3-DIMENSIONAL VARIABLE VISCOSITY CONVECTION OF AN INFINITE PRANDTL NUMBER BOUSSINESQ FLUID IN A SPHERICAL-SHELL

Citation
Jt. Ratcliff et al., 3-DIMENSIONAL VARIABLE VISCOSITY CONVECTION OF AN INFINITE PRANDTL NUMBER BOUSSINESQ FLUID IN A SPHERICAL-SHELL, Geophysical research letters, 22(16), 1995, pp. 2227-2230
Citations number
17
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
00948276
Volume
22
Issue
16
Year of publication
1995
Pages
2227 - 2230
Database
ISI
SICI code
0094-8276(1995)22:16<2227:3VVCOA>2.0.ZU;2-5
Abstract
We investigate a three-dimensional, spherical-shell model of mantle co nvection with strongly temperature-dependent viscosity. Numerical calc ulations of convection in an infinite Prandtl number, Boussinesq fluid heated from below at a Rayleigh number of Ra = 10(5) are carried out for the isoviscous case and for a viscosity contrast across the shell of 1,000. In the isoviscous case, convection is time dependent with qu asi-cylindrical upflow plumes and sheet-like downflows. When viscosity varies strongly across the shell, convection is also time dependent, but major quasi-cylindrical downflows with spider-like extensions occu r at both poles and interconnected upflow plumes occur all around the equator. The surface expression of mantle convection in the Earth (dow nwelling sheets at trenches, upwelling plumes at hot spots, and upwell ing sheets at midocean ridges) resembles structures seen in both the i soviscous and variable viscosity models. The dominance of spherical ha rmonic degree l = 2 in the variable viscosity model agrees with the l = 2 dominance in the Earth's geoid, topography, and seismic tomography . The overall pattern of convection in the variable viscosity case is similar to the distribution of major highlands and volcanic rises on V enus.