New Method for Determining Cloud Droplet Size


Cloud droplet size is an important variable for understanding the impact of clouds on Earth’s radiation budget because different size droplets reflect different amounts of sunlight. Cloud droplet size can be impacted by meteorology, cloud type, aerosol concentration, and other factors, so accurate observations of cloud droplet size are needed to evaluate the ability of models to reproduce the correct droplet size under different conditions. U.S. Department of Energy (DOE) scientists have developed a new method of determining cloud droplet size and liquid water path that uses zenith radiance measurements from single ground-based instruments at DOE Atmospheric Radiation Measurement (ARM) and the National Aeronautics and Space Administration’s Aerosol Robotic Network (AERONET) sites. The new retrieval has an accuracy of 11% to 22%, depending on the cloud conditions, and compares favorably to methods combining multiple instruments or using more expensive instruments such as cloud radars.  By using only a single instrument, the new retrieval can be implemented at more measurement sites worldwide, providing more information for climate models.


Chiu, J. C., A. Marshak, C. H. Huang, T. Varnai, R. J. Hogan, D. M. Giles, B. N. Holben, E. J. O’Connor, Y. Knyaikhin, and W. J. Wiscombe. 2012. “Cloud Droplet Size and Liquid Water Path Retrievals from Zenith Radiance Measurements: Examples from the Atmospheric Radiation Measurement Program and the Aerosol Robotic Network,” Atmospheric Chemistry and Physics 12, 10313–329. DOI: 10.5194/acp-12-10313-2012.