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Project Partners:

Dr. Markus Roth, Kiepenheuer-Institut für Sonnenphysik, Freiburg

Prof. Michael Stix, Kiepenheuer-Institut für Sonnenphysik, Freiburg

Dr. Rachel Howe, National Solar Observatory, Tucson, USA

Dr. Rudi Komm, National Solar Observatory, Tucson, USA


Project Description:

Large-scale flow components in the solar convection zone have a disturbing effect on the solar oscillations. This leads mainly to an interaction of the p-modes often called "coupling". The unperturbed pure eigenstates of solar oscillations get an intermixture of other coupling modes. In the case of stationary flow components, the effect is determined quantitatively by quasi-degenerate perturbation theory.

Flow component with an harmonic degree s=8 and azimuthal order t=8 (banana cells). The color code represents the magnitude of the flow speed (red=slow, blue=fast).

Large-scale poloidal flow components result in an additional shift of the solar eigenfrequencies.
This effect is small compared to the frequency splitting caused by solar differential rotation. But this effect needs to be taken into account, when the depth dependence of solar rotation is inverted from oscillation data. Moreover the sensitivity of inversion methods from global helioseismology to flow components can be tested.

The effect of temporally changing flow components is determined by time-dependent perturbation theory. This theory is more general and comprises the stationary quasi-degenerate approach. We find that convection does not change directly the frequencies but leads to the emergence of side lobes in the power spectrum. These side lobes arrange asymmetrically around the peak of the unperturbed mode frequency, which leads in total to an asysmmetric peak and a shift of the line center.