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Do water droplets cluster inside clouds? Researchers confirm two decades of theory with an airborne imaging instrument. Like raindrops streaking across the windows of your car while you drive through a rainstorm, water droplets in clouds travel in airflow streamlines -- following currents of air usually without touching. However, the air inside clouds tends to be turbulent, as any nervous flier can attest to, and swirling turbulent air causes droplets to cluster. For 20 years, atmospheric scientists have conjectured that water droplets do indeed cluster inside clouds, largely owing to the knowledge that turbulent airflows are full of spinning vortices that mix fluids well. But clouds swirl on such vast scales that doubts persisted whether the turbulence simulated by a computer or generated in a laboratory could be translated to the atmosphere. A team of atmospheric scientists has taken instruments to the atmosphere itself and have confirmed that water droplets do indeed cluster together inside clouds.