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, 1977
). He deduced that the effective diffusion rate was only 
and that it was
accompanied by a poleward meridional flow 
. 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 
), 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, 1979; Labonte and Howard, 1982), inferences based on flux evolution continued to accumulate
(Howard, 1979; Howard and Labonte, 1981; Topka et al., 1982), 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, 1974, 1977; Snodgrass, 1983). Rigid
rotations of coronal holes and other coronal structures were interpreted as fundamental manifestations of
rigidly rotating subsurface fields (Zirker, 1977; Howard, 1978, 1984). Solar physics had truly entered the
‘dark ages’ of understanding.
