Solar-Cycle Variation of Large-Scale Flows in the Near-Surface Shear Layer from SC 23 to SC 26

We study the long-term variation of the zonal and meridional flows from Solar Cycle 23 to 26 throughout the near-surface shear layer (NSSL) derived with ring-diagram analysis (RDA) applied to Dopplergrams obtained mainly by Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) and compare them with global helioseismic results. We also create super-synoptic maps of the divergence of the meridional and the acceleration of the zonal flow. The bands of decelerating zonal and converging meridional flows of a given solar cycle coincide with the locations of magnetic activity at mid- to low latitudes. They begin their latitudinal migration near 50^◦ at or shortly after the maximum of the previous cycle, such as near 2015 for Solar Cycle 25, while the band of fast zonal flow is close to two years ahead of these bands at mid- to low latitudes. The patterns move 5.20 ± 0.29^◦/Yr from 37.5^◦ to 7.5^◦ averaged over both hemispheres during Solar Cycle 25. The zonal-flow patterns vary little with depth throughout the NSSL at 7.5^◦ to 30.0^◦ where most active regions are present. However, the bands of converging meridional flows appear somewhat earlier at greater depths than at shallower ones. The bands of fast zonal flow of Solar Cycle 25 have reached latitudes near the equator during 2024, which is close to Solar Cycle 25 maximum. A band of fast zonal flow appeared at about 50^◦ at the same time and thus indicates the beginning of Solar Cycle 26. The amplitudes of the bands of fast zonal flows are anti-correlated with the strength of the associated solar cycles except close to the equator. The divergence minima are also anti-correlated with magnetic activity, while the acceleration minima are only weakly anti-correlated. With the derived flow parameters, we estimate the timing and strength of Solar Cycle 26 and predict that it will be close to an average sunspot cycle.