The p-mode sources as seen in oscillations with frequency greater than
the acoustic-cutoff frequency.
Lead investigator: Tom Duvall, NASA/GSFC
(+ 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.