The Strengthening and Westward Shift of the Tropical Walker Circulation Driven by Tropical Sea Surface Temperature Forcing

Tropical Walker circulation is one of the most important components in global climate system. In this work, the change of the tropical Pacific Walker Circulation including strength and shift during 1979-2015 are driven by tropical sea surface temperature forcing are discussed. In this study, by combining both satellite and in situ observations, the trend of mass stream function reveals that Walker circulation has significantly strengthened and shift westward. We then evaluate effects of the oceanic forcing on Walker circulation by changing the heat flux from the Ocean to the atmosphere (as well as the sea ice distribution, the Greenhouse Gas and Ozone) in CESM. The results show that the SST change in Atlantic plays a key role in enhancing Walker Circulation while Pacific and Indian Ocean also have some contribution. However, the westward shift is mainly caused by Atlantic and Indian Ocean. In addition, the magnitude of the simulated is much smaller than the magnitude of Reanalysis datasets. These important signs indicate that long-term change of Walker circulation are impacted by Inter-basin Interactions and deserves further investigation and discussion.