Simulating ENSO During the Last Glacial Maximum and Holocene

We simulate paleo ENSO variability using GENMOM, a non flux-corrected AOGCM comprised of the GENESIS V3.0 atmospheric model and the MOM2 ocean model. The model produces realistic present ENSO variability and characteristics comparable with similar models used in the 2007 IPCC AR4 assessment. Our model runs include 1000-yr equilibrium simulations for 21 ka, 11 ka, 6 ka and 0 ka that are forced with ICE4G orography, ice sheets, appropriate orbital configurations and atmospheric CO2 levels. Atmospheric CO2 is set at 180, 240, 280, 355 ppmv for 21 ka, 11 ka, 6 ka and 0 ka, respectively. An alternate simulation for 21ka was run with a changed CO2 level but with modern insolation to allow us to assess the influence of CO2 on ENSO. Modeled paleo ENSO variability is found to occur at lower frequency and and lower amplitude than at present, in agreement with some proxy records. The spatial patterns of paleo ENSO in the tropical Pacific and their related global teleconnection patterns exhibit substantial differences under changing CO2 and insolation. Additional scenarios for 16 ka and 9 ka are planned with the intent on creating a piecewise simulated record of ENSO throughout the last 21,000 years.