Persistent Near-Surface Flow Structures from Local Helioseismology

Near-surface flows measured by the ring-diagram technique of local helioseismology show structures that persist over multiple rotations. We examine these phenomena using data from the Global Oscillation Network Group (GONG) and the Helioseismic and Magnetic Imager (HMI) and show that a correlation analysis of the structures can be used to estimate the rotation rate as a function of latitude, giving a result consistent with the near-surface rate from global helioseismology and slightly slower than that obtained from a similar analysis of the surface magnetic field strength. At latitudes of 60∘ and above, the HMI flow data reveal a strong signature of a two-sided zonal flow structure. This signature may be related to recent reports of “giant cells” in solar convection.