Observations of trace constituents obtained from the Upper Atmosphere Research Satellite in late winter 1991/92 reveal a zone of quasi-horizontal stirring in the tropical stratosphere above 10 mb, equatorward of the subtropical jet. This mixing region was separated from the midlatitude surf zone by a strong gradient of potential vorticity and tracer along the jet axis. The jet and accompanying gradients are climatological features. Mixing equatorward of the jet evidently depends on the phase of the quasi-biennial oscillation. ¿ American Geophysical Union 1996