Electrodynamic Contributions to the Hall- and Parallel Electric Fields in Collisionless Magnetic Reconnection

In collisionless magnetic reconnection, the Hall electric field and the parallel electric field play important roles because they are responsible for acceleration of charged particles, especially electrons. Using particle-in-cell simulations, we study electrodynamic nature of the two electric fields in two-dimensional collisionless reconnection. We find that the Hall electric field is predominantly (greater than or similar to 90%) electrostatic; its electromagnetic (induced) component is small but nonzero (less than or similar to 10%). The parallel electric field or potential is contributed comparably by its electrostatic and induced components. In the electron inflow region, along the separatrix, and at the X-line, the electrostatic component of the parallel electric field (or potential) is larger; while in the electron outflow region, the electromagnetic (induced) component is larger. An initial guide field does not change the electrodynamic nature of the Hall electric field but does change that of the parallel electric field. In the guide field case, the parallel electric field is contributed predominantly by the electromagnetic component from the electron inflow region to the X-line and by the electrostatic component in the electron outflow region.