Complex principal component analysis of the outgoing longwave radiation observed by meteosat during summer from 1983 to 1985

Abstract

We have applied Complex Principal Component (CPC) analysis to METEOSAT ISCCP B2 data (3 hours resolution) for the IR atmospheric window channel and the Water Vapor (WV) band at 6.5 microns. CPC analysis of such a data set not only reveals the principal features of fluctuation of cloud cover for the region as a whole, but it also is useful for identifying traveling and standing waves over the African Tropical band. Applied to the whole METEOSAT field, CPC analysis describes both diurnal and seasonal fluctuations for the two channels with good stability from year to year. In the African Tropical band, CPC analysis applied in restricted spectral bands (3–4 days and 4–5 days) reveals the existence of traveling waves at particular areas of West Africa with substantial differences between the years 1983 and 84–85. Results of 84–85 are in very good agreement with those of previous studies using conventional meteorological data in 1979. This analysis reveals also the existence of a standing oscillation over Central Africa with a period around 3.5 days and good stability over the three years.