^{1}Department of Mathematics, Colorado State University, Fort Collins, CO 805231874, USA ^{2}Department of Atmospheric Science, Colorado State University, Fort Collins, CO 805231371, USA ^{3}Department of Meteorology, Naval Postgraduate School, Monterey, CA 939435114, USA Abstract. This paper studies Lagrangian mixing in a twodimensional barotropic model for hurricanelike vortices. Since such flows show high shearing in the radial direction, particle separation across shearlines is diagnosed through a Lagrangian field, referred to as Rfield, that measures trajectory separation orthogonal to the Lagrangian velocity. The shearlines are identified with the levelcontours of another Lagrangian field, referred to as Sfield, that measures the average shearstrength along a trajectory. Other fields used for model diagnostics are the Lagrangian field of finitetime Lyapunov exponents (FTLEfield), the Eulerian Qfield, and the angular velocity field. Because of the high shearing, the FTLEfield is not a suitable indicator for advective mixing, and in particular does not exhibit ridges marking the location of finitetime stable and unstable manifolds. The FTLEfield is similar in structure to the radial derivative of the angular velocity. In contrast, persisting ridges and valleys can be clearly recognized in the Rfield, and their propagation speed indicates that transport across shearlines is caused by Rossby waves. A radial mixing rate derived from the Rfield gives a timedependent measure of flux across the shearlines. On the other hand, a measured mixing rate across the shearlines, which counts trajectory crossings, confirms the results from the Rfield mixing rate, and shows high mixing in the eyewall region after the formation of a polygonal eyewall, which continues until the vortex breaks down. The location of the Rfield ridges elucidates the role of radial mixing for the interaction and breakdown of the mesovortices shown by the model. Citation: Rutherford, B., Dangelmayr, G., Persing, J., Schubert, W. H., and Montgomery, M. T.: Advective mixing in a nondivergent barotropic hurricane model, Atmos. Chem. Phys., 10, 475497, doi:10.5194/acp104752010, 2010. 
