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Sea surface temperature (SST) variability in the East China Sea–Kuroshio (EK) region has important implications for the surrounding weather, climate, and marine ecology. The year-to-year variations of the EK SST are expectedly linked to El Niño–Southern Oscillation (ENSO), the predominant predictability source of seasonal-to-interannual climate variability. Surprisingly, no significant SST signal is observed in the EK region when focusing on the ENSO autumn–winter season with the persistent and pronounced SST anomalies in the tropical Pacific. We find that a remarkable seasonal reversal appears in the ENSO–EK SST connection, shifting from a negative relationship in autumn [Aug(0)–Oct(0)] to a positive relationship in winter [Dec(0)–Feb(1)]. This reversal is mainly attributed to the seasonally varying ENSO-associated western North Pacific (WNP) atmospheric circulation patterns. During ENSO autumns, the anomalous WNP anticyclone is confined south of 20°N, which is accompanied with cyclonic circulation anomalies in the EK region. The associated anomalous northerly wind tends to enhance the background northerly wind, thereby facilitating the local SST cooling mainly via the wind–evaporation–SST effect. In the subsequent winter, the ENSO-related WNP anticyclonic anomalies intensify and extend toward the EK region. Consequently, the weakened background northerly wind induced by southerly wind anomalies leads to the increase of downward latent and sensible heat flux in the EK region, fostering the local SST warming. The observed seasonal reversal of ENSO impacts can be evidenced by the tropical Pacific pacemaker experiments, emphasizing the importance of seasonally modulated ENSO teleconnection and holding implications for the local SST climate prediction. [ABSTRACT FROM AUTHOR]

While the prominent influence of El Niño‐Southern Oscillation (ENSO) on the Indian Ocean Oscillation (IOD) is widely recognized, intricate relationships between them are often invoked that introduce challenges into seasonal predictions. Previous studies have shown that different flavors of El Niño exhibit distinct associations with the IOD. In this study, we demonstrate that La Niña's teleconnection to the IOD is primarily controlled by its longitudinal position. Westward‐displaced La Niña events tend to produce stronger negative convection anomalies in the central Pacific and more pronounced Walk Circulation anomalies, thereby triggering strong negative IOD events. In contrast, eastward‐displaced La Niña events are usually accompanied by feeble convection response due to the excessively cold conditions in the cold tongue, yielding insignificant IOD response. The pivotal role of La Niña's longitudinal position on the IOD's response is realistically reproduced by targeted pacemaker experiments, providing new insights into inter‐basin climate connections. Plain Language Summary: The tropical Indian Ocean usually witnesses a dipolar pattern of sea surface temperature (SST) anomalies, which is commonly referred to as the Indian Ocean Dipole (IOD). The IOD phenomenon has received much attention due to its profound global impacts, yet its seasonal prediction remains a large challenge for the climate community. The year‐to‐year variability of IOD has usually been linked to the El Niño–Southern Oscillation (ENSO), the predominant interannual climate variability in the tropical Pacific. The relationship between El Niño (i.e., warm phase of ENSO) and the intensity of IOD has been demonstrated in previous studies, which is shown to be dependent on the different El Niño flavors. In this study, we show that the longitudinal position of negative SST anomalies during La Niña events (i.e., cold phase of ENSO) in shaping their connection with IOD. Different from westward‐displaced La Niña events that can drive robust negative IOD events, eastward‐displaced La Niña events do not yield significant IOD anomalies due to the excessively cold conditions prevalent in the eastern Pacific cold tongue region. We highlight the importance of La Niña's longitudinal position in its teleconnection to other ocean basins and the associated regional climate anomalies. Key Points: The La Niña's regulation of Indian Ocean Oscillation (IOD) mainly depends on the La Niña longitudinal positionThe westward‐displaced La Niña events produce significant Walker Circulation anomalies, triggering robust negative IOD eventThe importance of La Niña longitudinal position on the IOD's response can be evidenced by the targeted pacemaker experiments [ABSTRACT FROM AUTHOR]

Westerly wind bursts (WWBs), aperiodic burst-like atmospheric disturbances in the tropics, play an important role during the development stage of El Niño–Southern Oscillation (ENSO) events and in turn can be strongly modulated by ENSO itself. Previous work argued that WWBs exhibit a pronounced seasonality at the equator during an El Niño evolution, i.e., being more frequent and vigorous during the developing boreal autumn compared to the decaying spring. Here we show that this seasonal difference in WWB activity at the equator is a segmentary manifestation of a meridional migration of WWB activity, which is closely linked to the southward displacement of the El Niño-related deep convection from the developing autumn to decaying spring. The highest climatological SSTs over the western-central Pacific are located mainly to the north of the equator in boreal autumn and south of it during boreal spring; hence the equatorially quasi-symmetric El Niño-related SST anomalies tend to induce deep convection and generate more WWBs in the Northern Hemisphere during the developing autumn and more in the Southern Hemisphere during the decaying spring. Despite some differences in the zonal distribution and intensity, there appears a close resemblance between the seasonal-varying features of WWBs during eastern Pacific (EP) and central Pacific (CP) El Niño events regarding the north–south displacement, due to similar meridional shifts of deep convection anomalies. This study provides a more comprehensive picture of the spatiotemporal characteristics of WWBs during El Niño events and improves our understanding of the relationship between ENSO and high-frequency atmospheric variability. [ABSTRACT FROM AUTHOR]

Reanalysis data are extensively employed in investigation of the tropical large-scale climate variability. In this study, we attempt to use the Advanced Microwave Sounding unit-A (AMSU-A) window channel brightness temperature (TB) observations to examine their relationship with the sea surface temperature (SST). A close relationship is found between the AMSU-A window channel TB and SST in the tropical oceans. A TB Niño Index (TNI) of AMSU-A window (sounding) channels is found to sometimes reach its maximum for about 2 months ahead of Oceanic Niño Index (ONI) for half of El Niño cases from 1998 to 2020. The AMSU-A sounding channels TNI had minimum values about 1–3 months behind ONI peak month. Spatial correlation maps of AMSU-A window channel TB anomalies with TNI are similar to those of SST anomalies with ONI, featuring a horseshoe-shaped pattern in the tropical Pacific and a dipole-shaped pattern in the tropical Indian Ocean. The AMSU-A retrieved liquid water path (LWP) is also highly correlated with the ONI, with larger values in El Niño years. An active development of tropical convective disturbances and their movement associated with westerly wind bursts may be the reason for the peak TNI to occur 1–3 months earlier than the peak ONI. The potential for AMSU-A TB observations to reveal El Niño signals adds additional satellite data source for El Niño research. [ABSTRACT FROM AUTHOR]

Extreme El Niño events have outsized global impacts and control the El Niño Southern Oscillation (ENSO) warm/cold phases asymmetries. Yet, a consensus regarding the relative contributions of atmospheric and oceanic nonlinearities to their genesis remains elusive. Here, we isolate the contribution of oceanic nonlinearities by conducting paired experiments forced with opposite wind stress anomalies in an oceanic general circulation model, which realistically simulates extreme El Niño events and oceanic nonlinearities thought to contribute to ENSO skewness (Tropical Instability Waves (TIWs), Nonlinear Dynamical Heating (NDH)). Our findings indicate a weak contribution of oceanic nonlinearities to extreme El Niño events in the eastern Pacific, owing to compensatory effects between lateral (NDH and TIWs) and vertical processes. These results hold across different vertical mixing schemes and modifications of the upper‐ocean heat budget mixed layer criterion. Our study reinforces previous research underscoring the pivotal role of atmospheric nonlinearities in shaping extreme El Niño events. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is the primary driver of year‐to‐year climate variations in the tropics and beyond. Originating from air‐sea interactions in the tropical Pacific, ENSO oscillates between warm (El Niño) and cold (La Niña) phases, modulating sea surface temperature in the central and eastern equatorial Pacific. Occasionally, El Niño events intensify into "super" El Niño events, causing widespread impacts globally. Utilizing a state‐of‐the‐art oceanic model, our research challenges previous results suggesting a strong oceanic contribution to the amplitude difference between "normal" and "super" El Niño events. Instead, our findings reveal that potential oceanic influences on "super" El Niño events tend to offset each other. This is consistent with recent research highlighting the crucial role of atmospheric processes in the transformation from a "normal" to a "super" El Niño. Key Points: A state‐of‐the‐art ocean model reproduces extreme El Niño events and the corresponding nonlinear oceanic processes realisticallyContributions from oceanic nonlinearities are isolated using paired simulations forced by opposite wind stress anomaliesEffects of oceanic nonlinearities on extreme El Niño events are small, due to compensation between lateral and vertical processes [ABSTRACT FROM AUTHOR]