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lmd_EMC31987_abstracts.html

1987 .

(6 publications)

A. Henderson-Sellers, G. SéZe, F. Drake, and M. Desbois. Surface-observed and satellite-retrieved cloudiness compared for the 1983 ISCCP Special Study Area in Europe. Journal of Geophysical Research, 92:4019-4033, April 1987. [ bib | DOI | ADS link ]

A comparison has been undertaken between surface-observed total low- and high-cloud amount and retrievals from METEOSAT radiance data made using the cluster technique of Desbois et al. (1982). The aim of the study was to establish whether surface-observed cloud information could be usefully exploited to benefit satellite-based cloud retrievals. Observations from 124 surface stations at 1200 UT for the 20-day period from July 22 to August 10, 1983, were compared with retrievals made from METEOSAT radiances measured at 1130 UT. The comparisons for total and low-cloud amount are made for France and southern Britain. The high-cloud amount comparison was limited to 34 stations in southern Britain. The location and time period were selected to coincide with one of the regions designated for special study in the International Satellite Cloud Climatology Project (ISCCP) (Schiffer, 1982). For total cloud amount, 29% of the retrievals were fully in agreement with the surface observations and 64% of differences were within 1 okta (1 eighth of sky cover). In the case of layer cloud amounts, 64% of the low-cloud amount differences and 50% of the high-cloud amount differences were within 1 okta, although many of these successes (71% in the low-cloud amount) were for cases of totally clear or totally cloudy skies. Surface observations, which offer the only source of accurate low-cloud amount evaluation in any multilayered situation, were found to identify thin cirrus which was not detected by the satellite retrieval and to detect small gaps in cloud decks and small clouds missed by the satellite retrieval. In addition, cloud retrievals in coastal locations seemed to be more successfully accomplished by surface observers than by the satellite retrieval algorithm used here, which does not take into account land-sea partition.

G. Seze and M. Desbois. Cloud Cover Analysis from Satellite Imagery Using Spatial and Temporal Characteristics of the Data. Journal of Applied Meteorology, 26:287-303, February 1987. [ bib | DOI | ADS link ]

New developments of a cloud classification scheme based on histogram clustering by a statistical method are presented. Use of time series of geostationary satellite pictures as well as for construction of composite images representative of the surface properties and then for the identification of significative cloud classes is discussed. Spatial variances are introduced as additional parameters of the classification, with the aim to better separate clouds from the surface and the different kinds of more or less homogeneous cloud classes.

L. Picon, M. Desbois, and G. Sèze. Use of meteosat ISCCP B2 data for the study of interannual variations of climatic elements in Africa. Advances in Space Research, 7:199-202, 1987. [ bib | DOI | ADS link ]

Composite monthly images corresponding to West African rainy seasons of 1983, 1984, and 1985, have been constructed from ISCCP B2 Meteosat data. Average and standard deviation images from thermal infrared and water vapor channels are studied. In the thermal infrared, differences between the three years appear principally in the mean structure of the ITCZ, North-South extend, northward boundary, longitudinal variations of the convection. In the water vapor channel, well defined “dry” areas appear, showing the location and extent of subsidence regions on a large scale. These locations and extents also vary from year to year.

T. Kayiranga, M. Desbois, and L. Picon. Diurnal variations of convective cloudiness in tropical Africa observed with Meteosat ISCCP B2 data. Advances in Space Research, 7:163-166, 1987. [ bib | DOI | ADS link ]

Monthly composite images have been constructed from 8 times of the day from the ISCCP B2 Meteosat data set. Average and standard deviation images in IR and WV channels have been constructed at first. These images allow to describe the mean diurnal cycle of convection over Africa, and show that this cycle is strongly influenced by the orography. Comparisons between two very different rainy seasons in West Africa, 1983 and 1985, show some differences in the diurnal cycles.

F. Drake, G. Sèze, M. Desbois, and A. Henderson-Sellers. European ISCCP sector surface and satellite retrieved cloud comparison. Advances in Space Research, 7:159-161, 1987. [ bib | DOI | ADS link ]

A comparison between surface-observed total, low and high cloud amount and retrievals from METEOSAT radiance data made using the cluster technique of Desbois et al. has been undertaken. Observations for 12.00 GMT for the 20 day period 22nd July to 10th August 1983 were compared with retrievals made from METEOSAT radiances measured at 11.30 GMT. The comparisons for total and low cloud amount were made for 204 stations covering France, southern Britain and West Germany although high cloud amount comparisons were not possible for France, so only 114 stations were used. The location and time period were selected to coincide with one of the regions designated for the validation phase of the International Satellite Cloud Climatology Project, ISCCP. The results are generally good: for total cloud amount 30% of retrievals were fully in agreement and 64% of the differences were within +/-1 okta. As anticipated, the surface observations offered additional information oin low cloud cover in multi-layer situations. Surface observers were also found to identify thin cirrus which was not detected by the satellite retrieval and to detect small gaps in cloud decks and small clouds missed by the satellite retrieval.

G. Sèze and W. Rossow. Time-cumulated visible and infrared histograms used as descriptor of cloud cover. Advances in Space Research, 7:155-158, 1987. [ bib | DOI | ADS link ]

To study the statistical behavior of clouds for different climate regimes, the spatial and temporal stability of VIS-IR bi-dimensional histograms is tested. Also, the effect of data sampling and averaging on the histogram shapes is considered; in particular the sampling strategy used by the International Satellite Cloud Climatology Project is tested.

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