Cyclic Changes of the Sun's Seismic Radius

Abstract

The questions whether the Sun shrinks with the solar activity and what causes this have been a subject of debate. Helioseismology provides means to measure with high precision the radial displacement of subsurface layers, co-called "seismic radius", through analysis of oscillation frequencies of surface gravity (f) modes. Here, we present results of a new analysis of twenty one years of helioseismology data from two space missions, Solar and Heliospheric Observatory (SoHO) and Solar Dynamics Observatory (SDO), which allow us to resolve previous uncertainties and compare variations of the seismic radius in two solar cycles. After removing the f-mode frequency changes associated with the surface activity we find that the mean seismic radius is reduced by 1-2 km during the solar maxima, and that most significant variations of the solar radius occur beneath the visible surface of the Sun at the depth of about 5 Mm, where the radius is reduced by 5-8 km. These variations can be interpreted as changes in the solar subsurface structure caused by predominately vertical ~10 kG magnetic field.

9 pages, 5 figures, to appear in ApJ

References in corpus (5)

• Solving the discrepancy between the seismic and photospheric solar radius
• Emergence of magnetic flux generated in a solar convective dynamo. I: Formation of Sunspots and Active regions, and Origin of Their Asymmetries
• Helioseismic test of non-homologous solar radius changes with the 11-year activity cycle
• Solar Cycle Variations of Rotation and Asphericity in the Near-Surface Shear Layer
• How do f-mode Frequencies Change with Solar Radius?

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• Eclipsing Spotted Giant Star With K2 and Historical Photometry
• Subterahertz Radius and Limb Brightening of the Sun Derived from SST and ALMA
• The Solar Radius at 37 GHz through Cycles 22 to 24
• Solar oblateness & asphericities temporal variations: outstanding some unsolved issues
• Nearly Century-scale Variation of the Sun's Radius
• Exploring the Temporal Variation of the Solar Quadrupole Moment J2
• Effects of Observational Data Shortage on Accuracy of Global Solar Activity Forecast
• Long-Term Variation of Helioseismic Far-Side Images and What Causes It