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.

Graphical Abstract

摘要

本文主要从季节内振荡的角度出发，采用周期分析、合成分析等方法，针对1982/83、1997/98和2015/16年超强El Niño冬季华南降水异常偏多的可能原因进行探讨。结果表明，沿中纬度西风急流东移的10–20天和20–50天低频波列的共同作用是导致1982/83年和2015/16年超强El Niño冬季华南降水增多的关键因素。由于1997/98年冬季缺少20–50天低频波列活动的参与，仅在10–20天低频大气振荡的影响下，华南冬季平均降水异常少于1982/83和2015/16年。

KEYWORDS:

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

关键词:

• 超强El Niño事件
• 华南
• 冬季降水
• 季节内振荡

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was jointly supported by the Special Fund for Public Welfare Industry [grant number GYHY20140619], the National Natural Science Foundation of China [grant numbers 41475057, 41775052 and 41505049] and the Basic Scientific Research and Operation Foundation of CAMS [grant numbers 2015Z001 and 2017R001].