Effect of Summer Arctic Sea Ice on the Reverse August Precipitation Anomaly in Eastern China Between 1998 and 2016

1997/1998 and 2015/2016 El Niño episodes are regarded as two super El Niño events on record and have exerted profound influence on eastern China summer rainfall, as expected. However, on the sub-seasonal time scale, summer rainfall in these two years shows dramatic diversity, although the characteristics of the two super El Niño are similar. This study reveals that the rainfall increases (decreases) over central China (approximately 30°−35°N) and decreases (increases) over southeastern China (approximately south of 25°N) in August 1998 (2016), exhibiting a dipole anomaly pattern over eastern China. Observational analyses indicate that, associated with negative interannual variability of the sea ice area (SIA) over the Barents-Kara Seas (BKS) in July and August, August rainfall shows significantly negative (positive) anomalies over central (southeastern) China. Further analyses reveal that negative SIA anomalies in the BKS induce significantly anomalous upper-level divergence over the polar region, accompanied with anomalous upper-level convergence over the Caspian Sea. The advections of vorticity by these anomalous divergent and convergent flow indicate notable Rossby wave sources near the Caspian Sea, yielding a Rossby wave train propagating eastward to East Asia, which causes positive barotropic and baroclinic energy convection near the exit of the Asian jet stream. The accumulation of perturbation energy in East Asia stimulates the formation of the Pacific-Japan teleconnection, which is favorable for the dipole rainfall anomaly pattern over eastern China. Thus, the positive and negative SIA anomaly over the BKS in 1998 and 2016 may contribute the reverse August precipitation anomaly in eastern China.