Summary of Abstract Submission

Abstract Submission No. IO50-07-0004PresentationOral

MULTIDECADAL VARIABILITY IN THE SOUTHWEST INDIAN OCEAN AFFECTING SOUTHERN AFRICAN CLIMATE

Yushi Morioka*1, Francois Engelbrecht2, Swadhin K. Behera1

1 JAMSTEC/APL, Japan
2 CSIR/NRE, The Republic of South Africa

ABSTRACT :

Multidecadal variability in the southwest Indian Ocean affecting southern African climate is extensively investigated by performing data analysis and coupled general circulation model (CGCM) experiments called SINTEX-F2s. Observation and reanalysis data available since 1982 show a distinct multidecadal variability in the southern African rainfall with a peak positive phase during 1999-2000. The rainfall variability is associated with the anomalous moisture advection from the southwest Indian Ocean, where the anticyclonic anomaly emerges. The circulation anomaly is also accompanied with the above-normal Sea Surface Temperature (SST). Both atmospheric and oceanic anomalies slowly propagate eastward from the South Atlantic to the southwest Indian Ocean. The analysis of mixed-layer heat balance reveals that the warm SST anomaly in the southwest Indian Ocean is mostly due to the eastward advection of the SST anomaly, apparently by the Antarctic Circumpolar Current. The eastward propagation of anticyclonic anomaly and warm SST anomaly is also simulated in the 270-yr outputs of CGCM control experiment, but in a sensitivity experiment, where the SST anomalies in the South Atlantic are suppressed by the model climatology, the eastward propagation of the anticyclonic anomaly becomes unclear. Although remote influences from the tropical Pacific and Antarctica were widely discussed, these results here suggest that the local air-sea interaction in the South Atlantic may also be important for the multidecadal variability in the southwest Indian Ocean affecting southern African climate.