Named after the Latin word meaning “curling lock of hair”, cirrus clouds form high in the atmosphere, and often signal that a deterioration in the weather is on the way. But these beautiful repeating wisps of cloud are also mysterious: little is known about what triggers the embryonic ice-crystals to grow, from which cirrus clouds grow. The question is important because these cold high-level clouds act like a blanket around Earth, trapping heat in, and their predisposition to form in the future could have big implications for the rate at which global warming progresses.
Now scientists from the US Department of Energy’s Pacific Northwest National Laboratory in Washington state have managed to watch the birth of a cirrus cloud in unprecedented detail, by recreating the temperature, pressure and humidity of the high atmosphere, inside a minute cloud-chamber – smaller than a poppy seed. Using a scanning electron microscope they watched how tiny particles (2 microns wide, equivalent to one tenth the width of human hair) attracted water vapour, and grew an ice-crystal, over the course of about 20 minutes. “Behind all these beautiful images were months and months of hard work,” says Alexander Laskin, one of the co-authors, whose findings have been published in Physical Chemistry Chemical Physics.
The images, which were taken every three seconds, resolved detail as small as 50 nanometres wide (one-thousandth the width of a human hair). Such high-resolution means that scientists can start to understand how a particle’s size, shape, chemistry and texture affect the way that ice crystals grow, and better understand what kind of conditions encourage these high-level clouds to form.
