The poleward transport of tropical air in the lower stratosphere during the winter period of the second Airborne Arctic Stratospheric Expedition (December 1991--March 1992) is examined using contour advection calculations. These calculations show that filaments of tropical air extend into mid-latitudes, and are wrapped around the equatorward edge of the polar jet. Simultaneously filaments are drawn from the polar vortex and are intermingled with the filaments of tropical air. The tropical filaments are consistent with measurements of chemical tracers taken aboard the ER-2 and DC-8 aircraft which show localized regions, in mid-latitudes, of air with the characteristics of tropical air. ¿ American Geophysical Union 1994