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Fluid motions can be separated into two kinds of modes: compressible and vortical (or solenoidal). In the interstellar medium, nearly all work has concentrated on ``clouds'' as the entities associated with the compressible modes, but there have been nearly no studies of the predicted vortical component of the velocity field. As pointed out by Fleck and others, vorticity will be generated by the baroclinic term behind curved or corrugated shocks, or behind plane shocks encountering an inhomogeneous ambient medium. Although viscosity will work to dissipate this vorticity, the compression of the gas behind radiative shocks will amplify it. We give an estimate of the vorticity generated by these mechanisms, integrated over the shock-producing events in galaxies, and discuss its implications.
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