, Volume 284, Issue 2, pp 297-314
Date: 08 Nov 2012

The Intensity–Velocity Phase Spectra of Evanescent Oscillations and Acoustic Sources

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There are three major issues in modeling solar evanescent oscillations: the variation of the intensity [I]–velocity [V] phase difference of p-modes close to the base of photosphere; the existence of a plateau of negative IV phase differences below and between the ridges of the low-frequency p-modes; the explanation of the IV cross-spectra of the evanescent oscillations. We present new interpretations for the first two issues, based on modeling intensity fluctuations taking steep temperature gradients, opacity, and non-adiabatic cooling into account.

We also discuss consequences of our model for the explanation of power spectra and cross-power spectra of p-modes. In particular, we present evidence that the acoustic sources that generate evanescent waves produce a coherent background that explains the plateau–interridge regime of negative IV phase difference.