Diodelike response of high‐latitude plasma in magnetosphere‐ionosphere coupling in the presence of field‐aligned currents

Abstract

The dynamic processes in the plasma along high‐latitude field lines plays an important role in ionosphere‐magnetosphere coupling process. We have created a time‐dependent, large‐scale simulation of these dynamics parallel to the geomagnetic field lines from the ionosphere well into the magnetosphere. The plasma consists of hot e− and H+ of magnetospheric origin and low‐energy e−, H+, and O+ of ionospheric origin. Including multiple electron species, a major improvement to the model, has allowed us for the first time to simulate the upward current region properly and to dynamically simulate the diodelike response of the field‐line plasma to the parallel currents coupling the ionosphere and magnetosphere. It is shown that return currents flow with small resistance, while upward currents produce kilovolt‐sized potential drops along the field, as concluded from satellite observations. The kilovolt potential drops are due to the effect of the converging magnetic field on the high‐energy magnetospheric electrons.

Multimoment convecting flux tube model of the polar wind system with return current and microprocesses

“…Here, we have generalized the earlier model (Mitchell et al, 1992;Ganguli et al, 1994) to include flux tube convection. The result of the generalization is a multimoment convecting flux tube model with anisotropic ion temperature and heat flows as well as field-aligned current and anomalous effects due to current-driven electrostatic ion-cyclotron (CDEIC) instability.…”

“…The multimoment models have been applied to a wide range of problems including large-scale modeling of the polar wind Schunk and Sojka, 1989), auroral return current regions , magnetosphere-ionosphere coupling (Mitchell et al, 1992), and potential structures generation (Ganguli et al, 1994). These investigations demonstrated importance of such non-Maxwellian features as temperature anisotropy, mirror force, field-aligned currents, and anisotropic heat flows for an accurate prediction of the large-scale plasma evolution.…”

“…To fill the gap between small-scale kinetic and global-scale MHD descriptions multimoment fluid models have been introduced (Barakat and Schunk, 1982;Mitchell and Palmadesso, 1983; Schunk and Sojka, 1989;Mitchell et al, 1992). In comparison with a MHD description, multimoment fluid models more accurately describe non-Maxwellian features, including temperature anisotropy, anisotropic heat flows, and can incorporate macroscopic consequences of the kinetic effects via anomalous transport coefficients (Mitchell and Palmadesso, 1983;.…”

“…Earlier flux tube models with non-Maxwellian features, field-aligned current and microprocesses (Mitchell et al, 1992;Ganguli et al, , 1994 were formulated for spatially stationary flux tubes, i.e., no flux tube convection was taken into account. However, horizontal motion is an important aspect of the high-latitude ionosphere-polar wind system.…”

A modified thermal conductivity for low density plasma magnetic flux tubes

“…More recently, as numerical simulations have become more sophisticated and more numerous, particularly for high latitudes, thermal conductivities have again been subjected to modification, frequently associated as much with the simulation conditions as with the plasma physical conditions [e.g. Mitchell et al 1992].…”