IOD, ENSO, and seasonal precipitation variation over Eastern China

Abstract

This study investigates seasonal precipitation variation over eastern China associated with Indian Ocean Dipole (IOD) forcing and emphasizes the distinction of such responses to preceding IOD events compared with responses to El Niño–Southern Oscillation (ENSO). Precipitation evolution patterns in response to the IOD from autumn to the ensuing summer are derived from singular value decomposition analysis, revealing that the IOD causes a large portion of the seasonal variation in precipitation over eastern China in the simultaneous autumn and time-lagged summer. The difference in the impacts associated with the IOD and ENSO revealed by multiple linear regression and partial correlation analysis is that the IOD contributes mainly to abnormal precipitation in South China during autumn and in the region between the Yangtze River and Yellow River during the ensuing summer; while ENSO primarily boosts precipitation over eastern China during winter and spring. The distinctive effects of the IOD on the ensuing summer precipitation contrast with the less significant signals related to ENSO during the ensuing summer. Such precipitation responses correspond to an anomalous anticyclonic circulation pattern around the South China Sea, which is sustained by direct IOD forcing during autumn and winter and an SST cooling pattern triggered by the IOD over the central equatorial Pacific during the ensuing spring and summer. The calculation of wave activity flux and anomalous AGCM model experiments further confirm the importance of the direct heating of the IOD during autumn and winter and the indirect heating sink over the central Pacific during the ensuing spring and summer for modulating the seasonal variation in precipitation over eastern China.