Local Helioseismology with GONG

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The Global Oscillation Network Group (GONG), recently upgraded to include higher resolution CCD cameras, is a community-based program to conduct a detailed study of the structure and dynamics of the Sun using helioseismology. What we now call global helioseismology has been invaluable for determining the radial structure of the Sun, as well as the depth and latitude variation of axisymmetric flows, such as rotation and torsional oscillations. However, global-mode frequencies are relatively insensitive to azimuthally varying structure, north/south hemispheric asymmetries, small-scale flows, and meridional flows. New diagnostics have been employed in recent years to explore the solar interior from a local rather than a global perspective. The investigators are developing computational seismic holography as an efficient and versatile tool designed to image the solar interior to the optimum spatial resolution permitted by wave diffraction. They are applying phase-sensitive seismic holography to GONG observations, spanning half a solar cycle, to study the short-term and long-term temporal properties of flows and sound-speed perturbations throughout much of the solar convection zone. They will explore the subsurface nature of meridional circulation, the nature of other subsurface flows and their connection with magnetic activity, and the local acoustic properties of the tachocline and the solar poles. Broader impacts: The project is increasing our understanding, and hence our predictive capability, of the solar cycle. This is essential for space exploration, earth sensing, weather forecasting, and communications that are all impacted by solar activity.