Particle-in-cell simulations of current shear-driven instabilities and the generation of broadband ELF fluctuations

Three-dimensional electromagnetic particle-in-cell (PIC) simulations are performed to study the properties of current shear-driven (CSD) instabilities, which are driven by the free energy stored in the inhomogeneous transverse magnetic field and associated with the transverse gradient of the field-aligned current. Current shear-driven instabilities are unstable in both a static field-aligned current equilibrium and the sheared field-aligned current sheet embedded in a transversely finite Alfven wave. The simulation results demonstrate that the electromagnetic fluctuations generated by CSD instabilities have characteristics similar to the broadband ELF (BBELF) fluctuations observed in the topside auroral region and at higher altitudes. It is also shown that CSD instabilities have the capacity to accelerate ions transversely. Comparison of the PIC simulations with the satellite observations and three-dimensional, two-fluid MHD simulations supports CSD instabilities as potential candidates for the generation of BBELF fluctuations and the correlated transverse acceleration of ions.