Quantification of Mixing and Transport Associated with Midlatitude Cyclones and Convective Outflow as Seen in START-08 Aircraft Flight Data and UWNMS Simulations

The NSF/NCAR Gulfstream V, High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) aircraft sampled the upper troposphere and lower stratosphere (UTLS) over North America during April – June 2008 in the Stratosphere-Troposphere Analyses of Regional Transport (START-08) campaign. Numerical simulations with the University of Wisconsin Nonhydrostatic Modeling System (UWNMS) were carried out for various flights to investigate stratosphere – troposphere exchange (STE) and air mass pathways associated with midlatitude cyclones and convective outflow regions. Flight paths are interpolated spatiotemporally into the UWNMS, extracting simulated dynamical, thermodynamical, and idealized tracer data; these may then be compared with parallel aircraft observations.

Times and areas of interest were targeted for quantification of STE, including regions surrounding negative equivalent potential vorticity (EPV), stratospheric underfolds and overfolds (intrusions), and convective outflow. Larger-scale calculations of STE for entire cyclone and convective events were also computed. Mixing profiles of idealized tracers in the UWNMS were also compared with aircraft tracer-tracer correlations, with emphasis on regional structure-related variability in mixing strength. Trajectory data also illuminated transport pathways through the various events.