It is plausible that the hydromagnetic flow in the Earth's core which sustains the geomagnetic field is driven by small-scale buoyant blobs, with the buoyancy being of either compositional or thermal origin. The possibility and importance of the $\alpha$-effect, a mean-field induction effect by small-scale flow and field, by blob convection in the Earth's core are studied assuming that the flows driven by blobs do not interact with each other. / In a rotating hydromagnetic system such as the Earth's core, various types of flows are possible due to the effects of Coriolis, Lorentz and viscous forces. With a balance between Coriolis and Lorentz forces and with Coriolis dominant, the wake is a foreshortened Taylor column. With same force balance but with Lorentz dominant, the wake is elongated in the direction of the ambient magnetic field. It is believed that one or both of the wakes having a Lorentz-Coriolis force balance are relevant for the Earth's core. / To dominant order in the magnetic Reynolds number (assumed small), the integral of helicity and electromotive force over all space, produced by any buoyancy field which decays to zero at infinity, is zero. Analyses of distribution of leading order helicity and electromotive force are carried out in detail for a spherically symmetric blob. The electromotive force integrated over the plane perpendicular to the rotation direction is found to be parallel to the ambient magnetic field, as modeled by the $\alpha$-effect. If there are enough blobs (of order $10\sp7$), this electromotive force contributes significantly to the geodynamo. / The constraint of symmetry must be broken to have non-zero net helicity. Four symmetry breakers are considered: non-linear effect, the effect of rigid non-conducting boundary, the effect of large-scale geostrophic flow, and the effect of non-uniform ambient magnetic field. Order of magnitude of helicities are estimated and found to be either zero or very small. Some other effect is necessary to get significant non-zero helicity. / Source: Dissertation Abstracts International, Volume: 57-06, Section: B, page: 3621. / Major Professor: David E. Loper. / Thesis (Ph.D.)--The Florida State University, 1996.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77725 |
| Contributors | Shimizu, Hisayoshi., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 238 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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