Lamination and polar vortex development in fall from ATMOS long‐lived trace gases observed during November 1994

Long‐lived trace‐gas profiles observed by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument around the developing polar vortex (the “protovortex”) during early November 1994 show distinctive inversions (laminae). High‐resolution profiles calculated using a reverse trajectory (RT) model reproduce the majority of these laminae, demonstrating that most of these features arise from advection by the large‐scale winds. The relationship between CH 4 and N 2 O sampled in filaments of low‐latitude air changes from the canonical midlatitude correlation to one typical of tropical air, confirming the identification of tropical laminae. N 2 O/CH 4 correlations for laminae in vortex filaments indicate that enough confined descent and mixing has already occurred in the middle and upper stratosphere by early November to alter the tracer relationship in the protovortex from that in midlatitudes. Distributions of laminae in ATMOS observations agree with regions of greater or less filamentation seen in high‐resolution RT maps. There is a deep minimum in laminae occurrence between 30° and 90°E at all levels, extending to about 150°E above ∼35 km. Maxima in lamination in the lower stratosphere near 90°–150°E and 210°–270°E are associated with the main regions where tropical air is drawn up around the developing vortex. Continuous filamentation associated with the developing vortex and anticyclone in early November 1994 shows that transport and mixing processes previously reported during winter are already important during fall.