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lmd_Li1999_abstracts.html

1999 .

(6 publications)

N. A. Scott, A. Chédin, R. Armante, J. Francis, C. Stubenrauch, J.-P. Chaboureau, F. Chevallier, C. Claud, and F. Cheruy. Characteristics of the TOVS Pathfinder Path-B Dataset. Bulletin of the American Meteorological Society, 80:2679-2702, December 1999. [ bib | DOI | ADS link ]

From 1979 to present, sensors aboard the NOAA series of polar meteorological satellites have provided continuous measurements of the earth's surface and atmosphere. One of these sensors, the TIROS-N Operational Vertical Sounder (TOVS), observes earth-emitted radiation in 27 wavelength bands within the infrared and microwave portions of the spectrum, thereby creating a valuable resource for studying the climate of our planet. The NOAA-NASA Pathfinder program was conceived to make these data more readily accessible to the community in the form of processed geophysical variables. The Atmospheric Radiation Analysis group at the Laboratoire de Météorologie Dynamique of the Centre National de la Recherche Scientifique of France was selected to process TOVS data into climate products (Path-B). The Improved Initialization Inversion (3I) retrieval algorithm is used to compute these products from the satellite-observed radiances. The processing technique ensures internal coherence and minimizes both observational and computational biases. Products are at a 1deg × 1deg latitude-longitude grid and include atmospheric temperature profiles (up to 10 hPa); total precipitable water vapor and content above four levels up to 300 hPa; surface skin temperature; and cloud properties (amount, type, and cloud-top pressure and temperature). The information is archived as 1-day, 5-day, and monthly means on the entire globe; a.m. and p.m. products for each satellite are stored separately. Eight years have been processed to date, and processing continues at the rate of approximately two satellite-months per day of computer time. Quality assessment studies are presented. They consist of comparisons to conventional meteorological data and to other remote sensing datasets.

Z. X. Li, X. H. Li, P. D. Kinny, and J. Wang. The breakup of Rodinia: did it start with a mantle plume beneath South China? Earth and Planetary Science Letters, 173:171-181, November 1999. [ bib | DOI | ADS link ]

Mafic to ultramafic dykes and sills in South China, dated as 8287 Ma old, are identical in age to the 8276 Ma Gairdner Dyke Swarm in Australia, thought to be of mantle plume origin. These intrusive rocks, accompanied by widespread granite intrusions and rapid unroofing at a lateral extent of ca. 1000 km, and followed by continental rifting, are interpreted to indicate the arrival of a plume head centred beneath South China. This interpretation supports the idea that South China lay between Australia and Laurentia in the Rodinia supercontinent, and suggests that Rodinia breakup may have started with a mantle plume which initiated continental rifting at about 820 Ma ago.

S. R. Lewis, M. Collins, P. L. Read, F. Forget, F. Hourdin, R. Fournier, C. Hourdin, O. Talagrand, and J.-P. Huot. A climate database for Mars. Journal of Geophysical Research, 104:24177-24194, October 1999. [ bib | DOI | ADS link ]

A database of statistics which describe the climate and surface environment of Mars has been constructed directly on the basis of output from multiannual integrations of two general circulation models developed jointly at Laboratoire de Météorologie Dynamique du Center National de la Recherche Scientifique, France, and the University of Oxford, United Kingdom, with support from the European Space Agency. The models have been developed and validated to reproduce the main features of the meteorology of Mars, as observed by past spacecraft missions. As well as the more standard statistical measures for mission design studies, the Mars Climate Database includes a novel representation of large-scale variability, using empirical eigenfunctions derived from an analysis of the full simulations, and small-scale variability using parameterizations of processes such as gravity wave propagation. The database may be used as a tool for mission planning and also provides a valuable resource for scientific studies of the Martian atmosphere. The database is described and critically compared with a representative range of currently available observations.

F. Forget, F. Hourdin, R. Fournier, C. Hourdin, O. Talagrand, M. Collins, S. R. Lewis, P. L. Read, and J.-P. Huot. Improved general circulation models of the Martian atmosphere from the surface to above 80 km. Journal of Geophysical Research, 104:24155-24176, October 1999. [ bib | DOI | ADS link ]

We describe a set of two “new generation” general circulation models of the Martian atmosphere derived from the models we originally developed in the early 1990s. The two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations. The vertical resolution near the surface has been refined, and the vertical domain has been extended to above 80 km. These changes are accompanied by the inclusion of state-of-the -art parameterizations to better simulate the dynamical and physical processes near the surface (boundary layer scheme, subgrid-scale topography parameterization, etc.) and at high altitude (gravity wave drag). In addition, radiative transfer calculations and the representation of polar processes have been significantly improved. We present some examples of zonal-mean fields from simulations using the model at several seasons. One relatively novel aspect, previously introduced by Wilson [1997], is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi-global, angular-momentum conserving Hadley cell which has no terrestrial equivalent. Within such a cell the Coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km. This winter polar warming had been observed but not properly modeled until recently. In fact, thermal inversions are generally predicted above one, and often both, poles around 60-70 km. However, the Mars middle atmosphere above 40 km is found to be very model-sensitive and thus difficult to simulate accurately in the absence of observations.

Z.-X. Li. Ensemble Atmospheric GCM Simulation of Climate Interannual Variability from 1979 to 1994. Journal of Climate, 12:986-1001, April 1999. [ bib | DOI | ADS link ]

The climate interannual variability is examined using the general circulation model (GCM) developed at the Laboratoire de Météorologie Dynamique. The model is forced by the observed sea surface temperature for the period 1979-94. An ensemble of eight simulations is realized with different initial conditions. The variability of the Southern Oscillation is studied. The simulated sea level pressure anomalies at both Tahiti and Darwin are realistic compared to observations. It is revealed, however, that the simulated convection activity response to the warm episode of El Niño is too weak over the eastern part of the tropical Pacific. This explains why the simulated Pacific-North American pattern is shifted westward. A global El Niño pattern index is defined and calculated for both the simulation and the National Centers for Environmental Prediction (NCEP) reanalysis data. This serves as a quantitative measure of El Niño's global impact. A singular value decomposition analysis performed with the tropical Pacific sea surface temperature and the Northern Hemisphere 500-hPa geopotential height shows that the model's teleconnection between the Tropics and high latitudes is similar to that of the NCEP reanalysis data.In an exploratory manner, the model's internal variability versus the external forced variability is studied. It is shown that, except for the equatorial strip, the internal model variability is larger than the external variability. An ensemble mean is thus necessary in order to focus on the model's response to external sea surface temperature anomalies. An attempt is also made to evaluate statistically the influence of the ensemble's size on the model's reproducibility. It is shown that, with this particular GCM, at least five realizations are necessary to correctly assess the teleconnection between the Tropics and the Northern Hemisphere extratropics. This dependency on the number of realizations is less for the tropical circulation.

Z. X. Li and H. Le Treut. Transient behavior of the meridional moisture transport across South America and its relation to atmospheric circulation patterns. Geophysical Research Letters, 26:1409-1412, 1999. [ bib | DOI | ADS link ]

The transient behavior of meridional moisture transport across the South American continent is examined with the reanalysis data provided by the European Centre for Medium-range Weather Forecasts (ECMWF). The results show clearly the effects of the valley between the Andes and the Brazilian Plateau in canalizing the southward moisture transport: an intense jet is episodically formed in this valley. The synoptic variability of this low-level jet and its relation to the large-scale atmospheric circulation are studied.

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