Cloud property variations in the cloudy-to-clear transition zones - a comparison of shortwave spectral observations on different ARM sites

The transition zone between cloudy and clear air is one of the ideal regions for the observing the strong aerosol-cloud interactions and mixing/entrainment of cloud and dry air. Studying cloud and aerosol properties in the transition zone helps to better understanding of cloud-aerosol interactions and mixing processes.

We used zenith radiance measurements from ground-based shortwave hyper-spectral radiometers (deployed at MAGIC (Marine ARM GPCI Investigation of Clouds) mobile site (LA-Hawaii-LA) and at SGP (Southern Great Plains) site (Oklahoma)) to analysis how the cloud droplet size changes during the transition from cloudy to clear sky. Our analysis results based on the spectrally-invariant method show that: during MAGIC, most of cases (in summer) show nearly no changes in the droplet size; while at SGP, most of cases (in summer) demonstrate decreasing tendencies during the cloudy-to-clear transitions. These results suggest that "homogeneous" mixing dominates in the transition zones of SGP rather than those during MAGIC.