A periodic dynamo sustains a magnetic field by fluid flow that repeats periodically either in space or time. Consider spatially periodic dynamos first. Their flows are best described in terms of a lattice. A simple, two‐dimensional flow that repeats in both y and z coordinates in shown on the left in Figure D32. The flow consists of rolls confined to rectangular cells. The roll structure by itself does not generate a magnetic field (Busse, 1973); dynamo action does result, however, with the addition of a shear flow in the x‐direction. This flow was investigated by G.O. Roberts in his PhD thesis of 1969, with supervisor H.K. Moffatt. He showed that most periodic flows are capable of generating magnetic fields. This came at a time when very few examples of homogeneous dynamo action was known, and was an important step forward toward our present view that almost any sufficiently complicated and vigorous flow will generate magnetic fields. Of more lasting consequence, probably, was the...
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Gubbins, D. (2007). Dynamos, Periodic. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_83
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