SUPERSONIC TURBULENCE IN THE INTERSTELLAR-MEDIUM - STELLAR EXTINCTIONDETERMINATIONS AS PROBES OF THE STRUCTURE AND DYNAMICS OF DARK CLOUDS

Lada et al. have described a method for studying the distribution of d ust in dark clouds using infrared imaging surveys. In particular, they show that the method provides some information about the structure of the gas (dust) on scales smaller than their resolution. In the presen t work we clarify the nature of the information provided by their meth od. We show that: 1. The three-dimensional density held of the gas is well described by a lognormal distribution down to very small scales. 2. The power spectrum and the standard deviation of the three-dimensio nal density held can be constrained. 3. Such a structure of the densit y field is likely to be the effect of random supersonic motions presen t in the gas. In fact, we find a qualitative and quantitative agreemen t between the predictions based on recent numerical simulations of ran domly forced supersonic flows by Nordlund & Padoan and by Padoan, Nord lund, & Jones and the constraints given by the infrared dust extinctio n measurements.