Evaluating drizzle formation parameterization using ensemble cloud retrievals from the MAGIC campaign

 

Authors

J.-Y. Christine Chiu — Colorado State University
Mark David Fielding — European Centre for Medium-Range Weather Forecasts
Robin J. Hogan — University of Reading

Category

Warm low clouds, including aerosol interactions

Description

Drizzle, common in marine boundary-layer clouds, plays a crucial role in microphysical, thermodynamic and dynamic processes that determine cloud structure and properties, and thus have a significant impact on both Earth’s radiative and hydrological energy budget. Yet, many global weather and climate models continue to produce drizzle too frequently by a factor of 1.5–2 at cloud base. Interestingly, evaluations in drizzle intensity have led to less consistent results – some suggest that models produce precipitation too lightly by a factor of 2, while some suggest that models could produce precipitation too strongly by a factor of 4. This calls into question the fidelity of models’ representation of drizzle formation, which has been predominantly parameterized using large eddy simulations rather than observations. The ARM Mobile Facility MAGIC deployment, featuring routine ship-based observations between Los Angeles and Hawaii in 2013, provides an excellent opportunity to evaluate drizzle formation parameterizations. We will evaluate both drizzle frequency and intensity, using simultaneous cloud and in-cloud precipitation properties, for the first time, retrieved from cloud radar, lidar and shortwave radiation measurements. The new retrievals allow us to disentangle model deficiencies between cloud and drizzle prediction, avoiding any potential compensation between formation terms and further providing a more observational-constrained parameterization.