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

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.

References in corpus (13)

• The NumPy array: a structure for efficient numerical computation
• The interior rotation of a sample of gamma Doradus stars from ensemble modelling of their gravity mode period spacings
• Global Seismology of the Sun
• Global-scale equatorial Rossby waves as an essential component of solar internal dynamics
• Theory and evidence of global Rossby waves in upper main-sequence stars: r-mode oscillations in many Kepler stars
• Rossby waves in "shallow water" magnetohydrodynamics
• Time-distance helioseismology of solar Rossby waves
• Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
• Signatures of Solar Cycle 25 in Subsurface Zonal Flows
• Exploring the latitude and depth dependence of solar Rossby waves using ring-diagram analysis
• Changes in the solar rotation over two solar cycles
• Solar Rossby waves observed in GONG++ ring-diagram flow maps
• Rossby modes in slowly rotating stars: depth dependence in distorted polytropes with uniform rotation

Cited by in corpus (4)

• Effect of latitudinal differential rotation on solar Rossby waves: Critical layers, eigenfunctions, and momentum fluxes in the equatorial $\beta$ plane
• Doppler velocity of $m=1$ high-latitude inertial mode over the last five sunspot cycles
• Viscous inertial modes on a differentially rotating sphere: Comparison with solar observations
• Towards inertial-mode helioseismology: Direct sensing of solar rotation at 75 deg latitude and 0.8 Rsun