Earth Planets Space, Vol. 57 (No. 6), pp. 515-520, 2005
I. A. Barghouthi
Department of Physics, AL-Quds University, P.O. Box 20002, Jerusalem, Palestine
(Received June 13, 2004; Revised May 7, 2005; Accepted May 9, 2005)
We have used Monte Carlo simulations of O+ velocity distributions in the high latitude F- region to improve the calculation of incoherent radar spectra in auroral ionosphere. The Monte Carlo simulation includes ion-neutral, O+-O+ collisions (resonant charge exchange and polarization interaction) as well as O+-O+Coulomb self-collisions. At high altitudes, atomic oxygen O and atomic oxygen ion + dominate the composition of the auroral ionosphere and consequently, the influence of O+-O+Coulomb collisions becomes significant. In this study we consider the effect of O+-O+Coulomb collisions on the incoherent radar spectra in the presence of large electric field (100 mVm-1). As altitude increases (i.e. the ion-to-neutral density ratio increases) the role of O+-O+Coulomb self-collisions becomes significant, therefore, the one-dimensional, 1-D, O+ ion velocity distribution function becomes more Maxwellian and the features of the radar spectrum corresponding to non-Maxwellian ion velocity distribution (e.g. baby bottle and triple hump shapes) evolve to Maxwellian ion velocity distribution (single and double hump shapes). Therefore, O+-O+Coulomb self-collisions act to isotropize the 1-D O+ velocity distribution by transferring thermal energy from the perpendicular direction to the parallel direction, however the convection electric field acts to drive the O+ ions away from equilibrium and consequently, non-Maxwellian O+ ion velocity distributions appeared. Therefore, neglecting O+-O+Coulomb self-collisions overestimates the effect of convection electric field.
Key words: Incoherent radar spectra, auroral ionosphere, Coulomb collision, convection electric field, Monte Carlo simulation.