The outer 30% of the solar interior covers the Sun’s convection zone. There, under the influence of rotation, convective motions drive the large-scale flows that power the global dynamo. The convection is also a source of stochastic excitation for the acoustic waves that permeate the solar interior.
Measurements of the frequencies of the modes of oscillation have been used very successfully to infer, for example, internal rotation as a function of radius and unsigned latitude. Current research focuses on developing improved methods to recover the 3D sound speed and vector flows in the interior from the correlations of the acoustic wavefield measured at the surface.
In this presentation, I intend to present recent uniqueness results for the passive inverse problem [1,2], as well as linear inversions of seismic data for the meridional flow [3], and advances in helioseismic holography – an imaging technique that enables us to see active regions on the Sun’s far side [4]. I will then discuss a new and promising iterative method, which combines the computational efficiency of helioseismic holography and the quantitative nature of helioseismic tomography [5]. If time permits, I will mention the possibility of extending helioseismology to the interpretation of the recently discovered inertial modes of oscillation [6].
[1] A. D. Agaltsov, T. Hohage, R. G. Novikov. Monochromatic identities for the Green function and uniqueness results for passive imaging. SIAM J. Appl. Math. 78:2865, 2018. doi:10.1137/18M1182218
[2] A. D. Agaltsov, T. Hohage, R. G. Novikov. Global uniqueness in a passive inverse problem of helioseismology. Inverse Problems 36:055004, 2020. doi:10.1088/1361-6420/ab77d9
[3] L. Gizon et al. Meridional flow in the Sun’s convection zone is a single cell in each hemisphere. Science 368:1469, 2020. doi:10.1126/science.aaz7119
[4] D. Yang, L. Gizon, H. Barucq. Imaging individual active regions on the Sun’s far side with improved helioseismic holography. Astron. Astrophys. 669:A89, 2023. doi:10.1051/0004-6361/202244923
[5] B. Mueller et al. Quantitative passive imaging by iterated back propagation: The example of helioseismic holography. 2023. in preparation
[6] L. Gizon et al. Solar inertial modes: Observations, identification, and diagnostic promise. Astron. Astrophys. 652:L6, 2021. doi:10.1051/0004-6361/202141462
