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lmd_Li2001_abstracts.html

2001 .

(7 publications)

X. K. Qiang, Z. X. Li, C. M. Powell, and H. B. Zheng. Magnetostratigraphic record of the Late Miocene onset of the East Asian monsoon, and Pliocene uplift of northern Tibet. Earth and Planetary Science Letters, 187:83-93, April 2001. [ bib | DOI | ADS link ]

Widespread eolian red clay underlying the Plio-Pleistocene loess-palaeosol succession in northern China has been dated magnetostratigraphically back to 8.35 Ma, indicating that the East Asian monsoon started at about the same time as the Indian monsoon. An initial sedimentation rate of 11 m/Myr increased gradually to 17.5 m/Myr by 6 Ma, and then decreased to 6 m/Myr between 5 Ma and 3.5 Ma. A marked increase in sedimentation rate and grain size beginning between 3.5 Ma and 3.1 Ma indicates that the East Asian winter monsoon strengthened at this time, and intensified further after 2.6 Ma. The temporal coincidence of the stronger winter monsoon and the Pliocene uplift of northwestern Tibet just before the onset of the Northern Hemisphere glaciation indicate that the three events could be causally linked.

P. Friedlingstein, L. Bopp, P. Ciais, J.-L. Dufresne, L. Fairhead, H. LeTreut, P. Monfray, and J. Orr. Positive feedback between future climate change and the carbon cycle. Geophysical Research Letters, 28:1543-1546, 2001. [ bib | DOI | ADS link ]

Future climate change due to increased atmospheric CO2 may affect land and ocean efficiency to absorb atmospheric CO2. Here, using climate and carbon three-dimensional models forced by a 1% per year increase in atmospheric CO2, we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of CO2, respectively by 54% and 35% at 4 × CO2. This negative impact implies that for prescribed anthropogenic CO2 emissions, the atmospheric CO2 would be higher than the level reached if climate change does not affect the carbon cycle. We estimate the gain of this climate-carbon cycle feedback to be 10% at 2 × CO2 and 20% at 4 × CO2. This translates into a 15% higher mean temperature increase.

Z. X. Li. Thermodynamic Air-Sea Interactions and Tropical Atlantic SST Dipole Pattern. Physics and Chemistry of the Earth B, 26:155-157, January 2001. [ bib | DOI | ADS link ]

G. L. Liberti, F. Chéruy, and M. Desbois. Land Effect on the Diurnal Cycle of Clouds over the TOGA COARE Area, as Observed from GMS IR Data. Monthly Weather Review, 129:1500, 2001. [ bib | DOI | ADS link ]

K. Ide, H. Le Treut, Z.-X. Li, and M. Ghil. Atmospheric radiative equilibria. Part II: bimodal solutions for atmospheric optical properties. Climate Dynamics, 18:29-49, 2001. [ bib | DOI | ADS link ]

A simple theoretical model of atmospheric radiative equilibrium is solved analytically to help understand the energetics of maintaining Earth's tropical and subtropical climate. The model climate is constrained by energy balance between shortwave (SW) and longwave (LW) radiative fluxes. Given a complete set of SW and LW optical properties in each atmospheric layer, the model yields a unique equilibrium-temperature profile. In contrast, if the atmospheric temperature profile and SW properties are prescribed, the model yields essentially two distinct LW transmissivity profiles. This bimodality is due to a nonlinear competition between the ascending and descending energy fluxes, as well as to their local conversion to sensible heat in the atmosphere. Idealized slab models that are often used to describe the greenhouse effect are shown to be a special case of our model when this nonlinearity is suppressed. In this special case, only one solution for LW transmissivity is possible. Our model's bimodality in LW transmissivity for given SW fluxes and temperature profile may help explain certain features of Earth's climate: at low latitudes the temperature profiles are fairly homogeneous, while the humidity profiles exhibit a bimodal distribution; one mode is associated with regions of moist-and-ascending, the other with dry-and-subsiding air. The model's analytical results show good agreement with the European Centre for Medium-Range Weather Forecasts' reanalysis data. Sensitivity analysis of the temperature profile with respect to LW transmissivity changes leads to an assessment of the low-latitude climate's sensitivity to the “runaway greenhouse” effect.

C. G. Menéndez, A. C. Saulo, and Z.-X. Li. Simulation of South American wintertime climate with a nesting system. Climate Dynamics, 17:219-231, 2001. [ bib | DOI | ADS link ]

A numerical nesting system is developed to simulate wintertime climate of the eastern South Pacific-South America-western South Atlantic region, and preliminary results are presented. The nesting system consists of a large-scale global atmospheric general circulation model (GCM) and a regional climate model (RCM). The latter is driven at its boundaries by the GCM. The particularity of this nesting system is that the GCM itself has a variable horizontal resolution (stretched grid). Our main purpose is to assess the plausibility of such a technique to improve climate representation over South America. In order to evaluate how this nesting system represents the main features of the regional circulation, several mean fields have been analyzed. The global model, despite its relatively low resolution, could simulate reasonably well the more significant large-scale circulation patterns. The use of the regional model often results in improvements, but not universally. Many of the systematic errors of the global model are also present in the regional model, although the biases tend to be rectified. Our preliminary results suggest that nesting technique is a computationally low-cost alternative for simulating regional climate features. However, additional simulations, parametrizations tuning and further diagnosis are clearly needed to represent local patterns more precisely.

E. Chassefière, F. Forget, F. Hourdin, F. Vial, H. Rème, C. Mazelle, D. Vignes, J.-A. Sauvaud, P.-L. Blelly, D. Toublanc, J.-J. Berthelier, J.-C. Cerisier, G. Chanteur, L. Duvet, M. Menvielle, J. Lilensten, O. Witasse, P. Touboul, E. Quèmerais, J.-L. Bertaux, G. Hulot, Y. Cohen, P. Lognonné, J. P. Barriot, G. Balmino, M. Blanc, P. Pinet, M. Parrot, J.-G. Trotignon, M. Moncuquet, J.-L. Bougeret, K. Issautier, E. Lellouch, N. Meyer, C. Sotin, O. Grasset, F. Barlier, C. Berger, P. Tarits, J. Dyment, D. Breuer, T. Spohn, M. Pätzold, K. Sperveslage, P. Gough, A. Buckley, K. Szego, S. Sasaki, S. Smrekar, D. Lyons, M. Acuna, J. Connerney, M. Purucker, R. Lin, J. Luhmann, D. Mitchell, F. Leblanc, R. Johnson, J. Clarke, A. Nagy, D. Young, S. Bougher, G. Keating, R. Haberle, B. Jakosky, R. Hodges, M. Parmentier, H. Waite, and D. Bass. Scientific objectives of the DYNAMO mission. Advances in Space Research, 27:1851-1860, 2001. [ bib | DOI | ADS link ]

DYNAMO is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/ CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for DYNAMO of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Additional data on the internal structure will be obtained by mapping the electric conductivity. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere and water from the planet.

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