Physics Research
Dipole Impedance of an Aperture
An effective circuit description of the low frequency diffraction of an aperture is developed and compared to results obtained using the Finite Element Method. The power radiated by the aperture is calculated using standard techniques at the interface between media with different impedances. The incorporation of standard network theory simplifies a theoretical description of the coupling between a system and an aperture. The effective aperture circuit closely follows the numerically obtained aperture impedance and radiated power.
Effective Aperture Behavior in the Geospace Environment and on the Sun
Based upon the similarity of the fields produced by an aperture to the cross polar cap potential and the Birkeland current distribution in the ionosphere, a model is developed where the polar cap is treated as an effective aperture. This model is consistent with the power transmitted into the Ionosphere during a geomagnetic substorm as measured by FAST, the structure and resonant frequencies of the Ionospheric Alfven resonator, and with frequencies measured by ground based magnetometers.
The same magnetic field distribution in the Earth's polar regions are also found on the Sun in the polar coronal holes and sunspots. Using the derived aperture impedance, this method predicts 5 minute Alfven waves across the transition region in the polar cap with an averaged power of 100 W/m2 over the coronal surface, sufficient to heat the quiet Corona and launch the solar wind.
Applied to sunspots, a 3 minute peak in Alfven waves is predicted along with a minimum temperature of 3850 K, consistent with observations. This model predicts that movement of magnetic field lines driven by gas oscillations in the photosphere excites the magnetic dipole in the effective sunspot aperture, converting acoustic waves into Alfven waves, cooling the sunspot.
Dissertation
This dissertation covers the above topics, plus includes research on Electromagnetic Musical Instruments.
International Research Experience for Students
Funded by the National Solar Observatory, I spent 8 weeks in India, and 7 of those in Bangalore at the Indian Institute for Astrophysics. I worked with Dr. Dipankar Banerjee and compared visible oscillations on the Sun using multiple wavelengths measured by TRACE with oscillations of the magnetic field using SOHO/MDI data. Information on the other students I went to India with can be found here, as well as some pictures of our trip.