University of Colorado
Ali, Ashar Fawad.
ULF Waves and Diffusive Radial Transport of Charged Particles.
Degree: PhD, Applied Mathematics, 2016, University of Colorado
The Van Allen radiation belts contain highly energetic particles which interact with a variety of plasma and magnetohydrodynamic (MHD) waves. Waves in the ultra low-frequency (ULF) range play an important role in the loss and acceleration of energetic particles. Considering the geometry of the geomagnetic field, charged particles trapped in the inner magnetosphere undergo three distinct types of periodic motions; an adiabatic invariant is associated with each type of motion. The evolution of the phase space density of charged particles in the magnetosphere in the coordinate space of the three adiabatic invariants is modeled by the Fokker-Planck equation. If we assume that the first two adiabatic invariants are conserved while the third invariant is violated, then the general Fokker-Planck equation reduces to a radial diffusion equation with the radial diffusion coefficient quantifying the rate of the radial diffusion of charged particles, including contributions from perturbations in both the magnetic and the electric fields.
This thesis investigates two unanswered questions about ULF wave-driven radial transport of charged particles. First, how important are the ULF fluctuations in the magnetic field compared with the ULF fluctuations in the electric field in driving the radial diffusion of charged particles in the Earth's inner magnetosphere? It has generally been accepted that magnetic field perturbations dominate over electric field perturbations, but several recently published studies suggest otherwise. Second, what is the distribution of ULF wave power in azimuth, and how does ULF wave power depend upon radial distance and the level of geomagnetic activity? Analytic treatments of the diffusion coefficients generally assume uniform distribution of power in azimuth, but in situ measurements suggest that this may not be the case. We used the magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) and the electric and the magnetic field data from the Radiation Belt Storm Probes (RBSP) to compute the electric and the magnetic component of the radial diffusion coefficient using the Fei et al.  formulation. We conclude that contrary to prior notions, the electric component is dominant in driving radial diffusion of charged particles in the Earth's inner magnetosphere instead of the magnetic component. The electric component can be up to two orders of magnitude larger than the magnetic component. In addition, we see that ULF wave power in both the electric and the magnetic fields has a clear dependence on Kp
with wave power decreasing as radial distance decreases. For both fields, the noon sectors generally contain more ULF wave power than the dawn, dusk, and the midnight magnetic local time (MLT) sectors. There is no significant difference between ULF wave power in the dawn, dusk, and the midnight sectors.
Advisors/Committee Members: Scot R. Elkington, Jem Corcoran, Howard Singer, Juan Restrepo, William Kleiber.
Subjects/Keywords: CRRES; Magnetospheric Physics; Radial Diffusion; RBSP; ULF Waves; Van Allen Radiation Belts; Applied Mathematics; Plasma and Beam Physics
to Zotero / EndNote / Reference
APA (6th Edition):
Ali, A. F. (2016). ULF Waves and Diffusive Radial Transport of Charged Particles. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/appm_gradetds/71
Chicago Manual of Style (16th Edition):
Ali, Ashar Fawad. “ULF Waves and Diffusive Radial Transport of Charged Particles.” 2016. Doctoral Dissertation, University of Colorado. Accessed January 23, 2021.
MLA Handbook (7th Edition):
Ali, Ashar Fawad. “ULF Waves and Diffusive Radial Transport of Charged Particles.” 2016. Web. 23 Jan 2021.
Ali AF. ULF Waves and Diffusive Radial Transport of Charged Particles. [Internet] [Doctoral dissertation]. University of Colorado; 2016. [cited 2021 Jan 23].
Available from: https://scholar.colorado.edu/appm_gradetds/71.
Council of Science Editors:
Ali AF. ULF Waves and Diffusive Radial Transport of Charged Particles. [Doctoral Dissertation]. University of Colorado; 2016. Available from: https://scholar.colorado.edu/appm_gradetds/71