Discovery of high-frequency retrograde vorticity waves in the Sun

• Published in: Nature astronomy Vol. 6; no. 6; pp. 708 - 714
• Main Authors: Hanson, Chris S., Hanasoge, Shravan, Sreenivasan, Katepalli R.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2022; Nature Publishing Group
• Subjects: 639/33/34/867; 639/33/525/870; Astronomy; Astrophysics and Cosmology; Convection; Coriolis force; Hydrodynamics; Magnetic fields; Magnetism; Physics; Physics and Astronomy
• ISSN: 2397-3366; 2397-3366
• DOI: 10.1038/s41550-022-01632-z

Classical helioseismology, which relies on acoustic waves, has been successfully applied to image the Sun’s interior rotation and structure. However, acoustic waves are insensitive to parameters such as magnetic fields, turbulent viscosity and entropy gradients in the deep convection zone, which are critical inputs to theories of solar dynamics. Inertial oscillations can bridge this gap with their complementary sensitivities to these parameters. Here, by employing helioseismic and correlation-tracking analyses of ground- and space-based observations, we detect equatorially antisymmetric vorticity waves, propagating retrograde at three times the phase speeds of Rossby–Haurwitz waves of the same wavenumber. This high-frequency dispersion relation cannot be explained by standard hydrodynamic mechanisms. We investigate three possibilities: that these vorticity waves are excited by the Coriolis force and modified by internal magnetic fields, gravity or compressibility. Incontrovertible identification of any of these coupled oscillations would influence our understanding of deep-interior magnetism, internal gravity oscillations or large-scale convection. Through observational evidence and theoretical arguments, however, we exclude these coupling mechanisms. The as-yet undetermined nature of these waves promises novel physics and fresh insight into solar dynamics. The discovery of high-frequency inertial waves in the near-surface layers of the Sun—travelling much faster than hydrodynamics alone would allow—points to hidden dynamics of unknown nature below the surface of the Sun.