Separation of time-scales in drift-diffusion equations on R2

Abstract We deal with the problem of separation of time-scales and filamentation in a linear drift-diffusion problem posed on the whole space R 2 . The passive scalar considered is stirred by an incompressible flow with radial symmetry. We identify a time-scale, much faster than the diffusive one, at which mixing happens along the streamlines, as a result of the interaction between transport and diffusion. This effect is also known as enhanced dissipation. The proofs are based on an adaptation of a hypocoercivity scheme and yield a linear semigroup estimate in a suitable weighted L 2 -based space.