Relationship Between Upper-Ocean Heat Content in the Tropical Indian Ocean and Summer Precipitation in China

An analysis of the Ishii ocean heat content (OHC) in the tropical Indian Ocean from the surface to 700-m depth shows that the OHC changes dramatically on the interannual timescale in the Indian Ocean. The first mode of empirical orthogonal function (EOF1) of the OHC shows that there is a strong air-sea interaction pattern in the Indian Ocean with a positive (negative) loading in the east and a negative (positive) loading in the west. This seesaw oscillation pattern influences the summer precipitation in China with a North-South reversed distribution. Composite analysis shows that during a positive (negative) OHC episode, an anomalous cyclonic (anticyclonic) circulation over the western Pacific and South China weakens (enhances) the monsoonal northward flow in the lower troposphere; meanwhile, anomalous meridional circulation connects the descending (ascending) branch over the Southeast Indian Ocean and the ascending (descending) branch in South China as well as a descending (ascending) branch over North China. Analysis of the mechanism behind these features suggests that (1) the accumulation of OHC-induced vorticity is related to the wave activity over the mid-latitudes and that (2) the meridional teleconnection induced by the Indo-Pacific air-OHC interaction appears over East Asia and the western Pacific. Both of these patterns can cause summer precipitation anomalies in China.