C. Prigent, N. Rochetin, F. Aires, E. Defer, J.-Y. Grandpeix, C. Jimenez, and F. Papa. Impact of the inundation occurrence on the deep convection at continental scale from satellite observations and modeling experiments. Journal of Geophysical Research (Atmospheres), 116:D24118, December 2011. [ bib | DOI | ADS link ]
This study is an attempt to evidence the impact of the inundation occurrence on the deep convection at continental scale. Three sources of satellite observations are carefully analyzed over the tropics for 3 years: A multisatellite wetland extent and dynamics data set, a deep convective activity index derived from passive microwave satellite measurements at 85 GHz, and precipitation estimates. Although many other effects contribute to the variability in the convection (e.g., large-scale circulation and weather regimes), careful examination of the seasonal and diurnal variations of the satellite-derived information makes it possible to observe two distinct regimes. The first regime corresponds to regions where the inundation is not generated by local precipitation. There it is shown that stronger convection happens during the minimum of the inundation, with a marked diurnal cycle of the deep convective activity. Simulations with a single-column model are in good agreement with these satellite observations. First, calculations show that during the season of minimum inundation, hydrometeors are present higher in altitude, increasing the likelihood of larger ice quantities aloft. Second, the diurnal cycle of the convective activity related to the presence of large ice quantities has a larger amplitude. The second regime corresponds to regions where the inundation is directly generated by local precipitation. There our observational analysis could not isolate any effect of the inundation on the convection.
N. Kurita, D. Noone, C. Risi, G. A. Schmidt, H. Yamada, and K. Yoneyama. Intraseasonal isotopic variation associated with the Madden-Julian Oscillation. Journal of Geophysical Research (Atmospheres), 116:D24101, December 2011. [ bib | DOI | ADS link ]
The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in the tropical atmosphere. This study examines the evolution of the hydrologic regime from before the onset of the MJO (pre-onset period) to the MJO onset period, using deuterated water vapor (HDO) measurements from the Tropospheric Emission Spectrometer (TES) and from ground-based stations. Ground-based observations reveal a clear transition between high HDO/H2O isotope ratios during the pre-onset period to a period of repeated abrupt decreases in the HDO/H2O isotope ratio associated with intense convection. Each observed minimum in the HDO/H2O ratio corresponded to a maximum in stratiform rainfall fraction, which was derived independently from radar precipitation coverage area. The ground-based observations are consistent with the satellite observations of the HDO/H2O ratio. In order to attribute the mechanisms that bring about the isotopic changes within the MJO convection, an isotope-enabled general circulation model (GCM) constrained by observed meteorological fields was used to simulate this MJO period. The GCM reproduced many of the observed isotopic features that accompanied the onset of an MJO. After the development of deep convection, large-scale stratiform cloud cover appears, and isotope ratios respond, as a consequence of diffusive exchange between stratiform raindrops and the surrounding vapor. In this diffusive exchange process, heavy isotopes tend to become enriched in precipitation and depleted in the surrounding vapor, and thus successive stratiform rainfall results in decreasing isotope values in the middle and lower troposphere. On the basis of these characteristics, isotope tracers can be used to partition stratiform and convective rainfall from observed isotope data and to validate the simulated proportions of convective/stratiform rainfall.
M. Kulmala, A. Asmi, H. K. Lappalainen, U. Baltensperger, J.-L. Brenguier, M. C. Facchini, H.-C. Hansson, Ø. Hov, C. D. O'Dowd, U. Pöschl, A. Wiedensohler, R. Boers, O. Boucher, G. de Leeuw, H. A. C. Denier van der Gon, J. Feichter, R. Krejci, P. Laj, H. Lihavainen, U. Lohmann, G. McFiggans, T. Mentel, C. Pilinis, I. Riipinen, M. Schulz, A. Stohl, E. Swietlicki, E. Vignati, C. Alves, M. Amann, M. Ammann, S. Arabas, P. Artaxo, H. Baars, D. C. S. Beddows, R. Bergström, J. P. Beukes, M. Bilde, J. F. Burkhart, F. Canonaco, S. L. Clegg, H. Coe, S. Crumeyrolle, B. D'Anna, S. Decesari, S. Gilardoni, M. Fischer, A. M. Fjaeraa, C. Fountoukis, C. George, L. Gomes, P. Halloran, T. Hamburger, R. M. Harrison, H. Herrmann, T. Hoffmann, C. Hoose, M. Hu, A. Hyvärinen, U. Hõrrak, Y. Iinuma, T. Iversen, M. Josipovic, M. Kanakidou, A. Kiendler-Scharr, A. Kirkevåg, G. Kiss, Z. Klimont, P. Kolmonen, M. Komppula, J.-E. Kristjánsson, L. Laakso, A. Laaksonen, L. Labonnote, V. A. Lanz, K. E. J. Lehtinen, L. V. Rizzo, R. Makkonen, H. E. Manninen, G. McMeeking, J. Merikanto, A. Minikin, S. Mirme, W. T. Morgan, E. Nemitz, D. O'Donnell, T. S. Panwar, H. Pawlowska, A. Petzold, J. J. Pienaar, C. Pio, C. Plass-Duelmer, A. S. H. Prévôt, S. Pryor, C. L. Reddington, G. Roberts, D. Rosenfeld, J. Schwarz, Ø. Seland, K. Sellegri, X. J. Shen, M. Shiraiwa, H. Siebert, B. Sierau, D. Simpson, J. Y. Sun, D. Topping, P. Tunved, P. Vaattovaara, V. Vakkari, J. P. Veefkind, A. Visschedijk, H. Vuollekoski, R. Vuolo, B. Wehner, J. Wildt, S. Woodward, D. R. Worsnop, G.-J. van Zadelhoff, A. A. Zardini, K. Zhang, P. G. van Zyl, V.-M. Kerminen, K. S. Carslaw, and S. N. Pandis. General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) - integrating aerosol research from nano to global scales. Atmospheric Chemistry & Physics, 11:13061-13143, December 2011. [ bib | DOI | ADS link ]
In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.
J.-B. Madeleine, F. Forget, E. Millour, L. Montabone, and M. J. Wolff. Revisiting the radiative impact of dust on Mars using the LMD Global Climate Model. Journal of Geophysical Research (Planets), 116:E11010, November 2011. [ bib | DOI | ADS link ]
Airborne dust is the main driver of Martian atmospheric temperature, and accurately accounting for its radiative effect in Global Climate Models (GCMs) is essential. This requires the modeling of the dust distribution and radiative properties, and when trying to simulate the true climate variability, the use of the observed dust column opacity to guide the model. A recurrent problem has been the inability of Mars GCMs to predict realistic temperatures while using both the observed dust radiative properties and column opacity. One would have to drive the model with a tuned opacity to reach an agreement with the observations, thereby losing its self-consistency. In this paper, we show that using the most recently derived dust radiative properties in the LMD (Laboratoire de Météorologie Dynamique) GCM solves this problem, which was mainly due to the underestimation of the dust single scattering albedo in the solar domain. However, an overall warm temperature bias remains above the 1 hPa pressure level. We therefore refine the model by implementing a semi-interactive dust transport scheme which is coupled to the radiative transfer calculations. This scheme allows a better representation of the dust layer depth in the model and thereby removes the remaining warm bias. The LMD/GCM is now able to predict accurate temperatures without any tuning of the dust opacity used to guide the model. Remaining discrepancies are discussed, and seem to be primarily due to the neglect of the radiative effect of water-ice clouds, and secondarily to persisting uncertainties in the dust spatial distribution.
V. Guemas and F. Codron. Differing Impacts of Resolution Changes in Latitude and Longitude on the Midlatitudes in the LMDZ Atmospheric GCM. Journal of Climate, 24:5831-5849, November 2011. [ bib | DOI | ADS link ]
L. Kerber, J. W. Head, J.-B. Madeleine, F. Forget, and L. Wilson. The dispersal of pyroclasts from Apollinaris Patera, Mars: Implications for the origin of the Medusae Fossae Formation. Icarus, 216:212-220, November 2011. [ bib | DOI | ADS link ]
The Medusae Fossae Formation (MFF) has long been thought to be of Amazonian age, but recent studies propose that a significant part of its emplacement occurred in the Hesperian and that many of the Amazonian ages represent modification (erosional and redepositional) ages. On the basis of the new formational age, we assess the hypothesis that explosive eruptions from Apollinaris Patera might have been the source of the Medusae Fossae Formation. In order to assess the likelihood of this hypothesis, we examine stratigraphic relationships between Apollinaris Patera and the MFF and analyze the relief of the MFF using topographic data. We predict the areal distribution of tephra erupted from Apollinaris Patera using a Mars Global Circulation Model (GCM) combined with a semi-analytical explosive eruption model for Mars, and compare this with the distribution of the MFF. We conclude that Apollinaris Patera could have been responsible for the emplacement of the Medusae Fossae Formation.
J. L. Fastook, J. W. Head, F. Forget, J.-B. Madeleine, and D. R. Marchant. Evidence for Amazonian northern mid-latitude regional glacial landsystems on Mars: Glacial flow models using GCM-driven climate results and comparisons to geological observations. Icarus, 216:23-39, November 2011. [ bib | DOI | ADS link ]
A fretted valley system on Mars located at the northern mid-latitude dichotomy boundary contains lineated valley fill (LVF) with extensive flow-like features interpreted to be glacial in origin. We have modeled this deposit using glacial flow models linked to atmospheric general circulation models (GCM) for conditions consistent with the deposition of snow and ice in amounts sufficient to explain the interpreted glaciation. In the first glacial flow model simulation, sources were modeled in the alcoves only and were found to be consistent with the alpine valley glaciation interpretation for various environments of flow in the system. These results supported the interpretation of the observed LVF deposits as resulting from initial ice accumulation in the alcoves, accompanied by debris cover that led to advancing alpine glacial landsystems to the extent observed today, with preservation of their flow texture and the underlying ice during downwasting in the waning stages of glaciation. In the second glacial flow model simulation, the regional accumulation patterns predicted by a GCM linked to simulation of a glacial period were used. This glacial flow model simulation produced a much wider region of thick ice accumulation, and significant glaciation on the plateaus and in the regional plains surrounding the dichotomy boundary. Deglaciation produced decreasing ice thicknesses, with flow centered on the fretted valleys. As plateaus lost ice, scarps and cliffs of the valley and dichotomy boundary walls were exposed, providing considerable potential for the production of a rock debris cover that could preserve the underlying ice and the surface flow patterns seen today. In this model, the lineated valley fill and lobate debris aprons were the product of final retreat and downwasting of a much larger, regional glacial landsystem, rather than representing the maximum extent of an alpine valley glacial landsystem. These results favor the interpretation that periods of mid-latitude glaciation were characterized by extensive plateau and plains ice cover, rather than being restricted to alcoves and adjacent valleys, and that the observed lineated valley fill and lobate debris aprons represent debris-covered residual remnants of a once more extensive glaciation.
T. C. Johns, J.-F. Royer, I. Höschel, H. Huebener, E. Roeckner, E. Manzini, W. May, J.-L. Dufresne, O. H. Otterå, D. P. van Vuuren, D. Salas Y Melia, M. A. Giorgetta, S. Denvil, S. Yang, P. G. Fogli, J. Körper, J. F. Tjiputra, E. Stehfest, and C. D. Hewitt. Climate change under aggressive mitigation: the ENSEMBLES multi-model experiment. Climate Dynamics, 37:1975-2003, November 2011. [ bib | DOI | ADS link ]
We present results from multiple comprehensive models used to simulate an aggressive mitigation scenario based on detailed results of an Integrated Assessment Model. The experiment employs ten global climate and Earth System models (GCMs and ESMs) and pioneers elements of the long-term experimental design for the forthcoming 5th Intergovernmental Panel on Climate Change assessment. Atmospheric carbon-dioxide concentrations pathways rather than carbon emissions are specified in all models, including five ESMs that contain interactive carbon cycles. Specified forcings also include minor greenhouse gas concentration pathways, ozone concentration, aerosols (via concentrations or precursor emissions) and land use change (in five models). The new aggressive mitigation scenario (E1), constructed using an integrated assessment model (IMAGE 2.4) with reduced fossil fuel use for energy production aimed at stabilizing global warming below 2 K, is studied alongside the medium-high non-mitigation scenario SRES A1B. Resulting twenty-first century global mean warming and precipitation changes for A1B are broadly consistent with previous studies. In E1 twenty-first century global warming remains below 2 K in most models, but global mean precipitation changes are higher than in A1B up to 2065 and consistently higher per degree of warming. The spread in global temperature and precipitation responses is partly attributable to inter-model variations in aerosol loading and representations of aerosol-related radiative forcing effects. Our study illustrates that the benefits of mitigation will not be realised in temperature terms until several decades after emissions reductions begin, and may vary considerably between regions. A subset of the models containing integrated carbon cycles agree that land and ocean sinks remove roughly half of present day anthropogenic carbon emissions from the atmosphere, and that anthropogenic carbon emissions must decrease by at least 50% by 2050 relative to 1990, with further large reductions needed beyond that to achieve the E1 concentrations pathway. Negative allowable anthropogenic carbon emissions at and beyond 2100 cannot be ruled out for the E1 scenario. There is self-consistency between the multi-model ensemble of allowable anthropogenic carbon emissions and the E1 scenario emissions from IMAGE 2.4.
N. Bellouin, J. Rae, A. Jones, C. Johnson, J. Haywood, and O. Boucher. Aerosol forcing in the Climate Model Intercomparison Project (CMIP5) simulations by HadGEM2-ES and the role of ammonium nitrate. Journal of Geophysical Research (Atmospheres), 116:D20206, October 2011. [ bib | DOI | ADS link ]
The latest Hadley Centre climate model, HadGEM2-ES, includes Earth system components such as interactive chemistry and eight species of tropospheric aerosols. It has been run for the period 1860-2100 in support of the fifth phase of the Climate Model Intercomparison Project (CMIP5). Anthropogenic aerosol emissions peak between 1980 and 2020, resulting in a present-day all-sky top of the atmosphere aerosol forcing of -1.6 and -1.4 W m-2 with and without ammonium nitrate aerosols, respectively, for the sum of direct and first indirect aerosol forcings. Aerosol forcing becomes significantly weaker in the 21st century, being weaker than -0.5 W m-2 in 2100 without nitrate. However, nitrate aerosols become the dominant species in Europe and Asia and decelerate the decrease in global mean aerosol forcing. Considering nitrate aerosols makes aerosol radiative forcing 2-4 times stronger by 2100 depending on the representative concentration pathway, although this impact is lessened when changes in the oxidation properties of the atmosphere are accounted for. Anthropogenic aerosol residence times increase in the future in spite of increased precipitation, as cloud cover and aerosol-cloud interactions decrease in tropical and midlatitude regions. Deposition of fossil fuel black carbon onto snow and ice surfaces peaks during the 20th century in the Arctic and Europe but keeps increasing in the Himalayas until the middle of the 21st century. Results presented here confirm the importance of aerosols in influencing the Earth's climate, albeit with a reduced impact in the future, and suggest that nitrate aerosols will partially replace sulphate aerosols to become an important anthropogenic species in the remainder of the 21st century.
J. M. Haywood, N. Bellouin, A. Jones, O. Boucher, M. Wild, and K. P. Shine. The roles of aerosol, water vapor and cloud in future global dimming/brightening. Journal of Geophysical Research (Atmospheres), 116:D20203, October 2011. [ bib | DOI | ADS link ]
Observational evidence indicates significant regional trends in solar radiation at the surface in both all-sky and cloud-free conditions. Negative trends in the downwelling solar surface irradiance (SSI) have become known as `dimming' while positive trends have become known as `brightening'. We use the Met Office Hadley Centre HadGEM2 climate model to model trends in cloud-free and total SSI from the pre-industrial to the present-day and compare these against observations. Simulations driven by CMIP5 emissions are used to model the future trends in dimming/brightening up to the year 2100. The modeled trends are reasonably consistent with observed regional trends in dimming and brightening which are due to changes in concentrations in anthropogenic aerosols and, potentially, changes in cloud cover owing to the aerosol indirect effects and/or cloud feedback mechanisms. The future dimming/brightening in cloud-free SSI is not only caused by changes in anthropogenic aerosols: aerosol impacts are overwhelmed by a large dimming caused by increases in water vapor. There is little trend in the total SSI as cloud cover decreases in the climate model used here, and compensates the effect of the change in water vapor. In terms of the surface energy balance, these trends in SSI are obviously more than compensated by the increase in the downwelling terrestrial irradiance from increased water vapor concentrations. However, the study shows that while water vapor is widely appreciated as a greenhouse gas, water vapor impacts on the atmospheric transmission of solar radiation and the future of global dimming/brightening should not be overlooked.
J. Teixeira, S. Cardoso, M. Bonazzola, J. Cole, A. Delgenio, C. Demott, C. Franklin, C. Hannay, C. Jakob, Y. Jiao, J. Karlsson, H. Kitagawa, M. Köhler, A. Kuwano-Yoshida, C. Ledrian, J. Li, A. Lock, M. J. Miller, P. Marquet, J. Martins, C. R. Mechoso, E. V. Meijgaard, I. Meinke, P. M. A. Miranda, D. Mironov, R. Neggers, H. L. Pan, D. A. Randall, P. J. Rasch, B. Rockel, W. B. Rossow, B. Ritter, A. P. Siebesma, P. M. M. Soares, F. J. Turk, P. A. Vaillancourt, A. von Engeln, and M. Zhao. Tropical and Subtropical Cloud Transitions in Weather and Climate Prediction Models: The GCSS/WGNE Pacific Cross-Section Intercomparison (GPCI). Journal of Climate, 24:5223-5256, October 2011. [ bib | DOI | ADS link ]
W. Chen, Z. Jiang, and L. Li. Probabilistic Projections of Climate Change over China under the SRES A1B Scenario Using 28 AOGCMs. Journal of Climate, 24:4741-4756, September 2011. [ bib | DOI | ADS link ]
P. Hanappe, A. Beurivé, F. Laguzet, L. Steels, N. Bellouin, O. Boucher, Y. H. Yamazaki, T. Aina, and M. Allen. FAMOUS, faster: using parallel computing techniques to accelerate the FAMOUS/HadCM3 climate model with a focus on the radiative transfer algorithm. Geoscientific Model Development, 4:835-844, September 2011. [ bib | DOI | ADS link ]
We have optimised the atmospheric radiation algorithm of the FAMOUS climate model on several hardware platforms. The optimisation involved translating the Fortran code to C and restructuring the algorithm around the computation of a single air column. Instead of the existing MPI-based domain decomposition, we used a task queue and a thread pool to schedule the computation of individual columns on the available processors. Finally, four air columns are packed together in a single data structure and computed simultaneously using Single Instruction Multiple Data operations. <BR /><BR /> The modified algorithm runs more than 50 times faster on the CELL's Synergistic Processing Element than on its main PowerPC processing element. On Intel-compatible processors, the new radiation code runs 4 times faster. On the tested graphics processor, using OpenCL, we find a speed-up of more than 2.5 times as compared to the original code on the main CPU. Because the radiation code takes more than 60 % of the total CPU time, FAMOUS executes more than twice as fast. Our version of the algorithm returns bit-wise identical results, which demonstrates the robustness of our approach. We estimate that this project required around two and a half man-years of work.
D. B. Clark, L. M. Mercado, S. Sitch, C. D. Jones, N. Gedney, M. J. Best, M. Pryor, G. G. Rooney, R. L. H. Essery, E. Blyth, O. Boucher, R. J. Harding, C. Huntingford, and P. M. Cox. The Joint UK Land Environment Simulator (JULES), model description - Part 2: Carbon fluxes and vegetation dynamics. Geoscientific Model Development, 4:701-722, September 2011. [ bib | DOI | ADS link ]
The Joint UK Land Environment Simulator (JULES) is a process-based model that simulates the fluxes of carbon, water, energy and momentum between the land surface and the atmosphere. Many studies have demonstrated the important role of the land surface in the functioning of the Earth System. Different versions of JULES have been employed to quantify the effects on the land carbon sink of climate change, increasing atmospheric carbon dioxide concentrations, changing atmospheric aerosols and tropospheric ozone, and the response of methane emissions from wetlands to climate change. <BR /><BR /> This paper describes the consolidation of these advances in the modelling of carbon fluxes and stores, in both the vegetation and soil, in version 2.2 of JULES. Features include a multi-layer canopy scheme for light interception, including a sunfleck penetration scheme, a coupled scheme of leaf photosynthesis and stomatal conductance, representation of the effects of ozone on leaf physiology, and a description of methane emissions from wetlands. JULES represents the carbon allocation, growth and population dynamics of five plant functional types. The turnover of carbon from living plant tissues is fed into a 4-pool soil carbon model. <BR /><BR /> The process-based descriptions of key ecological processes and trace gas fluxes in JULES mean that this community model is well-suited for use in carbon cycle, climate change and impacts studies, either in standalone mode or as the land component of a coupled Earth system model.
M. J. Best, M. Pryor, D. B. Clark, G. G. Rooney, R. L. H. Essery, C. B. Ménard, J. M. Edwards, M. A. Hendry, A. Porson, N. Gedney, L. M. Mercado, S. Sitch, E. Blyth, O. Boucher, P. M. Cox, C. S. B. Grimmond, and R. J. Harding. The Joint UK Land Environment Simulator (JULES), model description - Part 1: Energy and water fluxes. Geoscientific Model Development, 4:677-699, September 2011. [ bib | DOI | ADS link ]
This manuscript describes the energy and water components of a new community land surface model called the Joint UK Land Environment Simulator (JULES). This is developed from the Met Office Surface Exchange Scheme (MOSES). It can be used as a stand alone land surface model driven by observed forcing data, or coupled to an atmospheric global circulation model. The JULES model has been coupled to the Met Office Unified Model (UM) and as such provides a unique opportunity for the research community to contribute their research to improve both world-leading operational weather forecasting and climate change prediction systems. In addition JULES, and its forerunner MOSES, have been the basis for a number of very high-profile papers concerning the land-surface and climate over the last decade. JULES has a modular structure aligned to physical processes, providing the basis for a flexible modelling platform.
V. Masson-Delmotte, P. Braconnot, G. Hoffmann, J. Jouzel, M. Kageyama, A. Landais, Q. Lejeune, C. Risi, L. Sime, J. Sjolte, D. Swingedouw, and B. Vinther. Sensitivity of interglacial Greenland temperature and δ18O: ice core data, orbital and increased CO2 climate simulations. Climate of the Past, 7:1041-1059, September 2011. [ bib | DOI | ADS link ]
The sensitivity of interglacial Greenland temperature to orbital and CO2 forcing is investigated using the NorthGRIP ice core data and coupled ocean-atmosphere IPSL-CM4 model simulations. These simulations were conducted in response to different interglacial orbital configurations, and to increased CO2 concentrations. These different forcings cause very distinct simulated seasonal and latitudinal temperature and water cycle changes, limiting the analogies between the last interglacial and future climate. However, the IPSL-CM4 model shows similar magnitudes of Arctic summer warming and climate feedbacks in response to 2 × CO2 and orbital forcing of the last interglacial period (126 000 years ago). <BR /><BR /> The IPSL-CM4 model produces a remarkably linear relationship between TOA incoming summer solar radiation and simulated changes in summer and annual mean central Greenland temperature. This contrasts with the stable isotope record from the Greenland ice cores, showing a multi-millennial lagged response to summer insolation. During the early part of interglacials, the observed lags may be explained by ice sheet-ocean feedbacks linked with changes in ice sheet elevation and the impact of meltwater on ocean circulation, as investigated with sensitivity studies. <BR /><BR /> A quantitative comparison between ice core data and climate simulations requires stability of the stable isotope - temperature relationship to be explored. Atmospheric simulations including water stable isotopes have been conducted with the LMDZiso model under different boundary conditions. This set of simulations allows calculation of a temporal Greenland isotope-temperature slope (0.3-0.4 per degC) during warmer-than-present Arctic climates, in response to increased CO2, increased ocean temperature and orbital forcing. This temporal slope appears half as large as the modern spatial gradient and is consistent with other ice core estimates. It may, however, be model-dependent, as indicated by preliminary comparison with other models. This suggests that further simulations and detailed inter-model comparisons are also likely to be of benefit. <BR /><BR /> Comparisons with Greenland ice core stable isotope data reveals that IPSL-CM4/LMDZiso simulations strongly underestimate the amplitude of the ice core signal during the last interglacial, which could reach +8-10 degC at fixed-elevation. While the model-data mismatch may result from missing positive feedbacks (e.g. vegetation), it could also be explained by a reduced elevation of the central Greenland ice sheet surface by 300-400 m.
T. C. Johns, J.-F. Royer, I. Höschel, H. Huebener, E. Roeckner, E. Manzini, W. May, J.-L. Dufresne, O. H. Otterå, D. P. van Vuuren, D. Salas Y Melia, M. A. Giorgetta, S. Denvil, S. Yang, P. G. Fogli, J. Körper, J. F. Tjiputra, E. Stehfest, and C. D. Hewitt. Erratum to: Climate change under aggressive mitigation: the ENSEMBLES multi-model experiment. Climate Dynamics, 37:1269-1270, September 2011. [ bib | DOI | ADS link ]
A. Bodas-Salcedo, M. J. Webb, S. Bony, H. Chepfer, J.-L. Dufresne, S. A. Klein, Y. Zhang, R. Marchand, J. M. Haynes, R. Pincus, and V. O. John. COSP: Satellite simulation software for model assessment. Bulletin of the American Meteorological Society, 92:1023-1043, August 2011. [ bib | DOI | ADS link ]
F. Aires, F. Marquisseau, C. Prigent, and G. Sèze. A Land and Ocean Microwave Cloud Classification Algorithm Derived from AMSU-A and -B, Trained Using MSG-SEVIRI Infrared and Visible Observations. Monthly Weather Review, 139:2347-2366, August 2011. [ bib | DOI | ADS link ]
S. Verma, C. Venkataraman, and O. Boucher. Attribution of aerosol radiative forcing over India during the winter monsoon to emissions from source categories and geographical regions. Atmospheric Environment, 45:4398-4407, August 2011. [ bib | DOI | ADS link ]
We examine the aerosol radiative effects due to aerosols emitted from different emission sectors (anthropogenic and natural) and originating from different geographical regions within and outside India during the northeast (NE) Indian winter monsoon (January-March). These studies are carried out through aerosol transport simulations in the general circulation (GCM) model of the Laboratoire de Météorologie Dynamique (LMD). The model estimates of aerosol single scattering albedo (SSA) show lower values (0.86-0.92) over the region north to 10degN comprising of the Indian subcontinent, Bay of Bengal, and parts of the Arabian Sea compared to the region south to 10degN where the estimated SSA values lie in the range 0.94-0.98. The model estimated SSA is consistent with the SSA values inferred through measurements on various platforms. Aerosols of anthropogenic origin reduce the incoming solar radiation at the surface by a factor of 10-20 times the reduction due to natural aerosols. At the top-of-atmosphere (TOA), aerosols from biofuel use cause positive forcing compared to the negative forcing from fossil fuel and natural sources in correspondence with the distribution of SSA which is estimated to be the lowest (0.7-0.78) from biofuel combustion emissions. Aerosols originating from India and Africa-west Asia lead to the reduction in surface radiation (-3 to -8 W m -2) by 40-60% of the total reduction in surface radiation due to all aerosols over the Indian subcontinent and adjoining ocean. Aerosols originating from India and Africa-west Asia also lead to positive radiative effects at TOA over the Arabian Sea, central India (CNI), with the highest positive radiative effects over the Bay of Bengal and cause either negative or positive effects over the Indo-Gangetic plain (IGP).
N. Huneeus, M. Schulz, Y. Balkanski, J. Griesfeller, J. Prospero, S. Kinne, S. Bauer, O. Boucher, M. Chin, F. Dentener, T. Diehl, R. Easter, D. Fillmore, S. Ghan, P. Ginoux, A. Grini, L. Horowitz, D. Koch, M. C. Krol, W. Landing, X. Liu, N. Mahowald, R. Miller, J.-J. Morcrette, G. Myhre, J. Penner, J. Perlwitz, P. Stier, T. Takemura, and C. S. Zender. Global dust model intercomparison in AeroCom phase I. Atmospheric Chemistry & Physics, 11:7781-7816, August 2011. [ bib | DOI | ADS link ]
This study presents the results of a broad intercomparison of a total of 15 global aerosol models within the AeroCom project. Each model is compared to observations related to desert dust aerosols, their direct radiative effect, and their impact on the biogeochemical cycle, i.e., aerosol optical depth (AOD) and dust deposition. Additional comparisons to Angström exponent (AE), coarse mode AOD and dust surface concentrations are included to extend the assessment of model performance and to identify common biases present in models. These data comprise a benchmark dataset that is proposed for model inspection and future dust model development. There are large differences among the global models that simulate the dust cycle and its impact on climate. In general, models simulate the climatology of vertically integrated parameters (AOD and AE) within a factor of two whereas the total deposition and surface concentration are reproduced within a factor of 10. In addition, smaller mean normalized bias and root mean square errors are obtained for the climatology of AOD and AE than for total deposition and surface concentration. Characteristics of the datasets used and their uncertainties may influence these differences. Large uncertainties still exist with respect to the deposition fluxes in the southern oceans. Further measurements and model studies are necessary to assess the general model performance to reproduce dust deposition in ocean regions sensible to iron contributions. Models overestimate the wet deposition in regions dominated by dry deposition. They generally simulate more realistic surface concentration at stations downwind of the main sources than at remote ones. Most models simulate the gradient in AOD and AE between the different dusty regions. However the seasonality and magnitude of both variables is better simulated at African stations than Middle East ones. The models simulate the offshore transport of West Africa throughout the year but they overestimate the AOD and they transport too fine particles. The models also reproduce the dust transport across the Atlantic in the summer in terms of both AOD and AE but not so well in winter-spring nor the southward displacement of the dust cloud that is responsible of the dust transport into South America. Based on the dependency of AOD on aerosol burden and size distribution we use model bias with respect to AOD and AE to infer the bias of the dust emissions in Africa and the Middle East. According to this analysis we suggest that a range of possible emissions for North Africa is 400 to 2200 Tg yr-1 and in the Middle East 26 to 526 Tg yr-1.
J. Gao, V. Masson-Delmotte, T. Yao, L. Tian, C. Risi, and G. Hoffmann. Precipitation Water Stable Isotopes in the South Tibetan Plateau: Observations and Modeling*. Journal of Climate, 24:3161-3178, July 2011. [ bib | DOI | ADS link ]
F. Vimeux, G. Tremoy, C. Risi, and R. Gallaire. A strong control of the South American SeeSaw on the intra-seasonal variability of the isotopic composition of precipitation in the Bolivian Andes. Earth and Planetary Science Letters, 307:47-58, July 2011. [ bib | DOI | ADS link ]
Water stable isotopes (δ) in tropical regions are a valuable tool to study both convective processes and climate variability provided that local and remote controls on δ are well known. Here, we examine the intra-seasonal variability of the event-based isotopic composition of precipitation (δD Zongo) in the Bolivian Andes (Zongo valley, 16deg20'S-67deg47'W) from September 1st, 1999 to August 31st, 2000. We show that the local amount effect is a very poor parameter to explain δD Zongo. We thus explore the property of water isotopes to integrate both temporal and spatial convective activities. We first show that the local convective activity averaged over the 7-8 days preceding the rainy event is an important control on δD Zongo during the rainy season (˜ 40% of the δD Zongo variability is captured). This could be explained by the progressive depletion of local water vapor by unsaturated downdrafts of convective systems. The exploration of remote convective controls on δD Zongo shows a strong influence of the South American SeeSaw (SASS) which is the first climate mode controlling the precipitation variability in tropical South America during austral summer. Our study clearly evidences that temporal and spatial controls are not fully independent as the 7-day averaged convection in the Zongo valley responds to the SASS. Our results are finally used to evaluate a water isotope enabled atmospheric general circulation model (LMDZ-iso), using the stretched grid functionality to run zoomed simulations over the entire South American continent (15degN-55degS; 30deg-85degW). We find that zoomed simulations capture the intra-seasonal isotopic variation and its controls, though with an overestimated local sensitivity, and confirm the role of a remote control on δ according to a SASS-like dipolar structure.
V. Yankovsky, R. Manuilova, A. Babaev, A. Feofilov, and A. Kutepov. Model of electronic-vibrational kinetics of the O3and O2photolysis products in the middle atmosphere: applications to water vapour retrievals from SABER/TIMED 6.3 μm radiance measurements. International Journal of Remote Sensing, 32:3065-3078, June 2011. [ bib | DOI | ADS link ]
R. D. Wordsworth, F. Forget, F. Selsis, E. Millour, B. Charnay, and J.-B. Madeleine. Gliese 581d is the First Discovered Terrestrial-mass Exoplanet in the Habitable Zone. Astrophysical Journal, 733:L48, June 2011. [ bib | DOI | arXiv | ADS link ]
It has been suggested that the recently discovered exoplanet GJ581d might be able to support liquid water due to its relatively low mass and orbital distance. However, GJ581d receives 35% less stellar energy than Mars and is probably locked in tidal resonance, with extremely low insolation at the poles and possibly a permanent night side. Under such conditions, it is unknown whether any habitable climate on the planet would be able to withstand global glaciation and/or atmospheric collapse. Here we present three-dimensional climate simulations which demonstrate that GJ581d will have a stable atmosphere and surface liquid water for a wide range of plausible cases, making it the first confirmed super-Earth (exoplanet of 2-10 Earth masses) in the habitable zone. We find that atmospheres with over 10 bar CO2 and varying amounts of background gas (e.g., N2) yield global mean temperatures above 0degC for both land and ocean-covered surfaces. Based on the emitted IR radiation calculated by the model, we propose observational tests that will allow these cases to be distinguished from other possible scenarios in the future.
M. Lothon, B. Campistron, M. Chong, F. Couvreux, F. Guichard, C. Rio, and E. Williams. Life Cycle of a Mesoscale Circular Gust Front Observed by a C-Band Doppler Radar in West Africa. Monthly Weather Review, 139:1370-1388, May 2011. [ bib | DOI | ADS link ]
C. Delire, N. de Noblet-Ducoudré, A. Sima, and I. Gouirand. Vegetation Dynamics Enhancing Long-Term Climate Variability Confirmed by Two Models. Journal of Climate, 24:2238-2257, May 2011. [ bib | DOI | ADS link ]
C. Pilorget, F. Forget, E. Millour, M. Vincendon, and J. B. Madeleine. Dark spots and cold jets in the polar regions of Mars: New clues from a thermal model of surface CO 2 ice. Icarus, 213:131-149, May 2011. [ bib | DOI | ADS link ]
Observations of the martian CO 2 ice cap in late winter and spring have revealed exotic phenomena. Unusual dark spots, fans and blotches form as the south-polar seasonal CO 2 ice cap retreats. The formation mechanisms of these features are not clearly understood. Theoretical models suggest that photons could penetrate deep into the CO 2 ice down to the regolith, leading to basal sublimation and gas and dust ejection. We have developed a detailed thermal model able to simulate the temporal evolution of the regolith-CO 2 ice layer-atmosphere column. It takes into account heat conduction, radiative transfer within the ice and the atmosphere, and latent heat exchange when there is a phase transition. We found that a specific algorithm, fully coupling these three components, was needed to properly predict ice sublimation below the surface. Our model allows us to determine under what conditions basal sublimation is possible and thus when and where it can occur on Mars. Our results show that basal sublimation is possible if we consider large pathlengths and very little dust content within the ice. Moreover, the model can explain how dark spots can appear very early after the end of the polar night at high latitudes. We also evaluate the importance of the different parameters in our simulations. Contrary to what was suggested by theoretical models, the role of seasonal thermal waves is found to be limited. Solar radiation alone can initiate basal sublimation, which therefore only depends on the CO 2 ice properties. Three main modes were identified: one where condensation/sublimation only occurs at the surface (in the case of small grains and/or high dust content), one where basal sublimation is possible (large pathlengths and very little dust content) and an intermediate mode where sublimation within the ice may occur. We suggest that these different modes could be keys to understanding many processes that occur at the surface of Mars, like the anticryptic area behavior or the recent reported activity in gullies.
A. Léger, O. Grasset, B. Fegley, F. Codron, A. F. Albarede, P. Barge, R. Barnes, P. Cance, S. Carpy, F. Catalano, C. Cavarroc, O. Demangeon, S. Ferraz-Mello, P. Gabor, J.-M. Grießmeier, J. Leibacher, G. Libourel, A.-S. Maurin, S. N. Raymond, D. Rouan, B. Samuel, L. Schaefer, J. Schneider, P. A. Schuller, F. Selsis, and C. Sotin. The extreme physical properties of the CoRoT-7b super-Earth. Icarus, 213:1-11, May 2011. [ bib | DOI | arXiv | ADS link ]
The search for rocky exoplanets plays an important role in our quest for extra-terrestrial life. Here, we discuss the extreme physical properties possible for the first characterised rocky super-Earth, CoRoT-7b ( R pl = 1.58 0.10 R Earth, M pl = 6.9 1.2 M Earth). It is extremely close to its star ( a = 0.0171 AU = 4.48 R st), with its spin and orbital rotation likely synchronised. The comparison of its location in the ( M pl, R pl) plane with the predictions of planetary models for different compositions points to an Earth-like composition, even if the error bars of the measured quantities and the partial degeneracy of the models prevent a definitive conclusion. The proximity to its star provides an additional constraint on the model. It implies a high extreme-UV flux and particle wind, and the corresponding efficient erosion of the planetary atmosphere especially for volatile species including water. Consequently, we make the working hypothesis that the planet is rocky with no volatiles in its atmosphere, and derive the physical properties that result. As a consequence, the atmosphere is made of rocky vapours with a very low pressure ( P 1.5 Pa), no cloud can be sustained, and no thermalisation of the planet is expected. The dayside is very hot (2474 71 K at the sub-stellar point) while the nightside is very cold (50-75 K). The sub-stellar point is as hot as the tungsten filament of an incandescent bulb, resulting in the melting and distillation of silicate rocks and the formation of a lava ocean. These possible features of CoRoT-7b could be common to many small and hot planets, including the recently discovered Kepler-10b. They define a new class of objects that we propose to name “ Lava-ocean planets”.
O. Boucher. Atmospheric science: Seeing through contrails. Nature Climate Change, 1:24-25, April 2011. [ bib | DOI | ADS link ]
Contrails formed by aircraft can evolve into cirrus clouds indistinguishable from those formed naturally. These 'spreading contrails' may be causing more climate warming today than all the carbon dioxide emitted by aircraft since the start of aviation.
A. Spiga, F. Forget, J.-B. Madeleine, L. Montabone, S. R. Lewis, and E. Millour. The impact of martian mesoscale winds on surface temperature and on the determination of thermal inertia. Icarus, 212:504-519, April 2011. [ bib | DOI | ADS link ]
Radiative control of surface temperature is a key characteristic of the martian environment and its low-density atmosphere. Here we show through meteorological modeling that surface temperature can be far from radiative equilibrium over numerous sloping terrains on Mars, where nighttime mesoscale katabatic winds impact the surface energy budget. Katabatic circulations induce both adiabatic atmospheric heating and enhancement of downward sensible heat flux, which then becomes comparable to radiative flux and acts to warm the ground. Through this mechanism, surface temperature can increase up to 20 K. One consequence is that warm signatures of surface temperature over slopes, observed through infrared spectrometry, cannot be systematically associated with contrasts of intrinsic soil thermal inertia. Apparent thermal inertia maps retrieved thus far possibly contain wind-induced structures. Another consequence is that surface temperature observations close to sloping terrains could allow the validation of model predictions for martian katabatic winds, provided contrasts in intrinsic thermal inertia can be ruled out. The thermal impact of winds is mostly discussed in this paper in the particular cases of Olympus Mons/Lycus Sulci and Terra Meridiani but is generally significant over any sloped terrains in low thermal inertia areas. It is even general enough to apply under daytime conditions, thereby providing a possible explanation for observed afternoon surface cooling, and to ice-covered terrains, thereby providing new insights on how winds could have shaped the present surface of Mars.
K. Goubanova, V. Echevin, B. Dewitte, F. Codron, K. Takahashi, P. Terray, and M. Vrac. Statistical downscaling of sea-surface wind over the Peru-Chile upwelling region: diagnosing the impact of climate change from the IPSL-CM4 model. Climate Dynamics, 36:1365-1378, April 2011. [ bib | DOI | ADS link ]
The key aspect of the ocean circulation off Peru-Chile is the wind-driven upwelling of deep, cold, nutrient-rich waters that promote a rich marine ecosystem. It has been suggested that global warming may be associated with an intensification of upwelling-favorable winds. However, the lack of high-resolution long-term observations has been a limitation for a quantitative analysis of this process. In this study, we use a statistical downscaling method to assess the regional impact of climate change on the sea-surface wind over the Peru-Chile upwelling region as simulated by the global coupled general circulation model IPSL-CM4. Taking advantage of the high-resolution QuikSCAT wind product and of the NCEP reanalysis data, a statistical model based on multiple linear regressions is built for the daily mean meridional and zonal wind at 10 m for the period 2000-2008. The large-scale 10 m wind components and sea level pressure are used as regional circulation predictors. The skill of the downscaling method is assessed by comparing with the surface wind derived from the ERS satellite measurements, with in situ wind observations collected by ICOADS and through cross-validation. It is then applied to the outputs of the IPSL-CM4 model over stabilized periods of the pre-industrial, 2 × CO2 and 4 × CO2 IPCC climate scenarios. The results indicate that surface along-shore winds off central Chile (off central Peru) experience a significant intensification (weakening) during Austral winter (summer) in warmer climates. This is associated with a general decrease in intra-seasonal variability.
H. C. Steen-Larsen, V. Masson-Delmotte, J. Sjolte, S. J. Johnsen, B. M. Vinther, F.-M. BréOn, H. B. Clausen, D. Dahl-Jensen, S. Falourd, X. Fettweis, H. GalléE, J. Jouzel, M. Kageyama, H. Lerche, B. Minster, G. Picard, H. J. Punge, C. Risi, D. Salas, J. Schwander, K. Steffen, A. E. SveinbjöRnsdóttir, A. Svensson, and J. White. Understanding the climatic signal in the water stable isotope records from the NEEM shallow firn/ice cores in northwest Greenland. Journal of Geophysical Research (Atmospheres), 116:D06108, March 2011. [ bib | DOI | ADS link ]
Samples of precipitation and atmospheric water vapor were collected together with shallow firn/ice cores as part of the new deep drilling project in northwest Greenland: the NEEM project. These samples were analyzed for their isotope composition to understand the processes affecting the climatic signal archived in the water stable isotope records from the NEEM deep ice core. The dominant moisture source for the snow deposited at the NEEM-site may be originating as far south as 35degN from the western part of the Atlantic Ocean. The surface atmospheric water vapor appears in isotopic equilibrium with the snow surface indicating a large water exchange between the atmosphere and snowpack. The interannual variability of NEEM shallow firn/ice cores stable isotope data covering the last 40 years shows an unexpectedly weak NAO signal. Regional to global atmospheric models simulate a dominant summer precipitation in the NEEM area, suggesting that the intermittency of modern winter precipitation is responsible for the lack of a strong NAO imprint. The interannual variability of NEEM isotope data however shows a strong correlation with interannual variations of Baffin Bay sea ice cover, a relationship consistent with air mass trajectories. NEEM deep ice core isotopic records may therefore provide detailed information on past Baffin Bay sea ice extent. NEEM stable water isotope content increasing trend points to a local warming trend of 3.0degC over the last 40 years.
G. Gastineau, L. Li, and H. Le Treut. Some Atmospheric Processes Governing the Large-Scale Tropical Circulation in Idealized Aquaplanet Simulations. Journal of Atmospheric Sciences, 68:553-575, March 2011. [ bib | DOI | ADS link ]
D.-D. Rousseau, P. Antoine, N. Gerasimenko, A. Sima, M. Fuchs, C. Hatté, O. Moine, and L. Zoeller. North Atlantic abrupt climatic events of the last glacial period recorded in Ukrainian loess deposits. Climate of the Past, 7:221-234, March 2011. [ bib | DOI | ADS link ]
Loess deposits are widely distributed in the Northern Hemisphere, where they have recorded not only the glacial-interglacial cycles, but also millennial-timescale changes resembling those in marine and ice cores. Such abrupt variations are clearly marked in western European series, but have not yet been evidenced in the East of the continent. Here we present results of the high-resolution investigation of a Weichselian Upper Pleniglacial loess sequence (˜38-15 ka) from Stayky, Ukraine. The stratigraphy shows an alternation of loess horizons and embryonic soils, similar to sequences from western Europe. Similarities are also found between variations of a grain-size index (ratio between coarse and fine material fractions) in Stayky and in western European profiles. Based on these similarities and in agreement with the luminescence dates, the embryonic soils are associated with the Greenland interstadials (GIS) 7 to 2, and the Vytachiv paleosol at the base of the sequence, with GIS 8. Pollen analysis indicates a wetter climate for these interstadials, allowing the development of arboreal vegetation, than for the stadials, which are marked by loess formation. The grain-size index reaches the highest values for intervals correlated with the Heinrich events 3 and 2. Thus, it appears that the North Atlantic abrupt climate changes have extended their influence and modulated the loess sedimentation at least as far as eastern Europe. This result is supported by recent climate modeling experiments and recommends the Stayky sequence as a reference for further comparisons between profiles along the Eurasian loess belt centered at 50deg N.
A. Mangold, H. de Backer, B. de Paepe, S. Dewitte, I. Chiapello, Y. Derimian, M. Kacenelenbogen, J.-F. LéOn, N. Huneeus, M. Schulz, D. Ceburnis, C. O'Dowd, H. Flentje, S. Kinne, A. Benedetti, J.-J. Morcrette, and O. Boucher. Aerosol analysis and forecast in the European Centre for Medium-Range Weather Forecasts Integrated Forecast System: 3. Evaluation by means of case studies. Journal of Geophysical Research (Atmospheres), 116:D03302, February 2011. [ bib | DOI | ADS link ]
A near real-time system for assimilation and forecasts of aerosols, greenhouse and trace gases, extending the ECMWF Integrated Forecasting System (IFS), has been developed in the framework of the Global and regional Earth-system Monitoring using Satellite and in-situ data (GEMS) project. The GEMS aerosol modeling system is novel as it is the first aerosol model fully coupled to a numerical weather prediction model with data assimilation. A reanalysis of the period 2003-2009 has been carried out with the same system. During its development phase, the aerosol system was first run for the time period January 2003 to December 2004 and included sea salt, desert dust, organic matter, black carbon, and sulfate aerosols. In the analysis, Moderate Resolution Imaging Spectroradiometer (MODIS) total aerosol optical depth (AOD) at 550 nm over ocean and land (except over bright surfaces) was assimilated. This work evaluates the performance of the aerosol system by means of case studies. The case studies include (1) the summer heat wave in Europe in August 2003, characterized by forest fire aerosol and conditions of high temperatures and stagnation, favoring photochemistry and secondary aerosol formation, (2) a large Saharan dust event in March 2004, and (3) periods of high and low sea salt aerosol production. During the heat wave period in 2003, the linear correlation coefficients between modeled and observed AOD (550 nm) and between modeled and observed PM2.5 mass concentrations are 0.82 and 0.71, respectively, for all investigated sites together. The AOD is slightly and the PM2.5 mass concentration is clearly overestimated by the aerosol model during this period. The simulated sulfate mass concentration is significantly correlated with observations but is distinctly overestimated. The horizontal and vertical locations of the main features of the aerosol distribution during the Saharan dust outbreak are generally well captured, as well as the timing of the AOD peaks. The aerosol model simulates winter sea salt AOD reasonably well, however, showing a general overestimation. Summer sea salt events show a better agreement. Overall, the assimilation of MODIS AOD data improves the subsequent aerosol predictions when compared with observations, in particular concerning the correlation and AOD peak values. The assimilation is less effective in correcting a positive (PM2.5, sulfate mass concentration, Angström exponent) or negative (desert dust plume AOD) model bias.
T. Andrews, M. Doutriaux-Boucher, O. Boucher, and P. M. Forster. A regional and global analysis of carbon dioxide physiological forcing and its impact on climate. Climate Dynamics, 36:783-792, February 2011. [ bib | DOI | ADS link ]
An increase in atmospheric carbon dioxide concentration has both a radiative (greenhouse) effect and a physiological effect on climate. The physiological effect forces climate as plant stomata do not open as wide under enhanced CO2 levels and this alters the surface energy balance by reducing the evapotranspiration flux to the atmosphere, a process referred to as `carbon dioxide physiological forcing'. Here the climate impact of the carbon dioxide physiological forcing is isolated using an ensemble of twelve 5-year experiments with the Met Office Hadley Centre HadCM3LC fully coupled atmosphere-ocean model where atmospheric carbon dioxide levels are instantaneously quadrupled and thereafter held constant. Fast responses (within a few months) to carbon dioxide physiological forcing are analyzed at a global and regional scale. Results show a strong influence of the physiological forcing on the land surface energy budget, hydrological cycle and near surface climate. For example, global precipitation rate reduces by ˜3% with significant decreases over most land-regions, mainly from reductions to convective rainfall. This fast hydrological response is still evident after 5 years of model integration. Decreased evapotranspiration over land also leads to land surface warming and a drying of near surface air, both of which lead to significant reductions in near surface relative humidity (˜6%) and cloud fraction (˜3%). Patterns of fast responses consistently show that results are largest in the Amazon and central African forest, and to a lesser extent in the boreal and temperate forest. Carbon dioxide physiological forcing could be a source of uncertainty in many model predicted quantities, such as climate sensitivity, transient climate response and the hydrological sensitivity. These results highlight the importance of including biological components of the Earth system in climate change studies.
W. Chen, Z. Jiang, L. Li, and P. Yiou. Simulation of regional climate change under the IPCC A2 scenario in southeast China. Climate Dynamics, 36:491-507, February 2011. [ bib | DOI | ADS link ]
A variable-grid atmospheric general circulation model, LMDZ, with a local zoom over southeast China is used to investigate regional climate changes in terms of both means and extremes. Two time slices of 30 years are chosen to represent, respectively, the end of the 20th century and the middle of the 21st century. The lower-boundary conditions (sea-surface temperature and sea-ice extension) are taken from the outputs of three global coupled climate models: Institut Pierre-Simon Laplace (IPSL), Centre National de Recherches Météorologiques (CNRM) and Geophysical Fluid Dynamics Laboratory (GFDL). Results from a two-way nesting system between LMDZ-global and LMDZ-regional are also presented. The evaluation of simulated temperature and precipitation for the current climate shows that LMDZ reproduces generally well the spatial distribution of mean climate and extreme climate events in southeast China, but the model has systematic cold biases in temperature and tends to overestimate the extreme precipitation. The two-way nesting model can reduce the “cold bias” to some extent compared to the one-way nesting model. Results with greenhouse gas forcing from the SRES-A2 emission scenario show that there is a significant increase for mean, daily-maximum and minimum temperature in the entire region, associated with a decrease in the number of frost days and an increase in the heat wave duration. The annual frost days are projected to significantly decrease by 12-19 days while the heat wave duration to increase by about 7 days. A warming environment gives rise to changes in extreme precipitation events. Except two simulations (LMDZ/GFDL and LMDZ/IPSL2) that project a decrease in maximum 5-day precipitation (R5d) for winter, other precipitation extremes are projected to increase over most of southeast China in all seasons, and among the three global scenarios. The domain-averaged values for annual simple daily intensity index (SDII), R5d and fraction of total rainfall from extreme events (R95t) are projected to increase by 6-7, 10-13 and 11-14%, respectively, relative to their present-day values. However, it is clear that more research will be needed to assess the uncertainties on the projection in future of climate extremes at local scale.
P. M. Ruti, J. E. Williams, F. Hourdin, F. Guichard, A. Boone, P. van Velthoven, F. Favot, I. Musat, M. Rummukainen, M. Domínguez, M. Á. Gaertner, J. P. Lafore, T. Losada, M. B. Rodriguez de Fonseca, J. Polcher, F. Giorgi, Y. Xue, I. Bouarar, K. Law, B. Josse, B. Barret, X. Yang, C. Mari, and A. K. Traore. The West African climate system: a review of the AMMA model inter-comparison initiatives. Atmospheric Science Letters, 12:116-122, January 2011. [ bib | DOI | ADS link ]
C. Shi, V. Masson-Delmotte, C. Risi, T. Eglin, M. Stievenard, M. Pierre, X. Wang, J. Gao, F.-M. Bréon, Q.-B. Zhang, and V. Daux. Sampling strategy and climatic implications of tree-ring stable isotopes on the southeast Tibetan Plateau. Earth and Planetary Science Letters, 301:307-316, January 2011. [ bib | DOI | ADS link ]
We explore the potential of tree-ring cellulose δ18O and δ13C records for reconstructing climate variability in the southeast Tibetan Plateau. Our sampling strategy was designed to investigate intra and inter-tree variability, and the effects of the age of tree on δ18O variation. We show that intra-tree δ13C and δ18O variability is negligible, and inter-tree coherence is sufficient to build robust tree-ring δ18O or δ13C chronologies based on only four trees. There is no evidence of an age effect regarding δ18O, in contrast with tree-ring width. In our warm and moist sampling site, young tree δ13C is not clearly correlated with monthly mean meteorological data. Tree-ring δ18O appears significantly anti-correlated with summer precipitation amount, regional cloud cover, and relative humidity. Simulations conducted with the ORCHIDEE land surface model confirm the observed contribution of relative humidity to tree cellulose δ18O, and explain the weak correlation of δ13C with climate by the non-linear integration linked with photosynthesis. Altogether, the tree-ring cellulose δ18O is shown to be a promising proxy to reconstruct regional summer moisture variability prior to the instrumental period.
S. Danuor, A. Gaye, H. Yacouba, A. Mariko, M. I. Bouzou, M. Maiga, D. da, K. Ginoux, D. J. Parker, J. Polcher, K. Laval, D. Diallo, and B. Bourles. Education in meteorology and climate sciences in West Africa. Atmospheric Science Letters, 12:155-159, January 2011. [ bib | DOI | ADS link ]
C. M. Taylor, D. J. Parker, N. Kalthoff, M. A. Gaertner, N. Philippon, S. Bastin, P. P. Harris, A. Boone, F. Guichard, A. Agusti-Panareda, M. Baldi, P. Cerlini, L. Descroix, H. Douville, C. Flamant, J.-Y. Grandpeix, and J. Polcher. New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis. Atmospheric Science Letters, 12:38-44, January 2011. [ bib | DOI | ADS link ]