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1999 .

(17 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.

F. Hourdin, J.-P. Issartel, B. Cabrit, and A. Idelkadi. Reciprocity of atmospheric transport of trace species. Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 329:623--628, November 1999. [ bib | DOI | ADS link ]

We present a new approach for the inversion of atmospheric transport of trace species based on the time symmetry of the transport equations. Whereas the classical use of Lagrangian back-tracking only accounts for large-scale transport, our approach can also be applied to other transport processes such as turbulent mixing and linear sources and sinks. It hence provides a simple and systematic way of quantifying the source to detector connection with a wide field of potential applications. We present both theoretical background and numerical illustrations in the context of the European Transport Experiment (ETEX).

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.

C. Martineu, J.-Y. Caneill, and R. Sadourny. Potential Predictability of European Winters from the Analysis of Seasonal Simulations with an AGCM. Journal of Climate, 12:3033--3061, October 1999. [ bib | DOI | ADS link ]

The potential predictability of European winters on the seasonal scale is investigated with the cycle 5.3 version of the Laboratoire de Météorologie Dynamique general circulation model by analyzing the link between atmospheric low-frequency variability and oceanic temperature prescribed as boundary conditions. The word`potential' refers to the assumption that the SST is a priori known in the experiments, and to the use of a model to evaluate the real climate predictability. Eleven simulations of the 1971-92 winters have been performed with the model in SST-forced mode. The methodology used identifies atmospheric clusters by Ward clustering scheme, and atmospheric variability modes over Europe by matrix analysis of relationships between variables. Tropical Pacific surface temperature fluctuations play a prevailing role in the modulation of European variability:the model preferentially simulates negative phases of the North Atlantic Oscillation during El Niño episodes, and a high pressure pattern in western Europe during La Niña ones. These two situations are associated with modulations in the structure of the North Atlantic jet and of the North Atlantic storm track, in agreement with data analyses synthesized in the literature. They confirm the prevailing role of interactions between different scales of the flow in the maintenance of persistent anomalies in the North Atlantic/European area. The strong link simulated by the model between the Pacific-North American oscillation and the North Atlantic Oscillation plays an important role in the propagation of the impact of the forcing from the tropical Pacific to the North Atlantic.For some winters (1971, 1984, 1989, and 1992), the number of simulations has been increased to 30. The normality of the simulated 1984 winter suggests a weak role of the tropical Atlantic in specifying climate anomalies in Europe. The differences in strength of the European response between the 1971 and 1989 La Niña events are linked to differences in the Pacific/North American area. A stronger spread is found in the El Niño case (1992 winter) than in the two La Niña cases. The sensitivity of the response to the number of realizations demonstrates that one has to reach about 15 simulations to obtain a significant response over Europe.

A. Mathieu, G. Seze, C. Guerin, H. Dupuis, and A. Weill. Mesoscale boundary layer clouds structures as observed during the semaphore campaign. Physics and Chemistry of the Earth B, 24:933--938, September 1999. [ bib | DOI | ADS link ]

G. Seze, C. Vanbauce, J. C. Buriez, F. Parol, and P. Couvert. Cloud cover observed simultaneously from POLDER and METEOSAT. Physics and Chemistry of the Earth B, 24:921--926, September 1999. [ bib | DOI | ADS link ]

C. J. Stubenrauch, W. B. Rossow, F. Chéruy, A. Chédin, and N. A. Scott. Clouds as Seen by Satellite Sounders (3I) and Imagers (ISCCP). Part I: Evaluation of Cloud Parameters. Journal of Climate, 12:2189--2213, August 1999. [ bib | DOI | ADS link ]

The improved initialization inversion (3I) algorithms convert TIROS-N Operational Vertical Sounder observations from the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting environmental satellites into atmospheric temperature and water vapor profiles, together with cloud and surface properties. Their relatively good spectral resolution and coverage make IR sounders a very useful tool for the determination of cloud properties both day and night. The iterative process of detailed comparisons between cloud parameters obtained from this global dataset, which is available in the framework of the NOAA-National Aeronautics and Space Administration Pathfinder Program, with time-space-collocated observations of clouds from the recently reprocessed International Satellite Cloud Climatology Project (ISCCP) dataset has led to an improved 3I cloud analysis scheme based on a weighted-2 method described in the second article of this series. This process also provides a first evaluation of the ISCCP reanalysis. The new 3I cloud scheme obtains cloud properties very similar to those from ISCCP for homogeneous cloud scenes. Improvement is especially notable in the stratocumulus regimes where the new 3I scheme detects much more of the low-level cloudiness. Remaining discrepancies in cloud classification can now be explained by differences in cloud detection sensitivity, differences in temperature profiles used, and inhomogeneous or partly cloudy fields. Cirrus cloud identification during the daytime in the recent ISCCP dataset is improved relative to the first version of ISCCP, but is still an underestimate. At night only multispectral IR analyses like 3I can provide cirrus information. The reprocessed ISCCP dataset also shows considerable improvement in cloud cover at higher latitudes. Differences in 3I and ISCCP summertime cloud cover over deserts may be caused by different sensitivities to dust storms.

H. Teitelbaum, M. Moustaoui, R. Sadourny, and F. Lott. Critical levels and mixing layers induced by convectively generated gravity waves during CEPEX. Quarterly Journal of the Royal Meteorological Society, 125:1715--1734, July 1999. [ bib | DOI | ADS link ]

F. Parol, J.-C. Buriez, C. Vanbauce, P. Couvert, G. Seze, P. Goloub, and S. Cheinet. First results of the POLDER ”Earth Radiation Budget and Clouds” operational algorithm. IEEE Transactions on Geoscience and Remote Sensing, 37:1597--1612, May 1999. [ bib | DOI | ADS link ]

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.

O. Boucher. Air traffic may increase cirrus cloudiness. Nature, 397:30--31, January 1999. [ bib | DOI | ADS link ]

High-level cirrus clouds can evolve, from the condensation trails of aircraft, which form as the mixture of warm, humid exhaust gases and colder, drier air exceeds water saturation. In addition, the particles in exhaust plumes from aircraft may allow ice nucleation at lower supersaturations than those required under natural conditions. This mechanism is sensitive to environmental conditions, but may occur downstream of the exhaust aerosol source regions. Here I show that cirrus clouds increased in occurrence and coverage in the main air-traffic flight corridors between 1982 and 1991.

F. Hourdin and A. Armengaud. The Use of Finite-Volume Methods for Atmospheric Advection of Trace Species. Part I: Test of Various Formulations in a General Circulation Model. Monthly Weather Review, 127:822, 1999. [ bib | DOI | ADS link ]

A. Vintzileos, P. Delecluse, and R. Sadourny. On the mechanisms in a tropical ocean-global atmosphere coupled general circulation model. Part II: interannual variability and its relation to the seasonal cycle. Climate Dynamics, 15:63--80, 1999. [ bib | DOI | ADS link ]

The thirty year simulation of the coupled global atmosphere-tropical Pacific Ocean general circulation model of the Laboratoire de Métérologie Dynamique and the Laboratoire d'Océanographie Dynamique et de Climatologie presented in Part I is further investigated in order to understand the mechanisms of interannual variability. The model does simulate interannual events with ENSO characteristics; the dominant periodicity is quasi-biennial, though strong events are separated by four year intervals. The mechanism that is responsible for seasonal oscillations, identified in Part I, is also active in interannual variability with the difference that now the Western Pacific is dynamically involved. A warm interannual phase is associated with an equatorward shift of the ITCZ in the Western and Central Pacific. The coupling between the ITCZ and the ocean circulation is then responsible for the cooling of the equatorial subsurface by the draining mechanism. Cold subsurface temperature anomalies then propagate eastward along the mean equatorial thermocline. Upon reaching the Eastern Pacific where the mean thermocline is shallow, cold subsurface anomalies affect surface temperatures and reverse the phase of the oscillation. The preferred season for efficient eastward propagation of thermocline depth temperature anomalies is boreal autumn, when draining of equatorial waters towards higher latitudes is weaker than in spring by a factor of six. In that way, the annual cycle acts as a dam that synchronizes lower frequency oscillations.

A. Vintzileos, P. Delecluse, and R. Sadourny. On the mechanisms in a tropical ocean-global atmosphere coupled general circulation model. Part I: mean state and the seasonal cycle. Climate Dynamics, 15:43--62, 1999. [ bib | DOI | ADS link ]

The mechanisms responsible for the mean state and the seasonal and interannual variations of the coupled tropical Pacific-global atmosphere system are investigated by analyzing a thirty year simulation, where the LMD global atmospheric model and the LODYC tropical Pacific model are coupled using the delocalized physics method. No flux correction is needed over the tropical region. The coupled model reaches its regime state roughly after one year of integration in spite of the fact that the ocean is initialized from rest. Departures from the mean state are characterized by oscillations with dominant periodicites at annual, biennial and quadriennial time scales. In our model, equatorial sea surface temperature and wind stress fluctuations evolved in phase. In the Central Pacific during boreal autumn, the sea surface temperature is cold, the wind stress is strong, and the Inter Tropical Convergence Zone (ITCZ) is shifted northwards. The northward shift of the ITCZ enhances atmospheric and oceanic subsidence between the equator and the latitude of organized convention. In turn, the stronger oceanic subsidence reinforces equatorward convergence of water masses at the thermocline depth which, being not balanced by equatorial upwelling, deepens the equatorial thermocline. An equivalent view is that the deepening of the thermocline proceeds from the weakening of the meridional draining of near-surface equatorial waters. The inverse picture prevails during spring, when the equatorial sea surface temperatures are warm. Thus temperature anomalies tend to appear at the thermocline level, in phase opposition to the surface conditions. These subsurface temperature fluctuations propagate from the Central Pacific eastwards along the thermocline; when reaching the surface in the Eastern Pacific, they trigger the reversal of sea surface temperature anomalies. The whole oscillation is synchronized by the apparent meridional motion of the sun, through the seasonal oscillation of the ITCZ. This possible mechanism is partly supported by the observed seasonal reversal of vorticity between the equator and the ITCZ, and by observational evidence of eastward propagating subsurface temperature anomalies at the thermocline level.

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