  We report a unique conjugate observation of fast flows and associated current
sheet disturbances in the near-Earth magnetotail by MMS (Magnetospheric
Multiscale) and Cluster preceding a positive bay onset of a small substorm at
~14:10 UT, Sep. 8, 2018. MMS and Cluster were located both at X ~-14 RE. A
dipolarization front (DF) of a localized fast flow was detected by Cluster and
MMS, separated in the dawn-dusk direction by ~4 RE, almost simultaneously.
Adiabatic electron acceleration signatures revealed from comparison of the
energy spectra confirm that both spacecraft encounter the same DF. We analyzed
the change in the current sheet structure based on multi-scale multi-point data
analysis. The current sheet thickened during the passage of DF, yet, temporally
thinned subsequently associated with another flow enhancement centered more on
the dawnward side of the initial flow. MMS and Cluster observed intense
perpendicular and parallel current in the off-equatorial region mainly during
this interval of the current sheet thinning. Maximum field-aligned currents
both at MMS and Cluster are directed tailward. Detailed analysis of MMS data
showed that the intense field-aligned currents consisted of multiple
small-scale intense current layers accompanied by enhanced Hall-currents in the
dawn-dusk flow-shear region. We suggest that the current sheet thinning is
related to the flow bouncing process and/or to the expansion/activation of
reconnection. Based on these mesoscale and small-scale multipoint observations,
3D evolution of the flow and current-sheet disturbances was inferred preceding
the development of a substorm current wedge.

Earth and Planetary Astrophysics;Space Physics