Date of Award
7-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Aerospace, Physics, and Space Sciences
First Advisor
Jean Carlos Perez
Second Advisor
Aaron Welters
Third Advisor
Sofiane Bourouaine
Fourth Advisor
Hamid K. Rassoul
Abstract
An important challenge in the accurate estimation of power spectra of plasma fluctuations in the solar wind at very low frequencies is that it requires extremely long signals, which will necessarily contain a mixture of qualitatively different solar wind streams. This unavoidably affects the structure of the power spectra by conflating all these different properties into a single power spectrum. This work develops a conditional statistical analysis to accurately estimate the power spectrum at arbitrarily low frequencies for ``pure'' slow solar wind stream, based on estimated autocorrelation functions of signals excluding portions that do not satisfy the required conditions. The estimator's convergence to its true ensemble-averaged values is tested on contiguous data. This methodology is used on a 14-year-long Wind data interval to obtain the magnetic power spectrum of slow wind at extremely low frequencies to show a full 1/f range in the slow wind. It was only recently that a 1/f range was partially observed in some very long slow wind intervals, suggesting that not all slow wind streams have similar turbulence properties. Values of normalized cross helicity near unity are commonly associated with Alfvenic slow wind fluctuations, whereas values near zero are typically thought to be typical slow wind. Alfvenic fluctuations can still exist in a state of low cross helicity, i.e., one in which there is an equal energy flux in both directions with respect to the mean field. We find intervals of balanced Alfvenic slow wind with low mean cross helicity and magnetic compressibility.
Recommended Citation
Dorseth, Mason Alden, "On the nature of low-frequency power spectra in solar wind turbulence" (2024). Theses and Dissertations. 1476.
https://repository.fit.edu/etd/1476