ENSO Evolution and Teleconnections in IPCC’s Twentieth-Century Climate Simulations: Realistic Representation?

Abstract

This study focuses on the assessment of the spatiotemporal structure of ENSO variability and its winter climate teleconnections to North America in the Intergovernmental Panel on Climate Change?s (IPCC) Fourth Assessment Report (AR4) simulations of twentieth-century climate. The 1950?99 period simulations of six IPCC models are analyzed in an effort to benchmark models in the simulation of this leading mode of interannual variability: the Geophysical Fluid Dynamics Laboratory (GFDL) Coupled Model version 2.1 (CM2.1), the coupled ocean?atmosphere model of the Goddard Institute for Space Studies (GISS-EH), the NCAR Community Climate System Model version 3 (CCSM3), the NCAR Parallel Coupled Model (PCM), the Hadley Centre Coupled Atmosphere?Ocean General Circulation Model version 3 (HadCM3), and version 3.2 of the Model for Interdisciplinary Research on Climate at high resolution [MIROC3.2 (hires)]. The standard deviation of monthly SST anomalies is maximum in the Niño-3 region in all six simulations, indicating progress in the modeling of ocean?atmosphere variability. The broad success in modeling ENSO?s SST footprint?quite realistic in CCSM3?is however tempered by the difficulties in modeling ENSO evolution: for example, the biennial oscillation in CCSM3 and the lack of regular warm-to-cold phase transition in the MIROC model. The spatiotemporal structure, including seasonal phase locking, is, on the whole, well modeled by HadCM3; but there is room for improvement, notably, in modeling the SST footprint in the western Pacific. ENSO precipitation anomalies over the tropical Pacific and links to North American winter precipitation are also realistic in the HadCM3 simulation and, to an extent, in PCM. Hydroclimate teleconnections that lean on a stationary component of the flow, such as surface air temperature links, are however not well modeled by HadCM3 since the midlatitude ridge in the ENSO response is incorrectly placed in the simulation; PCM fares better. The analysis reveals that climate models are improving but are still unable to simulate many features of ENSO variability and its circulation and hydroclimate teleconnections to North America. Predicting regional climate variability/change remains an onerous burden on models.