Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 1 A parametric study

Abstract

Abstract. The transport patterns of non-thermal H + and O + field-aligned flows from the dayside cusp/cleft, associated with transverse heating by means of wave-particle interactions and in combination with the poleward motion due to the magnetospheric convection are investigated. This has been accomplished by developing a steady-state, two-dimensional, trajectory-based code. The ion heating is modelled by means of a Monte Carlo technique, via the process of ion cyclotron resonance (ICR), with the electromagnetic left-hand circular polarized component of a broad-band, extremely low-frequency (BBELF) turbulence. The altitude dependence of ICR heating from 1000 km to 3 Earth radii (RE) is modelled by a power law spectrum, with an index a, and a parameter w0 that is proportional to the spectral density at a referenced gyrofrequency. Because of the finite latitudinal extent of the cusp/cleft, the incorporation of the horizontal convection drift leads to a maximum residence time tD of the ions when being energized. A large set of simulations has been computed so as to study the transport patterns of the H + and O + bulk parameters as a function of tD , a, and w0. Residence time effects are significant in O + density patterns while negligible for H +. When comparing the results with analytical one-dimensional theories (Chang et al., 1986; Crew et al., 1990), we find that mean ion energies and pitch angles at the poleward edge of the heating region are slightly influenced by tD and may be used as a probe of ICR parameters ( a, w0). Conversely, poleward of the heating region, upward velocity and mean energy dispersive patterns depend mainly on tD (e.g. the magnitude of the convection drift) with latitudinal profiles varying versus tD . In short, the main conclusion of the paper is that any triplet (tD , a, w0) leads to a unique transport-pattern feature of ion flows associated with a cusp/cleft ionospheric source. In a companion paper, by using high-altitude (1.5–3 RE) ion observations as constraints, the results from the parametric study are used to determine the altitude dependence of transverse ion heating during a significant number of passes of the Interball-2 satellite.Key words. Magnetospheric physics (auroral phenomena) – Space plasma physics (numerical simultation studies; wave-particle interactions)