Articles | Volume 25, issue 10
https://doi.org/10.5194/angeo-25-2195-2007
https://doi.org/10.5194/angeo-25-2195-2007
06 Nov 2007
 | 06 Nov 2007

High-altitude and high-latitude O+ and H+ outflows: the effect of finite electromagnetic turbulence wavelength

I. A. Barghouthi, N. M. Doudin, A. A. Saleh, and V. Pierrard

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.