A comparison study between observations and simulation results of Barghouthi model for O<sup>+</sup> and H<sup>+</sup> outflows in the polar wind

Abstract

Abstract. To advance our understanding of the effect of wave-particle interactions on ion outflows in the polar wind region and the resulting ion heating and escape from low altitudes to higher altitudes, we carried out a comparison between polar wind simulations obtained using Barghouthi model with corresponding observations obtained from different satellites. The Barghouthi model describes O + and H + outflows in the polar wind region in the range 1.7 R E to 13.7 R E , including the effects of gravity, polarization electrostatic field, diverging geomagnetic field lines, and waveparticle interactions. Wave-particle interactions were included into the model by using a particle diffusion equation, which depends on diffusion coefficients determined from estimates of the typical electric field spectral density at relevant altitudes and frequencies. We provide a formula for the velocity diffusion coefficient that depends on altitude and velocity, in which the velocity part depends on the perpendicular wavelength of the electromagnetic turbulence λ ⊥ . Because of the shortage of information about λ ⊥ , it was included into the model as a parameter. We produce different simulations (i.e. ion velocity distributions, ions density, ion drift velocity, ion parallel and perpendicular temperatures) for O + and H + ions, and for different λ ⊥ . We discuss the simulations in terms of wave-particle interactions, perpendicular adiabatic cooling, parallel adiabatic cooling, mirror force, and ion potential energy. The main findings of the simulations are as follows: (1) O + ions are highly energized at all altitudes in the simulation tube due to wave-particle interactions that heat the ions in the perpendicular direction, and part of this gained energy transfer to the parallel direction by mirror force, resulting in accelerating O + ions along geomagnetic field lines from lower altitudes to higher altitudes.(2) The effect of wave-particle interactions is negligible for Correspondence to: I. A. Barghouthi (barghouthi@science.alquds.edu) H + ions at altitudes below ∼7 R E , while it is important for altitudes above 7 R E . For O + wave particle interaction is very significant at all altitudes. (3) For certain λ ⊥ and at points, altitudes, where the ion gyroradius is equal to or less than λ ⊥ , the effect of wave-particle interactions is independent of the velocity and it depends only on the altitude part of the velocity diffusion coefficient; however, the effect of waveparticle interactions reduce above that point, called saturation point, and the heating process turns to be self-limiting heating. (4) The most interesting result is the appearance of O + conics and toroids at low altitudes and continue to appear at high altitudes; however, they appear at very high altitudes for H + ions. We compare quantitatively and qualitatively between the simulation results and the corresponding observations. As a result of many comparisons, we find that the best agreement occurs when λ ⊥ equals to 8 km. The quantitative comparisons show that ma...

O<sup>+</sup> and H<sup>+</sup> ion heat fluxes at high altitudes and high latitudes

“…The net effect of variable heating and indeed sporadic field-aligned electric fields in limited altitude regions can be expected to have a relatively good similarity to this average result. In particular our simulation provides a good similarity to many observations (Barghouthi, 2008;Barghouthi et al, 2011). Another strong point with using our steady-state solution is that if we did not run our model until steady state is achieved, we would have to initialize the density profile with a realistic density profile, and this choice of density profile would strongly affect our results.…”

“…It has been discussed by Barghouthi et al (2011) and Barghouthi (2008). However, one of the main objectives of this study is to discuss H + and O + ion heat fluxes in polar wind and auroral regions and to investigate the relationship between the shape of the ion velocity distribution function and the ion heat flux.…”

“…Currently, we and Barghouthi et al (2011) are searching through a significant amount of observational literature on ion outflow at high altitude and high latitude (e.g., Yau and Andre, 1997;Andre and Yau, 1997;Paschmann et al, 2002;and Moore and Horwitz, 2007), and according to our knowledge, there is no observations related to O + and H + ion heat fluxes in the altitude range (1.7-10 R E ), i.e., the range of our of study.…”

“…We keep repeating this till the results converge. Different altitude profiles for ion potential energy in both regions are given in Barghouthi et al (2011) and Barghouthi (2008).…”

Storm‐time electron density enhancement in the cleft ion fountain

“…At high altitudes, the electron density profile has been approximated by a power function (n e ∝ r Àa ) [Persoon et al, 1983;Johnson and Wygant, 2003;Nsumei et al, 2008]. Assuming a constant isotropic electron temperature, we used the simplest form of ambipolar electric fields [Banks and Holzer, 1968;Barakat and Schunk, 1983;Barghouthi et al, 2011] Integration constants are neglected in equations (B4), (B5), and (B7). In this calculation, a = 6 was assumed, since n e becomes $1500 /cm 3 at 7000 km altitude under this assumption, assuming n e = 1 /cm 3 at 7 R E on the basis of He + and O + density observations by the Polar satellite at $1900 UT.…”