Role of kinetic instabilities driven by temperature anisotropy in the evolution of current sheets and magnetic reconnection

We investigate the role of kinetic instabilities driven by proton anisotropies on the onset and evolution of magnetic reconnection by means of 2-D hybrid simulations. The collisionless tearing of a current sheet is studied confirming that anisotropic protons within the current sheet region can significantly enhance/stabilize the tearing instability of the current. Moreover, fluctuations associated with linear instabilities excited by large proton temperature anisotropies can significantly influence the stability of the plasma and perturb the current sheets, triggering the tearing instability. Such coupling leads to faster tearing evolution when an ion-cyclotron instability is triggered by anisotropic proton distribution functions with large perpendicular temperatures. If instead the parallel temperature is sufficiently large compared to the perpendicular temperature, fire hose fluctuations excited by the unstable background protons are not able to efficiently destabilize current sheets, which remain stable for a long time after fire hose saturation. We discuss possible influences of this novel coupling on the solar wind and heliospheric plasma dynamics.