Introduction

The turbulence in Galactic molecular clouds has a rather different character from the other forms of interstellar turbulence discussed at this meeting. Strong molecular cooling brings the ambient temperatures to the range T = 10 – 30 K, which renders turbulence with velocities of a few km s−1 not just nonlinear, but hypersonic. Most observational evidence on magnetic field strengths suggest that Alfvén speeds are of same order than the turbulent speeds or a few times larger, and in any case unlikely to be smaller than the sound speed. Thus, the turbulence in molecular clouds is highly compressible, and strongly magnetic. In addition, although high-latitude unbound molecular clouds exist, most of the molecular material in the Galaxy resides in much more massive, self-gravitating, giant molecular clouds and cloud complexes (GMCs).