Tropical Pacific Decadal Variability and ENSO Precursor in CMIP5 Models

Observational analyses suggest that a significant fraction of the tropical Pacific decadal variability (TPDV) (similar to 60%-70%) is energized by the combined action of extratropical precursors of El Nino-Southern Oscillation (ENSO) originating from the North and South Pacific. Specifically, the growth and decay of the basin-scale TPDV pattern (time scale = similar to -1.5-2 years) is linked to the following sequence: ENSO precursors (extratropics, growth phase) -> ENSO (tropics, peak phase) -> ENSO successors (extratropics, decay phase) resulting from ENSO teleconnections. This sequence of teleconnections is an important physical basis for Pacific climate predictability. Here we examine the TPDV and its connection to extratropical dynamics in 20 models from phase 5 of the Coupled Model Intercomparison Project (CMIP). We find that most models (similar to 80%) can simulate the observed spatial pattern (R > 0.6) and frequency characteristics of the TPDV. In 12 models, more than 65% of the basinwide Pacific decadal variability (PDV) originates from TPDV, which is comparable with observations (similar to 70%). However, despite reproducing the basic spatial and temporal statistics, models underestimate the influence of the North and South Pacific ENSO precursors to the TPDV, and most of the models' TPDV originates in the tropics. Only 35 %-40% of the models reproduce the observed extratropical ENSO precursor patterns (R > 0.5). Models with a better representation of the ENSO precursors show 1) better basin-scale signatures of TPDV and 2) stronger ENSO teleconnections from/to the tropics that are consistent with observations. These results suggest that better representation of ENSO precursor dynamics in CMIP may lead to improved Pacific decadal variability dynamics and predictability.

Automated summary

Observational analyses indicate that a significant portion of the tropical Pacific decadal variability (TPDV) is influenced by extratropical precursors of the El Niño-Southern Oscillation (ENSO) from the North and South Pacific. Models from the Coupled Model Intercomparison Project find that while most can simulate the observed spatial pattern and frequency characteristics of the TPDV, they tend to underestimate the influence of extratropical ENSO precursors. Better representation of ENSO precursor dynamics in the models could lead to improved understanding and predictability of Pacific decadal variability.