Influence of strong South Atlantic Ocean Dipole on the Central African rainfall’s system

• Published in: Climate dynamics 2024, Vol.62 (1), p.1-16
• Main Authors: Nana, Hermann N., Tanessong, Roméo S., Tchotchou, Lucie A. Djiotang, Tamoffo, Alain T., Moihamette, Foupouapegnigni, Vondou, Derbetini A.
• Format: Article
• Language: English
• Subjects: Advection; Anomalies; Atmospheric circulation; Climate; Climatology; Cold; Convergence; Dipoles; Earth and Environmental Science; Earth Sciences; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; Geophysics/Geodesy; Influence; Moisture; Oceanography; Oceans; Precipitation; Rain; Rainfall; Rainfall anomalies; Rainfall variability; Regions; Seasons; Southern Oscillation; Variability
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-023-06892-7

This study examines the interlinkages between the South Atlantic Ocean Dipole (SAOD) and Central Africa (CA) rainfall variability from June to August, spanning from 1981 to 2018, using observational and reanalysis datasets. The results show that during positive SAOD events termed pSAOD, positive (negative) rainfall anomalies feature the southwestern CA termed zone I (the rest of CA landmass, termed zone II) more pronounced in reanalysis data. The reverse rainfall anomalies’ pattern characterises negative SAOD events termed nSAOD. The relationship between CA rainfall variability and SAOD strengthens when the signal of El Niño-Southern Oscillation (ENSO) is removed. However, the impact of ENSO on the SAOD is contrasted between the northern and southern CA, so that ENSO compensates for the reduced rainfall associated with the SAOD north of 10°N. South of 10°N, ENSO attenuates wetness over the southwestern zone, and reinforces the dryness over the southeastern zone. During the pSAOD events, increased precipitation is associated with increased moisture convergence over zone I, with advection originating from neighbouring oceanic regions. At the same time, convergent moisture towards zone II is weak and recirculates towards southern Africa and does not contribute to moistening the region. However, during nSAOD, zone I instead experiences strong moisture divergence, whereas zone II is a sink of moisture convergence originating from zone I and from Sahelian and west African regions. In general, the atmospheric circulation seems better developed throughout the tropospheric column during nSAOD events than during pSAOD events and would suggest strong modulating impacts of regional-and local-scale processes in the rainfall variability.