Generalized fluid model of plasma outflow processes in the topside ionosphere

Abstract

The classical and anomalous transport properties of a multifluid plasma are investigated in the presence of auroral field aligned return currents, using a multimoment fluid model with anomalous transport coefficients. This approach offers the possibility of simulating large scale dynamic phenomena without neglecting the important macroscopic consequences of microscopic processes such as anomalous resistivity, turbulent heating, etc. The macroscopic effects of the electrostatic ion cyclotron (EIC) instability (perpendicular ion heating) and of an EIC-related anomalous resistivity mechanism which heats the electrons are included in the present version of the model. The responses of the outflowing ionospheric plasma to the application of current, with and without instabilities, are exhibited. The simulations show that the electron drift velocity corresponding to a return current of 0.65 μA/m 2 is above the threshold for EIC waves. The onset of EIC related anomalous resistivity enhances ion heating in two ways: (1) by inhibiting the growth of the critical electron-ion drift velocity, which must be exceeded to excite the EIC instability and (2) by increasing the relative drift velocity between the electrons and the ions, through the formation of density cavities due to increased ambipolar electric field. The anomalous resistivity associated with the turbulence is limited by electron heating, so that the EIC turbulence eventually saturates, but at a substantially higher ion transverse temperature than would be the case in the absence of resistivity. This process demonstrates a positive feedback loop in the interaction between the current driven EIC instability (CDICI), anomalous resistivity, and parallel large scale dynamics in the topside ionosphere.