lmd_Li2000_abstracts.html

2000 .

Z. X. Li. Influence of tropical Pacific El Niño on the SST of the Southern Ocean Through Atmospheric Bridge. Geophysical Research Letters, 27:3505-3508, November 2000. [ bib | DOI | ADS link ]

El Niño is a major interannual climate signal resulting from complex ocean-atmosphere interactions in the Tropical Pacific. Its impact on the SST (Sea Surface Temperature) of the Southern Ocean through an atmospheric bridge are investigated with an atmospheric general circulation model coupled to a slab mixed-layer ocean. Simulated results suggest that SST changes in the mid- and high-latitude oceans and the Tropical Indian Ocean can be explained by modifications of heat-flux exchange at the air-sea interface. For the Tropical Atlantic, however, the discrepancy is large, indicating that the oceans dynamics are not negligible.

J.-L. Bertaux, D. Fonteyn, O. Korablev, E. Chassefière, E. Dimarellis, J. P. Dubois, A. Hauchecorne, M. Cabane, P. Rannou, A. C. Levasseur-Regourd, G. Cernogora, E. Quemerais, C. Hermans, G. Kockarts, C. Lippens, M. D. Maziere, D. Moreau, C. Muller, B. Neefs, P. C. Simon, F. Forget, F. Hourdin, O. Talagrand, V. I. Moroz, A. Rodin, B. Sandel, and A. Stern. The study of the martian atmosphere from top to bottom with SPICAM light on mars express. Planetary and Space Science, 48:1303-1320, October 2000. [ bib | DOI | ADS link ]

SPICAM Light is a small UV-IR instrument selected for Mars Express to recover most of the science that was lost with the demise of Mars 96, where the SPICAM set of sensors was dedicated to the study of the atmosphere of Mars (Spectroscopy for the investigation of the characteristics of the atmosphere of mars). The new configuration of SPICAM Light includes optical sensors and an electronics block. A UV spectrometer (118-320 nm, resolution 0.8 nm) is dedicated to Nadir viewing, limb viewing and vertical profiling by stellar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H ₂O, aerosols, atmospheric vertical temperature structure and ionospheric studies. An IR spectrometer (1.2- 4.8 μm, resolution 0.4-1 nm) is dedicated to vertical profiling during solar occultation of H ₂O, CO ₂, CO, aerosols and exploration of carbon compounds (3.5 kg). A nadir looking sensor for H ₂O abundances (1.0- 1.7 μm, resolution 0.8 nm) is recently included in the package (0.8 kg). A simple data processing unit (DPU, 0.9 kg) provides the interface of these sensors with the spacecraft. In nadir orientation, SPICAM UV is essentially an ozone detector, measuring the strongest O ₃ absorption band at 250 nm in the spectrum of the solar light scattered back from the ground. In the stellar occultation mode the UV Sensor will measure the vertical profiles of CO ₂, temperature, O ₃, clouds and aerosols. The density/temperature profiles obtained with SPICAM Light will constrain and aid in the development of the meteorological and dynamical atmospheric models, from the surface to 160 km in the atmosphere. This is essential for future missions that will rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow study of the ionosphere through the emissions of CO, CO ⁺, and CO ₂⁺, and its direct interaction with the solar wind. Also, it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAM Light IR sensor is inherited from the IR solar part of the SPICAM solar occultation instrument of Mars 96. Its main scientific objective is the global mapping of the vertical structure of H ₂O, CO ₂, CO, HDO, aerosols, atmospheric density, and temperature by the solar occultation. The wide spectral range of the IR spectrometer and its high spectral resolution allow an exploratory investigation addressing fundamental question of the possible presence of carbon compounds in the Martian atmosphere. Because of severe mass constraints this channel is still optional. An additional nadir near IR channel that employs a pioneering technology acousto-optical tuneable filter (AOTF) is dedicated to the measurement of water vapour column abundance in the IR simultaneously with ozone measured in the UV. It will be done at much lower telemetry budget compared to the other instrument of the mission, planetary fourier spectrometer (PFS).

F. Chevallier, F. Chéruy, R. Armante, C. J. Stubenrauch, and N. A. Scott. Retrieving the Clear-Sky Vertical Longwave Radiative Budget from TOVS: Comparison of a Neural Network-Based Retrieval and a Method UsingGeophysical Parameters. Journal of Applied Meteorology, 39:1527-1543, September 2000. [ bib | DOI | ADS link ]

At a time when a new generation of satellite vertical sounders is going to be launched (including the Infrared Atmospheric Sounder Interferometer and Advanced Infrared Radiometric Sounder instruments), this paper assesses the possibilities of retrieving the vertical profiles of longwave clear-sky fluxes and cooling rates from the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) radiometers aboard the polar-orbiting National Oceanic and Atmospheric Administration satellites since 1979. It focuses on two different methodologies that have been developed at Laboratoire de Météorologie Dynamique (France). The first one uses a neural network approach for the parameterization of the links between the TOVS radiances and the longwave fluxes. The second one combines the geophysical variables retrieved by the Improved Initialization Inversion method and a forward radiative transfer model used in atmospheric general circulation models. The accuracy of these two methods is evaluated using both theoretical studies and comparisons with global observations.

F. Chéruy and F. Chevallier. Regional and Seasonal Variations of the Clear Sky Atmospheric Longwave Cooling over Tropical Oceans. Journal of Climate, 13:2863-2875, August 2000. [ bib | DOI | ADS link ]

The vertical distribution of the clear sky longwave cooling of the atmosphere over tropical oceans is inferred from three different datasets. Two of the datasets refer to the TIROS-N Operational Vertical Sounder (TOVS) NOAA/NASA Pathfinder project, PathA and PathB, and the last one refers to the ECMWF reanalysis (ERA-15). Differences are identified originating from the temperature and water vapor fields. They affect the geographical distribution of the longwave fields to various degrees. However, the three datasets lead to similar conclusions concerning the sensitivity of the clear sky total longwave cooling to SST variations. For the highest values of the SST (greater than 27degC), positively correlated to the increased efficiency of the longwave trapping (super-greenhouse effect), the atmosphere shows a lesser efficiency to cool radiatively. The atmosphere does reradiate the longwave radiation toward the surface as efficiently as it traps it. This is verified on regional as well as on seasonal scales. Such longwave cooling behavior is due to an increased mid- and upper-tropospheric humidity resulting from convective transports. The three datasets agree with the vertical distribution of the radiative cooling variations from normal to favorable to super-greenhouse effect conditions, except in the boundary layer, where the coarse resolution of the TOVS-retrieved data makes them not reliable in it. In `normal' conditions the cooling uniformly increases over the vertical with the SST. Over 27degC, the cooling is intensified above 400 hPa and reduced between 900 and 400 hPa.

S. Bony, W. D. Collins, and D. W. Fillmore. Indian Ocean Low Clouds during the Winter Monsoon. Journal of Climate, 13:2028-2043, June 2000. [ bib | DOI | ADS link ]

While low-level clouds over the Pacific and Atlantic Oceans have been investigated extensively, low clouds over the Indian Ocean are not as well characterized. This study examines the occurrence of nonoverlapped low clouds over the Indian Ocean during the northeast monsoon using several sources of data. Climatologies derived from surface observations and from the International Satellite Cloud Climatology Project are reviewed. Another cloud climatology is developed using infrared and visible imagery from the Indian geostationary satellite. The new climatology has better spatial and temporal resolution than in situ observations. The three datasets are generally consistent and show several persistent features in the cloud distribution. During January-April, maxima in the occurrence of low clouds occur at subtropical latitudes over the Arabian Sea, the Bay of Bengal, the China Sea, and the southern Indian Ocean. The predominant types of low clouds differ in the northern and southern areas of the Indian Ocean region and China Sea. The Arabian Sea and the Bay of Bengal are covered mostly by cumulus clouds, while the southern Indian Ocean and the China Sea are covered mostly by large-scale stratiform clouds such as stratocumulus. These observations are consistent with atmospheric analyses of temperature, humidity, and stability over the Indian Ocean.

D. Cruette, A. Marillier, J. L. Dufresne, J. Y. Grandpeix, P. Nacass, and H. Bellec. Fast Temperature and True Airspeed Measurements with the Airborne Ultrasonic Anemometer Thermometer (AUSAT). Journal of Atmospheric and Oceanic Technology, 17:1020, 2000. [ bib | DOI | ADS link ]

F. Chevallier, J.-J. Morcrette, A. Chédin, and F. Cheruy. TIGR-like atmospheric-profile databases for accurate radiative-flux computation. Quarterly Journal of the Royal Meteorological Society, 126:777-785, January 2000. [ bib | DOI | ADS link ]

F. Chevallier, J.-J. Morcrette, F. Chéruy, and N. A. Scott. Use of a neural-network-based long-wave radiative-transfer scheme in the ECMWF atmospheric model. Quarterly Journal of the Royal Meteorological Society, 126:761-776, January 2000. [ bib | DOI | ADS link ]