Probing Depth Variations of Solar Inertial Modes through Normal Mode Coupling

Document Type

Article

Publication Date

5-1-2024

Abstract

Recently discovered inertial waves, observed on the solar surface, likely extend to the deeper layers of the Sun. Utilizing helioseismic techniques, we explore these motions, allowing us to discern inertial mode eigenfunctions in both radial and latitudinal orientations. We analyze 8 yr of space-based observations (2010-2017) taken by the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory using normal mode coupling. Couplings between the same and different-degree acoustic modes and different frequency bins are measured in order to capture the various length scales of the inertial modes. We detect inertial modes at high latitude with azimuthal order t = 1 and frequency ∼ −80 nHz, measured in a corotating frame with a rotation frequency of 453.1 nHz. This mode is present in the entire convection zone. The presence of Rossby modes may be seen down to a depth of ∼0.83R ⊙, and the Rossby signal is indistinguishable from noise below that depth for high azimuthal order. We find that the amplitudes of these modes increase with depth down to around 0.92R ⊙ and decrease below that depth. We find that the latitudinal eigenfunctions of Rossby modes deviate from sectoral spherical harmonics if we use a similar approach as adopted in earlier studies. We find that spatial leakage and even pure noise in the measurements of nonsectoral components can also explain the abovementioned characteristics of the latitudinal eigenfunctions. This realization underscores the necessity for careful interpretation when considering the latitudinal eigenfunctions of Rossby modes. Exploring the depth-dependent characteristics of these modes will enable us to capture interior dynamics distinctly, separate from p-mode seismology.

Identifier

85193699281 (Scopus)

Publication Title

Astrophysical Journal

External Full Text Location

https://doi.org/10.3847/1538-4357/ad391b

e-ISSN

15384357

ISSN

0004637X

Issue

1

Volume

967

Grant

WHOLESUN 810218

Fund Ref

Engineering Research Centers

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