Effects of energetic heavy ions on electromagnetic ion cyclotron wave generation in the plasmapause region

Abstract

An expression for the linear electromagnetic ion cyclotron convective growth rate has been derived, considering multiple ions in the energetic anisotropic component of the plasma (which provides the free energy for the instability) as well as in the cold component of the plasma. This represents a modification of recent treatments investigating electromagnetic ion cyclotron growth rates which have considered only hydrogen ions in the energetic component. Four major effects on the growth and propagation characteristics result from inclusion of heavy ions in the energetic component. Some wave growth occurs at low frequencies below the corresponding marginally unstable wave mode for each heavy ion. Enhanced quasi-monochronomatic peaks in the convective growth rate appear just below the O + and He + gyrofrequency and can be quite pronounced for certain plasma conditions. Stop bands, decreased group velocity and other effects normally attributed to cold heavy ions can be produced or enhanced by heavy ions in the energetic plasma component. Partial or complete suppression of wave growth at frequencies above the marginally unstable wave mode for a particular energetic heavy ion can greatly alter the growth rates that would occur in the absence of this energetic heavy ion. The expression for the linear electromagnetic ion cyclotron convective growth rate along with appropriate plasma parameters was used to investigate the nature of linear wave growth in the plasmapause region. The frequencies of peaks in the convective growth rate given by this model compare favorably with wave measurements in this region. It is conceivable that through wave-particle interactions, electromagnetic ion cyclotron waves could supply the energy source for various plasmapause region phenomena such as the O + torus, the plasma cloak, and stable auroral red arcs. during varying amounts of geomagnetic activity. This is consistent with the theory of Cornwall et al. [ 1970]. Although the indirect evidence presented above and by other investigators is convincing, there still remains the problem of reconciling existing wave measurements with ion cyclotron wave theory. A possible explanation may result from our changing concept of the near plasmapause environment. The presence of heavy ions in the magnetospheric plasma has recently been discovered (e.g., Cornwall and Schultz [1979] and references therein). The plasma in this region consists of an energetic component (ring current plasma) and a cold component (plasmaspheric plasma), both of which contain heavy ions. The ring current is dominated by positive ions with energy _< 200 keV [Williams, 1983]. During the recovery phase of magnetic storms, the low-energy (0.2-17 keV) portion of the ring current at or below L values of 4 is composed mainly of O + and He + [Lundin et al., 1980]. Furthermore, there appears to be a marked composition boundary near L -4, with the heavy ions O + and He + dominating equatorward and with H + dominating poleward. This may be consistent with the much shorter lifetime of H...

Storm‐time Pc1 activity at high and middle latitudes

“…Cold plasma density is expected to increase during storm recovery phase as a result of plasmasphere refilling. However, an increase in plasma density shifts the growth rate peak to a lower frequency [Kozyra et al, 1984], excluding the change in cold plasma density as an explanation for the observed increase of structured Pc1 frequency.…”

Ion cyclotron waves in the Earth’s magnetotail during CASSINI’s Earth swing-by

“…A variety of modes is possible, in principle. One of the main lines of distinction is whether the waves are dominated by a single ion species (Brinca et al, 1990;Chaston et al, 1994Chaston et al, , 1999 or interplay of multiple ion components should be invoked (Smith and Brice, 1964;Young et al, 1981;Gomberoff and Neira, 1983;Kozyra et al, 1984;Brinca et al, 1989). Based on wave data only, we shall have to question both hypotheses.…”

“…Simulation work on ion instabilities possible under magnetotail conditions has been reported by Gary and Winske (1990), Gary et al (1993, Gary and Lee (1994). Because of the multi-ion character of the plasmas in the inner magnetosphere and the near-Earth magnetotail, the dispersion in the low frequency range of multi-ion plasmas has also received considerable attention in works by Smith and Brice (1964), Young et al (1981), Gomberoff and Neira (1983), Kozyra et al (1984), Chaston et al (1997). Ion cyclotron heating of heavy ions by ion waves has been discussed by Chaston et al (2000).…”

Precipitation of relativistic electrons by interaction with electromagnetic ion cyclotron waves

“…However, helium ions may also play an important role. Although helium is probably not present in significant enough quantities to drive the wave growth, small quantities of helium ions can introduce stop bands in the frequency spectrum driven by hydrogen ions [Kozyra et al, 1984]. These stop bands are located at 0.25 DH+ and can change the EMIC mode wave spectra, influencing the energies of relativistic electrons precipitated.…”