International Satellite Cloud Climatology Project (ISCCP) Data Comments

ISCCP was established in 1982 as part of the World Climate Research Programme (WCRP) to collect and analyze satellite radiance measurements to infer the global distribution of clouds, their properties, and their diurnal, seasonal, and interannual variations. Data collection began on 1 July 1983 and is currently planned to continue through 30 June 2002. The resulting datasets and analysis products are being used to improve understanding and modeling of the role of clouds in climate, with the primary focus being the elucidation of the effects of clouds on the radiation balance. These data can also used to support many other cloud studies, including understanding of the hydrological cycle.

The major improvements and changes from the C2 datasets are detailed in Section 2 of Rossow et al (1999; BAMS, 80:2261-2287). The D2 datasets result from a complete reprocessing of the satellite data using improved algorithms. In addition, more variables are available for analysis.

While many variables are improved from the C2 archive some variables contained within the D2 files may still have problems. Two examples: the variable "CA_High" (Mean high cloud amount) exhibits a trend that may not be real. Specifically, global averages of "CA_High" indicates a decreasing trend from relatively stable 13-14% for 1983-1991 to about 11-12% in the late 90s. Global averages of the variable "PS_TOVS" (TOVS: Mean Surface pressure) exhibits distinct discontinuities in the global average which occur in 1987 and 1998.

Satellite information and "events" that may affect processing may be found at: http://isccp.giss.nasa.gov/docs/docSoftware.html (see: Satellite History Information).

Numerous links which describe the ISCCP Project:http://isccp.giss.nasa.gov/overview.html

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