The solar dynamo begins near the surface
| Autor: | Vasil, Geoffrey M, Lecoanet, Daniel, Augustson, Kyle, Burns, Keaton J, Oishi, Jeffrey S, Brown, Benjamin P, Brummell, Nicholas, Julien, Keith |
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| Rok vydání: | 2024 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | The Sun's magnetic dynamo cycle features a distinct pattern: a propagating region of sunspot emergence appears around 30 degrees latitude and vanishes near the equator every 11 years. Moreover, longitudinal flows called "torsional oscillations" closely shadow sunspot migration, undoubtedly sharing a common cause. Contrary to theories suggesting deep origins for these phenomena, helioseismology pinpoints low-latitude torsional oscillations to the Sun's outer 5-10%, the "Near-Surface Shear Layer". Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the Magneto-Rotational Instability prominent in accretion-disk theory and observed in laboratory experiments. Together, these two facts prompt the general question: Is it possible that the solar dynamo is a near-surface instability? Here, we report strong affirmative evidence in stark contrast to traditional paradigms focusing on the deeper tachocline. Simple analytic estimates show that the near-surface magneto-rotational instability better explains the spatiotemporal scales of the torsional oscillations and inferred subsurface magnetic field amplitudes. State-of-the-art numerical simulations corroborate these estimates and, strikingly, reproduce hemispherical magnetic current helicity laws. The dynamo resulting from a well-understood near-surface phenomenon improves prospects for accurate predictions of full magnetic cycles and space weather, impacting Earth's electromagnetic infrastructure. Comment: In press, Nature |
| Databáze: | arXiv |
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