Influences of ENSO and its combination mode on seasonal precipitation over eastern China

Recent studies have shown that ENSO in the lower atmosphere over the tropical Pacific is comprised of two dominant modes. One is the meridionally quasi-symmetric ENSO mode, and the other is the meridionally anti-symmetric combination mode produced by the interaction between the sea surface temperature (SST) annual cycle and ENSO variability. This paper discusses influences of the two different ENSO modes on seasonal precipitation over eastern China. Results show that significant positive precipitation anomalies occur over southwestern China and most of the area of the Yangtze River Valley and southern China in the autumn of El Niño years. Positive precipitation anomalies appear over southern and eastern China, and southeastern part of North China in the winter. Both these two seasonal precipitation anomalies are mainly affected by the ENSO mode. The ENSO-associated SST anomalies lead to anti-cyclonic circulation anomalies over the western North Pacific west of 120°E, which transports more warm and moist air to China and thus is favorable for more precipitation over eastern China. Positive precipitation anomalies occur from southern to northeast China in the following spring, which is mainly attributed to the combination mode of ENSO. The direct ENSO signal over the tropics is confined to the equatorial region and has no significant impact on precipitation over East Asia. The ENSO-associated equatorial anomalies can expand to off-equatorial regions by the combination mode through interaction between ENSO and the annual cycle of SST. The present study suggests that the combination mode has an important impact on ENSO-related precipitation over China during the El Niño decaying spring, which needs to be emphasized in future research and seasonal prediction.