Characterizing the pathways of ice formation in clouds

Scientists measured an important sub-process of the water cycle.


Ice formation in clouds is a key component of the hydrological cycle on Earth. Given the complex interaction of aerosols, atmospheric dynamics, and cloud microphysical properties, it is a challenge in weather and climate research to isolate the single process leading to the formation of ice in tropospheric clouds.

Characterizing the multitude of pathways of ice formation in clouds is difficult because the relevant processes take place in a turbulent environment on different scales.

For the first time, a team from Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig has observed vertical air motions increase ice formation in mixed-phase clouds. The team used laser and radar instruments to measure the vertical air velocity and ice formation in thin mixed-phase clouds. Such clouds contain ice particles, water vapor, just as supercooled liquid droplets.

The outcomes of this study are expected to provide detail information about the water cycle better in the weather and climate models in the future by ice formation in clouds.

Johannes Bühl of TROPOS reported, “Both lidar and radar instruments were, therefore, necessary to investigate the turbulence and ice formation in these clouds above Leipzig from the ground.”

“The effect only became visible when we observed the ice directly below the clouds’ top layer. Our findings enable for the first time quantitative and well-constrained insights into the relationship between turbulence and ice formation in the atmosphere. The stronger a cloud is ‘shaken’ by vertical air motions, the more ice falls out of it.”

“This correlation was measured for clouds colder than -12 °C. Next, the remote sensing scientists want to explore the influence of aerosols by taking a closer look at the beginning (ice nucleation) and end (precipitation of ice particles) of the ice formation process.”

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