Solar Cycle Variation of Meridional Flow

The solar meridional flow plays a crucial role in driving the solar dynamo. We study the near-surface hemispherical asymmetries in the meridional flow over 18 years using the velocities obtained from the Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) ring-diagram pipelines. Our analysis shows that the hemispherical asymmetry in the flow is strongly related to the solar cycle asymmetry. We observe a time-delayed anti-correlation with the asymmetry in meridional flow preceding the asymmetry in the sunspot cycle. We investigate the relationship between sunspot tilt angles and plasma inflows, and uncover the first observational evidence of the hypothesized non-linear quenching in the Babcock Leighton poloidal field generation mechanism mediated by surface plasma flows. Our observations illuminate feedback processes between magnetic fields and plasma flows and set new constraints on magneto-hydrodynamic dynamo models of the solar cycle.