A Scaling of Velocity and Magnetic field in Decaying Turbulence in Expanding/Collapsing Media

  • Park, Jun-Seong (Department of Astronomy and Space Science, Chungnam National University) ;
  • Ryu, Dong-Su (Department of Astronomy and Space Science, Chungnam National University) ;
  • Cho, Jung-Yeon (Department of Astronomy and Space Science, Chungnam National University)
  • Published : 2011.10.05

Abstract

We investigate decaying magnetohydrodynamic (MHD) turbulence by including the effects of expansion and collapse of the background medium. The problem has two time scales, the eddy turn-over time($t_{eddy}$) and the expansion/collapse time scale(${\tau}_H$). The turbulence is expected to behave differently in two regimes of $t_{eddy}$ < ${\tau}_H$ and $t_{eddy}$ > ${\tau}_H$. For instance, for $t_{eddy}$ < ${\tau}_H$, the turbulence would decay more or less as in a static medium. On the other hand, for $t_{eddy}$ > ${\tau}_H$, the effects of expansion and collapse would be dominant. We examine the properties of turbulence in the regimes of $t_{eddy}$ < ${\tau}_H$ and $t_{eddy}$ > ${\tau}_H$. Based on it, we derive a scaling for the time evolution of flow velocity and magnetic field.

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