Applied and Computational Math Seminar: Large-Scale Coherent Structure in Magnetohydrodynamic Turbulence

Speaker:John Shebalin, NASA/GMA 
Title: Large-Scale Coherent Structure in Magnetohydrodynamic Turbulence

Abstract: Many planets and stars possess magnetic fields that are mostly dipolar in nature and that are believed to arise from interior magnetohydrodynamic (MHD) processes. Our own planet Earth is a good example of this and numerical simulations of the ‘geodynamo’ have confirmed the belief that MHD processes are responsible[1]. However, fundamental questions still remain: “(i) how does the field regenerate itself? (ii) why is the external field dipole-like? (iii) why is the dipole aligned (more or less) with the rotation axis? (iv) what triggers a reversal in the dipole field?”[2]

The electrically conducting fluids that support MHD processes within planets and stars are expected to be highly turbulent. Thus, ‘the problem of the geodynamo’ overlaps ‘the problem of turbulence.’ More precisely, it is the study of MHD turbulence that may provide some answers to the questions posed above. Here, I will give a brief historical introduction and then discuss how computational and theoretical research on large-scale coherent structure in MHD turbulence may help provide answers to questions (i) and (ii) above, in particular.

[1] G.A. Glatzmaier and P.H. Roberts, “A three-dimensional self-consistent computer simulation of a geomagnetic field reversal”, Nature 377, 203-209 (1995).

[2] P.A. Davidson, Turbulence in Rotating and Electrically Conducting Fluids, (Cambridge U.P, Cambridge, UK, 2013). p. 532. 

Time: Friday, February 12, 2016, 1:30-2:30 p.m.

Place: Exploratory Hall, Room 4106