The Solar Intensity-Velocity Cross Spectrum: A Powerful Diagnostic for Helioseismology

We show that the solar intensity-velocity cross spectrum provides a sensitive diagnostic for the interaction between the oscillatory and nonoscillatory components of the solar velocity and intensity signals. In particular, we demonstrate that to simultaneously model the V and I power spectra, the I-V coherence spectrum, and the I-V phase difference spectrum requires a coherent, correlated background signal and a coherent, uncorrelated signal in both intensity and velocity. We speculate that these signals may be related to the ``acoustic events'' observed recently by Goode and colleagues. We also show why caution should be exercised in the interpretation of model fit parameters based only on measurements of the velocity or intensity power spectra, or both: specifically, the parameters associated with the oscillation source characteristics.