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Turbulence is ubiquitous in the interstellar medium (ISM) of the Milky Wayand other spiral galaxies. The energy source for this turbulence has been muchdebated with many possible origins proposed. The universality of turbulence,its reported large-scale driving, and that it occurs also in starless molecularclouds, challenges models invoking any stellar source. A more general processis needed to explain the observations. In this work we study the role ofgalactic spiral arms. This is accomplished by means of three-dimensionalhydrodynamical simulations which follow the dynamical evolution of interstellardiffuse clouds (100cm-3) interacting with the gravitational potential field ofthe spiral pattern. We find that the tidal effects of the arm's potential onthe cloud result in internal vorticity, fragmentation and hydrodynamicalinstabilities. The triggered turbulence result in large-scale driving, on sizesof the ISM inhomogeneities, i.e. as large as 100pc, and efficiencies inconverting potential energy into turbulence in the range 10 to 25 percent perarm crossing. This efficiency is much higher than those found in previousmodels. The statistics of the turbulence in our simulations are strikinglysimilar to the observed power spectrum and Larson scaling relations ofmolecular clouds and the general ISM. The dependency found from differentmodels indicate that the ISM turbulence is mainly related to local spiral armproperties, such as its mass density and width. This correlation seems inagreement with recent high angular resolution observations of spiral galaxies,e.g. M51 and M33.

The onset of large scale turbulence in the interstellar medium of spiral galaxies