Abstract
Abstract. The energization of ions, due to interaction with electromagnetic turbulence (i.e. wave-particle interactions), has an important influence on H+ and O+ ions outflows in the polar region. The effects of altitude and velocity dependent wave-particle interaction on H+ and O+ ions outflows in the auroral region were investigated by using Monte Carlo method. The Monte Carlo simulation included the effects of altitude and velocity dependent wave-particle interaction, gravity, polarization electrostatic field, and divergence of auroral geomagnetic field within the simulation tube (1.2–10 earth radii, RE). As the ions are heated due to wave-particle interactions (i.e. ion interactions with electromagnetic turbulence) and move to higher altitudes, the ion gyroradius ρi may become comparable to the electromagnetic turbulence wavelength λ⊥ and consequently (k⊥ρi) becomes larger than unity. This turns the heating rate to be negligible and the motion of the ions is described by using Liouville theorem. The main conclusions are as follows: (1) the formation of H+ and O+ conics at lower altitudes and for all values of λ⊥; (2) O+ toroids appear at 3.72 RE, 2.76 RE and 2 RE, for λ⊥=100, 10, and 1 km, respectively; however, H+ toroids appear at 6.6 RE, 4.4 RE and 3 RE, for λ⊥=100, 10, and 1 km, respectively; and H+ and O+ ion toroids did not appear for the case λ⊥ goes to infinity, i.e. when the effect of velocity dependent wave-particle interaction was not included; (3) As λ⊥ decreases, H+ and O+ ion drift velocity decreases, H+ and O+ ion density increases, H+ and O+ ion perpendicular temperature and H+ and O+ ion parallel temperature decrease; (4) Finally, including the effect of finite electromagnetic turbulence wavelength, i.e. the effect of velocity dependent diffusion coefficient and consequently, the velocity dependent wave-particle interactions produce realistic H+ and O+ ion temperatures and H+ and O+ toroids, and this is, qualitatively, consistent with the observations of H+ and O+ ions in the auroral region at high altitudes.
Highlights
Accelerated ions at altitudes ranging from a few hundred kilometers to several Earth radii at auroral and polar cusp latitudes have been observed (Klumpar et al, 1984; Winningham and Burch, 1984; Arnoldy et al, 1992; Lundin et al, 1995; Eklund et al, 1997; Moore et al, 1999; Huddleston et al, 2000; Arvelius et al, 2005)
Chang and Coppi (1981) suggested a mechanism by which wave-particle interactions of ions with intense turbulence near lower hybrid frequency lead to ion conic formation observed by satellite, and the intense lower-hybrid waves that are detected along the discrete auroral geomagnetic field lines could be the prime cause for the ion acceleration process
The formation of ion conics is due to altitude dependent waveparticle interaction, which heats the ions in the perpendicular direction, and to the mirror force, which converts some of the energy gained in the perpendicular direction to the parallel direction
Summary
Accelerated ions at altitudes ranging from a few hundred kilometers to several Earth radii at auroral and polar cusp latitudes have been observed (Klumpar et al, 1984; Winningham and Burch, 1984; Arnoldy et al, 1992; Lundin et al, 1995; Eklund et al, 1997; Moore et al, 1999; Huddleston et al, 2000; Arvelius et al, 2005). In a series of studies, Barakat and Barghouthi (1994a, b), Barghouthi and Barakat (1995), Barghouthi (1997), Barghouthi et al (1998), Pierrard and Barghouthi (2006) and Barghouthi and Atout (2006) used Monte Carlo simulation to investigate the effect of wave-particle interaction on H+ and O+ outflows in the polar wind and auroral region They reported that the effect of finite gyroradius is responsible for production of the H+ and O+ toroids at high altitudes equatorward of the cusp that are observed by TIDE and TIMAS ion instruments on board the polar spacecraft.
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