Main Research Focus
The focus of my research is determining the role played by plasma waves in transferring electromagnetic energy and particles from the solar wind to Earth’s magnetosphere (the geomagnetic plasma-filled cavity around Earth) and polar ionosphere. This includes the study of ULF waves in complex magnetic topologies, and wave-particle interactions affecting energetic particle populations in auroral plasma and in the Van-Allen radiation belts. The methodology that I employ includes theory and advanced computer models that are used to interpret observations from satellites, rockets, and arrays of ground-based instrumentation. Within my research group at present are three research associates, five graduate students, and two technical staff. Some recent research themes are:
ULF Waves in Complex Magnetic Fields - Earth’s geomagnetic field supports ULF (ultra-low frequency; 0.5-25 mHz) standing and propagating Alfven waves. The ionospheric footprint of their E and B fields can be observed using arrays of HF-radar, magnetometers and other instruments. The associated particle precipitation can be observed using all-sky cameras, multi-spectral photometers and riometers. Alfven waves are important for many reasons: They accelerate particles to energies (>1MeV) that are dangerous to satellites and astronauts. They resonantly mode convert to shear Alfven waves that produce muti-structured auroral arcs (current sheets and precipitation aligned with the geomagnetic field), a well known characteristic feature of aurora. They facilitate specification of cold plasma dynamics affecting ionospheric radio wave propagation, plasma transport, and energization and loss processes controlling the Van-Allen belts.
To accurately model ULF waves under variable solar wind conditions, it is necessary to determine their various excitation processes, and their polarization and frequency characteristics, on a global scale. This can be achieved by combining wave models with observations, e.g., using appropriately separated pairs of magnetometers (ground or space based). This “magnetoseismology” technique allows topological properties of ULF waves and of the magnetosphere to be probed. Since Earth’s magnetic field is continually distorted by the solar wind, understanding the global properties of ULF waves also reveals
features of Earth’s changing magnetic topology. Such changes can be compared with results from global models, implying that ULF waves are important for monitoring “space weather”. Ref.[1-6] summarize my research group's contributions to Magnetoseismology over the past six years. Ref. was selected as an “editor’s highlight paper” in Geophysical Review Letters. It presents a successful comparison of NASA THEMIS multi-satellite observations of ULF waves against models developed within my research program. The analysis is based on the procedure described in Ref.  and earlier papers, which describe how to solve the covariant ideal MHD equations for ULF waves in arbitrary magnetic fields.
Radiation Belt Electron Transport by ULF waves: Geomagnetic storms are manifestations of severe space weather in which energy and momentum from the solar wind are transferred to Earth's radiation belts. ULF waves are intimately involved in this process. The wave models developed within my research group have been extended to include coupling of waves to kinetic transport models of radiation belt electron phase space density (PSD). Refs. [7-10] describe applications of this approach. Ref.  summarizes the response of equatorially mirroring electrons to narrow-band ULF activity following a geomagnetic storm. Using observational constraints, it is found that observed ULF wave power on the dayside magnetosphere is sufficient to explain enhancements in electron radial transport observed by satellites.
By interpolating modeled PSD to the location of geosynchronous satellites, the observable features of the resonant interaction in the satellite particle energy channels has been reproduced. The ULF and particle transport models have also formed the basis of a successful grant application to NASA, which will further explore ULF wave-induced electron transport. The grant is led by Dr. Scott Elkington at the University of Colorado.
Multi-scale Structuring of the Aurora: Auroral electron and ion acceleration processes are poorly understood, although it is accepted that parallel (to geomagnetic field lines) electric fields are involved. This has been established by three decades of research utilizing observations from satellites that include the NASA FAST and POLAR spacecraft, the ESA Cluster satellites, and rocket payloads launched into auroral plasma. Over the past decade, I have established a world class research program in theory and comprehensive computer modeling of particle acceleration by propagating short perpendicular scale Alfven waves (SAWs); Refs. [10-21]. It has been shown how a self-consistent treatment of waves and particles can explain intricate details of wave fields and distribution functions measured by spacecraft such as the NASA FAST and POLAR satellites. A recent paper  shows how SAWs are able to survive without strong dissipation as they propagate from deep in the magnetosphere to the ionosphere.
The electrons that are initially trapped in the waves, c.f. Ref. are observed to leak out and are accelerated as the waves approach the ionosphere. This fundamentally new process contradicts the common view of how auroral particle acceleration occurs, and takes us one step closer to explaining the altitude range of wave-particle interactions producing the dominant auroral electron acceleration. Similar analysis was applied in Ref.  to the Io-Jupiter flux tube, revealing the universal nature of such processes, which may also be heating solar coronal plasma. Ref. extends the region of interaction of SAWs into the low altitude “ionospheric resonator” (IAR), which supports quantized higher frequency (~0.1-10Hz) wave modes due to waves impinging from the magnetosphere. The IAR wave modes an also strongly energize auroral electrons and ions.