#C03 Fully Coupled High-Resolution ACME V0.1 Approximate Present Day Transients

To provide a baseline for comparisons with subsequent ACME simulations, a 130-year 1850 pre-industrial control (PICNTRL) simulation and a 6-member ensemble of idealized present day (PD) transient simulations approximating 1970-2010 climate change, were carried out using fully coupled high-resolution ACME V0.1. This model has enhanced horizontal resolution in each of its components relative to standard coupled climate model resolution, and consists of the 1/4° Community Atmosphere Model 5 - Spectral Element (CAM5-SE) /Community Land Model 4 (CLM4), and 1/10° Parallel Ocean Program 2 (POP2)/CICE4 (sea ice model). The initialization protocol of branching present day transients off a multi-century PICNTRL and then running from 1850 to present day is precluded at these horizontal resolutions by lack of computer power. Consequently, our PD ensemble was initialized in three ways to test the viability of alternative approaches. Two members are branched off the PICNTRL at years 20 and 90, while three others were initialized from an atmospheric reanalysis-forced 0.1° POP2/CICE4 simulation run for 1948-2009 that was configured in the same framework as the fully coupled model. These latter initial conditions were selected to represent a spread in climate mode variability from the late 1960s to the late 1970s. Finally, a sixth transient was initialized from a two-year spun-up state of POP2/CICE, the same initial condition that was used to initialize the PICNTRL. All the PD transients started in 1970 and were run through 2000; the three started from the 60-year POP2/CICE4 continued through 2015.  All transient ensemble member TOA imbalances reduced to roughly the observed present-day value during the last decade of the simulations. The simulated climate system was also assessed in terms of drift and bias, especially focusing on comparisons of present-day observations and the transient ensemble. Particularly, we examined sea surface temperature biases, meridional ocean heat transport and overturning circulation, sea ice thickness and concentration biases, and simulated climate mode variability.