lmd_EMC32010_abstracts.html

2010 .

C. Risi, S. Bony, F. Vimeux, and J. Jouzel. Correction to ”Water-stable isotopes in the LMDZ4 general circulation model: Model evaluation for present-day and past climates and applications to climatic interpretations of tropical isotopic records”. Journal of Geophysical Research (Atmospheres), 115:24123, December 2010. [ bib | DOI | ADS link ]

C. Risi, S. Bony, F. Vimeux, C. Frankenberg, D. Noone, and J. Worden. Understanding the Sahelian water budget through the isotopic composition of water vapor and precipitation. Journal of Geophysical Research (Atmospheres), 115:24110, December 2010. [ bib | DOI | ADS link ]

The goal of this paper is to investigate the added value of water isotopic measurements to estimate the relative influence of large-scale dynamics, convection, and land surface recycling on the Sahelian water budget. To this aim, we use isotope data in the lower tropospheric water vapor measured by the SCIAMACHY and TES satellite instruments and in situ precipitation data from the Global Network for Isotopes in Precipitation and collected during the African Monsoon Multidisciplinary Analysis field campaign, together with water-tagging experiments with the Laboratoire de Météorologie Dynamique general circulation model (LMDZ) fitted with isotopes. We show that some isotopic biases in LMDZ reveal the misrepresentation of dehydrating processes that would be undetected without isotopic measurements. In dry regions, the vapor isotopic composition is primarily controlled by the intensity of the air dehydration. In addition, it may also keep some memory of dehydration pathways that is erased in the humidity distribution, namely the relative contribution of dehydration in the tropical upper troposphere versus midlatitudes. In wet regions, vapor and rain isotope compositions are primarily controlled by changes in convection, through rain reevaporation and through the progressive depletion of the vapor by convective mixing along air mass trajectories. Gradients in vapor isotope composition along air mass trajectories may help estimate continental recycling intensity, provided that we could quantify the effect of convection on the isotopic composition of water vapor.

F. M. O'Connor, O. Boucher, N. Gedney, C. D. Jones, G. A. Folberth, R. Coppell, P. Friedlingstein, W. J. Collins, J. Chappellaz, J. Ridley, and C. E. Johnson. Possible role of wetlands, permafrost, and methane hydrates in the methane cycle under future climate change: A review. Reviews of Geophysics, 48:4005, December 2010. [ bib | DOI | ADS link ]

We have reviewed the available scientific literature on how natural sources and the atmospheric fate of methane may be affected by future climate change. We discuss how processes governing methane wetland emissions, permafrost thawing, and destabilization of marine hydrates may affect the climate system. It is likely that methane wetland emissions will increase over the next century. Uncertainties arise from the temperature dependence of emissions and changes in the geographical distribution of wetland areas. Another major concern is the possible degradation or thaw of terrestrial permafrost due to climate change. The amount of carbon stored in permafrost, the rate at which it will thaw, and the ratio of methane to carbon dioxide emissions upon decomposition form the main uncertainties. Large amounts of methane are also stored in marine hydrates, and they could be responsible for large emissions in the future. The time scales for destabilization of marine hydrates are not well understood and are likely to be very long for hydrates found in deep sediments but much shorter for hydrates below shallow waters, such as in the Arctic Ocean. Uncertainties are dominated by the sizes and locations of the methane hydrate inventories, the time scales associated with heat penetration in the ocean and sediments, and the fate of methane released in the seawater. Overall, uncertainties are large, and it is difficult to be conclusive about the time scales and magnitudes of methane feedbacks, but significant increases in methane emissions are likely, and catastrophic emissions cannot be ruled out. We also identify gaps in our scientific knowledge and make recommendations for future research and development in the context of Earth system modeling.

W. J. Collins, S. Sitch, and O. Boucher. How vegetation impacts affect climate metrics for ozone precursors. Journal of Geophysical Research (Atmospheres), 115:23308, December 2010. [ bib | DOI | ADS link ]

We examine the effect of ozone damage to vegetation as caused by anthropogenic emissions of ozone precursor species and quantify it in terms of its impact on terrestrial carbon stores. A simple climate model is then used to assess the expected changes in global surface temperature from the resulting perturbations to atmospheric concentrations of carbon dioxide, methane, and ozone. The concept of global temperature change potential (GTP) metric, which relates the global average surface temperature change induced by the pulse emission of a species to that induced by a unit mass of carbon dioxide, is used to characterize the impact of changes in emissions of ozone precursors on surface temperature as a function of time. For NO_x emissions, the longer-timescale methane perturbation is of the opposite sign to the perturbations in ozone and carbon dioxide, so NO_x emissions are warming in the short term, but cooling in the long term. For volatile organic compound (VOC), CO, and methane emissions, all the terms are warming for an increase in emissions. The GTPs for the 20 year time horizon are strong functions of emission location, with a large component of the variability owing to the different vegetation responses on different continents. At this time horizon, the induced change in the carbon cycle is the largest single contributor to the GTP metric for NO_x and VOC emissions. For NO_x emissions, we estimate a GTP₂₀ of -9 (cooling) to +24 (warming) depending on assumptions of the sensitivity of vegetation types to ozone damage.

L. Zou, T. Zhou, L. Li, and J. Zhang. East China Summer Rainfall Variability of 1958-2000: Dynamical Downscaling with a Variable-Resolution AGCM. Journal of Climate, 23:6394-6408, December 2010. [ bib | DOI | ADS link ]

J. M. Haywood, A. Jones, L. Clarisse, A. Bourassa, J. Barnes, P. Telford, N. Bellouin, O. Boucher, P. Agnew, C. Clerbaux, P. Coheur, D. Degenstein, and P. Braesicke. Observations of the eruption of the Sarychev volcano and simulations using the HadGEM2 climate model. Journal of Geophysical Research (Atmospheres), 115:21212, November 2010. [ bib | DOI | ADS link ]

In June 2009 the Sarychev volcano located in the Kuril Islands to the northeast of Japan erupted explosively, injecting ash and an estimated 1.2 0.2 Tg of sulfur dioxide into the upper troposphere and lower stratosphere, making it arguably one of the 10 largest stratospheric injections in the last 50 years. During the period immediately after the eruption, we show that the sulfur dioxide (SO₂) cloud was clearly detected by retrievals developed for the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument and that the resultant stratospheric sulfate aerosol was detected by the Optical Spectrograph and Infrared Imaging System (OSIRIS) limb sounder and CALIPSO lidar. Additional surface-based instrumentation allows assessment of the impact of the eruption on the stratospheric aerosol optical depth. We use a nudged version of the HadGEM2 climate model to investigate how well this state-of-the-science climate model can replicate the distributions of SO₂ and sulfate aerosol. The model simulations and OSIRIS measurements suggest that in the Northern Hemisphere the stratospheric aerosol optical depth was enhanced by around a factor of 3 (0.01 at 550 nm), with resultant impacts upon the radiation budget. The simulations indicate that, in the Northern Hemisphere for July 2009, the magnitude of the mean radiative impact from the volcanic aerosols is more than 60% of the direct radiative forcing of all anthropogenic aerosols put together. While the cooling induced by the eruption will likely not be detectable in the observational record, the combination of modeling and measurements would provide an ideal framework for simulating future larger volcanic eruptions.

R. D. Wordsworth, F. Forget, F. Selsis, J.-B. Madeleine, E. Millour, and V. Eymet. Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling. Astronomy Astrophysics, 522:A22, November 2010. [ bib | DOI | arXiv | ADS link ]

The recently discovered exoplanet Gl 581d is extremely close to the outer edge of its system's habitable zone, which has led to much speculation on its possible climate. We have performed a range of simulations to assess whether, given simple combinations of chemically stable greenhouse gases, the planet could sustain liquid water on its surface. For best estimates of the surface gravity, surface albedo and cloud coverage, we find that less than 10 bars of CO₂ is sufficient to maintain a global mean temperature above the melting point of water. Furthermore, even with the most conservative choices of these parameters, we calculate temperatures above the water melting point for CO₂ partial pressures greater than about 40 bar. However, we note that as Gl 581d is probably in a tidally resonant orbit, further simulations in 3D are required to test whether such atmospheric conditions are stable against the collapse of CO₂ on the surface.

J. Cattiaux, R. Vautard, C. Cassou, P. Yiou, V. Masson-Delmotte, and F. Codron. Winter 2010 in Europe: A cold extreme in a warming climate. Geophysical Research Letters, 37:20704, October 2010. [ bib | DOI | ADS link ]

The winter of 2009/2010 was characterized by record persistence of the negative phase of the North-Atlantic Oscillation (NAO) which caused several severe cold spells over Northern and Western Europe. This somehow unusual winter with respect to the most recent ones arose concurrently with public debate on climate change, during and after the Copenhagen climate negotiations. We show however that the cold European temperature anomaly of winter 2010 was (i) not extreme relative to winters of the past six decades, and (ii) warmer than expected from its record-breaking seasonal circulation indices such as NAO or blocking frequency. Daily flow-analogues of winter 2010, taken in past winters, were associated with much colder temperatures. The winter 2010 thus provides a consistent picture of a regional cold event mitigated by long-term climate warming.

A. Rap, P. M. Forster, J. M. Haywood, A. Jones, and O. Boucher. Estimating the climate impact of linear contrails using the UK Met Office climate model. Geophysical Research Letters, 37:20703, October 2010. [ bib | DOI | ADS link ]

The HadGEM2 global climate model is employed to investigate some of the linear contrail effects on climate. Our study parameterizes linear contrails as a thin layer of aerosol. We find that at 100 times the air traffic of year 2000, linear contrails would change the equilibrium global-mean temperature by +0.13 K, corresponding to a climate sensitivity of 0.3 K/(Wm^-2) and a climate efficacy of 31% (significantly smaller than the only previously published estimate of 59%). Our model suggests that contrails cause a slight warming of the surface and, as noted by most global warming modelling studies, land areas are affected more than the oceans. Also, unlike the contrail coverage and radiative forcing, the contrail temperature change response is not geographically correlated with air traffic patterns. In terms of the contrail impact on precipitation, the main feature is the northern shift of the Inter-Tropical Convergence Zone. Finally, our model strongly indicates that the contrail impact on both the diurnal temperature range and regional climate is significantly smaller than some earlier studies suggested.

A. Landais, C. Risi, S. Bony, F. Vimeux, L. Descroix, S. Falourd, and A. Bouygues. Combined measurements of ¹⁷O _excess and d-excess in African monsoon precipitation: Implications for evaluating convective parameterizations. Earth and Planetary Science Letters, 298:104-112, September 2010. [ bib | DOI | ADS link ]

Water stable isotopes (δ ¹⁸O, δD) are useful tools to depict and to understand the atmospheric water cycle. In tropical regions, they record the variations of convective activity and their implementation in convection schemes brings constraints on our understanding and parameterization of this phenomena. Here, we present for the first time measurements of a new isotopic marker of the hydrological cycle ( ¹⁷O _excess resulting from the combination of δ ¹⁷O and δ ¹⁸O of water) in convective regions on two different time scales: (i) during the African monsoon onset and intra-seasonal variability (Banizoumbou, 2006) and (ii) during the squall line of the 11th of August 2006 (Niamey). ¹⁷O _excess responds to the monsoon onset by a ˜ 30 per meg increase as well as to different convective processes in squall lines by ˜ 20 per meg variations. These variations parallel those of d-excess at first order and display significant correlation with relative humidity in the lower troposphere. Still, higher correlation coefficients are observed between d-excess and relative humidity than between ¹⁷O _excess and relative humidity, suggesting a higher influence of relative humidity on d-excess than on ¹⁷O _excess. Using a simple reevaporation model and a more sophisticated 2D model of a squall line, we show that reevaporation is the process explaining the increase of d-excess and ¹⁷O _excess with relative humidity for these two studies. We also show that the combination of ¹⁷O _excess and d-excess is a powerful tool to constrain the representation of isotopic processes during rain reevaporation. In turn, a good representation of such processes enables to use water isotopes to evaluate convective parameterization in atmospheric models.

O. Boucher and G. A. Folberth. New Directions: Atmospheric methane removal as a way to mitigate climate change? Atmospheric Research, 44:3343-3345, September 2010. [ bib | ADS link ]

G. A. Morgan, J. W. Head, F. Forget, J.-B. Madeleine, and A. Spiga. Gully formation on Mars: Two recent phases of formation suggested by links between morphology, slope orientation and insolation history. Icarus, 208:658-666, August 2010. [ bib | DOI | ADS link ]

The unusual 80 km diameter Noachian-aged Asimov crater in Noachis Terra (46degS, 5degE) is characterized by extensive Noachian-Hesperian crater fill and a younger superposed annulus of valleys encircling the margins of the crater floor. These valleys provide an opportunity to study the relationships of gully geomorphology as a function of changing slope orientation relative to solar insolation. We found that the level of development of gullies was highly correlated with slope orientation and solar insolation. The largest and most complex gully systems, with the most well-developed fluvial landforms, are restricted to pole-facing slopes. In contrast, gullies on equator-facing slopes are smaller, more poorly developed and integrated, more highly degraded, and contain more impact craters. We used a 1D version of the Laboratoire de Météorologie Dynamique GCM, and slope geometries (orientation and angle), driven by predicted spin-axis/orbital parameter history, to assess the distribution and history of surface temperatures in these valleys during recent geological history. Surface temperatures on pole-facing slopes preferential for water ice accumulation and subsequent melting are predicted to occur as recently as 0.5-2.1 Ma, which is consistent with age estimates of gully activity elsewhere on Mars. In contrast, the 1D model predicts that water ice cannot accumulate on equator-facing slopes until obliquities exceed 45deg, suggesting they are unlikely to have been active over the last 5 Ma. The correlation of the temperature predictions and the geological evidence for age differences suggests that there were two phases of gully formation in the last few million years: an older phase in which top-down melting occurred on equator-facing slopes and a younger more robust phase on pole-facing slopes. The similarities of small-scale fluvial erosion features seen in the gullies on Mars and those observed in gullies cut by seasonal and perennial snowmelt in the Antarctic Dry Valleys supports a top-down melting origin for these gullies on Mars.

M. T. Woodhouse, K. S. Carslaw, G. W. Mann, S. M. Vallina, M. Vogt, P. R. Halloran, and O. Boucher. Low sensitivity of cloud condensation nuclei to changes in the sea-air flux of dimethyl-sulphide. Atmospheric Chemistry & Physics, 10:7545-7559, August 2010. [ bib | ADS link ]

The emission of dimethyl-sulphide (DMS) gas by phytoplankton and the subsequent formation of aerosol has long been suggested as an important climate regulation mechanism. The key aerosol quantity is the number concentration of cloud condensation nuclei (CCN), but until recently global models did not include the necessary aerosol physics to quantify CCN. Here we use a global aerosol microphysics model to calculate the sensitivity of CCN to changes in DMS emission using multiple present-day and future sea-surface DMS climatologies. Calculated annual fluxes of DMS to the atmosphere for the five model-derived and one observations based present day climatologies are in the range 15.1 to 32.3 Tg a^-1 sulphur. The impact of DMS climatology on surface level CCN concentrations was calculated in terms of summer and winter hemispheric mean values of ΔCCN/ΔFlux_DMS, which varied between -43 and +166 cm^-3/(mg m^-2 day^-1 sulphur), with a mean of 63 cm^-3/(mg m^-2 day^-1 sulphur). The range is due to CCN production in the atmosphere being strongly dependent on the spatial distribution of the emitted DMS. The relative sensitivity of CCN to DMS (i.e. fractional change in CCN divided by fractional change in DMS flux) depends on the abundance of non-DMS derived aerosol in each hemisphere. The relative sensitivity averaged over the five present day DMS climatologies is estimated to be 0.02 in the northern hemisphere (i.e. a 0.02% change in CCN for a 1% change in DMS) and 0.07 in the southern hemisphere where aerosol abundance is lower. In a globally warmed scenario in which the DMS flux increases by ˜1% relative to present day we estimate a ˜0.1% increase in global mean CCN at the surface. The largest CCN response occurs in the Southern Ocean, contributing to a Southern Hemisphere mean annual increase of less than 0.2%. We show that the changes in DMS flux and CCN concentration between the present day and global warming scenario are similar to interannual differences due to variability in windspeed. In summary, although DMS makes a significant contribution to global marine CCN concentrations, the sensitivity of CCN to potential future changes in DMS flux is very low. This finding, together with the predicted small changes in future seawater DMS concentrations, suggests that the role of DMS in climate regulation is very weak.

K. Goubanova, L. Li, P. Yiou, and F. Codron. Relation between Large-Scale Circulation and European Winter Temperature: Does It Hold under Warmer Climate? Journal of Climate, 23:3752-3760, July 2010. [ bib | DOI | ADS link ]

T. Andrews, P. M. Forster, O. Boucher, N. Bellouin, and A. Jones. Precipitation, radiative forcing and global temperature change. Geophysical Research Letters, 37:14701, July 2010. [ bib | DOI | ADS link ]

Radiative forcing is a useful tool for predicting equilibrium global temperature change. However, it is not so useful for predicting global precipitation changes, as changes in precipitation strongly depend on the climate change mechanism and how it perturbs the atmospheric and surface energy budgets. Here a suite of climate model experiments and radiative transfer calculations are used to quantify and assess this dependency across a range of climate change mechanisms. It is shown that the precipitation response can be split into two parts: a fast atmospheric response that strongly correlates with the atmospheric component of radiative forcing, and a slower response to global surface temperature change that is independent of the climate change mechanism, 2-3% per unit of global surface temperature change. We highlight the precipitation response to black carbon aerosol forcing as falling within this range despite having an equilibrium response that is of opposite sign to the radiative forcing and global temperature change.

A. Jones, J. Haywood, O. Boucher, B. Kravitz, and A. Robock. Geoengineering by stratospheric SO₂ injection: results from the Met Office HadGEM2 climate model and comparison with the Goddard Institute for Space Studies ModelE. Atmospheric Chemistry & Physics, 10:5999-6006, July 2010. [ bib | ADS link ]

We examine the response of the Met Office Hadley Centre's HadGEM2-AO climate model to simulated geoengineering by continuous injection of SO₂ into the lower stratosphere, and compare the results with those from the Goddard Institute for Space Studies ModelE. Despite the differences between the models, we find a broadly similar geographic distribution of the response to geoengineering in both models in terms of near-surface air temperature and mean June-August precipitation. The simulations also suggest that significant changes in regional climate would be experienced even if geoengineering was successful in maintaining global-mean temperature near current values, and both models indicate rapid warming if geoengineering is not sustained.

C. Risi, S. Bony, F. Vimeux, and J. Jouzel. Water-stable isotopes in the LMDZ4 general circulation model: Model evaluation for present-day and past climates and applications to climatic interpretations of tropical isotopic records. Journal of Geophysical Research (Atmospheres), 115:12118, June 2010. [ bib | DOI | ADS link ]

We present simulations of water-stable isotopes from the LMDZ general circulation model (the LMDZ-iso GCM) and evaluate them at different time scales (synoptic to interannual). LMDZ-iso reproduces reasonably well the spatial and seasonal variations of both δ¹⁸O and deuterium excess. When nudged with reanalyses, LMDZ-iso is able to capture the synoptic variability of isotopes in winter at a midlatitude station, and the interannual variability in mid and high latitudes is strongly improved. The degree of equilibration between the vapor and the precipitation is strongly sensitive to kinetic effects during rain reevaporation, calling for more synchronous vapor and precipitation measurements. We then evaluate the simulations of two past climates: Last Glacial Maximum (21 ka) and Mid-Holocene (6 ka). A particularity of LMDZ-iso compared to other isotopic GCMs is that it simulates a lower d excess during the LGM over most high-latitude regions, consistent with observations. Finally, we use LMDZ-iso to explore the relationship between precipitation and δ¹⁸O in the tropics, and we discuss its paleoclimatic implications. We show that the imprint of uniform temperature changes on tropical δ¹⁸O is weak. Large regional changes in δ¹⁸O can, however, be associated with dynamical changes of precipitation. Using LMDZ as a test bed for reconstructing past precipitation changes through local δ¹⁸O records, we show that past tropical precipitation changes can be well reconstructed qualitatively but not quantitatively. Over continents, nonlocal effects make the local reconstruction even less accurate.

C. Rio, F. Hourdin, F. Couvreux, and A. Jam. Resolved Versus Parametrized Boundary-Layer Plumes. Part II: Continuous Formulations of Mixing Rates for Mass-Flux Schemes. Boundary-Layer Meteorology, 135:469-483, June 2010. [ bib | DOI | ADS link ]

The conditional sampling of coherent structures in large-eddy simulations of the convective boundary layer (Couvreux et al. Boundary-layer Meteorol 134:441-458, 2010) is used to propose and evaluate formulations of fractional entrainment and detrainment rates for mass-flux schemes. The proposed formulations are physically-based and continuous from the surface to the top of clouds. Entrainment is related to the updraft vertical velocity divergence, while detrainment depends on the thermal vertical velocity, on buoyancy and on the moisture contrast between the mean plume and its environment. The proposed formulations are first directly evaluated in simulations of shallow clouds. They are then tested in single-column simulations with the thermal plume model, a mass-flux representation of boundary-layer thermals.

S. Lebonnois, F. Hourdin, V. Eymet, A. Crespin, R. Fournier, and F. Forget. Superrotation of Venus' atmosphere analyzed with a full general circulation model. Journal of Geophysical Research (Planets), 115:6006, June 2010. [ bib | DOI | ADS link ]

A general circulation model (GCM) has been developed for the Venus atmosphere, from the surface up to 100 km altitude, based on the GCM developed for Earth at our laboratory. Key features of this new GCM include topography, diurnal cycle, dependence of the specific heat on temperature, and a consistent radiative transfer module based on net exchange rate matrices. This allows a consistent computation of the temperature field, in contrast to previous GCMs of Venus atmosphere that used simplified temperature forcing. The circulation is analyzed after 350 Venus days (111 Earth years). Superrotation is obtained above roughly 40 km altitude. Below, the zonal wind remains very small compared to observed values, which is a major pending question. The meridional circulation consists of equator-to-pole cells, the dominant one being located within the cloud layers. The modeled temperature structure is globally consistent with observations, though discrepancies persist in the stability of the lowest layers and equator-pole temperature contrast within the clouds (10 K in the model compared to the observed 40 K). In agreement with observational data, a convective layer is found between the base of the clouds (around 47 km) and the middle of the clouds (55-60 km altitude). The transport of angular momentum is analyzed, and comparison between the reference simulation and a simulation without diurnal cycle illustrates the role played by thermal tides in the equatorial region. Without diurnal cycle, the Gierasch-Rossow-Williams mechanism controls angular momentum transport. The diurnal tides add a significant downward transport of momentum in the equatorial region, causing low latitude momentum accumulation.

C. Risi, A. Landais, S. Bony, J. Jouzel, V. Masson-Delmotte, and F. Vimeux. Understanding the ¹⁷O excess glacial-interglacial variations in Vostok precipitation. Journal of Geophysical Research (Atmospheres), 115:10112, May 2010. [ bib | DOI | ADS link ]

Combined measurements of δ¹⁸O, δ¹⁷O, and δD in ice cores, leading to d excess and ¹⁷O excess, are expected to provide new constraints on the water cycle and past climates. We explore different processes, both in the source regions and during the poleward transport, that could explain the ¹⁷O excess increase by 20 per meg observed from the Last Glacial Maximum (LGM) to Early Holocene (EH) at the Vostok station. Using a single-column model over tropical and subtropical oceans, we show that the relative humidity at the surface is the main factor controlling ¹⁷O excess in source regions. Then, using a Rayleigh-type model, we show that the ¹⁷O excess signal from the source region is preserved in the polar snowfall, contrary to d excess. Evaporative recharge over mid and high latitudes and δ¹⁸O seasonality in polar regions can also affect the Vostok ¹⁷O excess but cannot account for most of the 20 per meg deglacial increase from LGM to EH. On the other hand, a decrease of the relative humidity at the surface (rh_s) by 8 to 22% would explain the observed change in ¹⁷O excess. Such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity, if the surface thermodynamic disequilibrium decreased by 4degC. Such a change in rh_s would affect source and polar temperatures reconstructions from δ¹⁸O and d excess measurements, strengthening the interest of ¹⁷O excess measurements to better constrain such changes.

S. Diatta, F. Hourdin, A. T. Gaye, and N. Viltard. Comparison of Rainfall Profiles in the West African Monsoon as Depicted by TRMM PR and the LMDZ Climate Model. Monthly Weather Review, 138:1767-1777, May 2010. [ bib | DOI | ADS link ]

A. Rap, P. M. Forster, A. Jones, O. Boucher, J. M. Haywood, N. Bellouin, and R. R. de Leon. Parameterization of contrails in the UK Met Office Climate Model. Journal of Geophysical Research (Atmospheres), 115:10205, May 2010. [ bib | DOI | ADS link ]

Persistent contrails are believed to currently have a relatively small but significant positive radiative forcing on climate. With air travel predicted to continue its rapid growth over the coming years, the contrail warming effect on climate is expected to increase. Nevertheless, there remains a high level of uncertainty in the current estimates of contrail radiative forcing. Contrail formation depends mostly on the aircraft flying in cold and moist enough air masses. Most studies to date have relied on simple parameterizations using averaged meteorological conditions. In this paper we take into account the short-term variability in background cloudiness by developing an on-line contrail parameterization for the UK Met Office climate model. With this parameterization, we estimate that for the air traffic of year 2002 the global mean annual linear contrail coverage was approximately 0.11%. Assuming a global mean contrail optical depth of 0.2 or smaller and assuming hexagonal ice crystals, the corresponding contrail radiative forcing was calculated to be less than 10 mW m^-2 in all-sky conditions. We find that the natural cloud masking effect on contrails may be significantly higher than previously believed. This new result is explained by the fact that contrails seem to preferentially form in cloudy conditions, which ameliorates their overall climate impact by approximately 40%.

J. E. Williams, R. Scheele, P. van Velthoven, I. Bouarar, K. Law, B. Josse, V.-H. Peuch, X. Yang, J. Pyle, V. Thouret, B. Barret, C. Liousse, F. Hourdin, S. Szopa, and A. Cozic. Global Chemistry Simulations in the AMMA Multimodel Intercomparison Project. Bulletin of the American Meteorological Society, 91:611-624, May 2010. [ bib | DOI | ADS link ]

M. C. Wyant, R. Wood, C. S. Bretherton, C. R. Mechoso, J. Bacmeister, M. A. Balmaseda, B. Barrett, F. Codron, P. Earnshaw, J. Fast, C. Hannay, J. W. Kaiser, H. Kitagawa, S. A. Klein, M. Köhler, J. Manganello, H.-L. Pan, F. Sun, S. Wang, and Y. Wang. The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific. Atmospheric Chemistry & Physics, 10:4757-4774, May 2010. [ bib | ADS link ]

The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models for the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40deg S to the equator and from 110deg W to 70deg W, corresponding to the Pacific coast of South America. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region next to the coast. However they have greatly differing geographic patterns of mean cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the MBL depth by several hundred meters in the eastern part of the study region. The diurnal cycle of liquid water path is underestimated by most models at the 85deg W 20deg S stratus buoy site compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared to surface-based climatologies. Most models qualitatively capture the MBL deepening around 15 October 2006 at the stratus buoy, associated with colder air at 700 hPa.

J.-Y. Grandpeix, J.-P. Lafore, and F. Cheruy. A Density Current Parameterization Coupled with Emanuel's Convection Scheme. Part II: 1D Simulations. Journal of Atmospheric Sciences, 67:898-922, April 2010. [ bib | DOI | ADS link ]

C. Rio, F. Hourdin, and A. Chédin. Numerical simulation of tropospheric injection of biomass burning products by pyro-thermal plumes. Atmospheric Chemistry & Physics, 10:3463-3478, April 2010. [ bib | ADS link ]

The thermal plume model, a mass-flux scheme originally developed to represent the vertical transport by convective structures within the boundary layer, is adapted to the representation of plumes generated by fires, with the aim of estimating the height at which fire emissions are actually injected in the atmosphere. The parameterization, which takes into account the excess of near surface temperature induced by fires and the mixing between convective plumes and environmental air, is first evaluated on two well-documented fires. Simulations over Southern Africa performed with the general circulation model LMDZ over one month show that the CO₂ can be injected far above the boundary layer height, leading to a daily excess of CO₂ in the mid-troposphere of an order of 2 ppmv. These results agree with satellite retrievals of a diurnal cycle of CO₂ in the free troposphere over regions affected by biomass burning in the Tropics.

J.-Y. Grandpeix and J.-P. Lafore. A Density Current Parameterization Coupled with Emanuel's Convection Scheme. Part I: The Models. Journal of Atmospheric Sciences, 67:881-897, April 2010. [ bib | DOI | ADS link ]

R. Roca, J.-C. Bergès, H. Brogniez, M. Capderou, P. Chambon, O. Chomette, S. Cloché, T. Fiolleau, I. Jobard, J. Lémond, M. Ly, L. Picon, P. Raberanto, A. Szantai, and M. Viollier. On the water and energy cycles in the Tropics. Comptes Rendus Geoscience, 342:390-402, April 2010. [ bib | DOI | ADS link ]

The water and energy cycles are major elements of the Earth climate. These cycles are especially active in the intertropical belt where satellites provide the most suitable observational platform. The history of Earth observations of the water cycle and of the radiation budget viewed from space reveals that the fundamental questions from the early times are still relevant for today's research. The last 2 decades have seen a number of milestones regarding the documentation of rainfall, mesoscale convective systems (MCS), water vapour and radiation at the top of the atmosphere (TOA). Beyond dedicated missions that provided enhanced characterizations of some elements of the atmospheric water cycle and field campaigns that allowed the gathering of validation data, the advent of the long record of meteorological satellites lead to new questioning on the homogenisation of the data time series, etc. The use of this record to document the tropical climate brought new results of the distribution of humidity and reinforced the understanding of some robust features of the African monsoon. Challenges for the immediate future concerns the deepening of the understanding of the role of cloud systems in the monsoon circulation, the downscaling of the documentation of the water and energy cycle at the scale of these cloud systems, the research of better adequation between the users and the satellite estimate of rainfall and finally a much needed methodological effort to build exploitable time series for the estimation of climatic trends in the water and energy cycle in the Tropics. The required observations to address these challenges are rapidly presented with emphasis on the upcoming Megha-Tropiques (MT) mission.

F. Couvreux, F. Hourdin, and C. Rio. Resolved Versus Parametrized Boundary-Layer Plumes. Part I: A Parametrization-Oriented Conditional Sampling in Large-Eddy Simulations. Boundary-Layer Meteorology, 134:441-458, March 2010. [ bib | DOI | ADS link ]

A conditional sampling based on the combination of a passive tracer emitted at the surface and thermodynamic variables is proposed to characterise organized structures in large-eddy simulations of cloud-free and cloudy boundary layers. The sampling is evaluated against more traditional sampling of dry thermals or clouds. It enables the characterization of convective updrafts from the surface to the top of the boundary layer (or the top of cumulus clouds), describing in particular the transition from the sub-cloud to the cloud layer, and retrieves plume characteristics, entrainment and detrainment rates, variances and fluxes. This sampling is used to analyze the contribution of boundary-layer thermals to vertical fluxes and variances.

K. S. Carslaw, O. Boucher, D. V. Spracklen, G. W. Mann, J. G. L. Rae, S. Woodward, and M. Kulmala. A review of natural aerosol interactions and feedbacks within the Earth system. Atmospheric Chemistry & Physics, 10:1701-1737, February 2010. [ bib | ADS link ]

The natural environment is a major source of atmospheric aerosols, including dust, secondary organic material from terrestrial biogenic emissions, carbonaceous particles from wildfires, and sulphate from marine phytoplankton dimethyl sulphide emissions. These aerosols also have a significant effect on many components of the Earth system such as the atmospheric radiative balance and photosynthetically available radiation entering the biosphere, the supply of nutrients to the ocean, and the albedo of snow and ice. The physical and biological systems that produce these aerosols can be highly susceptible to modification due to climate change so there is the potential for important climate feedbacks. We review the impact of these natural systems on atmospheric aerosol based on observations and models, including the potential for long term changes in emissions and the feedbacks on climate. The number of drivers of change is very large and the various systems are strongly coupled. There have therefore been very few studies that integrate the various effects to estimate climate feedback factors. Nevertheless, available observations and model studies suggest that the regional radiative perturbations are potentially several Watts per square metre due to changes in these natural aerosol emissions in a future climate. Taking into account only the direct radiative effect of changes in the atmospheric burden of natural aerosols, and neglecting potentially large effects on other parts of the Earth system, a global mean radiative perturbation approaching 1 W m^-2 is possible by the end of the century. The level of scientific understanding of the climate drivers, interactions and impacts is very low.

O. Marti, P. Braconnot, J.-L. Dufresne, J. Bellier, R. Benshila, S. Bony, P. Brockmann, P. Cadule, A. Caubel, F. Codron, N. de Noblet, S. Denvil, L. Fairhead, T. Fichefet, M.-A. Foujols, P. Friedlingstein, H. Goosse, J.-Y. Grandpeix, E. Guilyardi, F. Hourdin, A. Idelkadi, M. Kageyama, G. Krinner, C. Lévy, G. Madec, J. Mignot, I. Musat, D. Swingedouw, and C. Talandier. Key features of the IPSL ocean atmosphere model and its sensitivity to atmospheric resolution. Climate Dynamics, 34:1-26, January 2010. [ bib | DOI | ADS link ]

This paper presents the major characteristics of the Institut Pierre Simon Laplace (IPSL) coupled ocean-atmosphere general circulation model. The model components and the coupling methodology are described, as well as the main characteristics of the climatology and interannual variability. The model results of the standard version used for IPCC climate projections, and for intercomparison projects like the Paleoclimate Modeling Intercomparison Project (PMIP 2) are compared to those with a higher resolution in the atmosphere. A focus on the North Atlantic and on the tropics is used to address the impact of the atmosphere resolution on processes and feedbacks. In the North Atlantic, the resolution change leads to an improved representation of the storm-tracks and the North Atlantic oscillation. The better representation of the wind structure increases the northward salt transports, the deep-water formation and the Atlantic meridional overturning circulation. In the tropics, the ocean-atmosphere dynamical coupling, or Bjerknes feedback, improves with the resolution. The amplitude of ENSO (El Niño-Southern oscillation) consequently increases, as the damping processes are left unchanged.

C. Risi, S. Bony, F. Vimeux, M. Chong, and L. Descroix. Evolution of the stable water isotopic composition of the rain sampled along Sahelian squall lines. Quarterly Journal of the Royal Meteorological Society, 136:227-242, January 2010. [ bib | DOI | ADS link ]

C. Risi, S. Bony, F. Vimeux, M. Chong, and L. Descroix. Evolution of the stable water isotopic composition of the rain sampled along Sahelian squall lines. Quarterly Journal of the Royal Meteorological Society, 136:227-242, January 2010. [ bib | DOI | ADS link ]

H. Chepfer, S. Bony, D. Winker, G. Cesana, J. L. Dufresne, P. Minnis, C. J. Stubenrauch, and S. Zeng. The GCM-Oriented CALIPSO Cloud Product (CALIPSO-GOCCP). Journal of Geophysical Research (Atmospheres), 115:0, January 2010. [ bib | DOI | ADS link ]

This article presents the GCM-Oriented Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud Product (GOCCP) designed to evaluate the cloudiness simulated by general circulation models (GCMs). For this purpose, Cloud-Aerosol Lidar with Orthogonal Polarization L1 data are processed following the same steps as in a lidar simulator used to diagnose the model cloud cover that CALIPSO would observe from space if the satellite was flying above an atmosphere similar to that predicted by the GCM. Instantaneous profiles of the lidar scattering ratio (SR) are first computed at the highest horizontal resolution of the data but at the vertical resolution typical of current GCMs, and then cloud diagnostics are inferred from these profiles: vertical distribution of cloud fraction, horizontal distribution of low, middle, high, and total cloud fractions, instantaneous SR profiles, and SR histograms as a function of height. Results are presented for different seasons (January-March 2007-2008 and June-August 2006-2008), and their sensitivity to parameters of the lidar simulator is investigated. It is shown that the choice of the vertical resolution and of the SR threshold value used for cloud detection can modify the cloud fraction by up to 0.20, particularly in the shallow cumulus regions. The tropical marine low-level cloud fraction is larger during nighttime (by up to 0.15) than during daytime. The histograms of SR characterize the cloud types encountered in different regions. The GOCCP high-level cloud amount is similar to that from the TIROS Operational Vertical Sounder (TOVS) and the Atmospheric Infrared Sounder (AIRS). The low-level and middle-level cloud fractions are larger than those derived from passive remote sensing (International Satellite Cloud Climatology Project, Moderate-Resolution Imaging Spectroradiometer-Cloud and Earth Radiant Energy System Polarization and Directionality of Earth Reflectances, TOVS Path B, AIRS-Laboratoire de Météorologie Dynamique) because the latter only provide information on the uppermost cloud layer.

F. Hourdin, I. Musat, F. Guichard, P. M. Ruti, F. Favot, M.-A. Filiberti*, M. Pham, J.-Y. Grandpeix, J. Polcher, P. Marquet, A. Boone, J.-P. Lafore, J.-L. Redelsperger, A. Dell'Aquila, T. L. Doval, A. K. Traore, and H. Gallée. AMMA-Model Intercomparison Project. Bulletin of the American Meteorological Society, 91:95, 2010. [ bib | DOI | ADS link ]

T. Wu, R. Yu, F. Zhang, Z. Wang, M. Dong, L. Wang, X. Jin, D. Chen, and L. Li. The Beijing Climate Center atmospheric general circulation model: description and its performance for the present-day climate. Climate Dynamics, 34:149-150, January 2010. [ bib | DOI | ADS link ]

T. Wu, R. Yu, F. Zhang, Z. Wang, M. Dong, L. Wang, X. Jin, D. Chen, and L. Li. The Beijing Climate Center atmospheric general circulation model: description and its performance for the present-day climate. Climate Dynamics, 34:123-147, January 2010. [ bib | DOI | ADS link ]

The Beijing Climate Center atmospheric general circulation model version 2.0.1 (BCC_AGCM2.0.1) is described and its performance in simulating the present-day climate is assessed. BCC_AGCM2.0.1 originates from the community atmospheric model version 3 (CAM3) developed by the National Center for Atmospheric Research (NCAR). The dynamics in BCC_AGCM2.0.1 is, however, substantially different from the Eulerian spectral formulation of the dynamical equations in CAM3, and several new physical parameterizations have replaced the corresponding original ones. The major modification of the model physics in BCC_AGCM2.0.1 includes a new convection scheme, a dry adiabatic adjustment scheme in which potential temperature is conserved, a modified scheme to calculate the sensible heat and moisture fluxes over the open ocean which takes into account the effect of ocean waves on the latent and sensible heat fluxes, and an empirical equation to compute the snow cover fraction. Specially, the new convection scheme in BCC_AGCM2.0.1, which is generated from the Zhang and McFarlanes scheme but modified, is tested to have significant improvement in tropical maximum but also the subtropical minimum precipitation, and the modified scheme for turbulent fluxes are validated using EPIC2001 in situ observations and show a large improvement than its original scheme in CAM3. BCC_AGCM2.0.1 is forced by observed monthly varying sea surface temperatures and sea ice concentrations during 1949-2000. The model climatology is compiled for the period 1971-2000 and compared with the ERA-40 reanalysis products. The model performance is evaluated in terms of energy budgets, precipitation, sea level pressure, air temperature, geopotential height, and atmospheric circulation, as well as their seasonal variations. Results show that BCC_AGCM2.0.1 reproduces fairly well the present-day climate. The combined effect of the new dynamical core and the updated physical parameterizations in BCC_AGCM2.0.1 leads to an overall improvement, compared to the original CAM3.

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. Corrigendum to ”Evaluation of black carbon estimations in global aerosol models” published in Atmos. Chem. Phys., 9, 9001-9026, 2009. Atmospheric Chemistry & Physics, 10:79-81, January 2010. [ bib | ADS link ]

No abstract available.

O. Boucher and G. A. Folberth. New Directions: Atmospheric methane removal as a way to mitigate climate change? Atmospheric Environment, 44:3343-3345, 2010. [ bib | DOI | ADS link ]