Ice Formation in Stratiform Mixed-phase Clouds at Warm Temperatures

Zhang, D., Brookhaven National Laboratory

Cloud Processes

High Latitude Processes

Zhang D, Z Wang, T Luo, Y Yin, and C Flynn. 2017. "The occurrence of ice production in slightly supercooled Arctic stratiform clouds as observed by ground-based remote sensors at the ARM NSA site." Journal of Geophysical Research: Atmospheres, 122(5), 10.1002/2016JD026226.


Occurrences and case amounts of ASCs in terms of cloud-top temperature and depolarization ratio over the NSA Barrow site from MPL (a and c) and HSRL measurements (b and d). The occurrence is normalized at each CTT. The dashed lines are CTTs of -4, -8, -10, and -20°C, respectively.


Occurrences and case amounts of ASCs in terms of cloud-top temperature and depolarization ratio over the NSA Barrow site from MPL (a and c) and HSRL measurements (b and d). The occurrence is normalized at each CTT. The dashed lines are CTTs of -4, -8, -10, and -20°C, respectively.

Science

Low-level stratiform clouds have a high occurrence in polar regions. Accurate cloud thermodynamic phase determination is required to perform cloud property retrievals and to study aerosol-cloud interactions with remote-sensing measurements. However, ice particle formation in slightly supercooled stratiform clouds is still not well documented or understood. 

Impact

The Atmospheric Radiation Measurement (ARM) Research Facility provides state-of-the-art measurements of cloud macrophysical, microphysical, and radiative properties using various ground-based remote sensing, in situ, and sounding measurements. In this study, four years of combined lidar depolarization and radar reflectivity measurements are analyzed to study ice particle formation in slightly supercooled Arctic stratiform clouds over the ARM North Slope of Alaska (NSA) Barrow site.

Summary

Combined lidar depolarization and radar reflectivity measurements offer reliable distinctions between cold drizzle drops and non-spherical ice crystals in slightly supercooled Arctic stratiform clouds (ASCs). The large data set used here provides robust evidence that, statistically, ice crystals are formed in slightly supercooled ASCs at cloud-top temperatures as high as -4 °C. However, more detailed analysis of the ice crystal formation mechanisms at high cloud-top temperatures is needed. In addition, due to small depolarization at the cloud-top temperature range between -8 and - 10°C, it is still challenging to determine cloud thermodynamic phase structures within this range. For strong ice precipitating ASCs (radar reflectivity > -20 dBZ), lidar depolarization correlates well with radar reflectivity at each temperature range, but the depolarization-reflectivity relationships vary with cloud-top temperature ranges, which might be related to different ice particle growth habits. The liquid water path (LWP) has different impacts on ice phase evolution in ASCs at different temperature ranges. Further interpretation of the impacts of LWP and other factors requires a combination of observations with modeling work.