near-surface-solar-flows-cycle24-timedistance-helioseismology

Using time-distance local helioseismology flow maps within 1 Mm of the solar photosphere, we detect inflows toward
activity belts that contribute to solar cycle scale variations in near-surface meridional flow. These inflows stretch out
as far as 30 degrees away from active region centroids. If active region neighborhoods are excluded, the solar cycle
scale variation in background meridional flow diminishes to below 2 m s−1, but still shows systematic variations in the
absence of active regions between sunspot cycles 24 and 25. We, therefore, propose that the near-surface meridional
flow is a three component flow made up of: a constant baseline flow profile that can be derived from quiet Sun regions,
variations due to inflows around active regions, and solar cycle scale variation of the order of 2 m s−1. Torsional
oscillation, on the other hand, is found to be a global phenomenon i.e. exclusion of active region neighborhoods does
not affect its magnitude or phase significantly. This non-variation of torsional oscillation with distance away from
active regions and the three-component breakdown of the near-surface meridional flow serve as vital constraints for
solar dynamo models and surface flux transport simulations.