VARIABILITY OF THE AFRICAN CONVECTION CENTER AS VIEWED BY OUTGOING LONGWAVE RADIATION RECORDS AND RELATIONSHIPS WITH SEA-SURFACE TEMPERATURE PATTERNS

The main African convection centre (ACC) is delimited by the 5 degrees square areas with outgoing longwave radiation less than 235 W m(-2) i n the domain 17.5 degrees N-17.5 degrees S and 18 degrees W-46 degrees E. Four parameters (latitude and longitude of the centre of gravity, mean intensity, and extension) were analysed during the period June 19 74 to December 1991. The relationships between the variability of the ACC and the main sea-surface temperature (SST) patterns were then stud ied. Correlation and composite analyses demonstrate that the first pri ncipal component of SST, representing mainly the variability of the ea stern and the central tropical Pacific, is associated strongly with th e extension and the mean intensity of the ACC. Both are strongest when cold conditions prevail in the eastern and central Pacific (= La Nina event) and smallest when warm conditions occur in the eastern and cen tral Pacific(= El Nino event). This relationship is strongest during t he boreal summer, when ACC is elongated from the Atlantic Ocean to the Ethiopian highlands. The second principal component, representative o f the south-eastern and equatorial Atlantic, is also linked with the e xtension and the longitudinal position of the ACC (greatest extension/ westernmost position when the equatorial and South Atlantic is anomous ly 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.