1. Trends in lower stratosphere Jean-François Lamarque (NCAR and NOAA) and Susan Solomon (NOAA)

2. Observed ozone trend (SAGE) Net ozone change (%) 1979-2005 Randel and Wu, 2007

3. Motivation/Methodology Identify the separate roles of changes in chemical composition and changes in climate on lower stratospheric trends (ozone, temperature) Perform a set of 1970-2000 simulations in which various parameters (CO2,CFCs) are kept at their 1970 level

4. Model setup CAM3 with interactive (feedback with radiation) chemistry 2° (latitude)x2.5°(longitude)x26 levels (up to 40 km) NMHC chemistry + stratospheric chlorine-bromine reactions (including PSCs) from WACCM Observed SSTs and boundary conditions for CFCs, CO2, CH4 and N2O. Fixed (2000) emissions for other reactive gases and aerosols.

5. Low-top issue? 20°S-20°N average (1975-2005) vertical velocity from CAM and WACCM (km/year). 20°S-20°N trend in vertical velocity (1975- 2005) from CAM and WACCM (%/decade).

6. Tropical ozone change

9. Vertical velocity Net chemical tendency

10. Tropopause pressure trends Obs. from Seidel et al., 2008

11. Tropopause pressure NCEP trends from S. Davis (NOAA) Trend 1980-2005 Not significant

12. Change in the width of the tropics Seidel et al., 2008

13. Total ozone column

14. Conclusions Tropical lower stratosphere ozone trend due to changes in vertical velocity, not chemistry Different agents are responsible for trends in various measures of tropopause position and width of the tropics in the model