Origins of Convective Variability over Equatorial Southern Africa during Austral Summer

Abstract

Abstract Analysis of NOAA/NESS outgoing longwave radiation (OLR) over the greater Africa region reveals a large area of low OLR (5°–20°S, 20°E–40°E) during three austral summers (November through February; 1982/83, 1983/84 and 1984/85). This low OLR area is consistent with the climatological rainy area and persistent convective activity. Using OLR as a proxy for synoptic and large-scale cloudiness and convection, OLR standard deviations are computed for the three summers. Highest OLR variability is observed across Africa along 15–17°S, which is about five degrees latitude south of the OLR minimum. Based on the region of maximum OLR standard deviations and minimum mean OLR, a box-average OLR index is derived. Time series of the OLR index for November through February indicate large (±40 W m−2), aperiodic OLR fluctuations within each of the three summers. Outgoing longwave radiation composites are constructed for periods of large OLR changes from negative OLR anomalies (wet conditions) to positive OLR anoma...