Day 3 - March 14, 2025 Meeting Agenda
08:30 AM - (Remote Talk) Keynote Speaker, Magdalena Alonso Balmaseda (ECMWF)
Title: ENSO forecasting: past, present and prospects
Abstract:
This talk will present an overview of the history of ENSO forecasting and how it has shaped our current understanding of this phenomena and its global impact. It will touch on the role of the observing system, ensemble prediction, general circulation models and conceptual models. The current prediction capabilities, success stories and challenges ahead will be discussed, as well as new frontiers regarding extending the ENSO forecast horizon.
09:00 AM - Jonathan Beverley (CIRES/CU Boulder and NOAA PSL)
Title: Rapid development of systematic ENSO-related seasonal forecast errors
Abstract:
In this study, we evaluate systematic ENSO-related seasonal forecast errors within eleven different operational forecast models, based on multi-decade seasonal hindcast datasets. We find that the predictions have a systematic westward SST anomaly bias, whereby the eastern-central tropical Pacific SST anomalies associated with ENSO events extend too far to the west for anomalies of either sign. Associated with this SST forecast error is a westward shift of ENSO rainfall anomalies, which in turn affects extratropical seasonal forecast skill through errors in wave propagation from the tropical Pacific. The ENSO-related forecast errors, which are also typical of long free-running climate model simulations, are apparent almost immediately; in fact, they develop so rapidly that they are primarily a function of the seasonal cycle, rather than lead time. That is, the pattern and even amplitude of ENSO-related tropical anomaly errors for a given month are very similar over a range of forecast lead times. Predicted ENSO events also tend to decay too slowly compared to observations, resulting in large systematic forecast errors in the eastern tropical Pacific in late winter/early spring, which are also well-developed at short forecast lead times.
We also evaluated the development of these errors in a 30-year UFS replay experiment, which nudges the atmosphere and ocean models to reanalysis, and found that the ENSO-related temperature errors in the background forecast look a lot like ENSO itself. These coherent errors in the 6-hour forecast suggest fast processes responding to SST anomalies are driving these errors.
09:15 AM - Tong Lee (NASA Jet Propulsion Laboratory)
Title: Raising the bar for evaluating ENSO prediction skill: ocean dynamic persistence
Abstract:
ENSO prediction skill from coupled models is contributed by the accuracy of the initial ocean state and the fidelity of coupled models in representing post-initialization ocean-atmosphere coupling. Coupled-model initialization shock/drift can suppress the positive contribution of an accurate initial ocean state to prediction skill. It begs the question of how much predictability the initial ocean state alone can provide without considering subsequent ocean-atmosphere coupling. Here, we address this question by performing 12-month hindcasts of the 3-D ocean state using a global ocean model. The ocean model is initialized from the ocean state at every month and every year from 1992 to 2017 obtained from ECCO ocean state estimation (https://ecco-group.org/). During each 12-month hindcast, the atmospheric forcings are set to their seasonal climatology. Interannual ocean anomalies in the hindcasts are solely due to the evolution of the initial ocean state without subsequent ocean-atmosphere coupling. We refer to this as ocean dynamic persistence (ODP). It contrasts statistical persistence (a common baseline metrics for evaluating predictions) that damps the initial anomaly as a function of prediction lead time. We show that ODP has better skill than statistical persistence in predicting Niño3.4 SST anomaly for all lead times. ODP also outperforms most dynamical and statistical models in predicting Niño3.4 SST anomaly up to several months of lead time. Therefore, ODP raises the bar for evaluating ENSO prediction skill. It also underscores the importance of reducing coupled model initialization shock/drift to maximize the positive contribution of an accurate initial ocean state to ENSO prediction skill.
09:30 AM - Sen Zhao (University of Hawaii)
Title: Conditional ENSO Predictability from Equatorial Pacific and Pan-Tropical States
Abstract:
The predictability of El Niño–Southern Oscillation (ENSO) at long lead times is largely based on subsurface ocean memory along the equatorial Pacific, a concept first introduced by Klaus Wyrtki’s idea of warm water accumulation, and well captured by the recharge oscillator (RO) theory. Recent studies highlighted the enhanced ENSO predictability from climate mode interactions. However, whether initial ENSO/recharged or climate mode states lead to a more predictable ENSO outcome remains a topic of ongoing debate. In this study, we utilize 43,000 years perfect model hindcasts from the extended nonlinear recharge oscillator (XRO) model that parsimoniously incorporates the core ENSO’s RO dynamics and ENSO’s seasonally modulated interactions with other modes of variability in the global oceans, fitted to observations. We show that predictive skill asymmetry arises from the initialized states of strong El Niño/La Niña events, recharged/discharged equatorial Pacific conditions, and neutral phases. Furthermore, we assess to what extent initial state of climate modes in global oceans increases predictability more for El Niño versus La Niña. Finally, we compare these findings with results based on perfect model XRO hindcasts using the four different large ensemble simulation to assess the influence of potential model biases. The insights gained from this study provide a deeper understanding of ENSO dynamics and predictability.
09:45 AM - Xian Wu (UT Dallas)
Title: Pinpointing sources of tropical Pacific climatological biases in GFDL’s SPEAR models
Abstract:
Coupled GCMs (CGCMs) exhibit biases in simulating tropical Pacific mean climate, including an excessively cold and westward-extended equatorial cold tongue. Such biases reduce accuracy in simulating and predicting tropical Pacific climate variations and their global impacts. To understand the sources of mean-state biases, we conduct experiments using GFDL's SPEAR global CGCM with various observational constraints, including surface flux adjustments (FA). By removing climatological biases in tropical SST and surface wind stress, FA improves the model’s tropical ocean temperatures and currents. These improvements stem mainly from weakened easterly wind stress along the equator, due to both the atmospheric response to corrected SST gradients, and the prescribed wind stress corrections that compensate for intrinsic biases in the atmospheric component. We further find that producing a realistic cold tongue SST given realistic winds requires additional equatorial air-to-sea heating during August–November and La Niña, exposing the role of intrinsic biases in the ocean model, such as insufficient tropical instability wave stirring and vertical mixing. The results also highlight the need for improved observations and reanalyses of the equatorial Pacific diurnal-to-interannual upper-ocean circulation, heat budget, and air-sea coupling, to better inform model development.
10:00 AM - Rohit Ghosh (Alfred Wegener Institute Helmholtz Center for Polar and Marine Research)
Title: ENSO Behavior and Teleconnections in a km-Scale Climate Model over a Century-Long Simulation
Abstract:
The El Niño-Southern Oscillation (ENSO) is a key driver of global climate variability, with far-reaching teleconnections that influence weather patterns worldwide. This study examines ENSO characteristics and its teleconnections using a novel km-scale coupled climate model, IFS-FESOM, featuring a 9 km atmosphere and a minimum 5 km ocean resolution, developed under the EU project EERIE (European Eddy-Rich Earth System Models). Our simulations, conducted according to the HighResMIP protocol, offer a unique opportunity to explore ENSO dynamics on centennial timescales in an ocean-eddy resolving model.
We investigate the temporal evolution of ENSO’s spatial patterns, amplitude, and frequency under changing climate conditions. The unprecedented resolution of our simulations allows for a detailed assessment of ENSO's global teleconnections, revealing notable changes in both tropical and extratropical pathways. These shifts carry significant implications for global precipitation and temperature patterns, particularly in regions like the Maritime Continent, where we observe potential changes in the zero-crossing longitude of the zonal-dipole ENSO teleconnection.
Our findings offer new insights into ENSO behavior and its teleconnections in a warming climate. This study highlights the critical role of high-resolution models like IFS-FESOM in enhancing future climate projections and improving the assessment of regional impacts with greater accuracy.
10:15 AM - Coffee Break
Makana Room
10:45 AM - Feng Jiang (LDEO, Columbia University)
Title: On The ENSO-Atlantic Niño Interaction Conundrum
Abstract:
Understanding the interaction between the tropical Pacific and Atlantic Oceans has challenged the climate community for decades. Typically, boreal summer Atlantic Niño events are followed by vigorous Pacific events of opposite sign around two seasons later. However, incorporating the equatorial Atlantic information to variabilities internal to the Pacific lends no significant additional predictive skill for the subsequent El Niño-Southern Oscillation (ENSO). Here we resolve this conundrum in a physically consistent frame, in which the nascent onset of a Pacific event rapidly induces an opposite-signed summer equatorial Atlantic event and the lead correlation of Atlantic over Pacific is highly likely a statistical artifact of ENSO’s autocorrelation. On this basis, we proposed a new approach to Atlantic Niño forecasting by leveraging longer-lasting precursors in the Pacific associated with ENSO events, which enables us to hindcast the Atlantic Niño with skill up to three seasons in advance. Our results highlight the critical role of inter-basin interactions in shaping regional and global climate patterns, and provide new hope for improving seasonal climate prediction capabilities in the tropical Atlantic.
11:00 AM - Antonietta Capotondi (University of Colorado/CIRES)
Title: The role of the tropical Atlantic in tropical Pacific climate variability
Abstract:
Interactions between Atlantic and Pacific Oceans can affect tropical Pacific variability and its global impacts at both interannual and decadal timescales, calling for a deepened understanding of the coupled Atlantic-Pacific interactions. While possible dynamical mechanisms by which the Atlantic can influence the Pacific have been identified, the effectiveness of those mechanisms is difficult to establish using climate model simulations where Atlantic SSTs are prescribed and Pacific feedbacks cannot be realistically included. As an alternative approach, here we use a Linear Inverse Model (LIM) trained on observations and capable of correctly reproducing the observed statistics, to assess the relative role of the Atlantic-to-Pacific and Pacific-to-Atlantic influences on tropical Pacific variability. Our results indicate that Atlantic internal variability can enhance interannual SST anomalies in the eastern equatorial Pacific, and decadal SST anomalies in the central equatorial Pacific, while Pacific influences on the Atlantic tend to significantly damp tropical Pacific decadal variability. This methodological framework could also be used to assess climate models’ fidelity and reconcile existing differences among models’ results.
11:15 AM - Keynote Speaker, Andrea S. Taschetto (University of New South Wales)
Title: ENSO atmospheric teleconnections to the Southern Hemisphere: the Australian case
Abstract:
The El Niño Southern Oscillation (ENSO) triggers atmospheric teleconnections that impact weather patterns in both the tropics and extratropics, affecting precipitation and temperature over land and oceans. ENSO-induced sea surface temperature anomalies alter large-scale circulations, modulating the Walker and Hadley circulations and exciting extratropical Rossby wave trains in both hemispheres. ENSO teleconnections to the Northern Hemisphere have been relatively well studied compared to those to the Southern Hemisphere.
In this talk, I will focus on ENSO atmospheric teleconnections with an emphasis on the Southern Hemisphere. El Niño events typically lead to a short-term rise in global mean temperatures and cause dry conditions in Australia, northern South America, and southern Africa, while inducing anomalously wet conditions in western Antarctica and eastern Africa. Conversely, La Niña events generally produce the opposite effects. However, there are asymmetries and complexities in these teleconnections due to ENSO diversity, resulting in more intricate climatic responses than expected.
I will explore these complexities, using Australia as a case study to discuss the mechanisms of teleconnections and illustrate the varied precipitation responses during Eastern Pacific El Niño, Central Pacific El Niño, La Niña, and multi-year ENSO events.
11:45 AM - Regina Rodrigues (Federal University of Santa Catarina, Brazil)
Title: Extreme Compound Events in the tropical and South Atlantic related to ENSO
Abstract:
It is well known that ENSO can cause extreme events over land, such as droughts, heatwaves, and floods. However, recent studies have shown that ENSO can also be responsible for an increase in the frequency and intensity of marine heatwaves (MHWs) globally. MHWs are analogues to atmospheric heatwaves, which can have devastating effects on marine ecosystems, ranging from habitat shifts and changes in population structure to high mortality of various marine species. The impacts of MHWs can be amplified when combined with other extreme events that can act synergistically. Here, we investigate the temporal-spatial distribution of compound events of MHW, high acidity and low chlorophyll in the tropical and South Atlantic, using observation-based datasets and reanalysis products. We show that the frequency and intensity of these triple compound events have increased dramatically over the past two decades, peaking in the most recent years, limiting the capacity of marine ecosystems to recover. We also show that El Niño events can lead not only to MHWs but also to compound extremes of low chlorophyll and high acidity in the most biologically rich regions of the tropical and South Atlantic: equatorial Atlantic, Angola-Benguela Front, Brazil-Malvinas Confluence and Agulhas Leakage regions.
The fact that triple compound extremes are widespread over the tropical and South Atlantic during El Niño events is important because recent studies show that MHWs can be skillfully predicted mainly due to ENSO. Thus, the results presented here can help improve models’ performance that are used in early warning systems.
12:00 PM - John Chiang (University of California, Berkeley)
Title: A tale of two annual cycles: the remarkable change in Pacific cold tongue seasonality under orbital forcing
Abstract:
We show the existence of a dynamic annual cycle of the Pacific cold tongue driven by earth-sun distance changes from Earth’s orbital eccentricity (hereafter the Distance Effect), in addition to the known annual cycle of the cold tongue arising from Earth’s axial tilt (hereafter the Tilt Effect). The dynamics of the two annual cycles are distinctly different, with the former arising through a seasonal zonal shift in the Walker circulation and subsequent wind forcing on the equatorial thermocline akin to that experienced by ENSO. The amplitude of the cold tongue annual cycle driven by the distance effect is significant even at today’s low eccentricity and is comparably large as the annual cycle driven by the tilt effect when Earth’s orbital eccentricity is at the larger end of its possible range (e > 0.05). The two cold tongue annual cycles also possess slightly different periodicities as the annual cycle from the tilt effect follows the Tropical year whereas the one from the distance effect follows the Anomalistic year; as a consequence, the superposition of the two annual cycles leads to pronounced changes in the net seasonality of the cold tongue over a precessional cycle. We will discuss the implications of this new cold tongue annual cycle for tropical Pacific paleoclimate, and more generally how Earth-Sun distance works its influence on Earth’s seasonal climate.
12:15 PM - Lunch
Wailana Room
01:45 PM - Alyssa Atwood (Florida State University)
Title: Data-Model Comparisons of Tropical Pacific Climate Change during the Mid-Holocene from Isotope-Enabled Climate Models
Abstract:
Paleoclimate records indicate that substantial changes in tropical Pacific climate occurred during the middle-to-late Holocene, including a cooler and drier mean state, a reduced annual cycle, and a 50-60% reduction in ENSO variance from 3,000-5,000 years ago relative to today. However, notable disagreement has been found between aspects of tropical Pacific climate change in climate model simulations of the mid-Holocene and proxy data. To enable more quantitative data-model comparisons and better understand the mechanisms of the tropical Pacific climate change during this time, we investigated mid-Holocene simulations of two global climate models enhanced with water isotope tracers and paired the model output with a proxy system model for coral oxygen isotope composition (δ18O). Under mid-Holocene forcing, the models simulate robust changes in the central tropical Pacific mean state and seasonal cycle that are broadly consistent with coral data. Namely, the central equatorial Pacific was cooler on average and modestly enriched in 18O, while the amplitude of the annual cycle of sea surface temperatures was reduced. In the models, the seasonality changes are driven by a reduced seasonal cycle of the tropical Pacific cold tongue, with the available evidence pointing to a combination of seasonal insolation changes and seasonal shifts of the Pacific Walker circulation as the driving mechanisms. Overall, these results help reconcile several key aspects of proxy-model disagreement for the mid-Holocene and provide important insight into the tropical Pacific climate response to external forcing.
02:00 PM - Xiang Li (Duke University)
Title: Persistently active El Niño–Southern Oscillation since the Mesozoic
Abstract:
The El Niño–Southern Oscillation (ENSO), originating in the central and eastern equatorial Pacific, is a defining mode of interannual climate variability with profound impact on global climate and ecosystems. However, an understanding of how the ENSO might have evolved over geological timescales is still lacking, despite a well-accepted recognition that such an understanding has direct implications for constraining human-induced future ENSO changes. Here, using climate simulations, we show that ENSO has been a leading mode of tropical sea surface temperature (SST) variability in the past 250 million years (Myr) but with substantial variations in amplitude across geological periods. We show this result by performing and analyzing a series of coupled time-slice climate simulations forced by paleogeography, atmospheric CO2 concentrations, and solar radiation for the past 250 Myr, in 10-Myr intervals. The variations in ENSO amplitude across geological periods are little related to mean equatorial zonal SST gradient or global mean surface temperature of the respective periods, but are primarily determined by inter-period difference in the background thermocline depth, according to a linear stability analysis. In addition, variations in atmospheric noise serve as an independent contributing factor to ENSO variations across inter-geological periods. The two factors together explain about 76% of the inter-period variations in ENSO amplitude over the past 250 Myr. Our findings support the importance of changing ocean vertical thermal structure and atmospheric noise in influencing projected future ENSO change and its uncertainty.
02:15 PM - Yukiko Imada (Atmosphere and Ocean Research Institute, the University of Tokyo)
Title: Impacts of ENSO on local extreme events from a global perspective
Abstract:
In examining ENSO and local extreme events, the use of long-term large-ensemble simulations that combines a regional climate model, which can account for detailed topography, with a global climate model revealed previously unknown relationships between various ENSO flavors and extreme events in different regions. In East Asia, for example, it was revealed that even in areas that are less than 100 km apart horizontally, the phases of ENSO that affect heavy rainfall or extreme temperature are completely different due to the mountainous terrain in between. This is because the wind direction created by the ENSO teleconnection pattern is an important factor in whether each region is upwind or downwind. These relationships between ENSO and local extreme events suggests that seasonal-scale probabilistic prediction of local extreme events is potentially possible.
02:30 PM - Jacob Gunnarson (University of Hawaii)
Title: ENSO’s Influence on Marine Heatwaves in the Current and Future Climates
Abstract:
The El Niño-Southern Oscillation (ENSO) is the largest source of interannual climate variability and a primary driver of sea surface temperature (SST) variability globally. Via atmospheric teleconnections, ENSO events often lead to widespread marine heatwaves: periods of extreme SSTs that damage marine ecosystems. Using several statistical methods, we quantify the extent to which the record-breaking marine heatwaves of 2023 were caused by the onset of an El Niño event. Looking forward, the projected future behavior of ENSO varies across different climate models, with corresponding differences in its effect on SST variability and marine heatwaves. We used a stochastic dynamical model to determine the influence of ENSO teleconnections relative to other drivers on changes to marine heatwaves in the future climate.
02:45 PM - Poster Session and Coffee Break (Makana Room)
04:45 PM - Keynote Speaker, Suzana J. Camargo (Columbia Climate School, Columbia University, New York, NY)
Title: Overview of the Relationship between ENSO and Tropical Cyclones in present and future climates
Abstract:
Tropical cyclone (TC) activity is modulated globally by the El Niño-Southern Oscillation (ENSO) on interannual time-scales. In order to simulate this relationship, models need to reproduce the characteristics of ENSO, TCs, as well as the TC modulation on various ENSO phases. Using a variety of model types and diagnostics, we will examine the ENSO-TC relationship in historical and future climates. First, we will analyze the models’ ENSO characteristics such as frequency, magnitude, pattern and diversity and compare with observations. Then, we will examine how well the ENSO-TC relationship is reproduced across a range of models. In the case of low-resolution climates models, such as CMIP6, we will consider the environmental fields associated with TCs, as well as TC proxies, such as genesis indices, and compare their ENSO composites with reanalysis. For the high-resolution model simulations, such as the HighResMIP multi-model ensemble, besides environmental fields, we will analyze the model TCs and use various diagnostics to analyze the TC-ENSO relationship. We will then consider synthetic TCs downscaled from CMIP6 models and the CESM2 large ensemble and examine their similarity with observed and model TCs ENSO composites. Possible changes in the ENSO-TC relationship in the future will be discussed, including their dependence on the models’ biases, such as the representation of ENSO diversity. We will conclude by showing the impact of ENSO on TC risk in the western North Pacific.
05:15 PM - Concluding Remarks (Malte Stuecker, University of Hawaii)
Keoni Room