Over the southeast Atlantic Ocean, a 2,000-mile-long plume of smoke from African agricultural fires meets a near-permanent cloud bank offshore. Their meeting makes a natural laboratory for studying the interactions between cloud droplets and the tiny airborne smoke particles. This month, NASA’s P-3 research aircraft and a team of scientists return on their third deployment to this region as part of the Observations of Aerosols Above Clouds and their Interactions mission, or ORACLES, gathering data on how aerosols such as smoke affect clouds and in turn Earth’s climate.