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El Niño–Southern Oscillation (ENSO) is a significant interannual phenomenon that occurs every 2–7 years in the tropical Pacific and has global climate impacts linked to natural disasters. Understanding and accurately modeling ENSO dynamics are crucial for predicting its climate impacts and for understanding the characteristics of ENSO itself, such as amplitude, periodicity, and spatial pattern. However, in the latest version of the Australian global climate model ACCESS-CM2 (CM2), the simulated ENSO mainly displays quasi-biennial oscillations (around 2–2.5 years) instead of the observed more irregular 2–7-yr cycles. Our analysis shows that the observed moderate coupling between anomalous western Pacific winds and eastern Pacific sea surface temperature (SST) in May–June is absent in this model. Furthermore, introducing this absence of May–June atmospheric Bjerknes (BJ) feedback in a simple conceptual model of ENSO shifts the ENSO cycle from about 4 years to approximately 2 years, consistent with that simulated in CM2. Subsequently, we conducted a series of idealized atmospheric general circulation model experiments to understand this weakening phenomenon in CM2. The findings demonstrate that the weakening of the May–June air–sea interaction is mainly associated with the representation of SST anomalies in CM2 rather than the simulated mean state bias of the model. This also suggests that biases in CM2's representation of the mean state did not directly impact this weakening of BJ feedback. However, they may play a role in developing SST anomaly biases. Significance Statement: El Niño–Southern Oscillation (ENSO) is a critical climate pattern affecting global weather. The ACCESS-CM2 model shows ENSO happening more regularly than observed, missing some important features. Specifically, the model fails to replicate the link between Pacific winds and sea temperatures during May and June. To understand this, we ran experiments focusing on these discrepancies. Our results indicate that the model's issue during May–June is mainly due to anomalous sea temperature structure rather than other climate factors. This highlights the importance of accurately modeling sea temperature changes to predict ENSO and its global impacts. [ABSTRACT FROM AUTHOR]

The Indian Ocean Basin (IOB) mode is believed to favor the decay of El Niño via modulating the zonal wind anomalies in the western equatorial Pacific, while the contribution of the Indian Ocean Dipole (IOD) mode to the following year's El Niño remains highly controversial. In this study, we use the evolution of fast and slow decaying El Niño events during 1950–2020 to demonstrate that the positive IOD with a strong western pole prompts the termination of El Niño, whereas a weak western pole has no significant effect. The strong western pole of a positive IOD leads to a strong IOB pattern peaking in the late winter (earlier than normal), enhancing local convection and causing anomalous rising motions over the tropical Indian Ocean and sinking motions over the western tropical Pacific. The surface equatorial easterly wind anomalies on the western flank of the sinking motions stimulate oceanic equatorial upwelling Kelvin waves, which shoal the thermocline in the eastern equatorial Pacific and rapidly terminate the equatorial warming during El Niño. However, a weak western pole of the IOD induces a weak IOB mode that peaks in the late spring, and the above-mentioned cross-basin physical processes do not occur. [ABSTRACT FROM AUTHOR]

In this study, the properties and related anomalies in sea surface wind and rainfall associated with marine heatwaves (MHWs) in the northern South China Sea (SCS) were investigated. The intensity and frequency (duration) of MHWs are high (short) along the coast and decrease (increase) when moving toward the open sea. On the continental shelf of the northern SCS, the wind anomalies associated with MHWs move in a northeastward direction in seasons other than summer. In the summer, MHW-induced wind anomalies were found to be statistically insignificant. In response to MHWs, there is a notable negative rainfall anomaly observed during the spring and summer, whereas a positive anomaly is observed in the fall. In the winter, the MHW-induced rainfall anomalies were deemed insignificant. The presence of an El Niño event can delay the influence of MHWs on rainfall anomalies and attenuate the amplitude of MHW-induced sea surface wind anomalies. [ABSTRACT FROM AUTHOR]

Southern China spring rainfall (SCSR) is significant for agricultural sowing and soil moisture accumulation before the rainy summer. A better prediction of the rainfall improves our ability to risk response to natural disasters. It is found that the SCSR can be promoted by multi‐year El Niño events through the high‐latitude pathway (HP) and low‐latitude pathway (LP). The long‐lasting El Niño warming heats the tropical troposphere persistently until the decaying spring, which strengthens the Arctic polar vortex and the mid‐latitude blockings. This HP is in favor of more southward transport of Rossby wave energy and cold air, resulting in strong ascending motions over southern China (SC) in spring. The multi‐year El Niño also induces an enhanced western North Pacific anticyclone and a secondary circulation transporting moisture to SC through the LP. The HP is more important in the early spring, while the LP dominates the heavy SCSR in the late spring. Plain Language Summary: Southern China (SC) experiences a period of rainy time in spring, with the rainband located from South China to the Yangtze River. The southern China spring rainfall (SCSR) is influential for agriculture and soil moisture accumulation before the flood season in summer. A better prediction of the SCSR improves our ability to risk response to natural disasters. El Niño‐Southern Oscillation (ENSO) is the dominant climate signal that exerts significant remote impacts, especially in East Asia. However, whether it can help to predict the SCSR is still unclear. In this study, we show that a particular type of ENSO event, the multi‐year El Niño, initiates remarkable impacts on the SCSR. The long‐lasting Pacific warming favors a HP that transports more cold air and wave energy southward to SC during the decaying spring. Moreover, it also strengthens the western North Pacific anticyclone and generates a meridional secondary circulation with low‐level moisture transport toward SC. The low‐latitude and HPs collaborate to generate strong ascending motions and water vapor convergence in SC, being responsible for the large SCSR. Thus, the remote climate impact of multi‐year ENSO events is distinctive from the other ENSO events. Key Points: Multi‐year El Niño enhances southern China (SC) spring rainfall through both the low‐latitude pathway (LP) and the high‐latitude pathway (HP)Long‐lasting tropical warming supports the HP which transports wave energy and cold air to SC and exerts ascending motionsThese ascending motions and moisture transportation by El Niño‐induced western Pacific anticyclone can be further intensified by the LP [ABSTRACT FROM AUTHOR]

New insight into the contribution of anomalous South China Sea (SCS) warming is proposed to understand strong southern China (SC) winter rainfall. El Niño events, which weaken the East Asian winter monsoon (EAWM), favor SC winter rainfall. However, the changes in SC winter rainfall are not always in phase with the El Niño‐Southern Oscillation, making the prediction of East Asian climate challenging. Here, we show that the increased moisture associated with the warming SCS induced by the weakening western boundary current leads to increased meridional moisture transport to SC. Particularly, during the El Niño mature winter phase, this effect works jointly with a weakened EAWM to determine an increased rainfall over SC. Therefore, we suggest that the thermal state of the SCS should be considered when large‐scale tropical ocean‐atmosphere variability is utilized to predict SC winter rainfall. Plain Language Summary: Climate extremes, such as strong southern China (SC) winter rainfall, greatly affect socioeconomic activities and raise great concerns. The South China Sea (SCS) acts as a "portal" to SC and significantly modulates the nonlinear moisture transport to SC. When the SCS is warm enough, the "portal" opens and allows abundant moisture transport toward SC. Particularly during the El Niño mature winter, this effect works jointly with a weakened East Asian winter monsoon to determine increased winter rainfall over SC. Key Points: Tropical air‐sea interaction indices sometimes fail to identify strong southern China (SC) winter rainfallThe role of the South China Sea (SCS) in modulating SC winter rainfall under large‐scale tropical air‐sea interactions is revealedA warmer SCS supports large nonlinear moisture transport from the SCS toward SC, resulting in strong SC winter rainfall [ABSTRACT FROM AUTHOR]

Responding to El Niño diversity, greater winter southern China (SC) rainfall is associated with an anomalous warming in the eastern tropical Pacific, but less rainfall with an anomalous warming in the central tropical Pacific. Compared with other widely used indices, the first two principal components of sea surface temperature anomalies in the tropical Pacific better represent the influences of the different El Niño anomaly patterns on winter SC rainfall. This is because these two indices can distinguish a zonal shift of the west North Pacific anticyclone, which conveys the tropical Pacific influence on SC rainfall. At a positive phase, the first principal component features a pattern similar to that of a canonical El Niño, whereas the second component is characterized by a warming in the central Pacific. Based on these two indices, performance of phase 5 of the Coupled Model Intercomparison Project models in simulating the SC rainfall response to El Niño is evaluated. About half of the models cannot reproduce the response to either principal component. The majority of the remaining models can only simulate the response to one principal component, and only five models produce a reasonable response to both principal components. Importantly, changes to SC rainfall in the future depend on the simulation of the SC rainfall response. Models that simulate the teleconnection of SC rainfall with only the first (second) principal component project an increase (decrease) in SC rainfall. Projection of a rainfall change in models that simulate the teleconnection with both principal components, that is, a moderate increase in SC winter rainfall, is more credible. [ABSTRACT FROM AUTHOR]

A pronounced shift of the North Pacific Oscillation (NPO), including its teleconnection with the East Asian winter monsoon, has been observed in recent decades, but the underlying mechanism remains unclear. In this study, we found that interannual variation of the NPO and its relationship with the dominant modes of winter mean and extreme temperatures over East Asia (EA) experienced a significant interdecadal shift in the mid-1980s. Before the shift (during 1950–1985), the NPO emerged and was maintained as a strong regional north-south dipole, manifesting a remarkable tropical-extratropical teleconnection. It significantly modulated the second mode of air temperature over EA (depicted by a north-south dipole) and extreme temperature events over southern EA, mainly through horizontal advection and adiabatic heating induced by the anomalous circulation in the southern lobe of the NPO. After the shift (during 1986–2021), the NPO was characterized by an intensified northern lobe and a weakened and northwestward shifted southern lobe, and by a close teleconnection with the Rossby wave trains at the mid-higher latitudes. In the meantime, tropical-extratropical teleconnections became apparently weak. Correspondingly, the NPO was mainly linked to the interannual variation of air temperature and extreme events over northern EA via horizontal advection. Importantly, the decadal shift of the relationships of the NPO with the Arctic Oscillation and El Niño–Southern Oscillation played an apparent role in modulating EA climate. • Interannual variation of the NPO and its connection with East Asian winter temperature shifted notably in the mid-1980s. • During 1950–1985, the NPO appeared as a local dipole and played a prominent role in modulating southern East Asian climate. • During 1986–2021, the NPO was linked to a global-scale wave-train pattern with its impact limited to northern East Asia. [ABSTRACT FROM AUTHOR]