Multiyear ENSO Dynamics as Revealed in Observations, Climate Model Simulations, and the Linear Recharge Oscillator
Multiyear ENSO Dynamics as Revealed in Observations, Climate Model Simulations, and the Linear Recharge Oscillator
复制标题
DOI：
10.1175/jcli-d-22-0108.1
复制
发表时间：
2022-12-01
影响因子：
4.9
通讯作者：
Watanabe, Masahiro
中科院分区：
文献类型：
--
作者：
Iwakiri, Tomoki;Watanabe, Masahiro
厄尔尼诺-南方涛动(ENSO)事件偶尔以相同的极地一个接一个地重演，称为多年ENSO。然而，动力学过程还没有被很好地理解。本研究旨在利用观测资料、耦合模式对比计划(CMIP6)第六阶段模式和理论线性再充电振子(RO)模式来阐明多年ENSO的统一机制。我们发现，多年的厄尔尼诺和拉尼娜事件基本上是对称的，除了在强厄尔尼诺之后的多年拉尼娜事件。合成的多年ENSO显示，赤道太平洋的异常海洋热含量(OHC)持续到第一个峰值之后，刺激了另一个事件。这种延长的OHC异常是由于经向Ekman热输送抵消了地转输送引起的补给-放电过程而引起的，否则就会改变OHC异常。在多年的ENSO期间观测到的经向宽海温异常模式是Ekman热输送的原因，年代际变化、副热带过程和ENSO多样性等多种因素调制了ENSO的经向结构。CMIP6多模式集合显示出ENSO经向宽度与多年ENSO出现率之间的显著相关，支持上述机制。用线性RO模式模拟了一个多年的类ENSO振荡，该模式结合了随季节变化的BJerkines增长率和代表Ekman输送效应的弱补给效率。当仅根据地转输送的再分析资料估算补给效率参数时，很少出现多年的ENSO，证实了Ekman输送在延缓补给-排放过程中的重要性。
El Nino-Southern Oscillation (ENSO) events occasionally recur one after the other in the same polarity, called multiyear ENSO. However, the dynamical processes are not well understood. This study aims to elucidate the unified mechanisms of multiyear ENSO using observations, phase 6 of the Coupled Model Intercomparison Project (CMIP6) models, and the theoretical linear recharge oscillator (RO) model. We found that multiyear El Nino and La Nina events are roughly symmetric except for cases of multiyear La Nina following strong El Nino. The composite multiyear ENSO reveals that anomalous ocean heat content (OHC) in the equatorial Pacific persists beyond the first peak, stimulating another event. This prolonged OHC anomaly is caused by meridional Ekman heat transport counteracting geostrophic transport-induced recharge-discharge process that otherwise acts to change the OHC anomaly. A meridionally wide pattern of sea surface temperature anomalies observed during multiyear ENSO is responsible for the Ekman heat transport and multiple factors such as decadal variability, subtropical processes, and ENSO diversity modulate the ENSO meridional structure. CMIP6 multimodel ensemble shows a significant correlation between the ENSO meridional width and the occurrence ratio of multiyear ENSO, supporting the aforementioned mechanism. A multiyear ENSO-like oscillation was simulated using the linear RO model that incorporates a seasonally varying Bjerknes growth rate and a weak recharge efficiency representing the effect of Ekman transport. When the recharge efficiency parameter was estimated using reanalysis data based on geostrophic transport alone, a multiyear ENSO rarely occurred, confirming the importance of Ekman transport in retarding the recharge-discharge process.