How clouds become rain is a mystery Credit: Jack Dykinga/naturep.com/Alamy
Soon after the supercold water froze, a strange spring-like ice was born. Researchers have observed this process for the first time, which may help explain how clouds containing millions of supercooled water droplets produce rainfall and affect Earth’s climate.
Clouds are made up of many tiny water droplets with temperatures below zero, which can exist as liquids before being penetrated by ice particles, triggering a series of complex and little-known freezing states.
The length and frequency of these different states are crucial for models that model how clouds produce rainfall and reflect light in the atmosphere, but this process happens so quickly that it is difficult to study.
Claudiu Stan of Rutgers University in Newark, New Jersey, and colleagues discovered that an ice that forms inside a supercooled water droplet is compressed and stretched at different points, like a spring in motion, which occurs a few microseconds after its first freezing. “It was very unexpected for us,” Stan said. “It took us a while to understand.”
To capture this ice and the entire freezing process, Stan’s team dripped a stream of water in a vacuum, cooling it to around minus 39 degrees Celsius. They then used microscopes and X-rays to image tens of thousands of these droplets. Although only one image can be captured at a particular stage of each droplet freezing, they can map the entire process by looking at many droplets, which is a bit like watching an animated book.
The researchers found that every drop of water turns into a ball of slush. Before it freezes completely from the outside in, the network of ice penetrates into the liquid water. This increases the internal pressure until the droplets break or water is ejected, both of which create ice particles that freeze other droplets. This, and the kind of ice that formed, may better explain how and when these droplets form ice in clouds that turn into rain, Stan says, even though differences in laboratory environments make it impossible to apply the results directly.
Stephen Cox of the University of Cambridge in the United Kingdom said the discovery of this strain ice did not fit the current understanding of the molecular level. “From climate science to food technology, trying to understand the molecular mechanisms of ice formation is important in many fields. This study shows that we still have a long way to go, and I hope it will inspire a lot of new research in this area.” ”
The researchers published the findings in the August 16 issue of Nature. (Source: China Science News Guo Yueying)
Related paper information:https://doi.org/10.1038/s41586-023-06283-2
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