Bipolar outflows contain sources of strong shear and turbulence:
bows, jets
and disk winds. The dissipation and decay of turbulence are themes
extensively discussed in fluid and physics journals. However, in molecular
outflows, the turbulence is supersonic and super-Alfvénic. Here we
discuss the recent 3D numerical simulations of Mac Low, Klessen, Burkert &
Smith (1997, Bull. Amer. Astron. Soc., in press)
of supersonic,
super-Alfvénic, isothermal turbulence using the well-tested
magnetohydrodynamic (MHD) code ZEUS-3D. We use resolutions as high as
2563
zones for both MHD and HD, allowing us to clearly
separate dissipation scales from turbulent scales. We find the
surprisingly
general result that the
kinetic energy of turbulence decays as t-s, with the decay
power-law s in the range 0.87 < s < 1.2 for all of the regimes
studied,
aside from the extreme subsonic approach to laminar
flow. We here review the decay concepts and discuss the ability of
turbulence
to support molecular clouds. Such a fast
decay rate, however, even in the presence of magnetic fields, rules out
models
of molecular clouds that do not include some form of energy input
driving the observed turbulence, whether it be galactic shear, blast
waves and ionization from massive stars, or jets from low-mass stars.