Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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Excursions into reversalsStefani, F.; Gerbeth, G.; Günther, U.; Xu, M.;
Despite the recent success of fully coupled three-dimensional numerical models of the geodynamo, the very nature of field reversals is still a matter of controversy. A mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha serves us as a sort of minimum dynamo model that exhibits a number of typical reversal features. These include the asymmetry of reversals, the correlation between field strength and interval length, the existence of an inhibition time, and the bimodal field distribution. We identify the existence of a branch point of the spectrum of the non-selfadjoint dynamo operator as the essential ingredient for reversals to happen (Phys. Rev. Lett. 94 (2005), 184506). We present some evidences for a self-tuning mechanism of highly supercritical dynamos that tend to saturate into a reversal-prone state by driving the branch point and its nearby local maximum of the growth rate towards the zero line (Earth Planet. Sci. Lett. 143 (2006), 828-840). The high supercriticality can also explain the typical time-scales of asymmetric reversals (arxiv.org/physics/0601011), without taking resort to a turbulent resistivity. The role of the inner core to increase the ratio of excursions to reversals is discussed in the framework of resonant appearance of branch points in dependence on the wavelength of the dynamo source (arxiv.org/math-ph/0602013).
10th Symposium of SEDI, 09.-14.07.2006, Prague, Czech Republic