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Nov 22, 2013 – “The influence of initial conditions in decaying MHD turbulence”


Speaker:Vassilios Dallas (Ecole Normale Superieure, Paris)
Date:Nov 22, 2013
Time:11:00 AM
Location:LASP Space Science Building, room N248 upstairs. Map

Seminar Abstract:

We investigate the origins of the k^{−2} spectrum in a decaying Taylor-Green (TG) magnetohydrodynamic flow with zero large scale magnetic flux. From our TG numerical simulations, we demonstrate that magnetic discontinuities in the form of strong current sheets are responsible for the −2 power law scaling of the energy spectra in this flow. Therefore, the presence of a clear k^{-2} spectrum due to strong current sheets could imply lack of universality in decaying MHD turbulence. However, an important point that has to be addressed before claiming non-universality, is the role of the TG symmetries imposed by the initial conditions and their self-preservation in time evolution of the flow. In other words, are the discontinuities formed due to the TG symmetries? Will the breaking of the symmetries lead to a different power law spectrum? Are there more general cases where the initial conditions give a −2 power law spectrum? If so, is lack of universality valid in the high Reynolds number limit? These are some of the questions I will address in this seminar.