Solar inertial modes: Observations, identification, and diagnostic promise

Gizon, Laurent; Cameron, R. H.; Bekki, Yuto; Birch, A. C.; Bogart, R. S.; Brun, Allan Sacha; Damiani, C.; Fournier, Damien; Hyest, Laura; Jain, Kiran; Lekshmi, B.; Liang, Zhangqian; Proxauf, Bastian

doi:10.1051/0004-6361/202141462

Cited by 49 publications

(142 citation statements)

References 33 publications

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“…The highest amplitude mode (∼ 10 -20 m s −1 above 50 • latitude) is the m = 1 mode with north-south antisymmetric longitudinal velocity v φ with respect to the equator. This m = 1 mode was identified by Gizon et al (2021) using linear calculations in two-dimensional model, which are further discussed in the present paper and Fournier et al (2022). It corresponds to the spiral-like velocity feature reported at high latitudes by Hathaway et al (2013), although it was there reported as giantcell convection.…”

Section: Solar Inertial Modessupporting

confidence: 64%

“…Fournier et al (2022) extended this model to a spherical geometry using a realistic differential rotation model and found that some Rossby modes can be unstable for m ≤ 3. Gizon et al (2021) also report a family of modes at midlatitudes that are localized near their critical latitudes. Several tens of critical-latitude modes have been identified in the range m ≤ 10.…”

Section: Solar Inertial Modesmentioning

confidence: 90%

“…Because the Sun is essentially symmetric about its rotation axis, the velocity of each mode in the rotating frame has the form v(r, θ) exp [i(mφ − ωt)], where r is the radius, θ is the colatitude, φ is the longitude, m is the azimuthal order, and ω is the mode eigenfrequency. Gizon et al (2021) provide all observed eigen-frequencies ω for each m, and the eigenfunctions (v θ and v φ at the surface) for a few selected modes.…”

Section: Solar Inertial Modesmentioning

confidence: 99%

“…Using 10 years of observations from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), Gizon et al (2021) discovered that the Sun supports a large number of global modes of inertial oscillations. The restoring force for these inertial modes is the Coriolis force, and thus the modes have periods comparable to the solar rotation period (∼ 27 days).…”

Section: Introductionmentioning

confidence: 99%

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Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone

Bekki,

Cameron,

Gizon

2022

Preprint

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Context. On the one hand, several types of global-scale inertial modes of oscillation have been observed on the Sun. They include the equatorial Rossby modes, critical-latitude modes, and high-latitude modes. On the other hand, the columnar convective modes (predicted by simulations; also known as banana cells or thermal Rossby waves) remain elusive. Aims. We aim to investigate the influence of turbulent diffusivities, non-adiabatic stratification, differential rotation, and a latitudinal entropy gradient on the linear global modes of the rotating solar convection zone. Methods. We solve numerically for the eigenmodes of a rotating compressible fluid inside a spherical shell. The model takes into account the solar stratification, turbulent diffusivities, differential rotation (determined by helioseismology), and the latitudinal entropy gradient. As a starting point, we restrict ourselves to a superadiabaticity and turbulent diffusivities that are uniform in space. We identify modes in the inertial frequency range including the columnar convective modes, as well as modes of mixed character. The corresponding mode dispersion relations and eigenfunctions are computed for azimuthal orders m ≤ 16. Results. The three main results are as follows. Firstly, we find that, for m 5, the radial dependence of the equatorial Rossby modes with no radial node (n = 0) is radically changed from the traditional expectation (r m ) for turbulent diffusivities 10 12 cm 2 s −1 . Secondly, we find mixed modes, i.e. modes that share properties of the equatorial Rossby modes with one radial node (n = 1) and the columnar convective modes, which are not substantially affected by turbulent diffusion. Thirdly, we show that the m = 1 high-latitude mode in the model is consistent with the solar observations when the latitudinal entropy gradient corresponding to a thermal wind balance is included (baroclinally unstable mode). Conclusions. To our knowledge, this work is the first realistic eigenvalue calculation of the global modes of the rotating solar convection zone. This calculation reveals a rich spectrum of modes in the inertial frequency range, which can be directly compared to the observations. In turn, the observed modes can inform us about the solar convection zone.

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Section: Solar Inertial Modessupporting

confidence: 64%

Section: Solar Inertial Modesmentioning

confidence: 90%

Section: Solar Inertial Modesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone

Bekki,

Cameron,

Gizon

2022

Preprint

Self Cite

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“…Notable local helioseismic results include imaging of the meridional flow (Giles et al 1997;Gizon et al 2020) through time-distance helioseismology (Duvall et al 1993), and farside imaging of active regions (Braun & Lindsey 2001) and their near side emergence (Birch et al 2016), through helioseismic holography (Lindsey & Braun 2000). The recent discovery of various inertial waves (Gizon et al 2021), including the equatorial Rossby wave (Löptien et al 2018), has been achieved through local helioseismic ring-diagram analysis (Hill 1988) and the non-helioseismic local correlation tracking (LCT, November & Simon 1988) of granulation.…”

Section: Introductionmentioning

confidence: 99%

Imaging the Sun's near-surface flows using mode-coupling analysis

Mani,

Hanson,

Hanasoge

2022

Preprint

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The technique of normal-mode coupling is a powerful tool with which to seismically image nonaxisymmetric phenomena in the Sun. Here we apply mode coupling in the Cartesian approximation to probe steady, near-surface flows in the Sun. Using Doppler cubes obtained from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, we perform inversions on mode-coupling measurements to show that the resulting divergence and radial vorticity maps at supergranular length scales (∼30 Mm) near the surface compare extremely well with those obtained using the Local Correlation Tracking method. We find that the Pearson correlation coefficient is ≥ 0.9 for divergence flows, while ≥ 0.8 is obtained for the radial vorticity.

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Equatorially trapped Rossby waves in radiative stars

Albekioni,

Zaqarashvili,

Kukhianidze

et al. 2023

Astron Nachr

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Observations by recent space missions reported the detection of Rossby waves (r‐modes) in light curves of many stars (mostly A, B, and F spectral types) with outer radiative envelope. This article aims to study the theoretical dynamics of Rossby‐type waves in such stars. Hydrodynamic equations in a rotating frame were split into horizontal and vertical parts connected by a separation constant (or an equivalent depth). Vertical equations were solved analytically for a linear temperature profile and the equivalent depth was derived through free surface boundary condition. It is found that the vertical modes are concentrated in the near‐surface layer with a thickness of several tens of surface density scale height. Then with the equivalent width, horizontal structure equations were solved, and the corresponding dispersion relation for Rossby, Rossby‐gravity, and inertia‐gravity waves was obtained. The solutions were found to be confined around the equator, leading to the equatorially trapped waves. It was shown that the wave frequency depends on the vertical temperature gradient as well as on stellar rotation. Therefore, observations of wave frequency in light curves of stars with known parameters (radius, surface gravity, rotation period) could be used to estimate the temperature gradient in stellar outer layers. Consequently, the Rossby mode may be considered as an additional tool in asteroseismology apart from acoustic and gravity modes.

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Solar inertial modes: Observations, identification, and diagnostic promise

Cited by 49 publications

References 33 publications

Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone

Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone

Imaging the Sun's near-surface flows using mode-coupling analysis

Equatorially trapped Rossby waves in radiative stars

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