The El Niño-Southern Oscillation (ENSO) and the variability in the Pacific subtropical highs (PSHs) have major impacts on social and ecological systems. Here we present an Atlantic capacitor effect mechanism to suggest that the Atlantic is a key pacemaker of the biennial variability in the Pacific including that in ENSO and the PSHs during recent decades. The ‘charging' (that is, ENSO imprinting the North Tropical Atlantic (NTA) sea surface temperature (SST) via an atmospheric bridge mechanism) and ‘discharging' (that is, the NTA SST triggering the following ENSO via a subtropical teleconnection mechanism) processes alternate, generating the biennial rhythmic changes in the Pacific. Since the early 1990s, a warmer Atlantic due to the positive phase of Atlantic multidecadal oscillation and global warming trend has provided more favourable background state for the Atlantic capacitor effect, giving rise to enhanced biennial variability in the Pacific that may increase the occurrence frequency of severe natural hazard events.

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The correlation between summertime Niño3.4 index and western North Pacific (WNP) summer monsoon index has strikingly enhanced since the early 1990s, with nonsignificant correlation before the early 1990s but significant correlation afterward. This observed interdecadal change around the 1990s may be associated with more frequent occurrences of central Pacific (CP) El Niño and the interdecadal changes in ENSO-associated SST anomalies. During the post-1990s period (the pre-1990s period), highly noticeable tropical Atlantic (Indian) Ocean SST anomalies tend to co-occur with the summertime Niño3.4 SST anomalies. The concurrent tropical Atlantic (Indian) Ocean SST anomalies could constructively reinforce (destructively mitigate) the WNP monsoon circulation anomalies induced by the summertime Niño3.4 SST, thus boosting (muting) the correlation between summertime Niño3.4 SST and WNP monsoon. In addition, the faster decaying pace of preceding-winter El Niño after the 1990s, which may have been mainly induced by the influences from the spring tropical North Atlantic SST anomalies, could also have contributed to the enhanced correlation between the summertime Niño3.4 index and WNP monsoon. These results suggest that the enhanced influences from the tropical Atlantic SST may have triggered the intensified correlation between summertime ENSO and WNP monsoon since the early 1990s. 摘要 西北太平洋夏季风指数与同时期夏季的Niño3.4指数的相关系数在90年代初期以后出现显著的 增强。两者相关系数的这种年代际变化可能跟中太平洋型ENSO的更频繁发生以及ENSO相关联 的其他热带洋盆的海表面温度异常有关。在90年代之后(之前)，显著的热带大西洋(印度 洋)海表面温度异常倾向伴随夏季Niño3.4海表面温度异常同时出现，并且能够增强(减弱) Niño3.4海表面温度异常所引起的西北太平洋夏季风异常，从而能够增强(减弱)Niño3.4海表 面温度与西北太平洋夏季风指数之间的相关系数。另一方面，由春季北大西洋海表面温度异常 所引起的前一年冬季El Niño更快的衰减速率，也能够促进夏季Niño3.4指数与西北太平洋夏季 风之间相关系数在90年代之后的增加。这些结果表明来自大西洋海温影响的增强可能导致了夏 季Niño3.4指数与西北太平洋夏季风指数之间的相关系数在90年代之后的显著增加。 ARTICLE HISTORY