Several transport scenarios have been advanced in the literature to account for the exchange of tracers between the extratropics and tropics in the lower stratosphere. Each scenario involves a slow, net upward transport at low latitudes and varying degrees of mixing at middle latitudes plus detrainment across a subtropical region of enhanced tracer gradients. In situ observations for differentiating among these scenarios are generally lacking above about 21 km altitude. Existing satellite data sets can provide useful information throughout the lower stratosphere. In particular, we have looked for such exchange by examining time series of the daily zonal variance of the Nimbus 7 limb infrared monitor of the stratosphere distributions of nitric acid vapor (HNO3) mixing ratio. This species is characterized by strong subtropical meridional gradients between about 10 and 100 hPa, which develop in response to extratropical wave activity and any associated mixing processes. The subtropical variance is a measure of that activity, its region of maximum values moving equatorward during late autumn and then relaxing and retreating in late spring. At and below the 45-hPa level there is not a clear maximum of variance at a given latitude, perhaps a result of the secondary circulation that was present during the 1978/1979 winter in response to the easterly phase of the quasi-biennial oscillation cycle. At the 30-hPa and 50-hPa levels, while we find occasions in winter when tongues of subtropical air were transported to higher latitudes, we find no clear evidence for a large-scale transport of extratropical air to lower latitudes through a subtropical region of enhanced gradients. ¿ American Geophysical Union 1996