Global map showing average ice asymmetry from remote sensing data
Remote sensing of the shape characteristics of ice crystals allows determination of their light scattering properties, which is important for determining the effects of ice clouds on climate. This figure shows the first global view of average ice asymmetry parameter, which quantifies the partitioning between forward and backward scattering of light when encountering a collection of ice crystals. Credit: van Diedenhoven et al. [2020], Figure 1c
Source: Journal of Geophysical Research: Atmospheres

There have been many gaps in our understanding of clouds because their formation and evolution is governed by physical processes on a large range of scales and by complex interactions with the rest of the atmosphere. For ice clouds, the sizes and shapes of ice crystals dictate how much sunlight they reflect.

van Diedenhoven et al. [2020] combine a year of observations by two satellites to produce the first global database of ice crystal size and shape at the tops of thick ice clouds. Both are found to vary with temperature in a manner that can be plausibly explained by a simple theoretical representation of ice crystal growth from water vapor. This simplicity is somewhat surprising and may indicate that the many more complex ice growth processes have limited effect on the variation of ice shape and size at the tops of such clouds.

The authors argue that some common assumptions need to be revisited regarding the influence of ice crystal size and shape on the amount of sunlight reflected by ice clouds. These findings may help improve other satellite observations and the representation of ice clouds in climate models.

Citation: van Diedenhoven, B., Ackerman, A. S., Fridlind, A. M., Cairns, B., & Riedi, J. [2020]. Global statistics of ice microphysical and optical properties at tops of optically thick ice clouds. Journal of Geophysical Research: Atmospheres, 125, e2019JD031811. 

—Zhanqing Li, Editor, JGR: Atmospheres

Text © 2020. The authors. CC BY-NC-ND 3.0
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