Evidence of Quasi-periodic Global-scale Oscillations of Flows in the Near-Surface Shear Layer

Analysis of high-resolution ring-diagram fits of low-order modes in data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory reveals evidence of global-scale oscillations in the near-surface shear layer. They appear as large-scale variations of radial shear in the flows relative to their mean values. These variations cover all or most of a visible hemisphere, and frequently reverse with a time scale on the order of a solar rotation. The comparatively rapid oscillations of the amplitude and direction of these anomalous shears appear to be modulated in a complex, not-quite annual way unrelated to known orbital nor instrumental effects. Small-scale shear anomalies in the neighborhood of active regions lend support to their solar origin and physical interpretation.