Rossby Waves in Astrophysics

Zaqarashvili, T. V.; Albekioni, M.; Ballester, J. L.; Bekki, Yuto; Biancofiore, Luca; Birch, A. C.; Dikpati, Mausumi; Gizon, Laurent; Gurgenashvili, Eka; Heifetz, Eyal; Lanza, A. F.; McIntosh, Scott W.; Ofman, L.; Oliver, R.; Proxauf, Bastian; Umurhan, O. M.; Yellin-Bergovoy, Ron

doi:10.1007/s11214-021-00790-2

Cited by 67 publications

(58 citation statements)

References 404 publications

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“…Finally, the statistical significance of Rieger-type periodicity in the southern hemisphere for cycles 17-18 is not above 95% confidence level but is still up to 92% confidence level. The early studies also found that the Rieger periodicity appears during cycles 17-18 (Gurgenashvili et al 2016;Zaqarashvili et al 2021). Moreover, our finding in this study indicates that the disappearance of Riegertype periodicity in the northern and southern hemispheres occurs only in those solar cycles with weaker hemispheric activity during sunspot maximum times.…”

Section: Discussionsupporting

confidence: 81%

“…Additionally, Zaqarashvili & Gurgenashvili (2018) showed that the Rieger-type periodicity can also be related to the equatorially trapped inertia-gravity waves in the solar tachocline. Recently, a comprehensive review of astrophysical Rossby waves introduced in detail the theory of Rossby waves and its study prospect in astrophysics (Zaqarashvili et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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The cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres of the sun

Xiang

Zhao

2021

Publ. Astron. Soc. Aust.

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We use a continuous wavelet transform to analyse the daily hemispheric sunspot area data from the Greenwich Royal Observatory during cycles 12–24 and then study the cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres during a certain cycle. The Rieger-type periodicity in the northern and southern hemispheres should be developed independently in the two hemispheres. This periodicity in the northern hemisphere is generally anti-correlated with the long-term variations in the mean solar cycle strength of hemispheric activity, but the correlation of the two parameters in the southern hemisphere shows a weak correlation. The appearance or disappearance of Rieger-type periodicity in the northern and southern hemispheres during a certain solar cycle is not directly correlated with their corresponding hemispheric mean activity strength but should be related to the strength of the hemispheric activity during sunspot maximum times, which hints the Rieger-type periodicity is more related to temporal evolution of toroidal magnetic field. The Rieger-type periodicity in the two hemispheres disappears in those solar cycles with relatively weak hemispheric activity during sunspot maximum times. The reason for the disappearance of this periodicity may be due to the combined influence of relatively weak toroidal magnetic fields and torsional oscillations, the differential rotation parameters vary through the solar cycle and may not remain more or less unchanged during some time, which does not permit the strong growth of magnetic Rossby waves.

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Section: Discussionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

The cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres of the sun

Xiang

Zhao

2021

Publ. Astron. Soc. Aust.

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“…Interested readers are referred to Zaqarashvili et al (2021) and references therein for a detailed review on Rossby waves in the Sun and other astrophysical problems. Although very powerful in its scope and inferential quality, the method of mode coupling is only slowly gaining traction in helioseismology (see Schad & Roth 2020;Hanson et al 2021;Kashyap et al 2021, for some other recent developments with this method); for instance, there is limited work on characterizing its limitations and developing mitigation strategies.…”

Section: Introductionmentioning

confidence: 99%

Detection of Rossby modes with even azimuthal orders using helioseismic normal-mode coupling

Mandal

Hanasoge

Gizon

2021

A&A

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Context. Retrograde Rossby waves, measured to have significant amplitudes in the Sun, likely have notable implications for various solar phenomena. Aims. Rossby waves create small-amplitude, very-low frequency motions, on the order of the rotation rate and lower, which in turn shift the resonant frequencies and eigenfunctions of the acoustic modes of the Sun. The detection of even azimuthal orders Rossby modes using mode coupling presents additional challenges and prior work therefore only focused on odd orders. Here, we successfully extend the methodology to measure even azimuthal orders as well. Methods. We analyze 4 and 8 years of Helioseismic and Magnetic Imager (HMI) data and consider coupling between different-degree acoustic modes (of separations 1 and 3 in the harmonic degree). The technique uses couplings between different frequency bins to capture the temporal variability of the Rossby modes. Results. We observe significant power close to the theoretical dispersion relation for sectoral Rossby modes, where the azimuthal order is the same as the harmonic degree, s = |t|. Our results are consistent with prior measurements of Rossby modes with azimuthal orders over the range t = 4 to 16 with maximum power occurring at mode t = 8. The amplitudes of these modes vary from 1 to 2 m s−1. We place an upper bound of 0.2 m s−1 on the sectoral t = 2 mode, which we do not detect in our measurements. Conclusions. This effort adds credence to the mode-coupling methodology in helioseismology.

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“…Carl Gustaf Rossby's discovery in the 1930s of a special class of waves that owe their existence to the spherical shape of the Earth, now widely known as Rossby waves, was one of the major breakthroughs in the development of a theoretical understanding of the large scale circulation of the atmosphere and ocean [1]. Rossby waves play an important role in the large scale dynamics of the atmosphere and ocean of the Earth and also different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars and planetary and exoplanetary atmospheres [2].…”

Section: Introductionmentioning

confidence: 99%

Variations in Wave Energy and Amplitudes along the Ray Paths of Barotropic Rossby Waves in Horizontally Non-Uniform Basic Flows

Jiping

Kang

2021

Atmosphere

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A non-divergent barotropic model on a sphere transformed to Mercator coordinates is used to examine the variations in wave energy and amplitude along the energy dispersion paths of barotropic Rossby waves in non-uniform basic flows. Wave energy can be easily solved by specifying the divergence of the group velocity along the corresponding rays. In an analytical non-uniform basic flow that represents the basic features of the observed one at middle latitudes, waves with different periods decay accompanying the decreases in wave energy and amplitude and the increase in the total wavenumber. This implies that the waves are trapped and the energy is eventually absorbed by the basic flow. For the observed non-uniform basic flow that can represent the basic features of the non-divergent wind field at 200 hPa, the situation is more complicated. The significant increase in wave energy can be caused by either the convergence of wave energy or the barotropic energy absorption from the basic flow or both of them. A significant increase in amplitude can also be observed if the total wavenumber varies moderately. This means waves can significantly develop. Waves may decay if both wave energy and amplitude decrease. Waves may propagate without significant developing or decaying to realize a long distance propagation. The propagating waves are mainly caused by oscillating wave energy as well as amplitude.

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Rossby Waves in Astrophysics

Cited by 67 publications

References 404 publications

The cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres of the sun

The cause of the appearance or disappearance of the Rieger-type periodicity in the northern and southern hemispheres of the sun

Detection of Rossby modes with even azimuthal orders using helioseismic normal-mode coupling

Variations in Wave Energy and Amplitudes along the Ray Paths of Barotropic Rossby Waves in Horizontally Non-Uniform Basic Flows

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