2 The 1970s

For his thesis research, Caltech student Jim Mosher compared the evolution of magnetic regions seen on small reproductions of Kitt Peak magnetograms with what he estimated from analytical calculations (Mosher, 1977Jump To The Next Citation Point). He deduced that the effective diffusion rate was only 200 – 400 km2 s–1 and that it was accompanied by a poleward meridional flow ∼ 3 m s–1. This was an apparent blow to Leighton’s model, which was able to reverse the polar field without the need for meridional flow (provided that the diffusion rate was ∼ 103 km2 s–1), and was especially appealing in the days when there was little observational evidence for the flow. Although Doppler observations of meridional flow were still uncertain (Duvall Jr, 1979Labonte and Howard, 1982Jump To The Next Citation Point), inferences based on flux evolution continued to accumulate (Howard, 1979Howard and Labonte, 1981Topka et al., 1982Jump To The Next Citation Point), and Leighton’s model was increasingly criticized. The status of the model at that time is described in Chapter 2 of the Skylab Active Region Workshop publication (Sheeley Jr, 1981b).

During this era, solar observations were often interpreted in terms of hypothetical properties of the subsurface field. The recurrence patterns of the Sun’s mean line-of-sight field and of the interplanetary field were supposed to originate in rigidly rotating primordial fields below the surface (Svalgaard and Wilcox, 1975). The quasi-rigid rotations of photospheric fields were thought to indicate rotational properties of the subsurface layers in which they were rooted (Stenflo, 19741977Snodgrass, 1983Jump To The Next Citation Point). Rigid rotations of coronal holes and other coronal structures were interpreted as fundamental manifestations of rigidly rotating subsurface fields (Zirker, 1977Howard, 19781984). Solar physics had truly entered the ‘dark ages’ of understanding.

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