The Connection between the Sea Surface Height Anomaly Preceding the Indian Ocean Dipole and Summer Rainfall in China

Abstract

The sea surface height anomaly (SSHA) sig- nals leading the fall Indian Ocean Dipole (IOD) are inves- tigated. The results suggest that, prior to the IOD by one year, a positive SSHA emerges over the western-central tropical Pacific (WCTP), which peaks during winter (January-February-March, JFM), persists into late spring and early summer (April-May-June, AMJ), and becomes weakened later on. An SSHA index, referred as to SSHA_WCTP, is defined as the averaged SSHA over the WCTP during JFM. The index is not only significantly positively correlated with the following-fall (Septem- ber-October-November, SON) IOD index, but also is higher than the autocorrelation of the IOD index crossing the two different seasons. The connection of SSHA_ WCTP with following-summer rainfall in China is then explored. The results suggest that higher (lower) SSHA_ WCTP corresponds to increased (reduced) rainfall over southern coastal China, along with suppressed (increased) rainfall over the middle-lower reaches of the Yangtze River, North China, and the Xinjiang region of north- western China. Mechanistically, following the preced- ing-winter higher (lower) SSHA_WCTP, the South Asia High and the Western Pacific Subtropical High are weak- ened (intensified), which results in the East Asian summer monsoon weakening (intensifying). Finally, the connec- tion between SSHA_WCTP and El Nino-Southern Oscil- lation (ENSO) is analyzed. Despite a significant correla- tion, SSHA_WCTP is more closely connected with sum- mer rainfall. This implies that the SSHA_WCTP index in the preceding winter is a more effective predictor of summer rainfall in comparison with ENSO. 