Evaluation of stratocumulus clouds in WRF-Chem simulations for VOCALS-REx

This study focuses on evaluating the representation of marine stratocumulus clouds and their radiative forcing in WRF-Chem (the chemistry version of the Weather Research and Forecasting model). The WRF-Chem (v3.2.1) simulations are conducted with fully coupled aerosol-cloud-interaction modules for the VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment) Modeling Experiment. Model simulations are evaluated against observed cloud properties such as cloud cover, liquid water path, optical thickness, and shortwave radiative forcing. In order to identify the key areas in the model that lead to potential biases in the simulated cloud properties, the following factors critical to the cloud processes are also compared to observations: cloud condensation nuclei (CCN) number concentration, mean cloud droplet size, boundary layer height, vertical velocity, and rain rate. The evaluation is based on observational data obtained during the VOCALS-REx from satellite remote sensors, shipborne lidar/radar, and aircraft in-situ measurements. The ability of WRF-Chem to simulate marine stratocumulus clouds is evaluated on different time scales (e.g., monthly average, daily mean and diurnal variation). Areas in WRF-Chem that require improvements in order to better reproduce marine stratocumulus clouds over the Southeast Pacific will be discussed.