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Solar magnetic fields and convection

I: Active regions and sunspots

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Abstract

A phenomenological model of solar magnetic fields is developed, which differs drastically from all currently popular (diffuse-field) models. Its acceptance would require a review of a major part of theoretical solar physics including convection. Active Regions (ARs), and the nature and effects of surface magnetic fields in general.

  1. (i)

    Magnetic flux concentrations seen in sunspots, in ARs and even in quiet regions are not caused by convective motions but by long-lived (⪞1yr) flux ropes. These widely separated, helically twisted ropes originate beneath the convection zone and throughout their lives are impervious to supergranule or granule motions.

  2. (ii)

    Upon reaching maturity a flux rope develops an upward loop whose horizontal section emerges through the solar surface during a period of ≈ 3 days, during which period numerous individual flux tubes erupt from the rope to form an Arch Filament System. The main features of the system are explained, including the puzzling swing of its axis.

  3. (iii)

    On emerging, the leading (I) rope end is vertical while the following (f) end is inclined as suggested by Babcock, and the two dominate convection in their vicinity. This model explains the main features of a spot group including the notable east-west asymmetry.

  4. (iv)

    A spot decays because the flux rope unwinds and then may either split into large sections or ‘fray’ by the loss of numerous flux tubes from its outer surface. The tubes are themselves twisted and so develop kinks.

  5. (v)

    Fraying slowly extends to depths of ⪞105 km, but all flux tubes remain attached to the rope ends; they are rigid enough to resist being upended, and so form a unipolar magnetic region. The fields of ⪞1000 G observed at supergranule boundaries are not due to the concentrating effect of gas motions as often stated; nearly vertical, quasi-permanent flux tubes are merely moved back and forth by the gas motions.

  6. (vi)

    The model provides a test for any convection zone model; in particular it is incompatible with the dynamo theory. It is also incompatible with models of convection which attribute the formation of sunspot fields to the supergranulation.

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Authors and Affiliations

  1. National Measurement Laboratory, CSIRO, Sydney, Australia

    J. H. Piddington

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  1. J. H. Piddington
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Piddington, J.H. Solar magnetic fields and convection. Astrophys Space Sci 34, 347–362 (1975). https://doi.org/10.1007/BF00644803

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