SUBTROPICAL STRATOSPHERIC MIXING LINKED TO DISTURBANCES IN THE POLAR VORTICES

RANDEL et al.1 have observed tongues of stratospheric air stretching f rom the tropics into middle latitudes, and conclude that such events m ay be responsible for transporting significant amounts of stratospheri c air across the tropical-mid-latitude barrier2. Here I examine the mo vements of air parcels during these events using high-resolution conto ur-trajectory calculations. My calculations suggest that the tongues o f tropical air are associated with disturbances of the stratospheric p olar vortices. The edge of the disturbed polar vortex reaches low lati tudes, and draws a long tongue of tropical air around the vortex into middle latitudes. This process occurs in the winter of both hemisphere s, although the edge of the larger Antarctic polar vortex reaches fart her toward the Equator, and draws up material from lower latitudes, th an its Arctic counterpart.