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.