Modeling of the Middle and Upper Atmosphere

1. Modeling of the Middle and Upper Atmosphere M. A. GiorgettaE. Manzini1, M. Charron2, H. Schmidt Current affiliations:1Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy 2 McGill University, Montreal, Canada

2. Outline • Introduction • Methodology and tools • Selected work:- Chemistry climate interaction, 1960 vs. 2000- Quasi-biennial oscillation- Thermospheric temperature dependence on CO2 profile • Conclusions • Outlook

3. Intro: Why Modeling the Middle and Upper Atmosphere (MUA) • MPI-Met objectiveunderstand phenomena, driving processes, variability and trends in the Earth system • MUA as a part of the Earth system • ozone hole • volcanic effects – Pinatubo • sensitivity to changes in composition: CO2, CH4, org. Cl“Miner’s canary bird” • solar cycle vs. CO2 • long term memory for dynamics and composition • feedback to the troposphere – seasonal predictability

4. Intro: MUA topics at MPI • Phenomena: • polar vortex in both hemispheres • equatorial oscillations: QBO, SAO • ozone hole, age of air, atmospheric tape recorder • coupling of atmospheric layers: troposphere - thermosphere • Driving processes: • wave mean-flow interaction, planetary waves, gravity waves • radiation (Voigt line, non-LTE, SR-B/C, EUV), molecular diffusion • photochemistry • interaction of dynamics, chemistry and radiation • Variability/trends/climate change: • intraseasonal to interannual variability in circulation and composition • changing greenhouse gases, volcanic forcing, solar cycle

5. Methodology and tools • Use state-of-the-art models based on a tropospheric GCM, compared with observations • Model development • Tools: • MAECHAM4/5 resolves the atmosphere up to 0.01 hPa • MAECHAM4/CHEM coupled chemistry-climate model for stratospheric ozone chemistryCo-op with MPI for Chemistry in Mainz (B. Steil et al., 2002) • HAMMONIA: MAECHAM5 extended to appr. 250 km coupled with comprehensive chemistry of MOZART3 CTM

6. Selected work • Dynamical chemical radiative coupling in the northern hemisphere stratosphere in the 1960s and in 2000 (Manzini et al., 2002) MAECHAM4/CHEM • Simulating the QBO and the time averaged effect of the QBO on the tropical upwelling (Giorgetta et al., 2002)MAECHAM5 • Simulating the general circulation from the surface to the lower thermosphere, sensitivity to assumed CO2 profilesHAMMONIA • Posters

7. Dynamical chemical radiative coupling in the NH stratosphere in the 1960s and in 2000 • Globally the stratosphere is cooling in the last decades. The Northern polar latitudes show the most pronounced changes in the last decade [Ramaswamy et al., 2001] • Are ozone depletion and the increase in greenhouse gases perturbing the atmosphere enough to influence the North Pole temperature variations of the 1990s with respect to the 1960s? • MAECHAM4/CHEM time slice experiments • 1990: comparison with HALOE/UARS (Steil et al., 2002) • 1960: pre ozone hole conditions • 2000: increased CO2, CH4, N2O, total org. Cl • GISS Hadley SST: average annual cycle of each period

8. Observed North Pole Temperature at 30 hPa in March(Labitzke, FU-Berlin)

9. Significant cooling in March/April in lower stratosphere only 1960 2000 Radiative temperature 5K lower in 2000 compared to 1960

10. Cooling of the stratosphere in March/April results from chemical radiative interaction

11. Simulating the QBO and the time averaged effect of the QBO on the tropical upwelling • The Quasi-Biennial Oscillation dominates the interannual variability in the equatorial stratosphere and has effects on circulation and composition in higher latitudes. • How does the QBO interfere with other modes of variability?Does the QBO feed back to the troposphere? Is the QBO stable? • Theory: Wave mean-flow interaction, eastward and westward vertically propagating waves excited in the troposphere • Wave spectrum: Kelvin, Rossby-gravity, inertia gravity, gravity waves • GCM: Excitation of resolved waves by parameterized deep convection,parameterization of the gravity wave propagation and dissipation

12. Simulation of the QBO in ECHAM5 • Equatorial Zonal Wind (m/ s): • Observations: QBO at Singapore (courtesy of B. Naujokat) • Simulation of the QBO with the middle atmosphere model at L90 vertical resolution. • Middle atmosphere model at standard L39 vertical resolution: • SAO too strong and deep • No QBO, easterlies

13. Simulated QBO is driven by resolved and parameterized wave mean-flow interaction. ›1000 km Kelvin waves,Rossby gravity waves,inertia gravity waves 100km gravity waves

14. Time average effect of the QBO on tropical upwelling as seen in the climatological Atmospheric Tape Recorder for water vapor Propagation of equatorial moisture anomalies from 90 hPa to 10 hPa lasts approximately 17 months (Mote et al., 1996). ATR with QBO: t = 18 mo ATR without QBO: t = 12 mo

15. Simulating the general circulation from the surface to the lower thermosphere, sensitivity to assumed CO2 profiles • How do solar variations affect circulation and composition across the atmospheric layers, from the thermosphere to the surface? • HAMMONIA: 67 model levels from the surface to ~250 km • Dynamics and physics based on the MAECHAM5-GCM extensions to account for upper atmosphere processes: • molecular diffusion and viscosity • solar heating (Schumann-Runge B&C and EUV to 5 nm) • non-LTE radiative cooling • ion drag • Chemistry of the MOZART-3 CTM (48 constituents, 152 gas phase reactions), currently run in a “CTM mode”

16. Zonal Mean Temperature [K] for January HAMMONIA 5-year mean MSIS climatology

17. Zonal Mean Zonal Wind [m/s] for January HAMMONIA 5-year mean MSIS climatology

18. Sensitivity to the prescribed CO2 profiles • „standard profile“ - climatology collected by Fomichev (1998) • CRISTA 1 + 2 profiles collected during the CRISTA missions onboard of the Space Shuttle in Nov 1994 and Aug 1997 (Kaufmann et al., 2002) • Standard profile differs strongest between 70 and 120 km • Large cooling difference between 100 and 120 km

19. CRISTA - “standard” difference in zonal mean temperature [K] for January

20. Summary 1998-2002 • Middle and polar latitude circulation in the middle atmosphere in MAECHAM4: • Wave mean-flow interaction and wave wave interaction of planetary waves and gravity waves explain observed polar vortex variability • Simulation of the QBO in ECHAM5: • QBO results from a broad spectrum of waves, planetary to gravity waves • Critical: variability of precipitation from deep convection • Net effect on the tropical upwelling in the middle atmosphere • Multi-year experiments with the interactive chemistry-climate model MAECHAM4/CHEM: • Large variability of the northern hemisphere stratospheric circulation easily masks perturbations due to changes in atmospheric composition. • Dynamical negative feedback from the mesosphere must be considered.

21. Outlook • HAMMONIA will allow to study the intraseasonal to interannual variability of the dynamics and atmospheric composition from surface to ca. 250 km • Investigation of solar cycle effects across the atmospheric layers from the thermosphere to the surface • Understand temperature trends in the mesosphere and lower thermosphere • Interannual to interdecadal variability of the middle atmosphere in a changing climate • QBO feedback to the troposphere