Manifestations of the Turbulent Component of the Global Solar Dynamo in an Activity Minimum
Tóm tắt
The solar dynamo generates a toroidal magnetic field that, forms active regions (ARs) on the surface of the Sun. The toroidal magnetic field lines rise through the turbulent convection zone, where distortions, deformation of already formed regular toroidal magnetic flux bundles and the formation of irregular, complex magnetic structures are possible. At the minimum of solar activity, the toroidal magnetic field of the old cycle disappears and the magnetic field of the new cycle is still very weak. During this period, it is possible to assess the role of the turbulence in the formation of an AR. In this paper, we analyzed ARs of two solar activity minima (between cycles 23–24 and between cycles 24–25). We analyzed ARs located within 60° from central meridian and exhibiting magnetic flux at the maximum development of at least 1021 Mx. Bipolar and multipolar ARs were divided into regular ones (consistent with the mean-field dynamo theory) and irregular ones, the formation of which was influenced by the turbulence of the convection zone (unipolar spots were considered separately). It was found that regular ARs significantly predominate during solar minima, their magnetic flux is a half or more of the total magnetic flux (0.6 for the first period, 0.5 for the second period). Irregular ARs are fewer in number than regular ones, and in terms of magnetic flux they make up about one-third of the total magnetic flux (0.3 and 0.2 in the first and second periods, respectively). Irregular ARs are predominantly represented by bipolar structures of improper orientation, while very complex multipolar ARs are extremely rare. It is concluded that the generation of ARs with the magnetic flux exceeding 1021 Mx occurs due to the global dynamo action, while the turbulence of the convection zone causes deformation of the magnetic flux bundles without significant magnetic flux generation.
Tài liệu tham khảo
Abramenko, V.I., Signature of the turbulent component of the solar dynamo on active region scales and its association with flaring activity, Mon. Not. R. Astron. Soc., 2021, vol. 507, pp. 3698–3706.
Abramenko, V.I., Suleymanova, R.A., and Zhukova, A.V., Magnetic fluxes of solar active regions of different magneto–morphological classes. I. Cyclic variations, Mon. Not. R. Astron. Soc., 2023, vol. 518, pp. 4746–4754.
Babcock, H.W., The topology of the Sun’s magnetic field and the 22-year cycle, Astrophys. J., 1961, vol. 133, pp. 572–587.
Bobra, M.G., Sun, X., Hoeksema, J.T., et al., The Helioseismic and Magnetic Imager (HMI) vector magnetic field pipeline: SHARPs-Space-Weather HMI Active Region Patches, Sol. Phys., 2014, vol. 289, no. 9, pp. 3549–3578.
Fisher, G.H., Fan, Y., and Howard, R.F., Comparisons between theory and observation of active region tilts, Astrophys. J., 1995, vol. 438, pp. 463–471.
Hagenaar, H., Ephemeral regions on a sequence of full-disk Michelson Doppler imager magnetograms, Astrophys. J., 2001, vol. 555, pp. 448–461.
Hale, G.E., Ellerman, F., Nicholson, S.B., et al., The magnetic polarity of sun-spots, Astrophys. J., 1919, vol. 49, pp. 153–178.
Ishikawa, R. and Tsuneta, S., Comparison of transient horizontal magnetic fields in a plage region and in the quiet Sun, Astron. Astrophys., 2009, vol. 495, pp. 607–612.
Leighton, R.B., A magneto–kinematic model of the solar cycle, Astrophys. J., 1969, vol. 156, pp. 1–26.
Liu, Y., Hoeksema, J.T., Scherrer, P.H., et al., Comparison of line-of-sight magnetograms taken by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager and Solar and Heliospheric Observatory/Michelson Doppler Imager, Sol. Phys., 2012, vol. 279, pp. 295–316.
Longcope, D.W. and Fisher, G.H., The effects of convection zone turbulence on the tilt angles of magnetic bipoles, Astrophys. J., 1996, vol. 458, pp. 380–390.
Longcope, D.W., Fisher, G.H., and Pevtsov, A.A., Flux-tube twist resulting from helical turbulence: the Σ-effect, Astrophys. J., 1998, vol. 507, no. 1, pp. 417–432.
McClintock, B.H., Norton, A.A., and Li, J., Re-examining sunspot tilt angle to include anti-Hale statistics, Astrophys. J., 2014, vol. 767, no. 2, p. 130.
Nagovitsyn, Yu.A. and Pevtsov, A.A., On the presence of two populations of sunspots, Astrophys. J., 2016, vol. 833, pp. 94–99.
Nagovitsyn, Yu.A., Pevtsov, A.A., and Osipova, A.A., Two populations of sunspots: Differential rotation, Astron. Lett., 2018, vol. 44, pp. 202–211.
Pietarila, G.J., Cameron, R., and Schüssler, M., Turbulent small-scale dynamo action in solar surface simulations, Astrophys. J., 2010, vol. 714, no. 2, pp. 1606–1616.
Rempel, M., Numerical simulations of quiet Sun magnetism: On the contribution from a small-scale dynamo, Astrophys. J., 2014, vol. 789, no. 2, pp. 132–154.
Scherrer, P.H., Bogart, R.S., Bush, R.I., et al., The solar oscillations investigation–Michelson Doppler Imager, Sol. Phys., 1995, vol. 162, pp. 129–188.
Scherrer, P.H., Schou, J., Bush, R.I., et al., The Helioseismic and Magnetic Imager (HMI) investigation for the Solar Dynamics Observatory (SDO), Sol. Phys., 2012, vol. 275, pp. 207–227.
Schou, J., Scherrer, P.H., Bush, R.I., et al., Design and ground calibration of the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO), Sol. Phys., 2012, vol. 275, pp. 229–259.
van Driel-Gesztelyi, L. and Green, L.M., Evolution of active regions, Living Rev. Sol. Phys., 2015, vol. 12, pp. 1–98.
Vögler, A. and Schüssler, M., A solar surface dynamo, Astron. Astrophys., 2007, vol. 465, no. 3, pp. L43–L46.
Zhukova, A., Khlystova, A., Abramenko, V., et al., Synthetic solar cycle for active regions violating the Hale’s polarity law, Mon. Not. R. Astron. Soc., 2022, vol. 512, p. 1365.