Show simple item record

dc.contributor.authorPonty, Y.en_GB
dc.contributor.authorGilbert, Andrew D.en_GB
dc.contributor.authorSoward, Andrew M.en_GB
dc.date.accessioned2009-03-17T17:02:33Zen_GB
dc.date.accessioned2011-01-25T10:33:43Zen_GB
dc.date.accessioned2013-03-20T12:28:30Z
dc.date.issued2001en_GB
dc.description.abstractA numerical investigation is presented of kinematic dynamo action in a dynamically driven fluid flow. The model isolates basic dynamo processes relevant to field generation in the Solar tachocline. The horizontal plane layer geometry adopted is chosen as the local representation of a differentially rotating spherical fluid shell at co-latitude ϑ; the unit vectors x^, y^ and z^ point east, north and vertically upwards respectively. Relative to axes moving easterly with the local bulk motion of the fluid the rotation vector Ω lies in the (y,z)-plane inclined at an angle ϑ to the z-axis, while the base of the layer moves with constant velocity in the x-direction. An Ekman layer is formed on the lower boundary characterized by a strong localized spiralling shear flow. This basic state is destabilized by a convective instability through uniform heating at the base of the layer, or by a purely hydrodynamic instability of the Ekman layer shear flow. The onset of instability is characterized by a horizontal wave vector inclined at some angle ε to the x-axis. Such motion is two-dimensional, dependent only on two spatial coordinates together with time. It is supposed that this two-dimensionality persists into the various fully nonlinear regimes in which we study large magnetic Reynolds number kinematic dynamo action. When the Ekman layer flow is destabilized hydrodynamically, the fluid flow that results is steady in an appropriately chosen moving frame, and takes the form of a row of cat's eyes. Kinematic magnetic field growth is characterized by modes of two types. One is akin to the Ponomarenko dynamo mechanism and located close to some closed stream surface; the other appears to be associated with stagnation points and heteroclinic separatrices. When the Ekman layer flow is destabilized thermally, the well-developed convective instability far from onset is characterized by a flow that is intrinsically time-dependent in the sense that it is unsteady in any moving frame. The magnetic field is concentrated in magnetic sheets situated around the convective cells in regions where chaotic particle paths are likely to exist; evidence for fast dynamo action is obtained. The presence of the Ekman layer close to the bottom boundary breaks the up-down symmetry of the layer and localizes the magnetic field near the lower boundary.en_GB
dc.identifier.citationVol. 435, pp. 261-287en_GB
dc.identifier.doi10.1017/S0022112001003755en_GB
dc.identifier.urihttp://hdl.handle.net/10036/56018en_GB
dc.language.isoenen_GB
dc.publisherCambridge University Pressen_GB
dc.relation.urlhttp://dx.doi.org/10.1017/S0022112001003755en_GB
dc.relation.urlhttp://www.journals.cambridge.org/abstract_S0022112001003755en_GB
dc.titleKinematic dynamo action in large magnetic Reynolds number flows driven by shear and convectionen_GB
dc.typeArticleen_GB
dc.date.available2009-03-17T17:02:33Zen_GB
dc.date.available2011-01-25T10:33:43Zen_GB
dc.date.available2013-03-20T12:28:30Z
dc.identifier.issn0022-1120en_GB
dc.identifier.issn1469-7645en_GB
dc.descriptionCopyright © 2001 Cambridge University Press. Published version reproduced with the permission of the publisher.en_GB
dc.identifier.journalJournal of Fluid Mechanicsen_GB


Files in this item

This item appears in the following Collection(s)

Show simple item record