SUBTROPICAL STRATOSPHERIC MIXING LINKED TO DISTURBANCES IN THE POLAR VORTICES

RANDEL et al.1 have observed tongues of stratospheric air stretching from the tropics into middle latitudes, and conclude that such events may be responsible for transporting significant amounts of stratospheric air across the tropical-mid-latitude barrier2. Here I examine the movements of air parcels during these events using high-resolution contour-trajectory calculations. My calculations suggest that the tongues of tropical air are associated with disturbances of the stratospheric polar vortices. The edge of the disturbed polar vortex reaches low latitudes, and draws a long tongue of tropical air around the vortex into middle latitudes. This process occurs in the winter of both hemispheres, although the edge of the larger Antarctic polar vortex reaches farther toward the Equator, and draws up material from lower latitudes, than its Arctic counterpart.