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1. The Impact of Eastern Pacific Warming on Future North Atlantic Tropical Cyclogenesis

   https://doi.org/10.1029/2023GL105551  

   Karnauskas, Kristopher B; Heede, Ulla K; Zhang, Lei (September 2023, Geophysical Research Letters)

   Abstract Tropical cyclogenesis in the Atlantic is influenced by environmental parameters including vertical wind shear, which is sensitive to forcing from the tropical Pacific. Reliable projections of the response of such parameters to radiative forcing are key to understanding the future of hurricanes and coastal risk. One of the least certain aspects of future climate is the warming of the eastern tropical Pacific Ocean. Using climate model experiments isolating the warming of the eastern Pacific and controlling for other factors including El Niño‐Southern Oscillation (ENSO), changes in Atlantic tropical cyclogenesis potential by the end of this century are ∼20% lower with enhanced eastern Pacific warming. The ENSO signal in Atlantic tropical cyclogenesis potential amplifies with global warming, and that amplification is larger with enhanced eastern Pacific warming. The largest changes and dependencies on eastern Pacific warming are found in the south‐central main development region, attributable to changes in zonal overturning. 

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2. Drivers of Marine Heat Waves in the North Pacific Ocean

   https://doi.org/10.1175/JCLI-D-25-0308.1  

   Cai, Cassia; Thompson, LuAnne; Maroon, Elizabeth A; Deppenmeier, Anna-Lena; Cohen, Jacob T; Staneva, Valentina (April 2026, Journal of Climate)

   Abstract Marine heat waves (MHWs) are extreme events characterized by prolonged periods of unusually high sea surface temperatures. The North Pacific has been a focus of MHW research due to the severe ecosystem impacts of several events in the 2010s. These events are influenced by global warming and climate variability patterns like El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO). We identify MHWs in the Community Earth System Model, version 2, large ensemble using an object-based tracking algorithm (Ocetrac) and classify them via hierarchical clustering, focusing on five dominant midlatitude types. All types are initiated by reduced wind stress, which results in suppressed ocean cooling. This initial warming is then amplified by a cloud–shortwave feedback making net surface heat flux anomalies the largest contributor to peak intensity. While this two-phase atmospheric forcing is consistent, the dominant heat flux component and large-scale precursors vary regionally. Enhanced shortwave radiation drives peak warming in the subarctic northwest Pacific (favored during negative ENSO/PDO) and northeast Pacific (favored during positive ENSO/PDO). The three other types are driven primarily by weaker cooling via reduction in evaporation. The subtropical northeast Pacific and central Pacific types are associated with positive PDO conditions, while northwest Pacific types are associated with negative phases of the PDO/ENSO. Significance StatementMarine heat waves (MHWs), prolonged periods of anomalously high sea surface temperatures, have been associated with biodiversity loss, species mortality, altered community structures, and changes in marine species’ geographical ranges. Analyzing MHWs in a large climate model dataset enables a robust characterization of different types of MHW events in the North Pacific and allows characterization of local atmospheric drivers and linkages to large-scale climate variability modes such as the Pacific decadal oscillation and El Niño–Southern Oscillation. 

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3. Explained predictions of strong eastern Pacific El Niño events using deep learning

   https://doi.org/10.1038/s41598-023-45739-3  

   Rivera_Tello, Gerardo A; Takahashi, Ken; Karamperidou, Christina (December 2023, Scientific Reports)

   Abstract Global and regional impacts of El Niño-Southern Oscillation (ENSO) are sensitive to the details of the pattern of anomalous ocean warming and cooling, such as the contrasts between the eastern and central Pacific. However, skillful prediction of such ENSO diversity remains a challenge even a few months in advance. Here, we present an experimental forecast with a deep learning model (IGP-UHM AI model v1.0) for theE(eastern Pacific) andC(central Pacific) ENSO diversity indices, specialized on the onset of strong eastern Pacific El Niño events by including a classification output. We find that higher ENSO nonlinearity is associated with better skill, with potential implications for ENSO predictability in a warming climate. When initialized in May 2023, our model predicts the persistence of El Niño conditions in the eastern Pacific into 2024, but with decreasing strength, similar to 2015–2016 but much weaker than 1997–1998. In contrast to the more typical El Niño development in 1997 and 2015, in addition to the ongoing eastern Pacific warming, an eXplainable Artificial Intelligence analysis for 2023 identifies weak warm surface, increased sea level and westerly wind anomalies in the western Pacific as precursors, countered by warm surface and southerly wind anomalies in the northern Atlantic. 

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4. Future Projections of the El Niño—Southern Oscillation and Tropical Pacific Mean State in CMIP6

   https://doi.org/10.1029/2022JD037563  

   Erickson, Nathan E.; Patricola, Christina M. (November 2023, Journal of Geophysical Research: Atmospheres)

   The El Niño—Southern Oscillation (ENSO) is an important mode of tropical Pacific atmosphere‐ocean variability that drives teleconnections with weather and climate globally. However, prior studies using state‐of‐the‐art climate models lack consensus regarding future ENSO projections and are often impacted by tropical Pacific sea‐surface temperature (SST) biases. We used 173 simulations from 29 climate models participating in the Coupled Model Intercomparison Project, version 6 (CMIP6) to analyze model biases and future ENSO projections. We analyzed two ENSO indices, namely the ENSO Longitude Index (ELI), which measures zonal shifts in tropical Pacific deep convection and accounts for changes in background SST, and the Niño 3.4 index, which measures SST anomalies in the central‐eastern equatorial Pacific. We found that the warm eastern tropical‐subtropical Pacific SST bias typical of previous generations of climate models persists into many of the CMIP6 models. Future projections of ENSO shift toward more El Niño‐like conditions based on ELI in 48% of simulations and 55% of models, in association with a future weakening of the zonal equatorial Pacific SST gradient. On the other hand, none of the models project a significant shift toward La Niña‐like conditions. The standard deviation of the Niño 3.4 index indicates a lack of consensus on whether an increase or decrease in ENSO variability is expected in the future. Finally, we found a possible relationship between historical SST and low‐level cloud cover biases in the ENSO region and future changes in ELI; however, this result may be impacted by limitations in data availability. 

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5. Low Cloud–SST Variability over the Summertime Subtropical Northeast Pacific: Role of Extratropical Atmospheric Modes

   https://doi.org/10.1175/JCLI-D-24-0015.1  

   Miyamoto, Ayumu; Xie, Shang-Ping (January 2025, Journal of Climate)

   Abstract Over the subtropical Northeast Pacific (NEP), highly reflective low clouds interact with underlying sea surface temperature (SST) to constitute a local positive feedback. Recent modeling studies showed that, together with wind–evaporation–SST (WES) feedback, the summertime low cloud–SST feedback promotes nonlocal trade wind variations, modulating subsequent evolution of El Niño–Southern Oscillation (ENSO). This study aims to identify drivers of summertime low-cloud variations, using satellite observations and global atmosphere model simulations forced with observed SST. A transbasin teleconnection is identified, where the north tropical Atlantic (NTA) warming induced by the North Atlantic Oscillation (NAO) increases precipitation, exciting warm Rossby waves that extend into the NEP. The resultant enhancement of static stability promotes summertime low cloud–SST variability. By regressing out the effects of the preceding ENSO and NTA SST, atmospheric internal variability over the extratropical North Pacific, including the North Pacific Oscillation (NPO), is found to drive the NEP cooling by latent heat loss and subsequent summer low cloud–SST variability. With the help of the background trade winds and WES feedback, the SST anomalies extend southwestward from the low-cloud region, accompanied by ENSO in the following winter. This suggests the nonlocal effects of low clouds identified by recent studies. Analysis of a 500-yr climate model simulation corroborates the NTA and NPO forcing of NEP low cloud–SST variability and subsequent ENSO. 

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