Evolution of ion cyclotron instability in the plasma convection system of the magnetosphere

Abstract

Liouville's theorem and approximate but extremely accurate expressions which reflect the invariance of µ and J can be used to determine analytically the evolution of an adiabatically convecting energetic particle distribution. Features of the convecting distribution which are reproduced by our model include positive pitch angle anisotropy, regions in velocity space in which ∂f/∂v⊥ >0, and the energy dependence of the degree of particle injection. The energy dependence of the injection yields upper and lower cutoffs to the distribution within the plasmasphere, and only an upper cutoff outside. We have used this approach to study the evolution of ion cyclotron waves in a convecting particle distribution, and have found that the upper cutoff to the distribution restricts the growth of these waves, both on and off the geomagnetic equator, to a narrow range of frequencies which grow only inside the plasmasphere. In addition, we found that the upper cutoff limits wave growth to a few hours on either side of dusk. We have examined the results for two source distributions, a power law and a Maxwellian, and we found that for distributions with equivalent mean energies the power law is unstable over a greater range of frequencies and radial distances than the Maxwellian.

Relativistic‐electron dropouts and recovery: A superposed epoch study of the magnetosphere and the solar wind

“… Mauk and Meng , 1983; Maurice et al , 1998; Korth et al , 2002]. The driving of EMIC waves by a geocorona‐produced temperature anisotropy of the dayside ion plasma sheet has been explored [e.g., Cornwall , 1977; Solomon and Picon , 1981]; we suggest further that local regions of produced by geocorona shadowing may also play a role in EMIC growth [see also Kaye et al , 1979].…”

Auroral plasmas in the evening sector: Satellite observations and theoretical interpretations

“…Because Alfv6n layers are so intimately related to the convection potential 4~, they are important to studies of the hot auroral plasma even though Alfv6n layers are usually a subauroral phenomenon (e.g., Kivelson et al, 1979;Kivelson and Southwood, 19765). Many authors have used Alfv6n layer models to approximate the particle observations of Explorer 45 (e.g., Kaye and Kivelson, 1979) and the ATS satellites (McIlwain, 1972). Important though the Alfv6n layer phenomenon may be, note that it exploits but a small fraction of the information available in subauroral plasma observations in the form of ion and electron distribution functions.…”

“…Despite the large amount of information available in convected particle distribution functions, few theoretical (Cowley and Ashour-Abdalla, 1975;Kaye et al, 1979) and virtually no observational attempts have been made to exploit them until particle distribution data from plasma observations of the SCATHA satellite were made available in 1981. Figure 19 shows ion distribution contours measured by the SCATHA satellite at L = 7.…”

Wave generation in the terrestrial magnetosphere

“…One can sensibly take an observed wave spectrum and examine the nature of the pitch angle diffusion it produces (Lyons and Thorne, 1973). Or as Kaye et al (1979) did (in examining ion convection and its interaction with electromagnetic ion cyclotron waves rather than the electrons and whistlers discussed above), one can compute the pitch angle anisotropy produced by a convection model and then compute the wave growth rate (based on uniform theory) produced by such distributions. Such a study cannot pretend to be a serious calculation of the time evolution of a system, rather the linear uniform plasma growth rate as calculated serves to parametrise the free energy available for wave generation at any point in the convection system.…”