The tropical Atlantic Ocean is characterized by energetic mean currents, pronounced equatorial wave activity, and enhanced seasonal upper-ocean instability. Variability and extreme events in this region exert a strong influence on weather and climate over adjacent continents and contribute to atmospheric teleconnections with the other tropical ocean basins. Despite this importance, sustained observations of equatorial Atlantic Ocean dynamics remain limited.

To address this gap, a moored observatory has been operated at 0°, 23°W since December 2001, with evolving configurations. In its current design the observatory consists of a subsurface mooring equipped with Acoustic Doppler Current Profilers measuring velocities in the upper 900 m and a McLane Moored Profiler sampling the 900-3,300 m depth range. Additional single-point current meters are deployed at variable depths. These time series are combined with current meter measurements from the nearby PIRATA moored surface buoy and with full-depth shipboard velocity profiles collected during regular French and U.S. PIRATA mooring service cruises.

In this presentation, we provide updated perspectives and new results on the structure, variability and trends of the zonal and meridional velocity components of the equatorial Atlantic circulation. For instance, in the upper ocean, the eastward Equatorial Undercurrent (EUC) exhibits a marked decline in volume transport since 2018, following a decade of strengthening transport and enhanced oxygen ventilation of the eastern equatorial Atlantic between 2008 and 2018. Consistent with this decadal variability, the mean core depth of the EUC has shoaled by approximately 10 m relative to 2018.

Variability in the meridional velocity component is dominated by intraseasonal time scales (~10-50 days), reflecting the presence of tropical instability waves (TIWs) in the upper 100 m, and equatorial Yanai waves at greater depths. While observations suggest an apparent increase in TIW activity, which are on average most pronounced from July to September, a detailed seasonal analysis indicates that the inferred long-term trends largely arise from a systematic shift toward an earlier onset of TIW activity rather than from a sustained intensification.

Since 2022, a combined full-depth velocity product has been released shortly after each mooring recovery (Tuchen et al., 2022). Maintaining long-term observations such as the equatorial moored observatory at 23°W is logistically and financially demanding, but remains essential for detecting and interpreting decadal variability and long-term trends in the tropical Atlantic.

Tuchen, F. P., Brandt, P., Hahn, J., Hummels, R., Krahmann, G., Bourlès, B., Provost, C., McPhaden, M. J., and Toole, J. M. (2022): Two Decades of Full-Depth Current Velocity Observations From a Moored Observatory in the Central Equatorial Atlantic at 0°N, 23°W. Front. Mar. Sci. 9:910979. https://doi.org/10.3389/fmars.2022.910979 

How to cite: Tuchen, F. P., Brandt, P., and Hummels, R.: Equatorial Atlantic Ocean dynamics across time scales from sustained velocity observations between 2001-2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5468, https://doi.org/10.5194/egusphere-egu26-5468, 2026.

The North Atlantic exhibits pronounced variability on decadal to multidecadal timescales, commonly referred to as Atlantic Multidecadal Variability (AMV). AMV has been linked to climate variability in many regions across the globe. Modelling studies indicate that the global teleconnections of AMV are sensitive to how the tropical branch is represented, though understanding the processes governing its development has received little attention. Moreover, coupled climate models show substantial diversity in simulating the tropical arm of AMV, yet the mechanisms responsible for this inter-model spread remain poorly understood. Here we show that tropical AMV exhibits a seasonal cycle in observations, with growth during boreal summer and decay during boreal winter. Coupled models differ markedly in their ability to capture this observed seasonality. Models that reproduce the observed seasonal evolution of tropical AMV provide insight into its underlying dynamics, revealing that variations in latent heat flux, shortwave radiation, and mixed-layer depth driven by changes in the trade winds are central to the growth and decay of tropical AMV. In contrast, models that fail to represent trade wind weakening and associated ocean-atmosphere interaction processes exhibit substantial deficiencies in simulating tropical AMV. Consequently, models that correctly capture the observed seasonality of tropical AMV also reproduce its associated climate impacts, including variability in Sahel rainfall and the Indian summer monsoon, whereas models that do not capture this seasonality fail to simulate these impacts properly. Given the sensitivity of global climate to tropical AMV, these results highlight the importance of accurately representing the processes linking the extratropical North Atlantic and tropical ocean-atmosphere interactions in coupled climate models.

How to cite: Senapati, B., O’Reilly, C. H., and Robson, J.: Mechanisms of Internal Tropical Atlantic Multidecadal Variability: Seasonality, Model Diversity, and Climate Impacts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8406, https://doi.org/10.5194/egusphere-egu26-8406, 2026.

Tropical north Atlantic sea surface temperature anomalies (TNA SSTAs) have far-reaching climate impacts both locally and remotely. For the first time, this study reveals pronounced multidecadal variations in the seasonal persistence of spring TNA SSTAs, which is relatively higher at the early and late 20^th century but significantly lower during the middle 20^th century. Contrast to the nonstationary El Niño-Southern Oscillation (ENSO)-TNA connection, these fluctuations in TNA SSTA seasonal persistence are mainly linked to multidecadal shifts in the North Atlantic Oscillation (NAO)-TNA connection. Specifically, the asymmetric impacts of extreme NAO events drive both multidecadal fluctuations in the TNA SSTA seasonal persistence and shifts of NAO-TNA connection. The asymmetric impacts of extreme NAO events are enhanced in historical periods by external forcings and is projected to amplify further under further climate conditions.

How to cite: Yan, X.: Multidecadal variations of the persistence of Tropical North Atlantic sea surface temperature, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4717, https://doi.org/10.5194/egusphere-egu26-4717, 2026.

Atmospheric cold pools are transient sub-mesoscale to mesoscale weather phenomena generated by convective precipitation. They are characterized by cool, dense air spreading laterally, which strongly alters near-surface atmospheric conditions and the thermohaline properties of the ocean skin layer (< 1 mm) and near-surface layer (NSL: < 1 m). The spatial extent and thermodynamic intensity of atmospheric cold pools are moderated by mixing within the moist marine boundary layer (MBL), the lowest ~0.5–1 km of air above the ocean. Despite this moderation, accompanying wind surges and intense precipitation drive short-lived intensifications of atmosphere–ocean fluxes that can abruptly restructure upper-ocean thermohaline structure, an aspect that remains poorly constrained by in situ measurements and is underrepresented in coupled atmosphere–ocean models.

Here we present observations of atmospheric cold pool passages over the tropical Atlantic Ocean, combining ship-based meteorological measurements, aerial drones, weather balloon profiles, and high-resolution observations from the autonomous surface vehicle HALOBATES. Equipped with meteorological and oceanographic sensors sampling at high-resolution (1 Hz), HALOBATES resolves the ocean skin layer and the NSL dynamics, allowing us to identify and characterize cold pools as they passed over the study area during the R/V METEOR M211 field campaign (14 June–27 July 2025).

Between 13 and 18 July 2025, cold pool passages were identified by rapid air-temperature drops of 0.6–1.8 °C and, during rainy events, rainfall rates of up to 37 mm h⁻¹. All cold pools induced transient ocean surface cooling, leading to sea surface temperature anomalies (T_skin-T_NSL) of 0.02 – 0.35 °C, and amplified cooling in the skin layer relative to the NSL. To quantify the cooling and recovery of the ocean skin layer following the cold pool passage, we consider two different skin-layer depths: the infrared (IR) skin layer observed by thermal cameras and the skin layer measured in situ by HALOBATES. This comparison shows that skin-temperature responses evolve on timescales of only a few minutes and therefore require high temporal resolution in situ measurements to be adequately resolved.

Salinity responses depended critically on precipitation: cold pools that passed the study area without measurable rainfall produced negligible changes, whereas intense-rain events freshened the skin by up to 1.3 g kg^-1 and the NSL by 0.4 g kg^-1, forming shallow freshwater lenses that re-stratified the upper meter within approximately 15 minutes. Pronounced cold pool passages were accompanied by enhanced latent and sensible heat fluxes, with maximum increases of −140 W m⁻² and −30 W m⁻², respectively, driven primarily by increased wind speeds and indicating intensified ocean-to-atmosphere heat exchange. These observations demonstrate that cold pools strongly affect short-term variability in upper-ocean thermohaline structure through short-lived intense peaks in atmosphere–ocean fluxes, emphasizing the need to include these transient events in future coupled atmosphere–ocean models.

How to cite: Bibi, R., Jaeger, L., Rauch, C., Mintah Ayim, S., Gassen, L., Ribas-Ribas, M., W. Freeman, S., Britton, K., D. Grant, L., M. Falk, N., A. Neumaier, C., van den Heever, S., L. Monroy, D., Härter, J., and Wurl, O.: Cold Pools Drive Short-Term Thermohaline Variability in the Ocean Skin Layer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14270, https://doi.org/10.5194/egusphere-egu26-14270, 2026.

The influence of equatorial Atlantic SST on the El Niño Southern Oscillation (ENSO) has remained robust over the 40 years, despite the strong weakening of Atlantic Niño variability post 2000. To investigate the nature of these interactions through pacemaker experiments with the Norwegian Earth System Model (NorESM). In these experiments tropical Atlantic sea surface temperatures (SST) are restored to observations over the period 1980 to 2020. We perform two experiments, one with long-term warming included and one with it removed linearly. Each experiment consists of 20 ensemble members, sampling internal variability, model uncertainty (NorESM1/NorESM2), and nudging approach (anomaly vs full field restoring). Our results show first that equatorial Atlantic SST variations in the west determine the impact on the ENSO, rather than those in the east. And second, that the long-term warming of the tropical Atlantic SST has opposed this interaction. While the first effect has maintained the robust connection during the last 40 years, we expect the second effect to dominate in the long-term, leading to weaker Atlantic Niño impacts on the Pacific.

How to cite: Chiu, P.-G. and Keenlyside, N.: Disentangling equatorial Atlantic’s influence on ENSO since 1980, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22469, https://doi.org/10.5194/egusphere-egu26-22469, 2026.

El Niño–Southern Oscillation (ENSO) is a major driver of climate variability in the North Atlantic through atmospheric teleconnections that influence circulation patterns and climate conditions across the Euro-Atlantic region. These teleconnections constitute an important source of interannual climate variability and predictability. Previous studies suggest that, under greenhouse-warming scenarios, ENSO teleconnections to the North Atlantic are likely to intensify, largely as a result of changes in the mean climate state and projected modifications in ENSO characteristics.

In this study, we show that changes in ENSO–North Atlantic teleconnections under global warming have significant implications for seasonal climate predictability over Europe. Our results show that a strengthening and reorganization of these teleconnections alters the robustness and spatial coherence of ENSO-related climate signals, thereby directly influencing predictability in the Euro-Atlantic sector.

In addition, we explore the potential role of the Tropical North Atlantic as a modulator of ENSO teleconnections to Europe. Previous studies suggest that variability in Tropical North Atlantic sea surface temperatures can influence the atmospheric response to ENSO, potentially modifying its impact on the North Atlantic and European climate. Our results support the idea that the Tropical North Atlantic may play an important role in shaping ENSO-related climate signals and their predictability. 

How to cite: Santuy Muñoz, D., Polo Sánchez, I., and Rodríguez Fonseca, B.: ENSO teleconnection to the North Atlantic under greenhouse warming and its modulation by the Tropical North Atlantic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12276, https://doi.org/10.5194/egusphere-egu26-12276, 2026.

El Niño-Southern Oscillation (ENSO) affects weather and climate around the world but its impact on the equatorial Atlantic has been surprisingly inconsistent, with some major El Niño events followed by cooling in the equatorial Atlantic, while others were followed by warming. Here we use climate change projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to examine how ENSO’s relation with the equatorial Atlantic may change under global warming.

Similar to ENSO, variability in the equatorial Atlantic, also known as the Atlantic Zonal Mode (AZM), is influenced by the Bjerknes feedback, in which sea-surface temperature (SST) anomalies drive deep convection and a surface wind response that amplifies the original SST anomalies. Due to the stabilization of the atmosphere under global warming, this Atlantic feedback weakens in the CMIP6 projections. Instead, many models suggest a scenario in which the AZM is dominantly driven by ENSO’s thermodynamic forcing, namely the tropics-wide tropospheric warming (cooling) that follows El Niño (La Niña) events. As a result, ocean dynamics and coupled air-sea feedbacks play a much weaker role, while ENSO’s influence on the AZM becomes more consistent. Analysis with a simple linear prediction scheme suggests that this can also increase the predictability of the AZM, due to the high predictability of ENSO.

While many models envision an ENSO-dominated future, some continue to simulate an independent, dynamically driven AZM until the end of the 21st century. The potential reasons for this disparate behavior will be discussed.

How to cite: Richter, I., Chang, P., Kataoka, T., Kido, S., Noel, K., Kosaka, Y., Okumura, Y., Tokinaga, H., Tozuka, T., and Vilela, I.: Changes in the ENSO-AZM connection under global warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15698, https://doi.org/10.5194/egusphere-egu26-15698, 2026.

The Pacific ENSO and the Atlantic Niño/Niña change oppositely in the 21^st century. Here, we find the weakened Atlantic Meridional Overturning Circulation (AMOC) plays a key role. Via reducing the equatorial Pacific trades and the Atlantic poleward heat transport, the weakened AMOC contributes to, at surface, a similar Niño-like sea surface temperature (SST) warming and a strengthened atmospheric stratification in both basins, while, at subsurface, a western Pacific cooling in comparison to an intense Atlantic warming. The distinct subsurface changes induce strengthened Pacific oceanic stratification to enhance Bjerknes feedback, in contrast to an insignificant change in the Atlantic. Moreover, the similar surface changes exert different impacts, with a strengthened atmospheric stratification suppressing the Atlantic Bjerknes feedback, an influence offset in the Pacific by an eastward shift of deep convection due to Niño-like SST warming. Such offset is absent in the Atlantic owing to the northern-hemisphere-located deep convection.

How to cite: Yang, Y., Wu, L., Cai, W., Cheng, X., Mei, X., Jia, F., Li, S., Geng, T., Chen, Y., and Wang, H.: Weakened Atlantic Meridional Overturning Circulation Contributes to Opposite Responses of ENSO and the Atlantic Niño/Niña to Greenhouse Warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2395, https://doi.org/10.5194/egusphere-egu26-2395, 2026.

The Benguela Niño/Niña events manifest the anomalous signals of sea surface temperature (SST) in the upwelling region off the west coast of Africa. These events are triggered by the interannual modulation of either equatorial waves or local atmospheric forcing. In the present study, the mechanism that equatorial waves induce the coastal SST anomaly is investigated in terms of the transfer episodes of wave energy by both numerical experiments and reanalysis data. The result of numerical experiments suggests that most of the coastal events can be reproduced by subseasonal wind forcing with an interannual modulation that excites oceanic waves of the first three baroclinic modes. The transfer routes of wave energy illustrate the role of wave dynamics that explains how the interannual variability of SST in the equatorial Atlantic is connected with that in coastal regions. The linearly superposed sign-indefinite potential energy flux owing to waves manifests its capability of sufficiently displacing the thermocline so as to trigger the coastal events. The diagnosis of wave energy for reanalysis data further confirms that there are clear wave energy routes from the equatorial Atlantic to the coastal region, along which different source regions for waves in the first-four modes are found, jointly contributing to the 2019 Niño event.

How to cite: Song, Q., Tang, Y., and Aiki, H.: The Role of Equatorially Forced Waves in Triggering Benguela Niño/Niña as Investigated by an Energy Flux Diagnosis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18445, https://doi.org/10.5194/egusphere-egu26-18445, 2026.

Upwelling processes bring nutrient-rich waters from the deep ocean to the surface. Areas of upwelling are often associated with high productivity, offering great economic value in terms of fisheries. Thus, predictive skill for regional oceanographic conditions is highly desirable. On this aspect, we analyzed the seasonal prediction of the marine ecosystem drivers such as the net primary production and phytoplankton biomass along the Senegalo-Mauritanian and Moroccan upwelling systems, using the latest version of the German Climate Forecast System GCFS2.2. Our results generally show that the Senegalo-Mauritanian upwelling system is predictable 1 to 4 months in advance during boreal winter, consistent with the sea surface temperature and wind forcing (physical variables). On the other hand, in the Morocco system the effective predictability horizon for the marine ecosystem drivers extends up to 4 months, whereas that for the physical variables hardly reaches one month. Our results highlight the different mechanisms and properties impacting the different predictability horizon one can expect in the Senegalo-Mauritanian and Moroccan upwelling systems.

How to cite: Sylla, A., Brune, S., Capet, X., Mignot, J., and Baehr, J.: Mechanisms and seasonal marine biochemical prediction over the Canary upwelling system using the German Climate Forecast System GCFS2.2, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7349, https://doi.org/10.5194/egusphere-egu26-7349, 2026.