Abstract
A qualitative analysis is given of the data on the full magnetic and velocity vector fields in a growing sunspot group, recorded nearly simultaneously with the Solar Optical Telescope on the Hinode satellite. Observations of a young bipolar subregion developing within AR 11313 were carried out on 9 – 10 October 2011. Our aim was to form an idea about the consistency of the observed pattern with the well-known rising-tube model of the formation of bipolar active regions and sunspot groups. We find from our magnetograms that the distributions of the vertical [\(B_{\mathrm {v}}\)] and the horizontal [\(B_{\mathrm {h}}\)] component of the magnetic field over the area of the magnetic subregion are spatially well correlated; in contrast, the rise of a flux-tube loop would result in a qualitatively different pattern, with the maxima of the two magnetic-field components spatially separated: the vertical field would be the strongest where either spot emerges, while the maximum horizontal-field strengths would be reached in between them. A specific feature, which we call the bordering effect, is revealed: some local extrema of \(B_{\mathrm {v}}\) are bordered with areas of locally enhanced \(B_{\mathrm {h}}\). This effect suggests a fountainlike spatial structure of the magnetic field near the \(B_{\mathrm {v}}\) extrema, which is also hardly compatible with the emergence of a flux-tube loop. The vertical-velocity field in the area of the developing active subregion does not exhibit any upflow on the scale of the whole subregion, which should be related to the rising-tube process. Thus, our observational data can hardly be interpreted in the framework of the rising-tube model.
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Notes
As frequently done in the literature on stellar and planetary dynamos, we use here the terms toroidal and azimuthal as synonyms, although they are not mathematically equivalent.
Since the area of interest was located near the solar-disc centre and, moreover, corrections for projection effects are not important from the standpoint of our goal, we do not make difference here between the line-of-sight and the vertical component and also between the transversal (tangential) and horizontal vector components.
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Acknowledgements
Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in cooperation with ESA and NSC (Norway). The work of A.V.G. and A.A.B. was supported by the Russian Foundation for Basic Research (project no. 12-02-00792-a). We are grateful to L.M. Alekseeva and to the reviewer for their comments.
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Getling, A.V., Ishikawa, R. & Buchnev, A.A. Development of Active Regions: Flows, Magnetic-Field Patterns and Bordering Effect. Sol Phys 291, 371–382 (2016). https://doi.org/10.1007/s11207-015-0844-3
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DOI: https://doi.org/10.1007/s11207-015-0844-3