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A Skumanich (High Alt Obs - National Center for Atmospheric Research)
We find that the dark regions of pores and spots (which include their penumbrae) have a nearly universal average flux density of 800 G ±32 while normal contrast Azimuth Centers (ACs) and pore sheaths, i.e. the associated magnetic envelope about the dark region, also show a similar constancy but at 334 G ±22, while spot sheaths are characterized by 107 G ±22. Using these flux density values and the observed dark and magnetic (dark + sheath) radii we derive a magnetic flux-dark flux relation which yields radius-flux relations for pores and spots. The magnetic radius vs flux relation for spots is distinct, with larger radii at one and the same flux than those for pores, while the curve for the dark radius is continuous with that for pores. Spots differ from pores only in the nature of their sheaths. The AC structure, a `pure' sheath, has a radius-flux relation different from, but bridging, those of pores and spots. We suggest these relations to be universal. The temporal magnetic evolution for two developing pores and a decaying spot in the radius-flux plane traces the universal dark radius curve for both types of features. The evolution of an AC into a pore, perhaps via a bifurcation, follows the universal curves for dark and magnetic radii. Any bifurcation in the transition from pores to spots must appear via a transition in the magnetic sheath.
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