Subseasonal variation of winter rainfall anomalies over South China during the mature phase of super El Niño events

Abstract

The authors explore the intraseasonal oscillation (ISO) of rainfall anomalies in South China, the related circulation regimes, and discuss the possible causes of the large variability of the positive rainfall anomalies over South China during the winter of the 1982/83, 1997/98 and 2015/16 super El Niño events. Case-by-case analysis shows that the 10–20-day ISO associated with the successive heavy rainfall events lead to the positive anomalies of winter rainfall in the three winters. Meanwhile, the 20–50-day ISO is relatively stronger in the winter of 1982/83 and 2015/16 but weaker in the winter of 1997/98. Except for a different speed, the anomalies of the 200-hPa wave train associated with the two ISOs both propagate eastward along the westerly jet between 20 N and 30 N. In the winter of 1982/83 and 2015/16, when the upper-level subseasonal wave trains in different periods pass through South China, the in-phase enhancement of upper-level divergences and the pumping effect could induce the persistent heavy rainfall events, which facilitate the stronger seasonal-mean rainfall. Although the 10–20-day ISO alone in the winter of 1997/98 could cause the higher-frequency rainfall events, the weaker 20–50-day ISO attenuates the anomalies of the South China winter rainfall. Therefore, the joint effects of the 10–20- and 20–50-day ISOs are critical for the larger amount of above-normal rainfall over South China during the mature phase of super El Niño events.

Keywords

• Super El Niño event
• South China
• winter rainfall
• Intraseasonal Oscillation (ISO)