Abstract This study examines historical simulations of ENSO in the E3SM-1-0, CESM2, and GFDL-CM4 climate models, provided by three leading U.S. modeling centers as part of the Coupled Model Intercomparison Project phase 6 (CMIP6). These new models have made substantial progress in simulating ENSO’s key features, including: amplitude; timescale; spatial patterns; phase-locking; spring persistence barrier; and recharge oscillator dynamics. However, some important features of ENSO are still a challenge to simulate. In the central and eastern equatorial Pacific, the models’ weaker-than-observed subsurface zonal current anomalies and zonal temperature gradient anomalies serve to weaken the nonlinear zonal advection of subsurface temperatures, leading to insufficient warm/cold asymmetry of ENSO’s sea surface temperature anomalies (SSTA). In the western equatorial Pacific, the models’ excessive simulated zonal SST gradients amplify their zonal temperature advection, causing their SSTA to extend farther west than observed. The models underestimate both ENSO’s positive dynamic feedbacks (due to insufficient zonal wind stress responses to SSTA) and its thermodynamic damping (due to insufficient convective cloud shading of eastern Pacific SSTA during warm events); compensation between these biases leads to realistic linear growth rates for ENSO, but for somewhat unrealistic reasons. The models also exhibit stronger-than-observed feedbacks onto eastern equatorial Pacific SSTAs from thermocline depth anomalies, which accelerates the transitions between events and shortens the simulated ENSO period relative to observations. Implications for diagnosing and simulating ENSO in climate models are discussed.
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Single- and multi-year ENSO events controlled by pantropical climate interactions
To better understand the diverse temporal evolutions of observed El Niño‒Southern Oscillation (ENSO) events, which are characterized as single- or multi-year, this study examines similar events in a 2200-year-long integration of Community Earth System Model, version 1. Results show that selective activation of inter- and intra-basin climate interactions (together, pantropical climate interactions) controls ENSO’s evolution pattern. When ENSO preferentially activates inter-basin interactions with tropical Indian and/or Atlantic Oceans, it introduces negative feedbacks into the ENSO phase, resulting in single-year evolution. When ENSO preferentially activates intra-basin interactions with subtropical North Pacific, it causes positive feedbacks, producing multi-year evolution. Three key factors (developing-season intensity, pre-onset Pacific condition, and maximum zonal location) and their thresholds, which determine whether inter- or intra-basin interactions are activated and whether an event will become a single- or multi-year event, are identified. These findings offer a way to predict ENSO’s evolution pattern by incorporating the controlling role of pantropical climate interactions.
more » « less- NSF-PAR ID:
- 10380080
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- npj Climate and Atmospheric Science
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2397-3722
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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