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"Synergistic Observing Network for Ocean Prediction (SynObs)" was launched in 2022 as a project of the United Nations Decade of Ocean Science for Sustainable Development to evaluate the importance of ocean observation systems and co-design the future evolution of the ocean observing network. SynObs is currently leading the flagship OSEs/OSSEs, an internationally coordinated activity in which observing system experiments (OSEs) and observing system simulation experiments (OSSEs) are conducted using a variety of ocean and coupled atmosphere–ocean prediction systems to evaluate ocean observation impacts consistent across most prediction systems. The flagship OSEs/OSSEs comprises the ocean prediction (OP) OSEs for high-resolution ocean predictions, the subseasonal-to-seasonal (S2S) OSEs for long-term lead-time coupled ocean–atmosphere predictions, and the OP OSSEs for evaluating new and future observing systems. SynObs plans to use the results of the flagship OSEs to contribute to the reports on the ocean observing network design made by international organizations and projects. Here, we introduce this initiative, and we report on some initial results. Some observation impacts consistent across four ocean prediction systems are found by a preliminary analysis of the analysis runs for the OP OSEs. For example, impacts of the altimetry data on the assimilated sea surface height (SSH) field are generally large in the westerly boundary current regions and around Antarctic Circumpolar Currents where SSH has large variability but are small in the tropical regions, despite the relatively large SSH variability there. The analysis also indicates the possibility that there are some characteristic differences in the observation impacts between low-resolution and eddy-resolving ocean prediction systems. Although OSE outputs of only four ocean prediction systems are available now, we will make further investigation, adding OSE outputs of other prediction systems that will be submitted in the near future. [ABSTRACT FROM AUTHOR]

The impact of El Niño–Southern Oscillation (ENSO) on the equatorial Atlantic zonal mode (AZM) is investigated using two atmospheric reanalysis products and 44 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). While the impact of ENSO on equatorial Atlantic SST is inconsistent, as previously reported, there is a very robust influence of decaying ENSO events in boreal spring on the contemporaneous surface zonal winds over the equatorial Atlantic, with El Niño events associated with anomalous easterlies that cool the equatorial Atlantic. This dynamic impact is counteracted by a thermodynamic impact, in which El Niño events cause changes in surface heat fluxes that lead to warming over the tropical Atlantic. The thermodynamic influence is active throughout the life cycle of the ENSO event, but the dynamic influence is highly seasonal with a pronounced peak in boreal spring. Thus, a quickly decaying El Niño event will lead to warming, while a slowly decaying event will lead to cooling in the equatorial Atlantic. The ENSO–AZM relation is further complicated by partially independent Atlantic variability, in particular that associated with the South Atlantic subtropical dipole (SASD). Prediction experiments with a simple linear regression model support the role of the SASD as an AZM precursor. Many CMIP6 models show skillful predictions of the June–August AZM based on SST indices in the preceding December–February, with correlations above 0.5. When predictions are restricted to ENSO years, even more models exceed this threshold, but skill in the reanalyses remains relatively low, possibly due to insufficient training data. Significance Statement: El Niño is the strongest climate signal on interannual time scales. Its influence on the equatorial Atlantic, however, is surprisingly inconsistent. Here, we show, using an ensemble of climate models and observation-based data, that El Niño has a very robust influence on equatorial Atlantic surface winds, but only in boreal spring. This leads to a large difference in how El Niño events influence the equatorial Atlantic, based on how quickly they decay in boreal spring. We also find that variability in the South Atlantic, which is partly independent of El Niño, has a strong influence on the equatorial Atlantic, supporting the result of previous studies. These findings suggest that the predictability of equatorial Atlantic temperature anomalies may be higher than previously thought. [ABSTRACT FROM AUTHOR]

Jiang et al. (2023), https://doi.org/10.1029/2023gl103777 argue that the apparent impact of the equatorial Atlantic on El Niño‐Southern Oscillation (ENSO) is a statistical artifact, and that the 6‐month lead correlation reported in previous studies stems from early developing ENSO events driving the equatorial Atlantic zonal mode (AZM) in boreal summer and maturing in winter. Closer examination, however, reveals that most AZM events develop too early to be driven by developing ENSO, and that the influence of decaying ENSO events has to be considered too. Thus, while early developing ENSO events may play a role, they do not fully explain observed AZM behavior. Our aim is not to argue for or against an AZM influence on ENSO, but rather to show that Jiang et al.'s analysis is insufficient to resolve this issue. More analysis will be needed for a deeper understanding of Atlantic‐Pacific interaction. Plain Language Summary: Jiang et al. (2023), https://doi.org/10.1029/2023gl103777 argue that year‐to‐year sea‐surface temperature variability in the equatorial Atlantic is driven by the equatorial Pacific and suggest that the Atlantic cannot remotely influence the Pacific. They suggest that the influence of the equatorial Atlantic on the equatorial Pacific reported in previous studies is a statistical artifact. The study makes some important points, but it primarily relies on correlation and regression analyses, which can only provide limited insight into causality. In addition, the authors do not fully consider the seasonality of variability patterns in the equatorial Pacific and Atlantic. Thus, their view of the equatorial Atlantic being a slave to the equatorial Pacific is too simplistic and does not account for the full nature of observed variability. Key Points: Some of the methods used by Jiang et al. (2023) are too simplistic to rule out an Atlantic influence on El NiñoEl Niño usually develops too late in the year to influence the Atlantic zonal mode and can therefore not be its dominant driverJiang et al. (2023) make some valid points but do not offer a complete explanation of Atlantic‐Pacific interaction [ABSTRACT FROM AUTHOR]

"Synergistic Observing Network for Ocean Prediction (SynObs)" was launched in 2022 as a project of the United Nations Decade of Ocean Science for Sustainable Development to evaluate the importance of ocean observation systems and co-design the future evolution of the ocean observing network. SynObs is currently leading the flagship OSEs/OSSEs, an internationally coordinated activity in which observing system experiments (OSEs) and observing system simulation experiments (OSSEs) are conducted using a variety of ocean and coupled atmosphere–ocean prediction systems to evaluate ocean observation impacts consistent across most prediction systems. The flagship OSEs/OSSEs comprises the ocean prediction (OP) OSEs for high-resolution ocean predictions, the subseasonal-to-seasonal (S2S) OSEs for long-term lead-time coupled ocean–atmosphere predictions, and the OP OSSEs for evaluating new and future observing systems. SynObs plans to use the results of the flagship OSEs to contribute to the reports on the ocean observing network design made by international organizations and projects. Here, we introduce this initiative, and we report on some initial results. Some observation impacts consistent across four ocean prediction systems are found by a preliminary analysis of the analysis runs for the OP OSEs. For example, impacts of the altimetry data on the assimilated sea surface height (SSH) field are generally large in the westerly boundary current regions and around Antarctic Circumpolar Currents where SSH has large variability but are small in the tropical regions, despite the relatively large SSH variability there. The analysis also indicates the possibility that there are some characteristic differences in the observation impacts between low-resolution and eddy-resolving ocean prediction systems. Although OSE outputs of only four ocean prediction systems are available now, we will make further investigation, adding OSE outputs of other prediction systems that will be submitted in the near future. [ABSTRACT FROM AUTHOR]

The ability of coupled general circulation models (CGCMs) to simulate a newly-discovered climate mode called Ningaloo Niño/Niña is examined using outputs from 17 CGCMs that participated in the Coupled Model Inter-comparison Project, phase 5. It is shown that 8 out of 17 models reproduce sea surface temperature (SST) anomalies associated with Ningaloo Niño/Niña with a pattern correlation coefficient of 0.7 or higher, but the location of peak SST anomalies is very different from the observation in 2 models. Also, fundamental features such as the seasonality and associated anomalous atmospheric circulation and precipitation are fairly well reproduced in most models, but the amplitude varies significantly among the models. The inter-model difference in the amplitude is found to be mainly due to that in the magnitude of remote influences from the El Niño-Southern Oscillation via oceanic and atmospheric teleconnections. On the other hand, the strength of local air-sea interaction does not contribute much to the inter-model difference. This study may pave the way for an improved representation of Ningaloo Niño/Niña in CGCMs. [ABSTRACT FROM AUTHOR]