Abstract
This paper reviews our attempts to understand the transport of magnetic flux on the Sun from the Babcock and Leighton models to the recent revisions that are being used to simulate the field over many sunspot cycles. In these models, the flux originates in sunspot groups and spreads outward on the surface via supergranular diffusion; the expanding patterns become sheared by differential rotation, and the remnants are carried poleward by meridional flow. The net result of all of the flux eruptions during a sunspot cycle is to replace the initial polar fields with new fields of opposite polarity. A central issue in this process is the role of meridional flow, whose relatively low speed is near the limit of detection with Doppler techniques. A compelling feature of Leighton’s original model was that it reversed the polar fields without the need for meridional flow. Now, we think that meridional flow is central to the reversal and to the dynamo itself.
Highlights
This paper reviews our attempts to understand the transport of magnetic flux on the Sun from the Babcock and Leighton models to the recent revisions that are being used to simulate the field over many sunspot cycles
My introduction to the random walk of magnetic flux on the Sun began on the morning of September 16, 1963 when the phone rang in the 60-foot tower telescope at Mount Wilson
We realized that the doublet source list and flux-transport code could be used to study a variety of solar magnetic field problems, and we successively considered the decay of the mean field (Sheeley Jr and DeVore, 1986a), the origin of the 28 – 29 day recurrent patterns (Sheeley Jr and DeVore, 1986b), the total flux on the Sun (Sheeley Jr et al, 1986), and the Sun’s polar magnetic fields (DeVore and Sheeley Jr, 1987)
Summary
My introduction to the random walk of magnetic flux on the Sun began on the morning of September 16, 1963 when the phone rang in the 60-foot tower telescope at Mount Wilson. Leighton used idealized ring doublets to represent the longitudinally averaged contribution of sunspot groups, and prepared the punched cards that enabled him to compute the axisymmetric field of the Sun from an equatorial migration of such sources He acknowledged that I had been working on other topics, but said that measurements to test this new flux-transport hypothesis would make a good thesis project. The first numerical simulation of the observed large-scale field was performed by Schatten et al (1972), who combined sources from Mount Wilson Observatory magnetograms with transport by Newton and Nunn (1951) differential rotation and supergranular diffusion at an unspecified rate (presumably in Leighton’s (1964) range of 770 – 1540 km s–1) Their simulations exhibited a quasi-rigid rotation poleward of the sunspot belts. Fifteen years elapsed before we realized that the quasi-rigid rotation was caused by the poleward component of flux transport, diffusion plus meridional flow (Sheeley Jr et al, 1987)
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