A two-field gyrofluid model including ion finite Larmor radius (FLR)
corrections, magnetic fluctuations along the ambient field and electron inertia
is used to study two-dimensional reconnection in a low βe​ collisionless
plasma, in a plane perpendicular to the ambient field. Both moderate and large
values of the ion-to-electron temperature ratio Ï„ are considered. The
linear growth rate of the tearing instability is computed for various values of
Ï„, confirming the convergence to reduced electron magnetodynamics (REMHD)
predictions in the large Ï„ limit. Comparisons with analytical estimates in
several limit cases are also presented. The nonlinear dynamics leads to a
fully-developed turbulent regime that appears to be sensitive to the value of
the parameter Ï„. For Ï„=100, strong large-scale velocity shears
trigger Kelvin-Helmholtz instability, leading to the propagation of the
turbulence through the separatrices, together with the formation of eddies of
size of the order of the electron skin depth. In the Ï„=1 regime, the
vortices are significantly smaller and their accurate description requires that
electron FLR effects be taken into account