Ma Tianjiao, Chen Wen, Feng Juan, Wu Renguang
Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100190, China.
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
Sci Rep. 2018 Sep 20;8(1):14107. doi: 10.1038/s41598-018-32492-1.
The present study investigates the modulation of the East Asian winter monsoon (EAWM) in the impacts of El Niño on the wintertime rainfall anomalies in southeastern China. Here, the variability of the EAWM that is independent of ENSO is considered, which is referred to as EAWM with a strong EAWM denoting anomalous northerly winds. Results demonstrate that strong (weak) EAWM weakens (enhances) the positive rainfall anomalies in southeastern China induced by El Niño, because anomalous downward motion over the western North Pacific (WNP) associated with El Niño is weakened (strengthened) by strong (weak) EAWM. The modulated convective activity over the WNP, on the one hand, changes the anomalous local Hadley circulation associated with El Niño. When El Niño is combined with strong (weak) EAWM, anomalous local Hadley circulation is weak (strong) and the resultant anomalous upward motion is weak (strong) over southeastern China, leading to small (larger) positive rainfall anomalies there. On the other hand, the modulated WNP convective activity induces different low-level atmospheric responses to El Niño. During an El Niño winter with strong (weak) EAWM, the weak (strong) anomalous suppressed convection produces a weak (strong) and insignificant (significant) anomalous low-level WNP anticyclone, resulting in correspondingly insignificant (significant) rainfall anomalies in southeastern China. Results from a linear baroclinic model further suggest that the different low-level atmospheric responses over WNP are mainly induced by different diabatic heating associated with El Niño under different EAWM conditions.
本研究调查了厄尔尼诺对中国东南部冬季降水异常影响中东亚冬季风（EAWM）的调制作用。在此，考虑了与ENSO无关的EAWM变率，其中强EAWM表示异常北风，即独立于ENSO的EAWM。结果表明，强（弱）EAWM会减弱（增强）厄尔尼诺引起的中国东南部正降水异常，因为与厄尔尼诺相关的北太平洋西部（WNP）上空的异常下沉运动被强（弱）EAWM减弱（增强）。WNP上调制的对流活动一方面改变了与厄尔尼诺相关的局地哈得莱环流异常。当厄尔尼诺与强（弱）EAWM结合时，局地哈得莱环流异常较弱（较强），导致中国东南部上空的异常上升运动较弱（较强），从而那里的正降水异常较小（较大）。另一方面，调制的WNP对流活动会引起对厄尔尼诺不同的低层大气响应。在强（弱）EAWM的厄尔尼诺冬季，较弱（较强）的异常对流抑制产生一个较弱（较强）且不显著（显著）的WNP低层异常反气旋，导致中国东南部相应的降水异常不显著（显著）。一个线性斜压模型的结果进一步表明，WNP上不同的低层大气响应主要是由不同EAWM条件下与厄尔尼诺相关的不同非绝热加热引起的。
