Wednesday 05 Feb 2014: Fluctuation dynamo amplified by shear bursts in convectively driven magnetohydrodynamic turbulence
Dr Jane Pratt - University of Exeter
Physics, 4th floor 14:00-15:00
Intermittent large-scale high-shear flows are found to occur frequently and spontaneously in direct numerical simulations of statistically stationary turbulent 3D Boussinesq magnetohydrodynamic (MHD) convection. The energetic steady state of the system is sustained by convective driving of the velocity field and small-scale dynamo action. The intermittent emergence of flow structures with strong velocity and magnetic shearing generates magnetic energy at an elevated rate over time scales longer than the characteristic time of the large-scale convective motion. The resilience of magnetic energy amplification suggests that these intermittent shear bursts are a significant driver of dynamo action in turbulent magnetoconvection. Pseudo-spectral simulations solve the Boussinesq approximation to the MHD convection equations for a geometric cube of plasma with an imposed mean temperature gradient. Boundary conditions are periodic and disallow vertical streamers. Lagrangian multi-particle statistics, calculated by tracking fluid particles, are used to examine the large-scale structures that form during shear bursts, and result in local regions of anomalous dispersion.