资源环境科技发展态势分析平台

The key assumption underlying convection parameterizations is that rising plumes develop in a horizontally homogeneous environment. With this in mind, we investigate the impact of environmental cloud layer heterogeneities on shallow convection using large-eddy simulation that applies a master-slave methodology. In the master-slave approach, two independent sets of thermodynamic variables (master and slave) are driven by one dynamics (coupled with the master) to remove the impact of internal variability of the dynamical system considered. The two thermodynamic sets include either a realistic heterogeneous environment or an environment that is homogenized outside clouds. The key is that homogenization also excludes subsiding shells surrounding cumulus clouds. The results show a small impact of the homogenization on cloud field properties. The physical explanation highlights the role of the subsiding shell shielding a shallow cumulus cloud from its environment.

Plain Language Summary Coarse-resolution weather and climate models need to use convection parameterizations for representing vertical transport by ascending plumes or bubbles. Those parameterizations typically assume that convective elements develop in a homogeneous environment. This key assumption was recently questioned in a study showing that plume properties critically depend on the local environment in which they rise. The current study revisits this assumption by explicitly simulating the development of shallow convective clouds using a method that facilitates comparing the same portions of cloudy air undergoing two different scenarios: mixing either with a heterogeneous or homogeneous environment. The results highlight an insignificant impact of environmental temperature and moisture perturbations on the cloud development and strongly support the homogeneous environment assumption in convection parameterizations.