Resolving Cloud at Decimeter Scales by a T2 Lidar (Invited Presentation)

Clouds, crucial for understanding climate, begin with droplet formation from aerosols, but observations of this key activation step are lacking in the atmosphere. Atmospheric lidars firing visible and/or near-infrared laser pulses into the atmosphere are well-suited for the detection of micron-sized cloud droplets due to strong backscatter. However, most atmospheric lidars with range resolutions on the order of 10 m lack the ability to resolve meter-scale processes at cloud base boundaries, such as droplet formation processes. Here we use a time-gated time-correlated single-photon counting lidar (T2 lidar) to observe cloud base structures up to 10 cm range resolution. Results show that the air-cloud interface is not a perfect boundary but rather is a transition zone where transformation of aerosol particles into cloud droplets occurs. The observed distributions of first-arriving photons within the transition zone reflect vertical development of a cloud, including droplet activation and condensational growth. Further, the highly resolved vertical profile of backscattered photons above cloud base enables remote estimation of droplet concentration, an elusive but critical property to understand aerosol-cloud interactions. Our results show the feasibility of remotely monitoring cloud properties at submeter scales, thus providing much needed insights into impacts of atmospheric pollution on clouds, and aerosol-cloud interactions that influence climate.