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1988 .

(4 publications)

Z. X. Li. A homogeneous z-term series of astrometric latitude observations (January 5, 1962-December 31, 1981). , 75:151-156, October 1988. [ bib | ADS link ]

Optical astrometric data for 1962-1982 has been reduced in order to redetermine the earth rotation parameters. A homogeneous series of z-terms of latitude observations has also been obtained. A total of 1461 z-terms at five-day intervals in the 20 years are given in this paper. The typical precisions of the z-terms are of the order of + or - 0.014 arcsec for the first five years and from + or - 0.008 arecsec to + or - 0.005 arcsec for the following years.

M. Desbois, T. Kayiranga, B. Gnamien, S. Guessous, and L. Picon. Characterization of Some Elements of the Sahelian Climate and Their Interannual Variations for July 1983, 1984 and 1985 from the Analysis of METEOSAT ISCCP Data. Journal of Climate, 1:867-904, September 1988. [ bib | DOI | ADS link ]

METEOSAT infrared and water vapor radiance data from the ISCCP dataset are used to describe climatic characteristics for the months of July 1983, 1984 and 1985, corresponding to very different rainy seasons in Sahelian Africa. Mean cloudiness distribution diurnal cycle of local convection, life cycle of squall lines and drift velocities computed from WV images are studied. The results and their interannual variations are shown to be consistent with analyses from other data sources, including conventional data. The utilization of both kinds of analyses allows not only the validation of the satellite approach but also an improved description of the climatic situations as different parameters are inferred. The main cloud systems and circulation differences between the driest and the wettest months studied are in general agreement with previous observational and simulation studies comparing dry and wet years.

N. Capitaine, Z. X. Li, and S. Z. Nie. Determination of the principal term of nutation from improved BIH astrometric data. Astronomy Astrophysics, 202:306-308, August 1988. [ bib | ADS link ]

New series of the common latitude term z as obtained by Li (1985) from an improved reduction, referred to the IAU - 1976 System of Astronomical Constants and to the IAU - 1980 theory of nutation, of the BIH astrometric data at five-day intervals from 1962 to 1982 are used for deriving the coefficients of the principal term of nutation. The derived coefficients are in good agreement with similar previous astrometric determinations (Feissel and Guinot, 1981; Capitaine and Xiao, 1982) with improved formal errors, which are, in the present work, of the order of 0arcsec.001.

H. Le Treut and Z.-X. Li. Using meteosat data to validate a prognostic cloud generation scheme. Atmospheric Research, 21:273-292, 1988. [ bib | DOI | ADS link ]

We have designed a cloud generation scheme for use in the LMD GCM. It predicts the mixing ratio of the cloud's condensed water as a new prognostic variable. At present it does not fully interact with the radiation schemes, but the aim is to predict the cloud optical properties. We have used the Meteosat/ISCCP data to evaluate this scheme. Such a comparison allows us to place some constraints on the coefficients which are used in the parameterizations, such as the precipitation thresholds for the cloud's liquid water content and the relative variability of water vapour within a grid box. There is generally a good agreement between observed and simulated results, although there appear some discrepancies in the cloud's apparent temperatures.

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