Remote Detection of Drizzle from Low-Altitude Clouds


DOE scientists developed a novel remote sensing method to detect drizzle from low-altitude water clouds using the Atmospheric Radiation Measurement (ARM) program millimeter wave cloud radar (MMCR). Low-altitude water clouds have a significant influence on Earth’s climate through their interaction with radiation to and away from Earth. It has been a major technical challenge to remotely determine if low-altitude clouds do or do not rain because of the low thermal contrast between these clouds and Earth’s surface. ARM investigators found that cloud drizzle is dictated by the vertical variation of rain drop size and total cloud water. Drizzling clouds usually exhibit a decreasing trend of rain droplet size with altitude, while non-drizzling clouds have an opposite trend. Both theoretical analyses and observations suggest that drizzle drops can significantly increase in size near the bottom of a cloud layer. These findings help improve remote sensing of precipitation amounts and understanding of aerosol effects on clouds, associated rain, and climate.


Chen, R, R Wood, Z Li, R Ferraro, and F Chang, 2008: “Studying the vertical variation of cloud droplet effective radius using ship and space-borne remote sensing data.” Journal of Geophysical Research 113, doi:10.1029/2007JD009596.