Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud.

然后上升气流将轻盈的、带正电荷的冰晶带到云的顶部。

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When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud.

当这些冰粒下落时，其中一些会撞到云团中心的更小的冰晶。

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All over the cloud, the number of ice crystals multiplies - and soon the whole cloud might be ice.

云层中的冰晶体数量会倍增，不久整块云层都会成为冰层。

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But officials said the flights also will serve as a partial replacement for one satellite: NASA's Ice, Cloud and Land Elevation Satellite, known as ICESat.

CNN: NASA flights will study Antarctic ice changes

In China, they use artillery shells, rockets and airplanes to spray existing cloud systems with silver iodide, a compound that triggers moisture in the clouds to form ice crystals, which then fall to earth as snow or rain.

WSJ: Blizzard Renews Storm Over China Making Snow

Less ice on rivers, lakes and the sea will lead to more evaporation, probably increasing cloud cover at mid-levels, which should have a cooling effect.

ECONOMIST: The science