List of Footnotes

1 Alternatively, the magnetic flux transport equation may be obtained through spatially averaging the radial component of the induction equation (see DeVore et al., 1984Jump To The Next Citation Point and McCloughan and Durrant, 2002Jump To The Next Citation Point).
2 The evolution of the axisymmetric (longitude-averaged) Br is independent of the differential rotation, as may be seen by averaging Equation (2View Equation) in longitude (Leighton, 1964Jump To The Next Citation Point).
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4 Originally, it was more common to match the line-of-sight magnetic field rather than the radial component, since this was thought to better utilise the observations (Altschuler and Newkirk Jr, 1969). But following Wang and Sheeley Jr (1992) matching the radial component is now considered more appropriate, because the photospheric magnetic field appears to be approximately radial.
5 Durrant (1989) suggested instead to minimise the horizontal field on r = Rss in a least-squares sense.
6 The expression for B quoted by Zhao et al. (2000Jump To The Next Citation Point) contains a typographical error (in their Equation 2), as does that by Ruan et al. (2008Jump To The Next Citation Point) (in their Equation 8).