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2015 .

(4 publications)

J. H. Jiang, H. Su, C. Zhai, T. Janice Shen, T. Wu, J. Zhang, J. N. S. Cole, K. von Salzen, L. J. Donner, C. Seman, A. Del Genio, L. S. Nazarenko, J.-L. Dufresne, M. Watanabe, C. Morcrette, T. Koshiro, H. Kawai, A. Gettelman, L. Millán, W. G. Read, N. J. Livesey, Y. Kasai, and M. Shiotani. Evaluating the Diurnal Cycle of Upper-Tropospheric Ice Clouds in Climate Models Using SMILES Observations. Journal of Atmospheric Sciences, 72:1022-1044, March 2015. [ bib | DOI | ADS link ]

H. Pang, S. Hou, A. Landais, V. Masson-Delmotte, F. Prie, H. C. Steen-Larsen, C. Risi, Y. Li, J. Jouzel, Y. Wang, J. He, B. Minster, and S. Falourd. Spatial distribution of 17O-excess in surface snow along a traverse from Zhongshan station to Dome A, East Antarctica. Earth and Planetary Science Letters, 414:126-133, March 2015. [ bib | DOI | ADS link ]

The influence of temperature on the triple isotopic composition of oxygen in water is still an open question and limits the interpretation of water isotopic profiles in Antarctic ice cores. The main limitation arises from the lack of 17O-excess measurements in surface snow and especially for remote regions characterized by low temperature and accumulation rate. In this study, we present new 17O-excess measurements of surface snow along an East Antarctic traverse, from the coastal Zhongshan station to the highest point of the Antarctic ice sheet at Dome A. The 17O-excess data significantly decrease inland, with a latitudinal gradient of - 1.33 0.41 per meg/degree, an altitudinal gradient of - 0.48 0.17 permeg / 100 m, and a temperature gradient of 0.35 0.11 permeg /degC. Theoretical calculations performed using a Rayleigh model attribute this inland decrease to kinetic isotopic fractionation occurring during condensation from vapor to ice under supersaturation conditions at low temperatures. However, large heterogeneity of 17O-excess in Antarctic precipitation cannot only be explained by temperature at condensation and/or influences of relative humidity in the moisture source region.

R. Locatelli, P. Bousquet, F. Hourdin, M. Saunois, A. Cozic, F. Couvreux, J.-Y. Grandpeix, M.-P. Lefebvre, C. Rio, P. Bergamaschi, S. D. Chambers, U. Karstens, V. Kazan, S. van der Laan, H. A. J. Meijer, J. Moncrieff, M. Ramonet, H. A. Scheeren, C. Schlosser, M. Schmidt, A. Vermeulen, and A. G. Williams. Atmospheric transport and chemistry of trace gases in LMDz5B: evaluation and implications for inverse modelling. Geoscientific Model Development, 8:129-150, February 2015. [ bib | DOI | ADS link ]

Representation of atmospheric transport is a major source of error in the estimation of greenhouse gas sources and sinks by inverse modelling. Here we assess the impact on trace gas mole fractions of the new physical parameterizations recently implemented in the atmospheric global climate model LMDz to improve vertical diffusion, mesoscale mixing by thermal plumes in the planetary boundary layer (PBL), and deep convection in the troposphere. At the same time, the horizontal and vertical resolution of the model used in the inverse system has been increased. The aim of this paper is to evaluate the impact of these developments on the representation of trace gas transport and chemistry, and to anticipate the implications for inversions of greenhouse gas emissions using such an updated model. <BR /><BR /> Comparison of a one-dimensional version of LMDz with large eddy simulations shows that the thermal scheme simulates shallow convective tracer transport in the PBL over land very efficiently, and much better than previous versions of the model. This result is confirmed in three-dimensional simulations, by a much improved reproduction of the radon-222 diurnal cycle. However, the enhanced dynamics of tracer concentrations induces a stronger sensitivity of the new LMDz configuration to external meteorological forcings. At larger scales, the inter-hemispheric exchange is slightly slower when using the new version of the model, bringing them closer to observations. The increase in the vertical resolution (from 19 to 39 layers) significantly improves the representation of stratosphere/troposphere exchange. Furthermore, changes in atmospheric thermodynamic variables, such as temperature, due to changes in the PBL mixing modify chemical reaction rates, which perturb chemical equilibriums of reactive trace gases. <BR /><BR /> One implication of LMDz model developments for future inversions of greenhouse gas emissions is the ability of the updated system to assimilate a larger amount of high-frequency data sampled at high-variability stations. Others implications are discussed at the end of the paper.

A. Berg, B. R. Lintner, K. Findell, S. I. Seneviratne, B. van den Hurk, A. Ducharne, F. Chéruy, S. Hagemann, D. M. Lawrence, S. Malyshev, A. Meier, and P. Gentine. Interannual Coupling between Summertime Surface Temperature and Precipitation over Land: Processes and Implications for Climate Change*. Journal of Climate, 28:1308-1328, February 2015. [ bib | DOI | ADS link ]

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