Computer Science – Sound
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........9m&link_type=abstract
Thesis (PHD). UNIVERSITY OF DELAWARE , Source DAI-B 58/05, p. 2470, Nov 1997, 730 pages.
Computer Science
Sound
1
Sun, Corona, Magnetic Waves
Scientific paper
The process by which the Sun's corona is heated is not well known. A leading model is the resonant absorption of Alfvenic surface waves. In order to be efficient as a heating mechanism, this process depends on the surface waves being well matched to the length of the coronal loop through the condition of global-mode resonance: v Alfvén = 2L/period (Davila 1987). The Yohkoh Soft X-Ray Telescope provides a means of recording the behavior and evolution of structures in the solar corona. Relatively fast-cadence sequences of CCD images become movies depicting the changing conditions in the X-ray emitting regions. By using software provided by the Yohkoh science team to measure the brightness of a selected subset of pixels in all the images of a movie, we can generate an X-ray light curve of a small portion of a given coronal structure. For the present dissertation, a number of SXT image sequences were selected from the Yohkoh archives. Light curves were generated in the manner outlined above, and these light curves were then examined for periodic modulations. It is shown that periodic modulations of X-ray brightness were detected with amplitudes of about 1%, and that the speeds implied by global-mode resonance are in the neighborhood of 1800-14000 km/s, consistent with Alfven wave speeds but much higher than sound speeds implied by the temperatures measured from the images. The wave speeds and the modulation amplitudes imply plasma beta values in the range β p ≈ 10-3-10-2. Tests for correlations among physical conditions (loop length L, temperature T, pressure p, modulation depth ΔI/I, quality Q, and period τ) in the periodically modulated loops tentatively support relationships like T ~ (pL)1/3, after Rosner et al. (1978), and Q ~ (Δ I/I)-2, after Zaitsev & Stepanov (1989), but do not support relationships like L ~ τ,/ L ~ p,/ L ~ T, or p ~ τ.
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