Simulation of low clouds from the CAM and the regional WRF with multiple nested resolutions

[1] Current climate models have shown systematic simulation biases of low clouds that have cast great uncertainties on the climate sensitivity of these models. Among them is the deficient amount of low clouds over the storm tracks. This study uses the NCAR Community Atmospheric Model (CAM) and the Weather Research and Forecasting model (WRF) to study the cause of the failure of the global model in simulating low clouds associated with a frontal passage over the North Atlantic. The global model is shown to simulate the large-scale circulation that can support the boundary layer instabilities responsible for the observed clouds, but because the global model does not resolve the unstable modes, the instability cannot be realized. The resolution requirement of cloud simulations is discussed. This study also demonstrates the feasibility of cloud parameterization by nesting high resolution models into coarse resolution models to tap into the dynamical properties of the large-scale flows.