CONTOUR ADVECTION WITH SURGERY - A TECHNIQUE FOR INVESTIGATING FINESCALE STRUCTURE IN TRACER TRANSPORT

We present a trajectory technique, contour advection with surgery (CAS ), for tracing the evolution of material contours in a specified (incl uding observed) evolving flow. CAS uses the algorithms developed by Dr itschel for contour dynamics/surgery to trace the evolution of specifi ed contours. The contours are represented by a series of particles, wh ich are advected by a specified, gridded, wind distribution. The resol ution of the contours is preserved by continually adjusting the number of particles, and finescale features are produced that are not presen t in the input data (and cannot easily be generated using standard tra jectory techniques). The reliability, and dependence on the spatial an d temporal resolution cf the wind field, of the CAS procedure is exami ned by comparisons with high-resolution numerical data (from contour d ynamics calculations and from a general circulation model), and with r outine stratospheric analyses. These comparisons show that the large-s cale motions dominate the deformation field and that CAS can accuratel y reproduce small scales from low-resolution wind fields. The CAS tech nique therefore enables examination of atmospheric tracer transport at previously unattainable resolution.