Removal of Active Region Inflows Reveals a Weak Solar Cycle Scale Trend in the 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 the near-surface meridional flow. These inflows stretch out as far as 30° away from the active region centroids. If active region neighborhoods are excluded, the solar-cycle-scale variation in the 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 about 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 significantly affect its magnitude or phase. This nonvariation in 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.
- Publication:
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The Astrophysical Journal
- Pub Date:
- June 2023
- DOI:
- arXiv:
- arXiv:2304.02158
- Bibcode:
- 2023ApJ...950...63M
- Keywords:
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- Solar meridional circulation;
- Helioseismology;
- Solar dynamo;
- Solar magnetic fields;
- Solar cycle;
- Solar active region velocity fields;
- Solar active regions;
- Solar active region magnetic fields;
- Solar differential rotation;
- Solar surface;
- Solar physics;
- Solar interior;
- 1874;
- 709;
- 2001;
- 1503;
- 1487;
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- 1974;
- 1975;
- 1996;
- 1527;
- 1476;
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- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 14 pages, 9 figures, accepted for publication in the Astrophysical Journal