Evaluation of modeled cloud properties against aircraft observations for air quality applications



[1] Cloud microphysical properties are critical for simulating cloud processing of gases and aerosols in air quality models. In this study, cloud liquid water contents (LWC) predicted from a meteorological model at two horizontal resolutions (15 and 2.5 km) are evaluated against aircraft observations during the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign. A point-by-point comparison along flight tracks shows good model-observation correlation for temperature and humidity but poor correlation for LWC due to the mismatch in timing and positioning of the clouds between model simulations and observations. Thus a statistical approach is used to compare properties of modeled and observed clouds over the flight domain. The model captures the observed vertical variation of LWC for the towering cumulus (TCu) cases and reproduces the observed variation of LWC from flight to flight independent of cloud types. The model is able to distinguish the difference in the mean and standard deviation of LWC between stratocumulus (SCu) and TCu. However, the “in-cloud” LWC values were generally overpredicted by the model at both resolutions. For SCu, the overprediction is 99% and 45% for the 15- and 2.5-km resolution simulations, respectively, while the overprediction for TCu is slightly smaller at 74% for the 15-km resolution and 24% for the 2.5-km resolution model simulations. The SCu observations were scaled up to enable comparisons at the model-grid scales for these flights. This comparison also shows overpredictions of LWC by the model, although the overprediction is smaller for the model at 15-km resolution.