Abstract
As the horizontal resolution of general circulation model (GCM) is increased, the sub-grid scale vertical transport has to be decreased appropriately. In the present study, a resolution-dependent (so-called scale-adaptive or scale-aware) deep convection was formulated by controlling the cumulus base mass flux. Using a three-dimensional cloud resolving model simulation, we estimated the appropriate ratios of the sub-grid scale vertical transport to the total vertical transport of moist static energy for different horizontal resolutions, whose values are about 0.8 for 100 km resolution and about 0.6 for 50 km resolution. Those values were used as a guideline to decrease to the ratio of convective precipitation to the total precipitation in a high-resolution GCM. The cumulus base mass flux is reduced by multiplying a reduction coefficient, which is 0.2 for the 100 km resolution and 0.09 for the 50 km resolution in the present GCM. The GCM with the scale-adaptive deep convection produces the climatological mean precipitation similar to that of the original GCM, whereas it simulates the heavy precipitation frequency and the Madden and Julian Oscillation much better than those of the original GCM.
Highlights
Conventional general circulation models (GCMs) have two processes to produce total precipitation
The GCM used in this study is the Seoul National University Atmospheric General Circulation Model (SNUAGCM)
The appropriate observation in the South Pacific Convergence Zone (SPCZ) and decrease ratio of the cumulus mass flux is examined with a threethe Intertropical Convergence Zone (ITCZ) regions as the dimensional Cloud Resolving Model (CRM) simulation in the section Ratio of sub-grid scale horizontal resolution increases
Summary
Conventional general circulation models (GCMs) have two processes to produce total precipitation. The main role of the convection scheme is parameterization of unresolved sub-grid scale vertical transport in coarse horizontal resolution GCMs, accompanying the convective condensation and precipitation process. The horizontal resolutions of GCMs have been increasing due to the development of computing power, and the highresolution GCMs have the capability to simulate more resolved grid scale vertical transport. As the horizontal resolution of GCMs becomes higher than the order of 10 km, convections can be partly resolved by grid scale vertical transport.[1] GCMs with the order of 10 km horizontal resolution have the problem of how to represent the convection, which is so-called the Grey Zone problem.[2]
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