On the relationship between the optical depth and effective radius of warm clouds using the unexploited solar background signals in lidar observations

Low-altitude boundary layer clouds strongly influence global climate through their impact on Earth's radiation and hydrological cycle. Long-term global measurements are crucial for providing direct observational constraints to improve our knowledge of cloud and precipitation formation, and to better represent these clouds in weather and climate models. While marine low clouds have been extensively studied, continental warm clouds receive relatively less attention.

To enhance ground-based observations for continental warm clouds, we introduce a novel retrieval method that exploits the previously untapped solar background signal present in current lidar measurements. We will demonstrate how this new method greatly extends lidar applications from cirrus to optically thick stratiform clouds. Using a three-year dataset over the Atmospheric Radiation Measurement Oklahoma site, we compare and contrast the relationships between optical depth and effective radius for both drizzling and non-drizzling clouds. This intercomparison is further used to develop a new approach for diagnosing the presence of drizzle. This new retrieval method can be easily applied to the existing lidar and European ceilometer networks.