Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications

Abstract. In this paper, we consider major ion energization mechanisms in the dayside cusp/cleft region. This includes transverse ion heating by ion cyclotron resonance (ICR), ion energization through structures of field-aligned electric potential drops, and transverse heating by lower hybrid (LH) waves. First, we present and discuss three typical cusp/cleft crossings associated with one of the first two mechanisms mentioned above. Then, we develop a procedure for finding the altitude dependence of ICR heating for any data set in the high-altitude cusp/cleft under the absence of field-aligned potential drops. This has been accomplished using a large set of numerical simulations from a two-dimensional, steady-state, Monte Carlo, trajectory-based code, as discussed in detail in the first companion paper (Bouhram et al., 2003). The procedure is applied and tested successfully for the first two events, by using patterns of ion moments along the satellite track as constraints. Then, we present a statistical study that uses 25 cusp/cleft crossings associated with steady IMF conditions, where ICR heating is expected to occur alone. It is pointed out that the ICR heating increases gradually versus geocentric distance as s 3.3 ± 1.8 . The inferred values of the wave power and the spectral index associated with the component responsible for ICR heating are lower than those characterizing the broad-band, extremely low-frequency (BBELF) turbulence usually observed in the cusp/cleft. This strengthens the idea that more than one wave-mode is contained in the BBELF turbulence, and only a small fraction of the observed turbulence is responsible for ICR heating. Then, we study the occurrence versus magnetic local time (MLT) of field-aligned potential drops. According to previous statistical studies, such structures are not common in the cusp and tend to be associated with the cleft region. We also discuss the effects of LH heating in the cusp on the observed ion distributions. However, this mechanism turns out to be of less importance than ICR heating.

Key words. Magnetospheric physics (Auroral phenomena) – Space plasma physics (charged particle motion and acceleration; wave-particle interactions)