Studies of stratospheric tropical-midlatitude transport using UARS data

The mean meridional (Brewer-Dobson) circulation generalizes stratospheric transport as upwelling motions in the tropics, movement to higher latitudes and descent over the polar regions. Recently more attention has been given to meridional transport that couples the tropical and midlatitude regions on shorter timescales and just above the tropopause. In this study we analyze data from the Upper Atmosphere Research Satellite (UARS) to diagnose the temporal and spatial behavior of transport from midlatitudes into the tropics. We will present frequency distributions of species, such as nitric acid, that indicate entrainment of midlatitude air into the tropical region and global maps showing geographic locations of these features. Based on these analyses, which are limited by the length of the UARS data record, we will discuss possible mechanisms for this transport phenomenon.