Drizzle Drop Size Distributions in Marine Warm Stratocumulus Clouds Derived from Doppler Cloud Radar and Lidar

Marine boundary layer stratocumulus clouds are routinely observed over the subtropical oceans, and have a significant impact on the Earth’s radiation budget. Previous modeling and observational studies have shown drizzle to be ubiquitous in these cloud systems. Although frequent, due to small nature of the hydrometeor sizes, much of the drizzle evaporates before reaching the surface yielding rates of only few mm per day. Drizzle in these clouds has a significant impact on the cloud lifetime through removal of cloud water and through its impact on the sub-cloud layer turbulence that maintains the cloud layer.

In this work we have used the observations made at the Atmospheric Radiation Measurement (ARM)’s Eastern North Atlantic (ENA) site to retrieve sub-cloud layer drizzle drop size distributions during warm marine boundary layer stratocumulus cloud conditions. Data from the Ka-band ARM Zenith Radar (KAZR) and the laser ceilometer was primarily used in this work along with that from the Microwave Radiometer (MWR), radiosondes and other instruments. The ceilometer was calibrated during non-precipitating stratocumulus cloud conditions following the technique proposed by O’Connor et al. (2004), while the KAZR was calibrated using CloudSat data from the overpasses near the ENA site. We have identified several cases of single layered precipitating stratocumulus clouds at the ARM-ENA site. We will demonstrate the applicability of this technique to the data from the ARM ENA site and report averaged profiles of parameters describing drizzle drop size distribution, drizzle water content, drizzle water flux, and cooling rates.