Feasibility of Using Ultra-High Resolution Radar Measurements to Detect Drizzle Particles in a Convection-Cloud Chamber

Drizzle formation is one of the most important microphysical processes in warm clouds. The mechanism of controlling drizzle formation, i.e., collision coalescence, is poorly represented in models, thus leadings to large discrepancies compared with observations in terms of cloud dynamical structure, lifetime, and precipitation characteristics. On the other hand, it has been proposed that drizzle formation can be achieved in a laboratory convection-cloud chamber, allowing aerosol-cloud-drizzle interactions to be studied on a fundamental level. However, detection of rare drizzle drops in a large cloud chamber is a challenging task due to the limited sampling volume of typical in situ droplet detection instruments. Instead, we envision using a remote sensing instrument to sample the cloud chamber with high temporal-spatial resolution, thereby providing frequent and continuous hydrometer detections.

In this study, we explore the feasibility of using radar observation to detect drizzle particles generated in convection-cloud chamber. Specifically, we propose a “small radar sampling” concept in which scenario the occurrence of drizzle particle in the radar sampling volume becomes a rare event and thus can be distinguished from the cloud particle signals. Theoretical estimates show that with the application of a radar volume of several cm3, the detection of single drizzle particle with diameter around 50 μm is achievable. Observations from the Pi Convection-Cloud Chamber are used to validate the theoretical estimation. Finally, an experiment using the THz radar with cm scale range resolution applied in a test spray chamber is conducted to demonstrate the feasibility of the drizzle detection concept in the convection-cloud chamber.