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Simulating the diurnal cycle of rainfall in global climate models: resolution versus parameterization
Authors:Paul A Dirmeyer  Benjamin A Cash  James L Kinter III  Thomas Jung  Lawrence Marx  Masaki Satoh  Cristiana Stan  Hirofumi Tomita  Peter Towers  Nils Wedi  Deepthi Achuthavarier  Jennifer M Adams  Eric L Altshuler  Bohua Huang  Emilia K Jin  Julia Manganello
Institution:1. Center for Ocean-Land–Atmosphere Studies, Calverton, MD, USA
2. George Mason University, Fairfax, VA, USA
3. The European Centre for Medium-Range Weather Forecasts, Reading, UK
4. Research Institute for Global Change/Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
5. Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan
Abstract:The effects of horizontal resolution and the treatment of convection on simulation of the diurnal cycle of precipitation during boreal summer are analyzed in several innovative weather and climate model integrations. The simulations include: season-long integrations of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) with explicit clouds and convection; year-long integrations of the operational Integrated Forecast System (IFS) from the European Centre for Medium-range Weather Forecasts at three resolutions (125, 39 and 16 km); seasonal simulations of the same model at 10 km resolution; and seasonal simulations of the National Center for Atmospheric Research (NCAR) low-resolution climate model with and without an embedded two-dimensional cloud-resolving model in each grid box. NICAM with explicit convection simulates best the phase of the diurnal cycle, as well as many regional features such as rainfall triggered by advancing sea breezes or high topography. However, NICAM greatly overestimates mean rainfall and the magnitude of the diurnal cycle. Introduction of an embedded cloud model within the NCAR model significantly improves global statistics of the seasonal mean and diurnal cycle of rainfall, as well as many regional features. However, errors often remain larger than for the other higher-resolution models. Increasing resolution alone has little impact on the timing of daily rainfall in IFS with parameterized convection, yet the amplitude of the diurnal cycle does improve along with the representation of mean rainfall. Variations during the day in atmospheric prognostic fields appear quite similar among models, suggesting that the distinctive treatments of model physics account for the differences in representing the diurnal cycle of precipitation.
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