Seminário do Departamento de Ciências Atmosféricas: "The influence of the Madden–Julian Oscillation on summertime precipitation and near-surface air temperature in southern Africa"

his study examines the austral summer (DJF) impact of the Madden–Julian oscillation (MJO) on intraseasonal variability of precipitation and near surface air temperature (SAT) over southern Africa (SAF), defined here as African landmass south 10S. Composite anomaly maps are constructed for each MJO phase using 20–90 day band-pass filtered outgoing longwave radiation (OLR), NCEP–NCAR reanalysis products, and three gridded precipitation datasets (GPCC, CHIRPS and CPC), for the 1982–2020 period. While MJO-related signals are not uniformly strong or statistically significant across all phases, wet (dry) conditions appear generally to occur during phases 6–1 (3–5). Initial convection anomalies emerge over the Angola–Namibia border in phase 5, intensify southeastward in phases 6–7 with tropical–temperate troughs (TTTs)-like structures, and evolve into the South Indian Convergence Zone (SICZ) by phase 1. TTTs – dominant summertime rain-producing synoptic systems – manifest as large-scale NW–SE oriented cloud bands that gradually consolidate into the SICZ, the primary summer rainfall feature in SAF. Despite differences among the precipitation datasets, all three broadly capture the observed OLR anomaly patterns. The appearance of wet conditions during suppressed MJO convection over the African/Indian Ocean sector (phases 5–7) suggests that rainfall is initially triggered by local processes, then amplified by PSA-like induced anomalies linking South America and SAF. During these suppressed phases, reduced cloud cover and subsidence promote surface warming over western SAF, increasing low-level instability and preconditioning the region for rainfall. As PSA-like influences strengthen in phases 8–1, convection intensifies and drives a drop in SAT anomalies, consistent with land–atmosphere feedback mechanism. These findings provide important insights into SAF’s subseasonal climate dynamics and show promise for improving prediction and extending early warning capabilities from a few days to up to 30 days.