Acceleration of hydrogen ions and conic formation along auroral field lines

Abstract

Electrostatic ion cyclotron turbulence and the formation of ion conics at low altitudes (• 1500 km) along auroral field lines have been investigated analytically and by plasma numerical simulations. Ion cyclotron waves are assumed to be driven unstable by the upgoing cold ionospheric electrons associated with the downward auroral current. When the electron drift speed is comparable to the electron thermal speed, it was found that the large-amplitude (e•b/T• • 1) coherent (w -f•i) ion cyclotron waves should exist along auroral field lines at low altitudes extending a few hundred kilometers. Ion conics are associated with ion cyclotron turbulence, and the ion bulk temperature is found to increase by a factor of 10 from the initial ionospheric temperature, while the temperature of the high-energy tail can be as much as 100 times the ionospheric temperature. Theory and simulations are in good agreement. 1. 899 900 OKUDA AND ASHOUR-ABDALLA: CONICS ALONG AURORAL FIELD LINES Perpendicular and Parallel Temperature versus Time T_L,(t)/T_L,(O) ß ß ß ß i ß ß r,, (t)/•, (o) ß ß ß ß ß ß ß ß ß ß , ß ß •11 I I A J ß ß ß 'r.j_;(t) / r.L;(O) ß ß ß ß ß Tiii(t) / Tlli(O) 0 40 80 120 160 200 Fig. 8. Perpendicular and parallel ion heating via a two-dimensional model. (Case 4.)

Simulation of electrostatic turbulence due to sheared flows parallel and transverse to the magnetic field

“…Since only a resonant group of electrons are involved in the energy transfer, the spectrum is peaked around the resonant frequency. Furthermore, the excited waves are saturated due to the ion perpendicular heating without frequency shifts [Okuda and Ashour-Abdalla, 1983]. On the other hand, Figures 12c and 12d are similar plots for the pure IEDDI case where R = oo.…”

Heating of heavy ions on auroral field lines in the presence of a large‐amplitude hydrogen cyclotron wave

“…The presence of such energy sources has been observed. The current-driven EIC waves have been studied extensively [Drummond and Rosenbluth, 1962;Kindel and Kennel, 1971;Pritchett et al, 1981;Okuda and Ashour-Abdalla, 1983]. It is shown that for an isothermal plasma (Te • T•) the critical electron drift for the onset of EHC wave is about 0.3v e. In the absence of an electron source such as the ionosphere, this instability is found saturated at a low level by a plateau formation of electrons, resulting in little ion heating.…”

Heating of Light Ions in the Presence of a Large Amplitude Heavy Ion Cyclotron Wave

“…Note, however, that the hydrogen perpendicular temperature increases monotonically in time without saturation until the end of the simulation. The final attainable perpendicular temperature may be given by the marginal stability theory for a given electron drift speed, which is about 4ve [Okuda and Ashour-Abdalla, 1983].…”