Impact of intra‐decadal variability of meridional heat transport on the rainfall over Southern Africa during austral summer

• Published in: International journal of climatology Vol. 43; no. 15; pp. 7256 - 7273
• Main Authors: Pai, Rahul U., Parekh, Anant, Halder, Subrota, Chowdary, Jasti S., Gnanaseelan, C.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 15.12.2023; Wiley Subscription Services, Inc
• Subjects: Anticyclonic circulation; Atmospheric conditions; austral summer rainfall; Circulation; Confidence intervals; Convection; Cyclonic circulation; Heat; Heat flux; Heat transfer; Heat transport; Indian Ocean; intra‐decadal variability; Low level; Lower troposphere; Meridional heat transport; Meridional overturning circulation; Moist static energy; Ocean circulation; Ocean currents; Oceans; Precipitation; Pressure anomalies; Rainfall; Rainfall anomalies; Rainfall variability; Sea level anomalies; Sea level pressure; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Southern Africa; Spectrum analysis; Summer; Summer rainfall; Surface temperature; Troposphere; Variability; Water circulation; Indian Ocean; South Africa; Southern Africa
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.8263

The present study examines the impact of intra‐decadal variability of Meridional Heat Transport (MHT) associated with Indian Ocean Shallow Meridional Overturning Circulation (SMOC) on the rainfall variability over Southern Africa (e.g., Zambia, Malawi, Mozambique, south‐eastern Congo, Zimbabwe, southern Tanzania and Madagascar) during austral summer (December to February). Century long ocean reanalysis, atmospheric reanalysis and rainfall observations are used for the study. Spectrum analysis of MHT index and rainfall anomaly displays intra‐decadal (5–7 years) variability significant at 95% confidence level. The oceanic and atmospheric conditions during strong and weak phases of intra‐decadal MHT variability are examined. Strong (weak) MHT years displayed reduction (increase) in Sea Surface Temperature (SST) in southwest Indian Ocean, which are out‐of‐phase with net heat flux but in phase with ocean circulation. The negative (positive) SST anomaly favours positive (negative) sea level pressure anomaly, which supports the low level moisture divergence (convergence) and anticyclonic (cyclonic) circulation in the lower troposphere. This circulation leads to anomalous subsidence (convection) and below (above) normal moist static energy over the study region resulting in below (above) normal convection, that causes negative (positive) rainfall anomaly over the Southern Africa. The association between intra‐decadal variability of MHT associated with SMOC and rainfall over Southern Africa during austral summer are reported for the first time. The study may pave the way for enhanced predictability of intra‐decadal Southern African austral summer rainfall. Study found intra‐decadal variability of austral summer Indian Ocean Meridional heat transport(MHT). Study deduces that SST, MSLP, low level circulation, moist static energy co‐evolution with MHT leads rainfall variability over Southern African countries. MHT intra‐decadal variability drives 30% of austral summer rainfall variability over Zambia, Malawi, northern Mozambique, Zimbabwe, southern Tanzania and Madagascar.