The Weakening Relationship between ENSO and the South China Sea Summer Monsoon Onset in Recent Decades

• Published in: Advances in atmospheric sciences Vol. 39; no. 3; pp. 443 - 455
• Main Authors: Hu, Peng, Chen, Wen, Chen, Shangfeng, Wang, Lin, Liu, Yuyun
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01-03-2022; Springer Nature B.V; College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China; Center for Monsoon System Research,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100190,China%Center for Monsoon System Research,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100190,China
• Subjects: Annual variations; Atmospheric Sciences; Earth and Environmental Science; Earth Sciences; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; Geophysics/Geodesy; Interannual oscillation; Interannual variability; Interannual variations; Intraseasonal oscillation; La Nina; Meteorology; Monsoon onset; Monsoons; Original Paper; Oscillations; Southern Oscillation; Summer; Summer monsoon; Tropical circulation; Tropical climate; Walker circulation; Wind; South China Sea; 夏季风爆发; South China Sea; ENSO; interdecadal change; 南海; 年代际变化; summer monsoon onset; 厄尔尼诺-南方涛动
• ISSN: 0256-1530; 1861-9533
• DOI: 10.1007/s00376-021-1208-6

The El Niño-Southern Oscillation (ENSO) is traditionally regarded as the most important factor modulating the interannual variation of the South China Sea summer monsoon (SCSSM) onset. A preceding El Niño (La Niña) usually tends to be followed by a delayed (an advanced) monsoon onset. However, the close relationship between ENSO and SCSSM onset breaks down after the early-2000s, making seasonal prediction very difficult in recent years. Three possible perspectives have been proposed to explain the weakening linkage between ENSO and SCSSM onset, including interdecadal change of the ENSO teleconnection (i.e., the Walker circulation), interferences of other interannual variability (i.e., the Victoria mode), and disturbances on intraseasonal time scales (i.e., the quasi-biweekly oscillation). By comparing the epochs of 1979–2001 and 2002–19, it is found that the anomalous tropical Walker circulation generated by ENSO is much weaker in the latter epoch and thus cannot deliver the ENSO signal to the SCSSM onset. Besides, in recent years, the SCSSM onset is more closely linked to extratropical factors like the Victoria mode, and thus its linkage with ENSO becomes weaker. In addition to these interannual variabilities, the intraseasonal oscillations like the quasi-biweekly oscillation can disrupt the slow-varying seasonal march modulated by ENSO. Thus, the amplified quasi-biweekly oscillation may also contribute to the weakening relationship after the early-2000s. Given the broken relationship between ENSO and SCSSM onset, the extratropical factors should be considered in order to make skillful seasonal predictions of SCSSM onset, and more attention should be paid to the extended-range forecast based on intraseasonal oscillations.