Simulation study of type 2 counterstreaming electrons along auroral field lines

Abstract

We examine the production of counterstreaming electrons associated with parallel fields along auroral field lines through the use of computer simulation. We use a 2½‐dimensional (two spatial and three velocity dimensions) electrostatic particle algorithm and auroral boundary conditions to set up a self‐consistent V potential structure. The simulation produces signatures of counterstreaming electrons resembling those observed by the Dynamics Explorer 1 (DE 1) satellite. The main signatures are as follows: (1) the phase space contours of the electron distribution function are elongated along the V∥ axis, and (2) the energy of electrons streaming in the upward direction is comparable to the energy of the accelerated electron beam. The simulation indicates that a portion of the accelerated electron beam is trapped by large amplitude electrostatic waves produced through the two‐stream instability. Strong wave‐particle interactions then thermalize the trapped electrons to produce suprathermal electrons streaming in the direction opposite to that of the accelerated electron beam. These results suggest a possible mechanism of producing counterstreaming electron fluxes through nonlinear processes of the two‐stream instability.