Long-term free decay of MHD turbulence

Institute of Continuous Media Mechanics - Korolyov str. 1, Perm, 614013, Russia

^a rodion.stepanov@gmail.com

Received: 31 August 2010
Accepted: 20 October 2010

Abstract

The free decay of MHD turbulence at large Reynolds numbers is studied numerically using a shell model. We study the statistical properties based on a representative sample of realisations (128 realisations for each type of initial conditions) over a period of 10⁵ large-scale turnover times. The performed simulations show that the free-decaying nonhelical MHD turbulence can demonstrate two different scenarios of evolution in spite of similar initial conditions. Within the first scenario, the cross-helicity accumulation is so fast that the energy cascade vanishes before significant magnetic energy dissipates. Then the system approaches the state of maximal cross-helicity. Within the second scenario, the cascade process continues to remain active until time 10⁴ in units of large-scale turnover time. Then the magnetic field becomes vastly helical due to magnetic helicity conservation. Thus the magnetic energy does not dissipate with kinetic energy.