The project will investigate the dynamical mechanisms producing interannual changes in stratospheric circulation and ozone, which also influence the seasonal climate of the troposphere, notably in winter. Variations in stratospheric polar vortex have been shown linked to seasonal anomalies in tropospheric zonal-mean zonal winds and circulation patterns (e.g., North Atlantic Oscillation/ Arctic Oscillation), which profoundly impact the European and North American climate and weather. Ozone variations in the lower stratosphere are also strongly linked with dynamics: The ozone distribution in the high latitudes is determined by the Brewer-Dobson overturning circulation, and radiative heating from ozone absorption in the ultraviolet and thermal bands, in turn, influences the temperature and thermal wind distribution. Drs. Salby and Callaghan will conduct a dynamically oriented analysis of interannual variability to ascertain the sensitivity of the stratosphere circulation to tropospheric forcing (upward fluxes of planetary wave activity) and stratospheric dynamical structure (Quasi-biennial oscillation phase). The PIs will use a 3D primitive equation model in isentropic coordinates for the analysis. The project will advance understanding of the forcing of circulation and constituent variability in the stratosphere, which will lead to improved modeling of troposphere-stratosphere interactions and variability on the seasonal-to-interannual time scales. This research should also significantly contribute in understanding the causes of observed ozone depletion in the northern hemisphere.