Simon George Shepherd

Research / Publications

My research as a fifth-year graduate student at Dartmouth is primarily concerned with observations of naturally occurring radio emissions originating from the auroral F region ionosphere.

Auroral Radio Emissions

Current efforts are focused on ground-based observations of auroral radio emissions at sites in Greenland and a chain in Northern Canada (map). The primary focus of our instruments located at these observation stations is to aid in determining the generation mechanisms of several types of observed emissions in the LF/MF/HF frequency range. In particular, auroral roar which is a relatively narrow-band emission observed at 2 and 3 times the electron cyclotron frequency (fce).

Specific experiments include:

• Fine structure measurements of auroral roar
• Polarization measurements of auroral radio frequency emissions
• Ionospheric structure during auroral roar observations
• FAST satellite conjunctions with ground stations during auroral roar observations

Computational Methods

Preliminary work involving the use of Hamilton's Variational Principle as a time-advancing algorithm for numerical solutions to ordinary differential equations with plasma physics applications.

Publications

1. Shepherd, S. G., J. LaBelle, and M. L. Trimpi, Further inverstigation of auroral roar fine structure, Journal of Geophysical Research, 103, 2219, 1998.



2. Shepherd, S. G., J. LaBelle, and M. L. Trimpi, The polarization of auroral radio emissions, Geophysical Review Letters, 24, 3161, 1997.



3. LaBelle J., S. G. Shepherd, and M. L. Trimpi, Observations of auroral medium frequency bursts, Journal of Geophysical Research, 102, 22221, 1997.



4. Letcher John S. Jr., D. Michael Shook, and Simon G. Shepherd, Relational geometric synthesis: Part 1 -- framework, Computer-Aided Design, 27, 821, 1995.

Conference Presentations

1. Shepherd, S. G., J. LaBelle, and C. W. Carlson, Polar Cap Location During Auroral Roar Emissions, Eos Trans. AGU, Spring Meeting, 1998.



2. Shepherd, S. G., J. LaBelle, and M. L. Trimpi, The polarization of auroral radio emissions, Eos Trans. AGU, Fall Meeting, 1997.



3. Shepherd, S. G., J. LaBelle, J. Hughes, M. L. Trimpi, M. McCready, R. Doe, and A. T. Weatherwax, Testing candidate mechanisms for auroral roar generation, Eos Trans. AGU (abstract), Spring Meeting, S272, 1997.



4. Shepherd, S. G., J. LaBelle, M. L. Trimpi, and R. Brittain, Further investigation of auroral roar structure, Eos Trans. AGU (abstract), Spring Meeting, S190, 1996.

Manuscripts in Preparation

1. Shepherd, S. G., J. LaBelle, R. A. Doe, and A. T. Weatherwax, Ionospheric Structure and the Generation of Auroral Roar, submitted to J. Geophys. Res..



2. Shepherd, S. G., J. LaBelle, and C. W. Carlson, Polar Cap Location During Auroral Roar Emissions, preparing for submission to J. Geophys. Res..



3. Yoon, P. H., A. T. Weatherwax, T. J. Rosenberg, J. LaBelle, and S. G. Shepherd, Propagation of Auroral Radio Waves to the Ground, preparing for submission to J. Geophys. Res..



4. Shepherd, S. G., Further Investigations of Auroral Roar Emissions, Ph. D. Thesis.

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