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

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 I-V phase differences below and between the ridges of the low-frequency p-modes; the explanation of the I-V 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 I-V phase difference.