A search for coherent structures in subsurface flows

Abstract

We search for coherent patterns in horizontal subsurface flows obtained from Global Oscillation Network Group (GONG) Dopplergram data using ring-diagram analysis. The existence of north-south aligned downflow patterns near the equator has been predicted by numerical models of the solar convection zone. We analyze time series of daily flow measurements near the solar equator focusing on the vertical velocity component and the derivative of the zonal flow in the east-west direction. To reduce the influence of surface magnetic activity, we analyze observations during the minimum phase of the solar cycle. We find coherent equatorial structures that persist for several days in the zonal velocity derivative and the vertical velocity component and are not associated with surface magnetic activity. We use a cross-correlation analysis to measure the strength and rotation rate of these coherent patterns. Our results are consistent with other studies that have observed north-south aligned patterns in supergranulation.