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  Time-distance helioseismology of solar Rossby waves

Liang, Z.-C., Gizon, L., Birch, A., & Duvall, T. (2019). Time-distance helioseismology of solar Rossby waves. Astronomy and Astrophysics, 626: A3. doi:10.1051/0004-6361/201834849.

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 Urheber:
Liang, Zhi-Chao1, Autor           
Gizon, Laurent1, Autor           
Birch, Aaron1, Autor           
Duvall, Thomas1, Autor           
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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Schlagwörter: Sun: helioseismology / Sun: oscillations / Sun: interior / waves
 MPIS_PROJECTS: SDO: German Data Center
 Zusammenfassung: Context. Solar Rossby waves (r modes) have recently been discovered in the near-surface horizontal flow field using the techniques of granulation-tracking and ring-diagram analysis applied to six years of SDO/HMI data.

Aims. Here we apply time-distance helioseismology to the combined SOHO/MDI and SDO/HMI data sets, which cover 21 years of observations from May 1996 to April 2017. The goal of this study is to provide an independent confirmation over two solar cycles and in deeper layers of the Sun.

Methods. We have measured south-north helioseismic travel times along the equator, which are sensitive to subsurface north-south flows. To reduce noise, the travel times were averaged over travel distances from 6° to 30°; the mean distance corresponds to a p-mode lower turning point of 0.91 R⊙. The 21-year time series of travel-time measurements was split into three seven-year subsets and transformed to obtain power spectra in a corotating frame.

Results. The power spectra all show peaks near the frequencies of the classical sectoral Rossby waves for azimuthal wavenumbers in the range 3 ≤ m ≤ 15. The mode frequencies and linewidths of the modes with m ≤ 9 are consistent with a previous study whereas modes with m ≥ 10 are shifted toward less negative frequencies by 10–20 nHz. While most of these modes have e-folding lifetimes on the order of a few months, the longest lived mode, m = 3, has an e-folding lifetime of more than one year. For each mode, the rms velocity at the equator is in the range of 1–3 m s−1, with the largest values for m ∼ 10. No evidence for the m = 2 sectoral mode is found in the power spectrum, implying that the rms velocity of this mode is below ∼0.5 m s−1.

Conclusions. This work confirms the existence of equatorial global Rossby waves in the solar interior over the past two solar cycles and shows that time-distance helioseismology is a promising technique to study them deep in the convection zone.

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Sprache(n): eng - English
 Datum: 2019
 Publikationsstatus: Online veröffentlicht
 Seiten: -
 Ort, Verlag, Ausgabe: -
 Inhaltsverzeichnis: -
 Art der Begutachtung: Expertenbegutachtung
 Identifikatoren: DOI: 10.1051/0004-6361/201834849
 Art des Abschluß: -

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Titel: Astronomy and Astrophysics
  Andere : Astron. Astrophys.
Genre der Quelle: Zeitschrift
 Urheber:
Affiliations:
Ort, Verlag, Ausgabe: Les Ulis Cedex A France : EDP Sciences
Seiten: - Band / Heft: 626 Artikelnummer: A3 Start- / Endseite: - Identifikator: Anderer: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1