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2009 .

(10 publications)

N. Huneeus, O. Boucher, and F. Chevallier. Simplified aerosol modeling for variational data assimilation. Geoscientific Model Development, 2:213-229, November 2009. [ bib | ADS link ]

We have developed a simplified aerosol model together with its tangent linear and adjoint versions for the ultimate aim of optimizing global aerosol and aerosol precursor emission using variational data assimilation. The model was derived from the general circulation model LMDz; it groups together the 24 aerosol species simulated in LMDz into 4 species, namely gaseous precursors, fine mode aerosols, coarse mode desert dust and coarse mode sea salt. The emissions have been kept as in the original model. Modifications, however, were introduced in the computation of aerosol optical depth and in the processes of sedimentation, dry and wet deposition and sulphur chemistry to ensure consistency with the new set of species and their composition. <BR /><BR /> The simplified model successfully manages to reproduce the main features of the aerosol distribution in LMDz. The largest differences in aerosol load are observed for fine mode aerosols and gaseous precursors. Differences between the original and simplified models are mainly associated to the new deposition and sedimentation velocities consistent with the definition of species in the simplified model and the simplification of the sulphur chemistry. Furthermore, simulated aerosol optical depth remains within the variability of monthly AERONET observations for all aerosol types and all sites throughout most of the year. Largest differences are observed over sites with strong desert dust influence. In terms of the daily aerosol variability, the model is less able to reproduce the observed variability from the AERONET data with larger discrepancies in stations affected by industrial aerosols. The simplified model however, closely follows the daily simulation from LMDz. <BR /><BR /> Sensitivity analyses with the tangent linear version show that the simplified sulphur chemistry is the dominant process responsible for the strong non-linearity of the model.

D. Koch, M. Schulz, S. Kinne, C. McNaughton, J. R. Spackman, Y. Balkanski, S. Bauer, T. Berntsen, T. C. Bond, O. Boucher, M. Chin, A. Clarke, N. de Luca, F. Dentener, T. Diehl, O. Dubovik, R. Easter, D. W. Fahey, J. Feichter, D. Fillmore, S. Freitag, S. Ghan, P. Ginoux, S. Gong, L. Horowitz, T. Iversen, A. Kirkevåg, Z. Klimont, Y. Kondo, M. Krol, X. Liu, R. Miller, V. Montanaro, N. Moteki, G. Myhre, J. E. Penner, J. Perlwitz, G. Pitari, S. Reddy, L. Sahu, H. Sakamoto, G. Schuster, J. P. Schwarz, Ø. Seland, P. Stier, N. Takegawa, T. Takemura, C. Textor, J. A. van Aardenne, and Y. Zhao. Evaluation of black carbon estimations in global aerosol models. Atmospheric Chemistry & Physics, 9:9001-9026, November 2009. [ bib | ADS link ]

We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) retrievals from AERONET and Ozone Monitoring Instrument (OMI) and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.7 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50N, the average model is a factor of 8 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC ratio is 0.4 and models underestimate the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

J. Quaas, Y. Ming, S. Menon, T. Takemura, M. Wang, J. E. Penner, A. Gettelman, U. Lohmann, N. Bellouin, O. Boucher, A. M. Sayer, G. E. Thomas, A. McComiskey, G. Feingold, C. Hoose, J. E. Kristjánsson, X. Liu, Y. Balkanski, L. J. Donner, P. A. Ginoux, P. Stier, B. Grandey, J. Feichter, I. Sednev, S. E. Bauer, D. Koch, R. G. Grainger, A. Kirkevåg, T. Iversen, Ø. Seland, R. Easter, S. J. Ghan, P. J. Rasch, H. Morrison, J.-F. Lamarque, M. J. Iacono, S. Kinne, and M. Schulz. Aerosol indirect effects - general circulation model intercomparison and evaluation with satellite data. Atmospheric Chemistry & Physics, 9:8697-8717, November 2009. [ bib | ADS link ]

Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterises aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (τa) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at least over the ocean. The relationship between τa and liquid water path is simulated much too strongly by the models. This suggests that the implementation of the second aerosol indirect effect mainly in terms of an autoconversion parameterisation has to be revisited in the GCMs. A positive relationship between total cloud fraction (fcld) and τa as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong fclda relationship, our results indicate that none can be identified as a unique explanation. Relationships similar to the ones found in satellite data between τa and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR-τa relationship show a strong positive correlation between τa and fcld. The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of τa, and parameterisation assumptions such as a lower bound on Nd. Nevertheless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred from the combination of these predictors for the modelled forcings with the satellite-derived statistical relationships yields a global annual mean value of -1.50.5 Wm-2. In an alternative approach, the radiative flux perturbation due to anthropogenic aerosols can be broken down into a component over the cloud-free portion of the globe (approximately the aerosol direct effect) and a component over the cloudy portion of the globe (approximately the aerosol indirect effect). An estimate obtained by scaling these simulated clear- and cloudy-sky forcings with estimates of anthropogenic τa and satellite-retrieved Nda regression slopes, respectively, yields a global, annual-mean aerosol direct effect estimate of -0.40.2 Wm-2 and a cloudy-sky (aerosol indirect effect) estimate of -0.70.5 Wm-2, with a total estimate of -1.20.4 Wm-2.

O. Boucher, P. Friedlingstein, B. Collins, and K. P. Shine. The indirect global warming potential and global temperature change potential due to methane oxidation. Environmental Research Letters, 4(4):044007, October 2009. [ bib | DOI | ADS link ]

Methane is the second most important anthropogenic greenhouse gas in the atmosphere next to carbon dioxide. Its global warming potential (GWP) for a time horizon of 100 years is 25, which makes it an attractive target for climate mitigation policies. Although the methane GWP traditionally includes the methane indirect effects on the concentrations of ozone and stratospheric water vapour, it does not take into account the production of carbon dioxide from methane oxidation. We argue here that this CO2-induced effect should be included for fossil sources of methane, which results in slightly larger GWP values for all time horizons. If the global temperature change potential is used as an alternative climate metric, then the impact of the CO2-induced effect is proportionally much larger. We also discuss what the correction term should be for methane from anthropogenic biogenic sources.

X. Jin, T. Wu, L. Li, and C. Shi. Cloudiness characteristics over Southeast Asia from satellite FY-2C and their comparison to three other cloud data sets. Journal of Geophysical Research (Atmospheres), 114:17207, September 2009. [ bib | DOI | ADS link ]

Fengyun-2C (FY-2C), launched in October 2004, is the first operational geostationary meteorological satellite in China. It can provide 1-h interval cloudiness products with a spatial resolution of 0.04deg latitude × 0.04deg longitude. The main characteristics of the regional-scale clouds from a 2-year FY-2C data set (from July 2005 to June 2007) are presented, including the spatial distribution and the annual and diurnal cycles of cloudiness. The reliability of FY-2C cloud products over Southeast Asia is investigated through comparisons to cloud cover from the International Satellite Cloud Climatology Project, the Moderate Resolution Imaging Spectroradiometer on board Terra and Aqua satellites, and conventional ground observations. It is shown that the FY-2C cloud mask performs consistently with other cloud mask products over Southeast Asia. In the boreal winter, the whole domain is dry with little cloudiness. More extensive cloudiness can be observed over the Sichuan Basin, in the East China Sea and the South China Sea, along the northwestern border of China, and around the ITCZ in the Southern Hemisphere. In the boreal summer, the summer monsoon is the dominant system for the studied domain, which is generally humid with extensive cloudiness, corresponding to zones of strong convective activities. Results also reveal considerable discrepancies among different cloud products over extended areas of north China and Mongolia. The Sichuan Basin is another region of large discrepancies among the four cloud products. Diurnal cycles of FY-2C cloudiness for the four seasons of a year are analyzed. The diurnal range of cloudiness is generally larger over land than over ocean. Remarkable diurnal variation is found over the Tibetan Plateau, the northern part of the Indian Peninsula, and central Asia where there is generally less precipitation. The peaks of diurnal cycle of cloudiness appear around local noon over the subtropical land, in the morning over the Indian Peninsula, and in the afternoon near the equator.

Z. Ke, P. Zhang, W. Dong, and L. Li. A New Way to Improve Seasonal Prediction by Diagnosing and Correcting the Intermodel Systematic Errors. Monthly Weather Review, 137:1898-1907, June 2009. [ bib | DOI | ADS link ]

A. Lenton, F. Codron, L. Bopp, N. Metzl, P. Cadule, A. Tagliabue, and J. Le Sommer. Stratospheric ozone depletion reduces ocean carbon uptake and enhances ocean acidification. Geophysical Research Letters, 36:12606, June 2009. [ bib | DOI | ADS link ]

Observational and atmospheric inversion studies find that the strength of the Southern Ocean carbon dioxide (CO2) sink is not increasing, despite rising atmospheric CO2. However, this is yet to be captured by contemporary coupled-climate-carbon-models used to predict future climate. We show that by accounting for stratospheric ozone depletion in a coupled-climate-carbon-model, the ventilation of carbon rich deep water is enhanced through stronger winds, increasing surface water CO2 at a rate in good agreement with observed trends. We find that Southern Ocean uptake is reduced by 2.47 PgC (1987-2004) and is consistent with atmospheric inversion studies. The enhanced ventilation also accelerates ocean acidification, despite lesser Southern Ocean CO2 uptake. Our results link two important anthropogenic changes: stratospheric ozone depletion and greenhouse gas increases; and suggest that studies of future climate that neglect stratospheric ozone depletion likely overestimate regional and global oceanic CO2 uptake and underestimate the impact of ocean acidification.

X. C. Wang, X. H. Li, J. Li, Z. X. Li, and W. X. Li. Nature of mantle lithological heterogenity and its role in generation of ca. 825Ma komatiitic basalts, South China. Geochimica et Cosmochimica Acta Supplement, 73:1414, June 2009. [ bib | ADS link ]

G. Gastineau, L. Li, and H. Le Treut. The Hadley and Walker Circulation Changes in Global Warming Conditions Described by Idealized Atmospheric Simulations. Journal of Climate, 22:3993, 2009. [ bib | DOI | ADS link ]

A. Plana-Fattori, G. Brogniez, P. Chervet, M. Haeffelin, O. Lado-Bordowsky, Y. Morille, F. Parol, J. Pelon, A. Roblin, G. Sèze, and C. Stubenrauch. Comparison of High-Cloud Characteristics as Estimated by Selected Spaceborne Observations and Ground-Based Lidar Datasets. Journal of Applied Meteorology and Climatology, 48:1142, 2009. [ bib | DOI | ADS link ]

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