HR: 0800h
AN: T51A-0435 INVITED     [Abstracts]
TI: Controls on Plume Spacing and Plume Population in 3-D High Rayleigh Number Thermal Convection
AU: * Zhong, S
EM: szhong@anquetil.colorado.edu
AF: University of Colorado, Dept. of Physics, University of Colorado, Boulder, CO 80309 United States
AB: Dynamics of mantle plumes are important for understanding intra-plate volcanism and heat transfer in the mantle. Using 3D numerical models and scaling analyses, we investigated the controls of convective vigor or Ra on the dynamics of thermal plumes in isoviscous and basal heating thermal convection. We examined Ra-dependence of plume population, plume spacing, plume vertical velocity, and plume radius. We found that plume population does not increase with Ra monotonically. At relatively small Ra ($<$10$^{6}$), plume population is insensitive to Ra. For 3x10$^{6}$$<$Ra$<$3x10$^{7}$, plume population scales as Ra$^{0.31}$ and plume spacing $\sim$ Ra$^{-0.16}$ $\sim$ $\delta$$^{1/2}$, where $\delta$ is the thermal boundary layer thickness. However, for larger Ra ($\sim$ 10$^{8}$) plume population and plume spacing become insensitive to Ra again. This indicates that the box depth poses a limit on plume spacing and plume population. We demonstrated from both scaling analyses and numerical experiments that the scaling exponents for plume population, n, heat flux, $\beta$, and average velocity on the bottom boundary, v, satisfy n = 4$\beta$ - 2v. Our scaling analyses also suggest that vertical velocity in upwelling plumes V$_{up}$ $\sim$ Ra$^{2(1-n+\beta/2)/3}$ and that plume radius R$_{up}$ $\sim$ Ra$^{2(\beta-1-n/2)/3}$, differing from the scalings for the bottom boundary velocity and boundary layer thickness.
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting