Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: ENSO skewness hysteresis and associated changes in strong El Niño under a CO2 removal scenario
El Niño-Southern Oscillation (ENSO) sea surface temperature (SST) anomaly skewness encapsulates the nonlinear processes of strong ENSO events and affects future climate projections. Yet, its response to CO2 forcing remains not well understood. Here, we find ENSO skewness hysteresis in a large ensemble CO2 removal simulation. The positive SST skewness in the central-to-eastern tropical Pacific gradually weakens (most pronounced near the dateline) in response to increasing CO2, but weakens even further once CO2 is ramped down. Further analyses reveal that hysteresis of the Intertropical Convergence Zone migration leads to more active and farther eastward-located strong eastern Pacific El Niño events, thus decreasing central Pacific ENSO skewness by reducing the amplitude of the central Pacific positive SST anomalies and increasing the scaling effect of the eastern Pacific skewness denominator, i.e., ENSO intensity, respectively. The reduction of eastern Pacific El Niño maximum intensity, which is constrained by the SST zonal gradient of the projected background El Niño-like warming pattern, also contributes to a reduction of eastern Pacific SST skewness around the CO2 peak phase. This study highlights the divergent responses of different strong El Niño regimes in response to climate change.  more » « less
Award ID(s):
2141728 2219257
PAR ID:
10497233
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
Springer Nature
Date Published:
Journal Name:
npj Climate and Atmospheric Science
Volume:
6
Issue:
1
ISSN:
2397-3722
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Science Advances)
    El Niño–Southern Oscillation (ENSO) is the strongest interannual climate variability with far-reaching socioeconomic consequences. Many studies have investigated ENSO-projected changes under future greenhouse warming, but its responses to plausible mitigation behaviors remain unknown. We show that ENSO sea surface temperature (SST) variability and associated global teleconnection patterns exhibit strong hysteretic responses to carbon dioxide (CO2) reduction based on the 28-member ensemble simulations of the CESM1.2 model under an idealized CO2 ramp-up and ramp-down scenario. There is a substantial increase in the ensemble-averaged eastern Pacific SST anomaly variance during the ramp-down period compared to the ramp-up period. Such ENSO hysteresis is mainly attributed to the hysteretic response of the tropical Pacific Intertropical Convergence Zone meridional position to CO2 removal and is further supported by several selected single-member Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulations. The presence of ENSO hysteresis leads to its amplified and prolonged impact in a warming climate, depending on the details of future mitigation pathways. 
    more » « less
  2. ; ; ; ; ; ; ; ; (, Geophysical Research Letters)
    Abstract Linear Inverse Models (LIMs) are widely used data‐driven tools for studying El Niño Southern Oscillation (ENSO). However, standard LIMs struggle to simulate the observed asymmetry and diversity of ENSO events. Observations reveal that strong Central Pacific (CP) La Niñas and extreme Eastern Pacific (EP) El Niños occur more frequently than their counterparts, a feature standard LIMs fail to capture. We introduce a modified model, the Non‐Gaussian LIM (NG‐LIM), which transforms the LIM variables to better simulate ENSO asymmetry and diversity. Specifically, the NG‐LIM reproduces the spatial pattern of sea surface temperature (SST) skewness and the inverted U‐shaped relationship between the first two principal components of Tropical Pacific SST anomalies, reflecting more frequent strong CP La Niñas and extreme EP El Niños. NG‐LIM simulations also show El Niños that are stronger and evolve more rapidly than La Niñas. This improved inverse model generates synthetic events to supplement the limited observational record. 
    more » « less
  3. ; ; ; ; ; ; ; (, Proceedings of the National Academy of Sciences)
    null (Ed.)
    El Niño’s intensity change under anthropogenic warming is of great importance to society, yet current climate models’ projections remain largely uncertain. The current classification of El Niño does not distinguish the strong from the moderate El Niño events, making it difficult to project future change of El Niño’s intensity. Here we classify 33 El Niño events from 1901 to 2017 by cluster analysis of the onset and amplification processes, and the resultant 4 types of El Niño distinguish the strong from the moderate events and the onset from successive events. The 3 categories of El Niño onset exhibit distinct development mechanisms. We find El Niño onset regime has changed from eastern Pacific origin to western Pacific origin with more frequent occurrence of extreme events since the 1970s. This regime change is hypothesized to arise from a background warming in the western Pacific and the associated increased zonal and vertical sea-surface temperature (SST) gradients in the equatorial central Pacific, which reveals a controlling factor that could lead to increased extreme El Niño events in the future. The Coupled Model Intercomparison Project phase 5 (CMIP5) models’ projections demonstrate that both the frequency and intensity of the strong El Niño events will increase significantly if the projected central Pacific zonal SST gradients become enhanced. If the currently observed background changes continue under future anthropogenic forcing, more frequent strong El Niño events are anticipated. The models’ uncertainty in the projected equatorial zonal SST gradients, however, remains a major roadblock for faithful prediction of El Niño’s future changes. 
    more » « less
  4. ; (, Communications Earth & Environment)
    Abstract El Niño/Southern Oscillation variability has conspicuous impacts on ecosystems and severe weather. Here, we probe the effects of anthropogenic aerosols and greenhouse gases on El Niño/Southern Oscillation variability during the historical period using a broad set of climate models. Increased aerosols significantly amplify El Niño/Southern Oscillation variability primarily through weakening the mean advection feedback and strengthening the zonal advection and thermocline feedbacks, as linked to a weaker annual cycle of sea surface temperature in the eastern equatorial Pacific. They prevent extreme El Niño events, reduce interannual sea surface temperature skewness in the tropical Pacific, influence the likelihood of El Niño/Southern Oscillation events in April and June and allow for more El Niño transitions to Central Pacific events. While rising greenhouse gases significantly reduce El Niño/Southern Oscillation variability via a stronger sea surface temperature annual cycle and attenuated thermocline feedback. They promote extreme El Niño events, increase SST skewness, and enlarge the likelihood of El Niño/Southern Oscillation peaking in November while inhibiting Central Pacific El Niño/Southern Oscillation events. 
    more » « less
  5. ; ; ; ; (, Journal of Climate)
    Abstract This study investigates the impacts of anthropogenic warming on the El Niño–Southern Oscillation (ENSO) modulation of tropical cyclones (TCs) in CMIP6 models using synthetic storms downscaled by the Columbia Hazard (CHAZ) model. The multimodel mean of CHAZ–CMIP6 simulations accurately captures the observed ENSO–TC relationship, defined as the differences between anomalous TC activity during El Niño and La Niña events. TC activity is represented by density maps of genesis, track, and accumulated cyclone energy. We found that anthropogenic warming indeed affects the historical ENSO–TC relationship. There is an overall reduction (increase) in TC activity during El Niño (La Niña) events in both the North Atlantic and eastern North Pacific, where the historical ENSO–TC relationships have opposite signs. A warming climate reduces this contrast between the two regions. Other ENSO–TC relationship changes include increased (reduced) TC activity in the South Pacific during El Niño (La Niña) events, which enhances the historically positive anomaly in tropical South Pacific TC activity but weakens the negative anomaly south of 15°S. There is also a westward shift of the positive anomaly of the southeast–northwest dipole pattern in the western North Pacific. These changes, however, are relatively small, and thus, the currently known ENSO–TC relationship persists as the climate warms. The analysis of individual CMIP6 models suggests that warming-induced changes in the ENSO–TC relationship vary by model and basin, with differences likely due to the changes in ENSO characteristics within the models. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email