Interstellar Turbulence I: Observations and Processes

This two-part review summarizes interstellar turbulence and its implications. The first part begins with diagnostics and energy sources. Turbulence theory is considered in detail, including the basic fluid equations, solenoidal and compressible modes, global inviscid quadratic invariants, scaling arguments, energy transfer and cascade, velocity probability distributions, and turbulent pressure. Theories of magnetohydrodynamic turbulence, including collisionless MHD turbulence, are discussed, emphasizing various proposals for energy spectra. A large variety of numerical simulations of interstellar turbulence are reviewed. Models have reproduced many of the basic features of the observed scaling relations,…