1. Interannual variations in global OH radicals over the period 1987-2005 in GEOS-Chem, and preliminary comparisons to other models I. Bey 1, S. Koumoutsaris 1, S. Generoso 1, J. Drevet 1, A. Fiore 2, T. van Noije 3, S. Rast 4, M. Schultz 5, and S. Szopa 6 Contact: isabelle.bey@epfl.ch, http://lmca.epfl.ch 1 EPFL, 2 GFDL, 3 KNMI, 4 MPI-Met, 5 FZ Jüelich, 6 IPSL Paris

2. GEOS-Chem simulation set up GEOS-Chem 3D Chemical-Transport Model Version 7.02.04 – Meteorological fields from NASA GMAO GEOS-4 – 4°x5°, 30 levels (from surface to 0.01 hPa) – 24 tracers for tropospheric O 3 -NOx-HC chemistry Interannual variation of input parameters – Biomass burning emissions IAV prescribed using TOMS AI (1987-07/1996) [Duncan et al., 2003] and AATSR (08/1996-12/2005) [Generoso et al., 2003] – Anthropogenic emissions Fossil fuel emissions based on climatological inventories scaled using CO 2 trends (-> 1998) and change in aircraft emissions (+3%/yr with a base year in 1992) – Methane concentrations Prescribed using CH 4 CMDL data (latitudinal bands) up to 2004 – Total O 3 column Prescribed TOMS satellite data up to 2002 (Nimbus 7, Meteor 3, Eptoms and climatology when data are missing, e.g. 1995)

3. CO anomalies (ppb) Barrow, Alaska 71°N - 20m Mauna Loa, Hawaii 19°N - 3397m Niwot Ridge, Colorado 40°N - 3475m Alert, Canada 82°N - 210m Mace Head, Ireland 53°N - 25mTutor Hill, Bermuda 32°N - 30m 1987199019952000200519871990199520002005 Observations — monthly mean 12-month running mean Model — monthly mean 12-month running mean

4. Mauna Loa, Pacific 19°N - 3397m Mace Head, Ireland 53°N - 15m O 3 anomalies (ppb) Observations — monthly mean 12-month running mean Model — monthly mean 12-month running mean Stratospheric contribution 12-month running mean Jungfraujoch, Switzerland 46°N - 3578m See also Ordóñez et al., GRL, 2007: Changes in trop O 3 driven by changes in O 3 in the lowermost stratosphere (due to changes in dynamics)

5. Interannual variability in global mean OH in GEOS-Chem OH global air mass weighted mean (1e5 molec. cm -3 ) Annual anomalies (1e4 molec. cm -3 ) => Implications for CH 4 trends

6. Extra tropics NHTropics NHTropics SHExtra tropics SH Column (surface- 250 hPa) Surface- 750 hPa 750- 500 hPa 500- 250 hPa Interannual variability in OH in different regions (1e4 molec. cm -3 )

7. Parameters contributing to OH interannual variability standard – simulation with fixed anthropogenic emissions standard – simulation with fixed meteorology (1988 recycled) standard – simulation with fixed lightning emissions standard – simulation with fixed TOMS column standard – simulation with fixed methane concentrations standard – simulation with fixed biomass burning emissions OH (1e5 molec cm -3 ) OH (1e5 molec cm -3 )

8. Interannual variability in J(O 1 D) Standard simulation Simulation with a fixed total ozone column J(O 1 D) (s -1 )

9. Interannual variability in global P(OH)= J(O 1 D) × k H2O [H 2 O]/ k X [X](s -1 ) Standard simulation Simulation with a fixed total ozone column J(O 1 D) × k H2O [H 2 O]/ k X [X] (s -1 )

10. Interannual variability in water vapour Q (g kg -1 ) Trenberth et al., Trends and variability in column-integrated atmospheric water vapor, Climate Dynamics, 2005: “Precipitable water variability for 1988–2001 is dominated by the evolution of ENSO and especially the structures that occurred during and following the 1997–98 El Niño event. … but … Users of these data (ECMWF ERA-40, NCEP, etc.) should take great care in accepting results as real. ”

11. Available observations during the reanalysis SSM/I dataTOVS data Total precipitable water and surface winds No data before 1987 Temperature, moisture, … TOVS (HIRS, MSU, SSU) to ATOVS (HIRS-2, AMSU) in 1998 Courtesy: Steven Pawlson => Impact of the various observations used in the re- analysis on the water vapor variability & trends?

12. Variability in OH in GEOS-Chem compared to other models GEOS-Chem (GEOS-4, CTM) TM4 (CTM, ECMWF, RETRO emissions, T. van Noije) MOZECH (GCM, ECMWF, RETRO emissions, S. Rast & M. Schultz) LMDzINCA (GCM, ECMWF, RETRO em., S. Szopa & D. Hauglustaine) OH anomaly (1e4 molec cm -3 )

13. Variability in OH in GEOS-Chem compared other models (no change in anthropogenic emissions) GEOS-Chem (GEOS-4) MOZART-2 (CTM, NCEP, A. Fiore) OH anomaly 1e4 molec cm -3 )

14. Variability in water vapor in GEOS-Chem & other models GEOS-Chem (CTM, GEOS-4) MOZECH (GCM, ECMWF) TM4 (CTM, ECMWF) LMDzINCA (GCM, ECMWF) Q (kg kg -1 )

15. Conclusions GEOS-Chem has some success in reproducing the CO anomalies over the 1987-2005 period. GEOS-Chem has some success in reproducing the O 3 anomalies over the 1987-2005 period, but not in regions influenced by a too large interannual variability in stratospheric-tropospheric exchange. Global air mass weighted mean OH shows some rather large interannual variability (with implications for the methane and CO variability and trends). Interannual variability in global air mass weighted mean OH are mainly driven by changes in NO x emissions (anthropogenic and lightning) and changes in water vapor. Different models indicate very different OH interannual variability over the period 1987-2000. This is probably associated to the simulated changes in water vapor and in lightning emissions. => An issue to be further investigated.