Turbulent cooling flows in molecular clouds

We propose that inward, subsonic flows arise from the local dissipation of turbulent motions in molecular clouds. Such "turbulent cooling flows" may a ccount for recent observations of spatially extended inward motions toward dense cores. These pressure-driven flows may arise from various types of tu rbulence and dissipation mechanisms. For the example of MHD waves and turbu lence damped by ion-neutral friction, sustained cooling flow requires that the outer gas be sufficiently turbulent, that the inner gas have marginal f ield-neutral coupling, and that this coupling decrease sufficiently rapidly with increasing density. These conditions are most likely met at the trans ition between outer regions ionized primarily by UV photons and inner regio ns ionized primarily by cosmic rays. If so, turbulent cooling flows can hel p form dense cores, with speeds faster than expected for ambipolar diffusio n. Such motions could reduce the time needed for dense core formation and c ould precede and enhance the motions of star-forming gravitational infall.