Turbulence associated with magnetopause reconnection

Abstract:

We present a detailed analysis of the turbulence produced in
three-dimensional particle-in-cell simulations of magnetic
reconnection at the magnetopause. The parameters are representative of
an electron diffusion region encounter made by the Magnetospheric
Multiscale (MMS) mission. The turbulence is found to develop around
both the magnetic x-line and separatrices, is electromagnetic in
nature, is characterized by a wavevector k given by
kρ_e ~(m_e/m_i)^1/4 with ρ_e the electron Larmor
radius, and has the ion pressure gradient as its source of free
energy. Taken together, these results suggest the instability is a
variant of the lower-hybrid drift instability. The turbulence
produces electric field fluctuations in the out-of-plane direction
(the direction of the reconnection electric field) with an amplitude
of around ±10mV/m, which is much greater than the large-scale
reconnection electric field of around 0.1mV/m. Such large values of
the out-of-plane electric field have been identified in the MMS
data. The turbulence in the simulations controls the scale lengths of
the density profile and current layers in asymmetric reconnection,
driving them closer to (ρ_eρ_i)^1/2 than the ρ_e or
d_e scalings seen in 2D reconnection simulations. Ongoing
investigations include whether this electromagnetic turbulence leads
to small scale reconnection events and associated large but localized
reconnection electric fields and whether the electron temperature
anisotropy that develops along the magnetospheric separatrix due to
the electron cusp orbits is strong enough to drive whistlers unstable.