Removal of Active Region Inflows Reveals a Weak Global Trend in Near-Surface Meridional Flow
Abstract
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 and can be as strong as 30 m/s. We parameterize these inflows around active regions as a function of their net unsigned flux. If active region neighborhoods are excluded, the solar cycle scale variation in background meridional flow diminishes to below 2 m/s, but still shows systematic variations in the absence of active regions at high latitudes 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. 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, the three-component breakdown of the near-surface meridional flow and the parameterization of active region inflows serve as vital constraints for solar dynamo models and surface flux transport simulations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMSH25B..01M