Evaluating ENSO's Spatiotemporal Complexity in the CWB CFS 1‐Tiered Model Hindcasts

Abstract

AbstractUsing hindcasts produced by a coupled climate model, this study evaluates whether the model can forecast the observed spatiotemporal complexity in the El Niño−Southern Oscillation (ENSO) during the period 1982−2011: the eastern Pacific (EP), central Pacific‐I (CP‐I) and ‐II (CP‐II) types of El Niño, and the multi‐year evolution events of El Niño occurred in 1986–1988 (i.e., 1986/87/88 El Niño) and La Niña occurred in 1998–2000 (i.e., 1998/99/00 La Niña). With regard to the spatial complexity, it is found that the CP‐I type of El Niño is the easiest to hindcast, the CP‐II is second, and the EP is most difficult to hindcast as its amplitude is significantly underestimated in the model used here. The model deficiency in hindcasting the EP El Niño is related to a warm bias in climatological sea surface temperatures (SSTs) in the tropical eastern Pacific. This warm bias is related to model biases in the strengths of the Pacific Walker circulation and South Pacific high, both of which are notably weaker than observed. As for the temporal complexity, the model successfully hindcasts the multi‐year evolution of the 1998/99/00 La Niña but fails to accurately hindcast the 1986/87/88 El Niño. This contrasting model performance in hindcasting multi‐year events is found to be related to a cold bias in climatological SSTs in the tropical central Pacific. This cold bias result enables the model La Niña, but not El Niño, to activate intrabasin tropical‒subtropical interactions associated with the Pacific Meridional Mode that produce the multi‐year evolution pattern.