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

Abstract

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, steadystate, 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.

The structure of high altitude O<sup>+</sup> energization and outflow: a case study

“…Heating over extended altitude intervals as reported in Bouhram et al (2003b) is essentially consistent with the observations, as further indicated by the simple estimate we performed according to the scheme described in Sect. 3.5.…”

“…The energies reported in the above cited papers tend to increase with observation altitude, consistent with heating over extended altitude intervals, as inferred by Miyake et al (1993); Bouhram et al (2003b). However, it is an important question as to how much further energization takes place at high altitude.…”

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

“…They combined oxygen data from the Akebono, Interball-2, and Cluster satellites and followed the global development of the energetic (up to ∼10 keV) ion outflow over a continuous and broad altitude range up to about 5.5 R E . They confirmed the results of Bouhram et al (2003b), such as the fact that transverse ion heating in the cusp/cleft is height-integrated at radial distance below 4 R E . The results inferred from Cluster observations put forward evidence of a saturation of both a transverse energization rate and ion gyroradii.…”

“…They found that any triplet of (residence time of the ions when being energized, α, and ω 0 ) leads to a unique transport pattern feature of ion flows associated with a cusp/cleft ionospheric source. Bouhram et al (2003b) used high-altitude (1.5-3 R E ) ion observation as constraints and the results of Bouhram et al (2003a) are used to determine the altitude dependence of transverse ion heating during a significant number of the Interball-2 satellites. Bouhram et al (2004) focused on the altitude dependence of oxygen ion conics in the dayside cusp/cleft region.…”

Oxygen ion energization by waves in the high altitude cusp and mantle

“…The ions have seldom experienced the heating for as long as is assumed by the theory at the time of observation. Some of the most intense heating is known to occur in a very limited region at the equatorward side of the cusp, sometimes called the "cusp heating wall" (Bouhram et al, 2003), possibly caused by a combination of waves and quasi-static electric fields (Lindstedt et al, 2010). This could provide O + ions with energies of several keV.…”