Abstract
This study undertakes a multi-model comparison with the aim to describe and quantify systematic changes of the global energy and water budgets when the horizontal resolution of atmospheric models is increased and to identify common factors of these changes among models. To do so, we analyse an ensemble of twelve atmosphere-only and six coupled GCMs, with different model formulations and with resolutions spanning those of state-of-the-art coupled GCMs, i.e. from resolutions coarser than 100 km to resolutions finer than 25 km. The main changes in the global energy budget with resolution are a systematic increase in outgoing longwave radiation and decrease in outgoing shortwave radiation due to changes in cloud properties, and a systematic increase in surface latent heat flux; when resolution is increased from 100 to 25 km, the magnitude of the change of those fluxes can be as large as 5 W m−2. Moreover, all but one atmosphere-only model simulate a decrease of the poleward energy transport at higher resolution, mainly explained by a reduction of the equator-to-pole tropospheric temperature gradient. Regarding hydrological processes, our results are the following: (1) there is an increase of global precipitation with increasing resolution in all models (up to 40 × 103 km3 year−1) but the partitioning between land and ocean varies among models; (2) the fraction of total precipitation that falls on land is on average 10% larger at higher resolution in grid point models, but it is smaller at higher resolution in spectral models; (3) grid points models simulate an increase of the fraction of land precipitation due to moisture convergence twice as large as in spectral models; (4) grid point models, which have a better resolved orography, show an increase of orographic precipitation of up to 13 × 103 km3 year−1 which explains most of the change in land precipitation; (5) at the regional scale, precipitation pattern and amplitude are improved with increased resolution due to a better simulated seasonal mean circulation. We discuss our results against several observational estimates of the Earth's energy budget and hydrological cycle and show that they support recent high estimates of global precipitation.
Highlights
The state of the climate results from the complex balance of fluxes of energy in and out of the Earth system, as well as fluxes of energy and water between its components
We provide the number of years used for each simulation and in column 8, the number of ensemble members used in this study
Pope and Stratton (2002) showed that a similar cooling occurred in dynamical core experiments which they attributed to the non-linear interactions of stratospheric gravity waves at higher resolution
Summary
The state of the climate results from the complex balance of fluxes of energy in and out of the Earth system, as well as fluxes of energy and water between its components. Large uncertainties remain: surface radiative fluxes, which are difficult to measure from space, are only known within ± 10 W m−2; the Global Precipitation Climatology Project (GPCP), which is the best available dataset for global precipitation, appears to be underestimating precipitation by at least 10% in the light of recent CloudSat observations (Stephens et al 2012) Climate models, despite their inherent biases, have the potential to ensure consistency between the intertwined energy budget and hydrological cycle. Pope and Stratton 2002; Bacmeister et al 2014; Demory et al 2014) have assessed the resolution sensitivity of the energy budget and hydrological cycle in global climate models Those which did often focused on changes at the regional scale or on a single model.
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