Solar large-scale flows obtained from the HMI time-distance data-analysis pipeline

Using the subsurface flow maps obtained from the HMI time-distance data-analysis pipeline, I examine the temporal evolution of torsional oscillation, meridional flow, and long-living large-scale structures in high-latitude areas. During the 5.5-year analysis period, both the torsional oscillation and meridional flow show strong hemispheric asymmetry while persisting the converging-flow patterns toward the activity belts. Meanwhile, for both hemispheres in the mid-latitude zone, the meridional-flow speed shows an anti-correlation with the magnetic flux being transported toward the pole, slowing down (speeding up) when following-polarity (leading-polarity) magnetic flux is transported. In the latitudinal band studied, the meridional-flow speed and magnetic field remained relatively unchanged from 2012 through 2015 in the northern hemisphere, but varied substantially during the same period in the southern hemisphere. Long-living large-scale structures, characterized by their low zonal speed, are observed in high-latitude areas, but the nature and cause of these structures are unknown.