EARLY TIME EVOLUTION OF A CHEMICALLY PRODUCED ELECTRON DEPLETION

The early time evolution of an ionospheric electron depletion produced by a radially expanding electron attachment chemical release is studi ed with a two-dimensional simulation model. The model includes electro n attachment chemistry, incorporates fluid electrons, particle ions an d neutrals, and considers the evolution in a plane perpendicular to th e geomagnetic field for a low beta plasma. Timescales considered are o f the order of or less than the cyclotron period of the negative ions that result as a by-product of the electron attachment reaction. This corresponds to time periods of tenths of seconds during recent experim ents. Simulation results show that a highly sheared azimuthal electron flow velocity develops in the radially expanding depletion boundary. This sheared electron flow velocity and the steep density gradients in the boundary give rise to small-scale irregularities in the form of e lectron density cavities and spikes. The nonlinear evolution of these irregularities results in trapping and ultimately turbulent heating of the negative ions.