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Simulation of the mesospheric ozone response to natural and anthropogenic climate variability H. Schmidt and G. P. Brasseur Max Planck Institute for Meteorology, Hamburg, Germany two simulations of 20 years each with permanent solar Introduction minimum and solar maximum conditions, respectively, based on solar spectra from Lean et al. (1997) were The newly developed Hamburg Model of the Neutral performed. Additionally a 10-year run with doubled CO2 and Ionized Atmosphere (HAMMONIA) is a general mixing ratio (720 ppm) is compared to the solar minimum circulation and chemistry model covering the atmospheric experiment. altitude range from the Earth's surface up to about 250 km. It is designed to study interactions between chemistry, Results dynamics and radiation in the whole atmosphere but in particular the mesosphere, lower thermosphere (MLT) Due to the space limitations we concentrate here only region, and the coupling between the atmospheric spheres. on zonal mean results above the stratopause for some This paper concentrates on the response of trace gases selected parameters and the month of January. For solar (in particular ozone) in the MLT region to natural and maximum conditions the ozone pattern seems to be anthropogenic climate variability. Results of different amplified with respect to solar minimum. The mixing ratio simulations with HAMMONIA for low and high solar increases for the secondary (in the mesopause region) and activity on the one hand and for present day and doubled the tertiary (winter high latitudes between 0.1 and 0.01 CO2 concentration on the other hand are presented. Similar hPa) maxima, and decreases for the minimum below the studies were until now performed only with 2D models (e.g. mesopause (Figs. 1 a and c). The doubling of CO2 leads to Khosravi et al., 2002) or with 3D GCMs that use an increase of ozone almost everywhere (Fig. 1e) which is prescribed chemical fields for the computation of radiative very likely a consequence of reaction rates changing due to heating (e.g. Akmaev and Fomichev, 1998). the temperature decrease (Fig. 1f). The small areas of Studying the response of the MLT region to different ozone decrease at polar latitudes are due to changes in types of forcing is interesting with respect to at least two dynamics. The total solar heating (direct + chemical issues of the current climate change discussion: 1) Recently heating, not shown) increases for solar maximum by about there have been numerous and sometimes contradictory 0.5 to 3 K/day around the mesopause. At this height region reports on observed temperature trends in this altitude the increase is more due to the change in chemical heating region (for a review see Beig et al., 2003) which still wait than a direct radiative effect. For CO2 doubling, heating for a concise explanation. Some people also argue that rate changes are less significant. Concerning temperature, MLT trends might serve as an early indicator for climate maximum solar irradiance leads to an increase in the change (Thomas, 1996). 2) It is still unclear how strongly mesopause region by about 2 to 7 K (Fig. 1d). This value and through which mechanisms solar variability influences agrees quite well with some numbers listed by Beig et al. the Earth’s atmosphere. For the numerical simulation of (2003) for different analyses of observational data. CO 2 these phenomena it should be helpful to include the doubling would lead to a simulated temperature decrease atmospheric altitude range upward of, say, 50 km where the everywhere above the tropopause with smallest values in part of the solar spectrum is absorbed that shows the largest the mesopause region. Please note, that all results are variability. presented with pressure as the vertical reference system. Using height coordinates would lead to significantly different results in particular for the comparison of the Model description and setup of numerical “360 ppm” and “720 ppm” CO2 simulations. This is due to experiments the shrinking of the atmosphere for doubled CO2 and the HAMMONIA combines the 3D dynamics and physics strong vertical gradients in e.g. ozone and temperature. from the ECHAM5 (Roeckner et al., 2003) and MAECHAM4 (Manzini et al., 1979) models with the MOZART3 chemistry scheme (an offspring of the Acknowledgments The authors would like to thank M. Charron (now at Meteorological Service of Canada), E. Manzini MOZART2 scheme, Horowitz et al., 2003, that should be (now at INGV, Bologna, Italy), M. Giorgetta (MPI, Hamburg), T. valid for a very large altitude range) and some extensions Diehl (now at NASA, MD, USA), V. Fomichev (York University, to account for important processes in the upper atmosphere. Toronto, Canada), D. Kinnison, S. Walters, D. Marsh, and R. These new parameterizations include the treatment of Garcia (all NCAR, Boulder, USA) who contributed to the model development. J. Lean (Naval Res. Lab., Washington, USA) is molecular diffusion and heat conduction, chemical heating, acknowledged for providing the solar irradiance data. The work the ion drag (Hong and Lindzen, 1976), solar heating was funded by the German ministry for education and science shortward of 250 nm (from Richards et al., 1994, for the (BMBF). Computations were performed at the (German climate EUV, 5-105 nm, and from the MOZART 3 computing center (DKRZ). photo-dissociation rate computation for 120 to 250 nm), and non-LTE effects in infrared cooling (Fomichev et al., References 1998). Akmaev, R. A. and V. I. Fomichev, Cooling of the mesosphere In order to study the effect of the 11-year solar cycle, and lower thermosphere due to doubling of CO2. Ann. Geophysicae, 16, 1501-1512, 1998. in solar mid- and near-ultraviolet radiation (200-400nm), J. Beig, G. et al., Review of mesospheric temperature trends, Geophys. Res., 102, 29939-29956, 1997. Reviews of Geophysics, doi:10.1029/2002RG000121, 2003. Manzini, E., N. A. McFarlane, and C. McLandress, Impact of the Fomichev, V. I., J. P. Blanchet, and D. S. Turner, Matrix Doppler spread parameterization on the simulation of the parameterization of the 15 mum CO2 band cooling in the middle atmosphere circulation using the MA/ECHAM4 middle and upper atmosphere for variable CO2 concentration, general circulation model, J. Geophys. Res., 102, J. Geophys. Res., 103, 11505-11528, 1998. 25751-25762, 1997. Hong, S. S., and R. S. Lindzen, Solar semidiurnal tide in the Richards, P. G., J. A. Fennelly, and D. G. Torr, A solar EUV flux thermosphere, J. Atm. Sc., 33, 135-153, 1976. model for aeronomic calculations, J. Geophys Res., 99, Horowitz, L. W., et al., A global simulation of tropospheric ozone 8981-8992, 1994. and related tracers: Description and evaluation of MOZART, Roeckner, E. et al., The atmospheric general circulation model version 2, J. Geophys Res , doi:10.1029/2002JD002853, 2003. ECHAM 5. PART I: Model description, Rep. 349, MPI for Khosravi, R., G. Brasseur, A. Smith, D. Rusch, S. Walters, S. Meteorology, Hamburg, Germany, 2003. Chabrillat, and G. Kockarts, Response of the mesosphere to Thomas, G. E., Is the polar mesosphere the miner’s canary of human-induced perturbations and solar variability calculated global change?, Adv. Space Res., 18, 149, 1996. by a 2-D model, J. Geophys. Res., doi:10.1029/2001JD001235, 2002. Lean, J. L., G. J. Rottmann, H. L. Kyle, T. N. Woods, J. R. Hickey, and L. C. Puga, Detection and parameterization of variations a b ) ) c d ) ) e f ) Figure 1. Ozone mixing ratio (a) and temperature (b, K) for the reference simulations (“solar minimum” , 360 ppm CO2). c) and d) show differences “solar maximum” – “solar minimum”, e) and f) show differences “720 ppm CO2” – “360 ppm CO2”. c), e): ozone (%). d), f): temperature (K). Statistical confidence levels of 90% and 99% are indicated by light and dark gray shading, respectively. All figures show zonal mean values for January as simulated by HAMMONIA.
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