The poleward transport of tropical air in the lower stratosphere durin
g the winter period of the second Airborne Arctic Stratospheric Expedi
tion (December 1991 - March 1992) is examined using contour advection
calculations. These calculations show that filaments of tropical air e
xtend into mid-latitudes, and are wrapped around the equatorward edge
of the polar jet. Simultaneously filaments are drawn from the polar vo
rtex and are intermingled with the filaments of tropical air. The trop
ical filaments are consistent with measurements of chemical tracers ta
ken aboard the ER-2 and DC-8 aircraft which show localized regions, in
mid-latitudes, of air with the characteristics of tropical air.