We compute 3D models of supersonic, sub-Alfvénic, and super-Alfvénic decaying turbulence, with an isothermal equation of state appropriate for star-forming interstellar clouds of molecular gas. We find that in 3D the kinetic energy decays as $t^{-\eta }$, with $0.85<\mathrm{}\eta <1.2\mathrm{}$. In 1D magnetized turbulence actually decays faster than unmagnetized turbulence. We compared different algorithms, and performed resolution studies reaching ${256}^3$ zones or ${70}^3$ particles. External driving must produce the observed long lifetimes and supersonic motions in molecular clouds, as undriven turbulence decays too fast.

• Received 1 December 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.2754