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You searched for +publisher:"University of Colorado" +contributor:("Howard Singer"). Showing records 1 – 3 of 3 total matches.

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University of Colorado

1. 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. [2006] 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

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

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 19, 2021. https://scholar.colorado.edu/appm_gradetds/71.

MLA Handbook (7th Edition):

Ali, Ashar Fawad. “ULF Waves and Diffusive Radial Transport of Charged Particles.” 2016. Web. 19 Jan 2021.

Vancouver:

Ali AF. ULF Waves and Diffusive Radial Transport of Charged Particles. [Internet] [Doctoral dissertation]. University of Colorado; 2016. [cited 2021 Jan 19]. 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


University of Colorado

2. Califf, Sam Tindal. Investigation of Quasi-Static Electric Fields and Coupled Plasma Populations in the Inner Magnetosphere.

Degree: PhD, Aerospace Engineering Sciences, 2016, University of Colorado

Electric fields are a critical component to understanding the dynamics of plasma in the Earth’s magnetosphere – large-scale electric fields control the shape of the low-energy (~1 eV) plasmasphere, they are responsible for transporting plasma sheet particles (~keV) into the inner magnetosphere, forming much of the trapped energetic particle population, and they affect the high-energy radiation belts (100s keV to MeV) both directly and through coupled interactions with the lower-energy populations. This dissertation focuses on in situ electric field measurements and particle dynamics in the inner magnetosphere with an emphasis on the most inner region below ~4 RE in the equatorial plane, where extensive particle and fields observations have only recently been available through the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and the Van Allen Probes missions. We address the measurement of electric fields using double-probe instruments onboard spacecraft, including some of the unique challenges for making accurate measurements in the inner magnetosphere. Next, we explore the average structure of the quasi-static electric field in the inner magnetosphere using many years of in situ measurements near the equatorial plane from THEMIS. These results reveal a spatially structured electric field with stronger electric fields in the dusk sector, which we connect to a magnetopshere-iononsphere coupling mechanism through a detailed event study. Finally, we relate electric field measurements deep within the inner magnetosphere to 100s keV electron enhancements in the slot region. Advisors/Committee Members: Xinlin Li, Robert Ergun, Howard Singer, David Malaspina, Zoltan Sternovsky.

Subjects/Keywords: convection; electric field; magnetosphere; magnetosphere-ionosphere coupling; radiation belts; slot region; Aerospace Engineering; Electromagnetics and Photonics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Califf, S. T. (2016). Investigation of Quasi-Static Electric Fields and Coupled Plasma Populations in the Inner Magnetosphere. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/asen_gradetds/153

Chicago Manual of Style (16th Edition):

Califf, Sam Tindal. “Investigation of Quasi-Static Electric Fields and Coupled Plasma Populations in the Inner Magnetosphere.” 2016. Doctoral Dissertation, University of Colorado. Accessed January 19, 2021. https://scholar.colorado.edu/asen_gradetds/153.

MLA Handbook (7th Edition):

Califf, Sam Tindal. “Investigation of Quasi-Static Electric Fields and Coupled Plasma Populations in the Inner Magnetosphere.” 2016. Web. 19 Jan 2021.

Vancouver:

Califf ST. Investigation of Quasi-Static Electric Fields and Coupled Plasma Populations in the Inner Magnetosphere. [Internet] [Doctoral dissertation]. University of Colorado; 2016. [cited 2021 Jan 19]. Available from: https://scholar.colorado.edu/asen_gradetds/153.

Council of Science Editors:

Califf ST. Investigation of Quasi-Static Electric Fields and Coupled Plasma Populations in the Inner Magnetosphere. [Doctoral Dissertation]. University of Colorado; 2016. Available from: https://scholar.colorado.edu/asen_gradetds/153


University of Colorado

3. Zhao, Hong. Unveiled Characteristics of Energetic Electrons and Ions: the Inner Radiation Belt, Slot Region, and Ring Current.

Degree: PhD, Aerospace Engineering Sciences, 2015, University of Colorado

Earth’s inner magnetosphere is a highly dynamic region consisting of various charged particle populations and current systems. Composed of relativistic electrons and protons, the radiation belt is a hazardous environment for both spacecraft and humans in space; while the variations of ring current, an electric current flowing around Earth consisting of energetic ions and electrons, can cause severe disruption of electrical systems on the ground. In the following, we focus on the dynamics of relativistic electrons (>~100 keV) in the inner radiation belt and slot region and energetic ions and electrons (>~keV) in the ring current, which are subject to influence from many different physical processes and commonly exhibit great changes on various spatial and temporal scales. Using data from SAMPEX and DEMETER satellites, we find that in the inner belt and slot region, though MeV electrons only exhibit flux enhancements during severe solar wind conditions, 100s of keV electron flux variations occur much more often. Using a radial diffusion model, a penetration event of 100s of keV electrons into the inner belt and slot region is modeled, and the results indicate that the penetration can be well explained by inward radial transport, but the radial diffusion coefficient is different from those of previous studies. Also, using data from the Van Allen Probes, we perform detailed analysis of 100s of keV electron pitch angle distributions (PADs) in the inner belt and slot region. A new type of PADs with minima at 90° persistent near the magnetic equator is unveiled, which is contradictory to the theoretical predictions from known physical processes and shows the complexity in the inner belt dynamics. Finally, the evolution of ring current ions and electrons are investigated during geomagnetic storms using data from the Van Allen Probes. The contribution of electrons and ions to the ring current energy is calculated and intriguing results are found. Our studies on the energetic electrons and ions in the inner belt, slot region and ring current contribute to a more comprehensive picture of inner magnetosphere dynamics. Advisors/Committee Members: Xinlin Li, Dan Baker, Howard Singer, Scot Elkington, Zoltan Sternovsky.

Subjects/Keywords: Deep Penetration; Energetic Particles; Wave-particle Interaction; Aerospace Engineering; Geophysics and Seismology; Plasma and Beam Physics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Zhao, H. (2015). Unveiled Characteristics of Energetic Electrons and Ions: the Inner Radiation Belt, Slot Region, and Ring Current. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/asen_gradetds/117

Chicago Manual of Style (16th Edition):

Zhao, Hong. “Unveiled Characteristics of Energetic Electrons and Ions: the Inner Radiation Belt, Slot Region, and Ring Current.” 2015. Doctoral Dissertation, University of Colorado. Accessed January 19, 2021. https://scholar.colorado.edu/asen_gradetds/117.

MLA Handbook (7th Edition):

Zhao, Hong. “Unveiled Characteristics of Energetic Electrons and Ions: the Inner Radiation Belt, Slot Region, and Ring Current.” 2015. Web. 19 Jan 2021.

Vancouver:

Zhao H. Unveiled Characteristics of Energetic Electrons and Ions: the Inner Radiation Belt, Slot Region, and Ring Current. [Internet] [Doctoral dissertation]. University of Colorado; 2015. [cited 2021 Jan 19]. Available from: https://scholar.colorado.edu/asen_gradetds/117.

Council of Science Editors:

Zhao H. Unveiled Characteristics of Energetic Electrons and Ions: the Inner Radiation Belt, Slot Region, and Ring Current. [Doctoral Dissertation]. University of Colorado; 2015. Available from: https://scholar.colorado.edu/asen_gradetds/117

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