Influence of Indian Ocean subtropical dipole on spring rainfall over China

Abstract

ABSTRACTThis study investigates the influence of the South Indian Ocean subtropical dipole (IOSD) on spring (March‐April‐May; MAM) rainfall over central‐eastern China (CEC) and its dynamic processes by using station observations of China, Met Office Hadley Centre SST data for the period 1951–2012 and European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis data for the period 1958–2012. It is found that the IOSD event which peaks in the boreal winter can persist to the following spring, with strength slightly weakening. Boreal spring rainfall over CEC, i.e. the middle‐lower reaches of Yangtze River, the Yellow River valley as well as regions between them, has a significant correlation with the IOSD event. When the positive (negative) IOSD event occurs in the previous winter, the CEC is dry (wet) in the spring. One of possible mechanisms that the IOSD affects the China spring rainfall is the modulation of the meridional circulation, especially the Hadley cell in the tropic along 100–120°E. In the positive IOSD years, associated with the cold sea surface temperature anomalies (SSTA) and warm SSTA in the southeastern Indian Ocean (SEIO) and southwestern Indian Ocean, there is anomalous ascent over the equatorial Indian Ocean, whereas downward flows over the SEIO and CEC. The Hadley cell over this region intensifies. Anomalous northerly wind at 850 hPa prevails, preventing wet and warm air flow from the low latitudes, which in turn transports less moisture into CEC and favours decreased rainfall. Meanwhile, the CEC is located at the sinking region of the Hadley cell. The atmosphere is fed by low moisture content over this area, also unfavourable for the occurrence of precipitation. This paper suggests that the SSTA in the southern Indian Ocean can be a good predictor for the China spring precipitation and proposes a possible mechanism for the connection of the mid‐latitude climate variations of both hemispheres induced by air–sea interaction.