Date of Award
Program or Major
Doctor of Philosophy
Roy B Torbert
Charles W Smith
Marc R Lessard
This work is comprised of two main efforts: the design, construction, and flight of a rocket-borne fluxgate magnetometer, and the examination of Pc1 pearl pulsations using data from the Van Allen Probes and MMS missions.
Our first concentration regards the design and fabrication of an improved fluxgate magnetometer. The instrument makes use of an elongated racetrack geometry to improve on the signal-to-noise ratio of previous designs. We additionally examined refined heat treatment procedures to optimize the crystal structure of the magnetically permeable core material and were able to increase the size of crystal grains. The magnetometer was successfully flown on the RENU2 auroral sounding rocket mission, although the recorded data were coarser than would allow for current identification. We go on to demonstrate the methods employed to perform a flight orthogonalization and calibration of the instrument using comparisons of the measured field to the modeled IGRF field.
Our second effort concerns the in situ examination of Pc1 pearl pulsations using data from the Van Allen Probes and MMS missions. These waves were found to differ from traditional unstructured EMIC waves in their spatial and storm-time occurrence, as well as in the independence of their excitation frequency relative to the background magnetic field. This independence, as well as conjugate observations showing similar behavior in space and on the ground, contradicts previously proposed generation mechanisms. We found a dependence of both occurrence and wave propagation directionality on the formation of a gradient in the dominance of heavy ions in the inner magnetosphere near the plasmapause. Additionally, we recorded cases of pearl pulsation events alternately displaying the characteristics of magnetosonic and ion cyclotron waves. We propose that pearl pulsations are generated through the coupling of incident magnetosonic wave energy with the ion cyclotron wave mode at the dispersion surface created by this heavy ion boundary. Closely-spaced harmonics of wave activity in the magnetosonic mode would constructively interfere to form a beating pattern identical to the periodicity found in pearl pulsations.
Paulson, Kristoff, "In Situ Observations of Pearl Pulsations and Development of a Low-Noise Fluxgate Magnetometer" (2018). Doctoral Dissertations. 2427.