lmd_Li2007_abstracts.html

2007 .

J.-L. Bertaux, D. Nevejans, O. Korablev, E. Villard, E. Quémerais, E. Neefs, F. Montmessin, F. Leblanc, J. P. Dubois, E. Dimarellis, A. Hauchecorne, F. Lefèvre, P. Rannou, J. Y. Chaufray, M. Cabane, G. Cernogora, G. Souchon, F. Semelin, A. Reberac, E. Van Ransbeek, S. Berkenbosch, R. Clairquin, C. Muller, F. Forget, F. Hourdin, O. Talagrand, A. Rodin, A. Fedorova, A. Stepanov, I. Vinogradov, A. Kiselev, Y. Kalinnikov, G. Durry, B. Sandel, A. Stern, and J. C. Gérard. SPICAV on Venus Express: Three spectrometers to study the global structure and composition of the Venus atmosphere. Planetary and Space Science, 55:1673-1700, October 2007. [ bib | DOI | ADS link ]

Spectroscopy for the investigation of the characteristics of the atmosphere of Venus (SPICAV) is a suite of three spectrometers in the UV and IR range with a total mass of 13.9 kg flying on the Venus Express (VEX) orbiter, dedicated to the study of the atmosphere of Venus from ground level to the outermost hydrogen corona at more than 40,000 km. It is derived from the SPICAM instrument already flying on board Mars Express (MEX) with great success, with the addition of a new IR high-resolution spectrometer, solar occultation IR (SOIR), working in the solar occultation mode. The instrument consists of three spectrometers and a simple data processing unit providing the interface of these channels with the spacecraft. A UV spectrometer (118-320 nm, resolution 1.5 nm) is identical to the MEX version. It is dedicated to nadir viewing, limb viewing and vertical profiling by stellar and solar occultation. In nadir orientation, SPICAV UV will analyse the albedo spectrum (solar light scattered back from the clouds) to retrieve SO ₂, and the distribution of the UV-blue absorber (of still unknown origin) on the dayside with implications for cloud structure and atmospheric dynamics. On the nightside, γ and δ bands of NO will be studied, as well as emissions produced by electron precipitations. In the stellar occultation mode the UV sensor will measure the vertical profiles of CO ₂, temperature, SO ₂, SO, clouds and aerosols. The density/temperature profiles obtained with SPICAV will constrain and aid in the development of dynamical atmospheric models, from cloud top (60 km) to 160 km in the atmosphere. This is essential for future missions that would rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow studies of the ionosphere through the emissions of CO, CO ⁺, and CO ₂⁺, and its direct interaction with the solar wind. It will study the H corona, with its two different scale heights, and it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAV VIS-IR sensor (0.7-1.7 μm, resolution 0.5-1.2 nm) employs a pioneering technology: an acousto-optical tunable filter (AOTF). On the nightside, it will study the thermal emission peeping through the clouds, complementing the observations of both VIRTIS and Planetary Fourier Spectrometer (PFS) on VEX. In solar occultation mode this channel will study the vertical structure of H ₂O, CO ₂, and aerosols. The SOIR spectrometer is a new solar occultation IR spectrometer in the range λ=2.2-4.3 μm, with a spectral resolution λ/Δ λ15,000, the highest on board VEX. This new concept includes a combination of an echelle grating and an AOTF crystal to sort out one order at a time. The main objective is to measure HDO and H ₂O in solar occultation, in order to characterize the escape of D atoms from the upper atmosphere and give more insight about the evolution of water on Venus. It will also study isotopes of CO ₂ and minor species, and provides a sensitive search for new species in the upper atmosphere of Venus. It will attempt to measure also the nightside emission, which would allow a sensitive measurement of HDO in the lower atmosphere, to be compared to the ratio in the upper atmosphere, and possibly discover new minor atmospheric constituents.

R. A. Betts, O. Boucher, M. Collins, P. M. Cox, P. D. Falloon, N. Gedney, D. L. Hemming, C. Huntingford, C. D. Jones, D. M. H. Sexton, and M. J. Webb. Projected increase in continental runoff due to plant responses to increasing carbon dioxide. Nature, 448:1037-1041, August 2007. [ bib | DOI | ADS link ]

In addition to influencing climatic conditions directly through radiative forcing, increasing carbon dioxide concentration influences the climate system through its effects on plant physiology. Plant stomata generally open less widely under increased carbon dioxide concentration, which reduces transpiration and thus leaves more water at the land surface. This driver of change in the climate system, which we term `physiological forcing', has been detected in observational records of increasing average continental runoff over the twentieth century. Here we use an ensemble of experiments with a global climate model that includes a vegetation component to assess the contribution of physiological forcing to future changes in continental runoff, in the context of uncertainties in future precipitation. We find that the physiological effect of doubled carbon dioxide concentrations on plant transpiration increases simulated global mean runoff by 6 per cent relative to pre-industrial levels; an increase that is comparable to that simulated in response to radiatively forced climate change (11+/-6 per cent). Assessments of the effect of increasing carbon dioxide concentrations on the hydrological cycle that only consider radiative forcing will therefore tend to underestimate future increases in runoff and overestimate decreases. This suggests that freshwater resources may be less limited than previously assumed under scenarios of future global warming, although there is still an increased risk of drought. Moreover, our results highlight that the practice of assessing the climate-forcing potential of all greenhouse gases in terms of their radiative forcing potential relative to carbon dioxide does not accurately reflect the relative effects of different greenhouse gases on freshwater resources.

C. Textor, M. Schulz, S. Guibert, S. Kinne, Y. Balkanski, S. Bauer, T. Berntsen, T. Berglen, O. Boucher, M. Chin, F. Dentener, T. Diehl, J. Feichter, D. Fillmore, P. Ginoux, S. Gong, A. Grini, J. Hendricks, L. Horowitz, P. Huang, I. S. A. Isaksen, T. Iversen, S. Kloster, D. Koch, A. Kirkevâg, J. E. Kristjansson, M. Krol, A. Lauer, J. F. Lamarque, X. Liu, V. Montanaro, G. Myhre, J. E. Penner, G. Pitari, M. S. Reddy, Ø. Seland, P. Stier, T. Takemura, and X. Tie. The effect of harmonized emissions on aerosol properties in global models an AeroCom experiment. Atmospheric Chemistry & Physics, 7:4489-4501, August 2007. [ bib | ADS link ]

The effects of unified aerosol sources on global aerosol fields simulated by different models are examined in this paper. We compare results from two AeroCom experiments, one with different (ExpA) and one with unified emissions, injection heights, and particle sizes at the source (ExpB). Surprisingly, harmonization of aerosol sources has only a small impact on the simulated inter-model diversity of the global aerosol burden, and consequently global optical properties, as the results are largely controlled by model-specific transport, removal, chemistry (leading to the formation of secondary aerosols) and parameterizations of aerosol microphysics (e.g., the split between deposition pathways) and to a lesser extent by the spatial and temporal distributions of the (precursor) emissions. The burdens of black carbon and especially sea salt become more coherent in ExpB only, because the large ExpA diversities for these two species were caused by a few outliers. The experiment also showed that despite prescribing emission fluxes and size distributions, ambiguities in the implementation in individual models can lead to substantial differences. These results indicate the need for a better understanding of aerosol life cycles at process level (including spatial dispersal and interaction with meteorological parameters) in order to obtain more reliable results from global aerosol simulations. This is particularly important as such model results are used to assess the consequences of specific air pollution abatement strategies.

T. Ngo-Duc, K. Laval, G. Ramillien, J. Polcher, and A. Cazenave. Validation of the land water storage simulated by Organising Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) with Gravity Recovery and Climate Experiment (GRACE) data. Water Resources Research, 43:4427, April 2007. [ bib | DOI | ADS link ]

The Gravity Recovery and Climate Experiment (GRACE) mission provides measurements of spatiotemporal change in land water storage that may improve simulation results of land surface models (LSMs). We show that a transfer scheme recently developed within the Organising Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) LSM significantly improves the simulated land water storage. Over large tropical rivers basins, model results without the transfer scheme provide significantly smaller amplitudes of water storage than observed by GRACE. Including the transfer scheme that accounts for water stored in the river systems and aquifers during its transfer to the oceans leads to predicted land water storage that are comparable to GRACE observations. Water stored in aquifers contributes about half the seasonal variation of water storage over large basins such as the Amazon, Congo, Yangtze, Ganges, Brahmaputra, and Mekong.

O. Coindreau, F. Hourdin, M. Haeffelin, A. Mathieu, and C. Rio. Assessment of Physical Parameterizations Using a Global Climate Model with Stretchable Grid and Nudging. Monthly Weather Review, 135:1474, 2007. [ bib | DOI | ADS link ]