  We investigate numerically the combined effects of supersonic turbulence,
strong magnetic fields and ambipolar diffusion on cloud evolution leading to
star formation. We find that, in clouds that are initially magnetically
subcritical, supersonic turbulence can speed up star formation, through
enhanced ambipolar diffusion in shocks. The speedup overcomes a major objection
to the standard scenario of low-mass star formation involving ambipolar
diffusion, since the diffusion time scale at the average density of a molecular
cloud is typically longer than the cloud life time. At the same time, the
strong magnetic field can prevent the large-scale supersonic turbulence from
converting most of the cloud mass into stars in one (short) turbulence crossing
time, and thus alleviate the high efficiency problem associated with the
turbulence-controlled picture for low-mass star formation. We propose that
relatively rapid but inefficient star formation results from supersonic
collisions of somewhat subcritical gas in strongly magnetized, turbulent
clouds. The salient features of this shock-accelerated, ambipolar
diffusion-regulated scenario are demonstrated with numerical experiments.
