Interactions between synoptic, intraseasonal and interannual convective variability over Southern Africa

International audienceAfter removing the annual cycle, a Principal Component Analysis is applied to the daily Outgoing Longwave Radiation (OLR) anomaly field, used here as a proxy for atmospheric convection. The analysis is carried out over the southern African region (7.5ºE - 70ºE, 10ºS - 40ºS) for austral summer (November through February) for the period 1979-80 to 2006-07. The first 5 Principal Components (PC) are retained. The first two PCs describe spatial patterns oriented north-west to south-east from tropical southern Africa to the mid-latitudes. They are interpreted to be different possible locations for synoptic-scale Tropical-Temperate Troughs (TTT), one dominant rainfall-producing synoptic system in the region. The phase relationship between these two PCs describes a tendency for these TTT to propagate eastwards from southern Africa to the Mozambique Channel and southern Madagascar. The next three PCs describe convective fluctuations respectively located over the north-west, the south and the centre of southern Africa. Their time series are significantly associated with Madden-Julian Oscillation activity in the tropics. However, we find that TTT systems are statistically independent of the MJO, i.e., they are equally liable to occur during any phase of the MJO. Three PCs out of five also show a significant association with El Niño Southern Oscillation (ENSO), confirming that El Niño years mostly coincide with suppressed convection at the intra-seasonal time-scales, a result consistent with its impact on seasonal averages diagnosed in previous studies