Ion cyclotron resonance heated conics: Theory and observations

Abstract

A general theoretical treatment of energetic oxygen ion conic formation through cyclotron resonance with magnetospheric electromagnetic plasma turbulence is presented. With suitable assumptions, there exists a similarity regime in which the process may be profitably characterized by two parameters v o and o, corresponding roughly to the velocity scale and pitch angle of the ion distribution. These may be independently determined from the wave and particle observations of a conic event, as is illustrated here using typical auroral passes of the Dynamics Explorer 1 satellite. The predictions of the theory are found to be in excellent agreement with the observations. INTRODUCTIONThis article is concerned with a class of the energetic ion populations found within the Earth's ionosphere-magnetosphere system which are generically referred to as ion conics. The etymology of the term begins with its application to ion populations where the greatest concentration of ions lies on a cone in velocity space, but with the proliferation of both observations and theoretical models the correct application of the term has become considerably less restricted. Observationally, the term now includes a veritable zoo of ion observation events, with a variety not solely attributable to differences in instrumentation; and theoretically, there are now a number of reasonably plausible mechanisms which might be engaged to create ion populations suitable for inclusion in this zoo. The challenge to the experimentalist is to construct events sufficiently complete in their observations to allow a discrimination between theories, and the challenge to the theorist is to collect a subset of the events into a class which may be understood through the invocation of a single theory. With the aim of meeting this challenge and for the immediate goals of this paper, we are inclined to make the following definition:Definition. An "ion cyclotron resonance heated conic," which we shall abbreviate as "ICRH conic," is an ion population of ionospheric origin which was energized primarily through an ion cyclotron resonance interaction with electromagnetic plasma turbulence. This is a resonant wave-particle interaction where the ions are extracting energy from that portion of the electric field turbulence which includes their cyclotron frequency. The result of this extraction is a net gain for the ions in their energy of motion perpendicular to the magnetic field orientation.Unfortunately, this still results in a wide range of morphologies for the ion population, which is primarily due to the geometry in which this process takes place and the point of observation. In this paper we shall be concerned with geometries where the source of the ions lies in the ionosphere, the turbulent spectrum exists along an entire (auroral) field line, and the point of observation lies in the magnetosphere. There clearly are many other possible applications for the heating mechanism. The term "auroral" appears in parentheses because although the events we shall consider are indee...

On the altitude dependence of transversely heated O<sup>+</sup> distributions in the cusp/cleft

“…Many wave modes may be contained in the BBELF turbulence and their relative contribution to the observed spectra is still under investigation (see Paschmann et al (2002) for a review). However, in terms of transverse ion energization, several authors (Chang et al, 1986;Retterer et al, 1987;Crew et al, 1990, Norqvist et al, 1996; to name just a few) carried out onedimensional (1D), Monte Carlo, kinetic simulations to point out that the observed conics can be explained by considering ion cyclotron resonance (ICR) heating over an extended altitude range with the electromagnetic left-hand circular polarized component (LHCP) of BBELF turbulence. It was confirmed that only a small fraction of the wave power at the ion gyrofrequency in the BBELF turbulence is needed to cause the observed ion energies.…”

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

“…Adopting a power law, altitude-dependent ion heating profile and computing Monte-Carlo simulations, many authors confirmed that only a small fraction of the wave intensity in the BBELF spectrum is needed to cause the observed ion energies through ICR heating (Retterer et al, 1987;Crew et al, 1990;André et al, 1990;Norqvist et al, 1996). This paper reports on a statistical study of energization mechanisms in the dayside cusp/cleft using particle instruments aboard the Interball-2 satellite.…”

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

“…They described the ion velocity distribution by a quasi-linear diffusion equation which is solved by the Monte Carlo technique. Crew et al (1990) presented a general theoretical treatment of energetic oxygen ion conics formation through cyclotron resonance with magnetospheric electromagnetic plasma turbulence; their theoretical predictions were found to be in excellent agreement with observations. Retterer et al (1994) interpreted the data from the rocket campaigns MARIE and TOPAZ III, within regions of low-altitude transversely accelerated ions, to explain the acceleration of the ions.…”

“…However, the adoption of this altitude dependent diffusion coefficient and similar ones such as that adopted by Crew et al (1990), Barghouthi (1997), and Barghouthi et al (1998) results in unrealistically high H + and O + ion temperatures at high altitudes. Also, it did not explained the non-Maxwellian features of ions at middle (∼4 R E ) and high (∼8 R E ) altitudes, such as H + and O + ion toroids and H + and O + ions temperatures.…”