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RESEARCH PRODUCT

Variability of the African convection centre as viewed by outgoing longwave radiation records and relationships with sea-surface temperature patterns

subject

description

International audience; The main African convection centre (ACC) is delimited by the 5"-square areas with outgoing longwave radiation less than 235 W m-' in the domain 17.5°N-17.5"S and 18"W-46"E. Four parameters (latitude and longitude of the centre of gravity, mean intensity, and extension) were analysed during the period June 1974 to December 1991. The relationships between the variability of the ACC and the main sea-surface temperature (SST) patterns were then studied. Correlation and composite analyses demonstrate that the first principal component of SST, representing mainly the variability of the eastern and the central tropical Pacific, is associated strongly with the extension and the mean intensity of the ACC. Both are strongest when cold conditions prevail in the eastern and central Pacific (= La Niiia event) and smallest when warm conditions occur in the eastern and central Pacific (= El Nifio event). This relationship is strongest during the boreal summer, when ACC is elongated from the Atlantic Ocean to the Ethiopian highlands. The second principal component, representative of the southeastern and equatorial Atlantic, is also linked with the extension and the longitudinal position of the ACC (greatest extension/westernmost position when the equatorial and SY' outh Atlantic is anomously warm, and inversely). The intermonthly variability of the latitude seems more noisy and less related to the large-scale SST patterns than the other parameters.