CloudLab researchers use a giant white balloon to hoist a device that measures ice crystals high in the airCloudLabSomeone taking a walk in the snowy hills near the Swiss capital of Bern last winter would have been perplexed by a giant white balloon rising into the low-lying clouds. Near the hilltop where the balloon was tethered, they would have found a group of researchers launching a drone, then flying it upwind to sprinkle crystals of silver powder into the fog.We use the natural cloud as a laboratory, says Ulrike Lohmannat ETH Zurich in Switzerland, a member