Other
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmgp33a..01s&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #GP33A-01
Other
1507 Core Processes (8115), 1510 Dynamo Theories, 5734 Magnetic Fields And Magnetism, 6255 Neptune, 6293 Uranus
Scientific paper
In an effort to model the Earth's magnetic field, current numerical dynamo models have produced fields dominated by an axial dipole. In these models, the dynamo is usually generated by convection in a thick, electrically conducting fluid shell surrounding a solid conducting inner core. The Voyager II observations of Uranus and Neptune revealed that these planets have non-dipolar, non-axisymmetric magnetic fields, in sharp contrast to the axially dipolar fields of Earth, Jupiter and Saturn. Determining why Uranus and Neptune possess a different field morphology is crucial for the study of these planets' interiors, as well as for understanding the dynamo process in all planetary bodies. Uranus' and Neptune's magnetic fields are most likely generated in their ionically conducting 'ice' shells. Thermal evolution models for Uranus and Neptune (Podolak et al. 1991, Hubbard et al. 1995) suggest that interior portions of these ice shells may be compositionally stably stratified and therefore unable to convect. This suggests that Uranus and Neptune may possess a different convective region geometry from the other planets: their dynamos may be generated in a thin convecting shell surrounding a stably-stratified fluid interior. We have implemented this geometry in the Kuang and Bloxham 3-D numerical dynamo model and found the resulting magnetic fields contain significant non-dipolar, non-axisymmetric structure, similar to those of Uranus and Neptune. Here we examine the dynamical processes causing this field morphology in our numerical models. We discuss the interactions between the convectively stable and unstable shells, and between the velocity and magnetic fields. We also examine the partitioning of energy into the various components of the field (axi- and nonaxisymmetric, toroidal and poloidal) and compare these characteristics to numerical dynamo models operating in thin shells surrounding solid inner cores.
Bloxham Jeremy
Stanley Sabine
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