#03 ATM Hydrologic Cycle in the ACME v0.3 Model

Abstract

We examine the global water cycle characteristics in the ACME v0.3 model (a close relative to CAM5.3) in atmosphere-only simulations spanning the years 1980-2005. We evaluate the simulations using observational and reanalysis datasets, examine how the simulations change with different horizontal resolution, and compare the simulations against models participating in the CMIP5 AMIP experiment. Regardless of resolution, the model exhibits several biases: global-mean precipitation, evaporation, and  precipitable water are too high, drizzle occurs too frequently, and the atmospheric residence time of water is too short. Regional biases in precipitation are identified and found to arise for differing reasons. Although increasing the resolution does not drastically change the water cycle, it does lead to a few differences: an increase in global mean precipitation rate, an increase in the fraction of total precipitation that falls over land, more frequent days of heavy precipitation (>30 mm d^-1), and a decrease in precipitable water. Some of these differences are found to result from changes in model tuning. This work was conducted under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM-Release: LLNL-ABS-692379.