to the dipolarization region. This is consistent with the
observations that the Cowling electrojet peaked around ~67deg-68deg geomagnetic
latitudes and extended from ~20 to ~02 MLT, which overlaps the substorm
onset arcs and the footprints of THEMIS-D and -E satellites.
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