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arXiv · 2007.14387

Predicting frequency changes of global-scale solar Rossby modes due to solar cycle changes in internal rotation

C. R. Goddard·A. C. Birch·D. Fournier·L. Gizon
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Abstract

Context. Large-scale equatorial Rossby modes have been observed on the Sun over the last two solar cycles. Aims. We investigate the impact of the time-varying zonal flows on the frequencies of Rossby modes. Methods. A first-order perturbation theory approach is used to obtain an expression for the expected shift in the mode frequencies due to perturbations in the internal rotation rate. Results. Using the time-varying rotation from helioseismic inversions we predict the changes in Rossby mode frequencies with azimuthal orders from m = 1 to m = 15 over the last two solar cycles. The peak-to-peak frequency change is less than 1 nHz for the m = 1 mode, grows with m, and reaches 25 nHz for m = 15. Conclusions. Given the observational uncertainties on mode frequencies due to the finite mode lifetimes, we find that the predicted frequency shifts are near the limit of detectability.

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C. R. Goddard, A. C. Birch, D. Fournier, L. Gizon. 2020-07-28. Predicting frequency changes of global-scale solar Rossby modes due to solar cycle changes in internal rotation. https://doi.org/10.1051/0004-6361%2F202038539

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