Investigations of STE and Transport Pathways near Midlatitude Cyclones using START-08 Aircraft Flight data and the UWNMS

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 Non-hydrostatic Modeling System (UWNMS) were carried out for each flight to investigate stratosphere – troposphere exchange and air mass pathways associated with midlatitude cyclones. When each 4D flight path is introduced into the UWNMS, winds, temperature, and idealized tracers in the model may be compared with aircraft winds, temperature and an array of observed trace constituents.

Particle trajectories and synoptic analysis support the conceptual model of interpreting stratospheric intrusions as being due to the “overfold” and “underfold” process. Flow structures diagnosed in the UWNMS are not consistent with the idea of a transverse circulation around a jet. The degree of inertial instability has a moderate effect in determining the magnitude of overfold and underfold structures, but the morphology of a stratospheric intrusion originates primarily from quasi-horizontal differential advection. Tracer-tracer correlation plots are examined for situations with and without inertial instability present. Of specific interest is the pattern of chemical mixing relative to the jet cores as diagnosed in the UWNMS.

Schematic diagrams of differential advection in the UTLS as a primary agent in creating tropopause folds. The effects of sloping convection (baroclinic energy conversion) on folds can be accelerated by inertial instability.