The Replication of ENSO-related anomalies over the United States by several AMIP Models

Atmospheric Model Intercomparison Project (AMIP) model integrations serve as a major diagnostics and attribution tool for determining whether extratropical climate anomalies are forced externally from the ocean surface or are internal to the atmosphere. One such external forcing, that has considerable impact on global climate anomalies, is the El Niño-Southern Oscillation (ENSO). The global ENSO teleconnections simulated by the models, however, contain model biases that are determined by model physics. In order to have confidence in the model representation of the ENSO teleconnection patterns and how they vary from event to event, the ENSO-related signal must be consistent across many atmospheric general circulation models (AGCM). This study examines how well several AMIP models replicate the ENSO response over the United States.

Based on a fifty-five year period, a set of observed ENSO composites are created and compared with the ensemble mean ENSO response simulated in AMIP model runs from five different AGCMs (each made up of 9-16 members). The composites show the seasonally varying pattern of temperature and precipitation over the United States and the associated 200-hPa circulation over the PNA-region of the North Pacific Ocean and United States. The focus is on the degree to which the AMIP models capture the spatial-scale of the observed ENSO composite anomalies (i.e. their agreement and biases). Lastly, the potential forcing region and strength (“flavors”) of ENSO events will be examined.