Turbulent flow-driven molecular cloud formation: A solution to the post-T tauri problem?

We suggest that molecular clouds can be formed on short timescales by compr essions from large scale streams in the interstellar medium (ISM). In parti cular, we argue that in the Taurus-Auriga complex, with filaments of 10-20 x 2-5 pc, most have been formed by H I flows in less than or similar to 3 M yr, explaining the absence of post-T Tauri stars in the region with ages gr eater than or similar to 3 Myr. Observations in the 21 cm line of the H I " halos" around the Taurus molecular gas show many features (broad asymmetric profiles, velocity shifts of H I relative to (CO)-C-12) predicted by our M HD numerical simulations, in which large-scale H I streams collide to produ ce dense filamentary structures. This rapid evolution is possible because t he H I hows producing and disrupting the cloud have much higher velocities (5-10 km s(-1)) than are present in the molecular gas resulting from the co lliding flows. The simulations suggest that such flows can occur from the g lobal ISM turbulence without requiring a single triggering event such as a supernova explosion.