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lmd_EMC31993_abstracts.html

1993 .

(4 publications)

R. D. Cess, M.-H. Zhang, G. L. Potter, H. W. Barker, R. A. Colman, D. A. Dazlich, A. D. del Genio, M. Esch, J. R. Fraser, V. Galin, W. L. Gates, J. J. Hack, W. J. Ingram, J. T. Kiehl, A. A. Lacis, H. Le Treut, Z.-X. Li, X.-Z. Liang, J.-F. Mahfouf, B. J. McAvaney, V. P. Meleshko, J.-J. Morcrette, D. A. Randall, E. Roeckner, J.-F. Royer, A. P. Sokolov, P. V. Sporyshev, K. E. Taylor, W.-C. Wang, and R. T. Wetherald. Uncertainties in Carbon Dioxide Radiative Forcing in Atmospheric General Circulation Models. Science, 262:1252-1255, November 1993. [ bib | DOI | ADS link ]

Global warming, caused by an increase in the concentrations of greenhouse gases, is the direct result of greenhouse gas-induced radiative forcing. When a doubling of atmospheric carbon dioxide is considered, this forcing differed substantially among 15 atmospheric general circulation models. Although there are several potential causes, the largest contributor was the carbon dioxide radiation parameterizations of the models.

E. Nesme-Ribes, E. N. Ferreira, R. Sadourny, H. Le Treut, and Z. X. Li. Solar dynamics and its impact on solar irradiance and the terrestrial climate. Journal of Geophysical Research, 98:18923, November 1993. [ bib | DOI | ADS link ]

Among the various uncertainties present in climate modeling, the variability of total solar irradiance is not one of the least. For lack of any direct measure of the solar irradiance in the past, substitutes are needed. However, the difficulties are twofold: (1) the reliability of the proxies and (2) the need for some physical mechanism relating these proxies to the solar luminosity. On the basis of a better understanding of the solar machinery we can now propose a plausible scenario connecting the exchanges of energy between the various reservoirs: magnetic, thermal, gravitational, and kinetic. In the present paper we discuss the available proxies and suggest a way to reconstruct total solar irradiance over the past four centuries. The response of the Laboratoire de Meteorologie Dynamique atmospheric general circulation model to magnetoconvective solar forcing during the Maunder minimum is discussed. The simulated cooling appears to be compatible with temperature data from the Little Ice Age; in addition, it is found that variations of globally homogeneous external forcing parameters, like incoming solar flux or greenhouse gas loading, yield climate responses with very similar geographical patterns.

F. Hourdin, P. Le van, F. Forget, and O. Talagrand. Meteorological Variability and the Annual Surface Pressure Cycle on Mars. Journal of Atmospheric Sciences, 50:3625-3640, November 1993. [ bib | DOI | ADS link ]

N. I. Ducoudré, K. Laval, and A. Perrier. SECHIBA, a New Set of Parameterizations of the Hydrologic Exchanges at the Land-Atmosphere Interface within the LMD Atmospheric General Circulation Model. Journal of Climate, 6:248-273, February 1993. [ bib | DOI | ADS link ]

A simple parameterization of the hydrologic exchanges between the soil-vegetation system and the atmosphere (SECHIBA) has been developed for use within atmospheric general circulation models (AGCM).For each grid box of the model, eight land surface types (bare soil plus seven vegetation classes) are defined, each of them covering a fractional area of the grid box and allowed to be found simultaneously. Over each of these covers the transfers are computed: evaporation from soil, transpiration from plants through a resistance defined by the concepts of stomatal resistance and architectural resistance, and interception loss from the water reservoir over the canopy. These fluxes are then averaged over the grid box to derive the total amount of water vapor that is transferred to the first atmospheric level of the AGCM. Parameterization of soil water allows for the moistening of an upper layer, of variable depth, during a rainfall event.This new scheme is quite simple and requires prescription of a restricted number of parameters: seven for each class of vegetation and four for the soil. Nevertheless, it is demonstrated that the latent heat fluxes it simulates are quite comparable to the ones simulated by the Biosphere-Atmosphere Transfer Scheme or calculated by Shuttleworth over the tropical rainforest of the Reserva Ducke (Amazon), with no tuning involved.

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