The 3-D Structure of Reconnection Jets

Abstract:

We explore the propagation and structure of 3-D reconnection jets in
the Earth's magnetotail using a kinetic model. The finite cross-tail
extent of the flow burst significantly changes the structure and
evolution of the jet. Ambient ions reflected from the jet front
produce a region of enhanced pressure that deflects the jet in the
cross-tail direction and dissipates a significant fraction of the bulk
flow energy. Thus, even subsonic jet fronts are dissipation sites for
bulk flow energy. Jets that are narrow in the cross-tail direction are
deflected dominantly in the direction of the ambient ion drift (dusk
direction) while wider jets are deflected in both directions. Mass
loading of the jet due to ions drifting into the jet from the dawn
reduce the peak jet velocity below the Walen prediction. The body of
the jet does not remain laminar but instead becomes strongly turbulent
as a result of instabilities growing on the sharp boundaries that
develop on dawn and dusk sides of the jet. Both sheared flow and
reconnection are drivers of this turbulence. These instabilities cause
the reconnection component of the magnetic field B_z to be highly
variable on spatial scales of around six ion inertial lengths, which
is consistent with that inferred from the typically bursty behavior of
B_z in satellite observations of the jet body. Finally, we discuss
the mechanisms that control the finite duration of flow bursts in the
magnetotail.