New Diagnostics of MHD Turbulence in the Multiphase Interstellar Medium

Our current view of the interstellar medium (ISM) is as a multiphase environment where turbulence affects many key processes. These include star formation, cosmic ray acceleration, and the evolution of structure in the diffuse ISM. It is therefore essential to study and quantify interstellar turbulence using the strengths of numerical simulations in concert with observational studies.  In this talk, I shall discuss progress in the development of new techniques for comparing observational data with numerical MHD simulations in the molecular medium, in neutral gas as traced by HI, and warm ionized gas as traced by synchrotron polarization. I will show how a confluence of simulations and novel multiwavelength measurements have taught us that: 1) The ISM in our Galaxy and nearby galaxies is supersonic in both the diffuse and molecular media, 2) Turbulence is primarily driven at scales larger than 100 parsecs, and 3) the magnetic field is a critical regulator of star formation. I will demonstrate how these measurements open up new avenues for studying star formation, cosmic ray acceleration and the formation of molecules in the ISM.