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Hoerling, M. P., M. Ting, and M. L. Blackmon, 1992: Simulating the atmospheric response to the 1985-87 El Niño cycle. J. Climate, 5, 669-682.


The atmospheric response to the evolution of global sea surface temperatures (SSTs) from 1985 to 1987 is studied using the NCAR Community Climate Model (CCM1). Five separate 2-year integrations are performed, and results are presented for the ensemble-averaged response during the pre-El Niño 1985/86 winter and the mature El Niño 1986/87 winter.

No skill is found in CCM1's simulation for 1985/86. The simulation for the following winter, when tropical Pacific SST anomalies approached 2°C, is more successful. A large-amplitude wave train extends poleward and eastward from the location of anomalous central Pacific convection in CCM1, although the model's wave train is shifted 30° too far east compared to observations.

A linear barotropic stationary wave model is used to diagnose CCM1's response during 1986/87. The eastward-shifted PNA response is easily excited by a dipole pattern of upper-level forcing with convergence over the western tropical Pacific and divergence over the central tropical Pacific. In contrast, the observed anomaly pattern during 1986/87 is most ettectively forced by anomalous subtropical convergence over the central Pacific. Zonally asymmetric features of CCM1's climate drift, in particular the pattern of zonal wind biases over the tropical and midialitude North Pacific, are shown to account for these different sensitivities.