Impact of Integrated Vertical Overlap of Cumulus and Stratus on the Global Precipitation and Radiation Processes in the Seoul National University Atmosphere Model Version 0 With a Unified Convection Scheme (SAM0‐UNICON)

摘要

The previously proposed parameterization for the integrated vertical overlap of cumulus and stratus is implemented online into the cloud microphysics and radiation schemes of the Seoul National University Atmosphere Model version 0 with a Unified Convection Scheme (SAM0‐UNICON). Instead of a single‐merged cloud, the modified radiation scheme handles cumulus, stratus, and stratiform snow, separately, with each type having its own optical properties and vertical overlap structures. The integrated cloud overlap parameterization implemented into the cloud microphysics schemes do not reduce the biases of surface precipitation rate (PRECT) and cloud radiative forcing. Although it changes the overlap structures of clouds and precipitation areas, as well as the associated cloud microphysical processes either directly or indirectly, strong cancelation occurs among these terms, resulting in small changes to the global‐mean PRECT and cloud radiative forcing. The integrated cloud overlap parameterization implemented into the radiation scheme has a substantial impact on the simulated climate: the global‐mean cloud radiative forcing decreases substantially, mainly due to the separate treatment of radiative properties of individual cumulus, stratus, and stratiform snow, and PRECT exhibits strong regional responses. Sensitivity simulations showed that vertical cloud overlap exerts a weaker influence on the global‐mean PRECT than the previous off‐line simulations, implying that the indirect effect offsets the direct effect. In contrast to the off‐line simulations, the enhanced randomness of cumulus overlap increases PRECT over the western Pacific warm pool region. Our study indicates that vertical cloud overlap has substantial impacts on global climate through complex interactions with other physical processes.