The p-mode sources as seen in oscillations with frequency greater than the acoustic-cutoff frequency.

Lead investigator: Tom Duvall, NASA/GSFC

Team Members:
Phil Scherrer,
Stuart Jefferies,
Jack Harvey,
Pawan Kumar,
Ted Tarbell
(+ Players to be named later)

Abstract/Technical Summary: The solar atmosphere is transperant to acoustic waves above a certain frequency, termed the acoustic cutoff frequency. The acoustic radiation at higher frequencies that we detect at the surface either comes directly from a source or has followed a path from the source to a subsurface turning point and then been refracted back to the surface. It continues outwards and is lost to the system after making its presence known to our detectors as it passes through the atmosphere. The correlation between the direct wave and the once-refracted wave leads to an approximately sinusoidal pattern in the high-freqency nu-l power spectrum characteristic of a two-beam interference pattern. This sinusoidal pattern is what we see as the extensions of the lower frequency p-mode ridges. The peaks have been called pseudo-modes.

The locations of the pseudo-modes are sensitive to the source position. The source position has been derived for measurements of the pseudo-mode positions up to a frequency of 7 mHz. This is greater than the peak acoustic cutoff frequency of 5.3 mHz but not greatly so. The pseudo-mode positions at 7 mHz are still sensitive to the atmospheric structure somewhat and the conclusions about the source position would be more secure if the pseudo-mode positions were observed at higher frequencies. It is the purpose of this investigation to obtain high-frequency observations, develop spectra, and measure via a modelling effort the depth of the source of p-mode oscillations at higher frequencies than have been done before.

Complete text of proposal.