Understanding Active Region Origins and Emergence on the Sun and Other Cool Stars

Weber, Maria A.; Schunker, Hannah; Jouve, Laurène; Işık, Emre

doi:10.1007/s11214-023-01006-5

Cited by 11 publications

(4 citation statements)

References 149 publications

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“…For this reason, numerous articles have been written on the statistical properties of the tilt of active regions. This role has been included in recent reviews (Cliver, 2014;Hathaway, 2015;Weber et al, 2023). There is no need to reiterate the role of tilt in this review.…”

Section: Candidate Magnetic Fields To Replace the Polar Fields Every ...mentioning

confidence: 97%

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Observations key to understanding solar cycles: a review

Martin

2024

Front. Astron. Space Sci.

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A paradigm shift is taking place in the conception of solar cycles. In the previous conception, the changing numbers of sunspots over intervals of 9–14 years have been regarded as the fundamental solar cycle although two average 11-year cycles were necessary to account for the complete magnetic cycle. In the revised picture, sunspots are a phase in the middle of two 22-year overlapping solar cycles that operate continuously with clock-like precision. More than 20 researchers have contributed to the initial research articles from 2014 through 2021 which are dramatically altering the perception of solar cycles. The two 22-year cycles overlap in time by 11 years. This overlap is coincidentally the same average duration as the sunspot phase in each 22-year cycle. This coincidence and the relative lack of knowledge of the large numbers of small active regions without sunspots is what led to the previous paradigm in which the 11-year sunspot phases were misinterpreted as a single fundamental solar cycle. The combination of the two 22-year solar cycles, with their large numbers of short-lived active regions and ephemeral active regions are now understood to be the fundamental cycle with the proposed name “The Hale Solar Cycle.” The two 22-year solar cycles each occupy separate but adjacent bands in latitude. The orientations of the majority of bipolar magnetic regions in the two adjacent bands differ from each other by ∼180°. Both bands continuously drift from higher to lower latitudes as has been known for sunspot cycles. However, the polarity reversal occurs at the start of each 22-year cycle and at higher latitudes than it does for the sunspot cycles. This paradigm shift in the concept of solar cycles has resulted in major reconsiderations of additional topics on solar cycles in this review. These are 1) the large role of ephemeral active regions in the origin of solar cycles, 2) the depth of the origin of active regions and sunspots, 3) the mechanisms of how areas of unipolar magnetic network migrate to the solar poles every 11 years, and 4) the nature of the polarity reversal in alternate 22-year cycles rather than 11-year cycles.

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Section: Candidate Magnetic Fields To Replace the Polar Fields Every ...mentioning

confidence: 97%

“…Martin 10.3389/fspas.2023.1177097 Weber et al (2023) and other review articles referenced therein. In this limited review, solar observations are first discussed as occurring in eras that span decades of solar research and are identified as paradigms.…”

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confidence: 99%

Observations key to understanding solar cycles: a review

Martin

2024

Front. Astron. Space Sci.

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“…Figure 1 in Schunker et al 2019). It takes about 2 d on average from the time of emergence for an active region to reach its maximum flux (see Figure 2 in Weber et al 2023).…”

Section: Identification Of Persistent Magnetic Bipoles Before Emergencementioning

confidence: 99%

“…Recently, it has become apparent that the near-surface convective flows themselves are important in the emergence process (see Weber et al 2023, for a summary of the recent paradigm shift). By comparing the observed surface flows at the time of active region emergence with simulations, Birch et al (2016) showed that flux tubes cannot be rising faster than about 100 ms −1 through the upper convection zone, which is on the order of the convective velocities themselves.…”

Section: Introductionmentioning

confidence: 99%

Evolution of the magnetic field and flows of solar active regions with persistent magnetic bipoles before emergence

Alley,

Schunker

2023

Publ. Astron. Soc. Aust.

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Magnetic active regions on the Sun are harbingers of space weather. Understanding the physics of how they form and evolve will improve space weather forecasting. Our aim is to characterise the surface magnetic field and flows for a sample of active regions with persistent magnetic bipoles prior to emergence. We identified 42 emerging active regions (EARs), in the Solar Dynamics Observatory Helioseismic Emerging Active Region survey (Schunker et al. 2016, A&A. 595, A107), associated with small magnetic bipoles at least one day before the time of emergence. We then identified a contrasting sample of 42 EARs that emerge more abruptly without bipoles before emergence. We computed the supergranulation-scale surface flows using helioseismic holography. We averaged the flow maps and magnetic field maps over all active regions in each sample at each time interval from 2 d before emergence to 1 d after. We found that EARs associated with a persistent pre-emergence bipole evolve to be, on average, lower flux active regions than EARs that emerge more abruptly. Further, we found that the EARs that emerge more abruptly do so with a diverging flow of $(3\pm 0.6) \times 10^{-6}$ s $^{-1}$ on the order of 50–100 ms $^{-1}$ . Our results show that there is a statistical dependence of the surface flow signature throughout the emergence process on the maximum magnetic flux of the active region.

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