p-mode intensity-velocity phase differences and convective sources

We study the origin of the solar p-mode intensity-velocity phase difference s at high degree (l > 100). Observations show phase differences that are ve ry different from those derived from linear theory alone. The theory predic ts a smooth variation with frequency, dependent only on atmospheric paramet ers, while observations show large fluctuations across modal frequencies. W e support previous suggestions that fluctuations in the intensity-velocity phase differences and line asymmetries in the intensity and velocity power spectra are produced by "contamination" of the p-mode signal with noise cor related with the excitation sources. It is demonstrated that the qualitativ e shares of the observed phase-difference and power spectra can be realized only if both temperature (intensity) and velocity (Doppler shift) observat ions contain correlated noise. Moreover, the details of the observed spectr a allow only a limited choice of noise parameters and constrain well the co nvective process responsible for p-mode excitation. The inferred correlated noise signals are consistent with the (visible) formation of convective do wnflows accompanied by darkening (lowered emergent intensity) and subsequen t acoustic excitation. An upward velocity pulse follows after the wave exci tation, which suggests overshoot of inflowing material that fills in the ev acuated volume in the wake of the new downflow.