ENSO variability in an ultra-high resolution CCSM simulation

An ultra-high-resolution global climate simulation with development version 4 of Community Climate System Model (CCSM) was conducted as part of the Lawrence Livermore National Laboratory (LLNL) Grand Challenge computing program. The atmospheric model was run using a finite volume dynamical core with a horizontal resolution of ~0.25 degrees in latitude and longitude with 26 vertical levels. The ocean and sea-ice model were run using a tripole grid with a horizontal resolution of ~0.1 degrees in latitude and longitude with 42 vertical levels. Here we present analysis of the ENSO variability in the twenty year integration. We validate the model mean state, annual, and interannual variability of key model variables. The climatological mean sea surface temperature (SST) is in a good agreement with the observed. A bias of excessive simulated precipitation rate is observed in the tropical Eastern Pacific. The model underestimates the magnitude of the annual SST variations in the Eastern Pacific. The model has statistically significant power at ENSO time-scales, though it overestimates the power at 4 years of the Nino3.4 SST variability. Linear regression demonstrates that the model has a realistic ENSO behavior, though the precipitation anomalies extend too far east in the Eastern Pacific. In the ocean there are consistent ENSO signatures in SST, sea surface height, and the depth of 20°C isotherm. Where possible this simulation will be compared with lower resolution simulations CCSM simulations to assess the impact that using ultra-high resolution has on the fidelity of ENSO and its teleconnections.

Acknowledgement. This work was supported under the auspices of the US Department of Energy Office of Science, Regional and Global Climate Modeling Program by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.