Chemical Lagrangian Model of the Stratosphere (ClaMS) is used to investigate stratosphere-troposphere exchange and mixing in the vicinity of the subtropical jet. The model results are combined with LIDAR measurements of ozone and Microwave Temperature Profiler (MTP) measurements of thermal tropopause during SONEX mission to investigate the transport across the extratropical tropopause. Fine scale PV field generated using a simple advection (Reverse Domain Filling) technique are compared to the results from advection with mixing to examine the mixing time/length scale that produces a structure comparable to the observations.