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R. Giles Harrison, Keri A. Nicoll, Douglas J. Tilley, Graeme J. Marlton, Stefan Chindea, Gavin P. Dingley, Pejman Iravani, David J. Cleaver, Jonathan L. du Bois, and David Brus


Electric charge is always present in the lower atmosphere. If droplets or aerosols become charged, their behavior changes, influencing collision, evaporation, and deposition. Artificial charge release is an unexplored potential geoengineering technique for modifying fogs, clouds, and rainfall. Central to evaluating these processes experimentally in the atmosphere is establishing an effective method for charge delivery. A small charge-delivering remotely piloted aircraft has been specially developed for this, which is electrically propelled. It carries controllable bipolar charge emitters (nominal emission current ±5 μA) beneath each wing, with optical cloud and meteorological sensors integrated into the airframe. Meteorological and droplet measurements are demonstrated to 2 km altitude by comparison with a radiosonde, including within cloud, and successful charge emission aloft verified by using programmed flight paths above an upward-facing surface electric field mill. This technological approach is readily scalable to provide nonpolluting fleets of charge-releasing aircraft, identifying and targeting droplet regions with their own sensors. Beyond geoengineering, agricultural, and biological aerosol applications, safe ionic propulsion of future electric aircraft also requires detailed investigation of charge effects on natural atmospheric droplet systems.

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Tuukka Petäjä, Ewan J. O’Connor, Dmitri Moisseev, Victoria A. Sinclair, Antti J. Manninen, Riikka Väänänen, Annakaisa von Lerber, Joel A. Thornton, Keri Nicoll, Walt Petersen, V. Chandrasekar, James N. Smith, Paul M. Winkler, Olaf Krüger, Hannele Hakola, Hilkka Timonen, David Brus, Tuomas Laurila, Eija Asmi, Marja-Liisa Riekkola, Lucia Mona, Paola Massoli, Ronny Engelmann, Mika Komppula, Jian Wang, Chongai Kuang, Jaana Bäck, Annele Virtanen, Janne Levula, Michael Ritsche, and Nicki Hickmon


During Biogenic Aerosols—Effects on Clouds and Climate (BAECC), the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program deployed the Second ARM Mobile Facility (AMF2) to Hyytiälä, Finland, for an 8-month intensive measurement campaign from February to September 2014. The primary research goal is to understand the role of biogenic aerosols in cloud formation. Hyytiälä is host to the Station for Measuring Ecosystem–Atmosphere Relations II (SMEAR II), one of the world’s most comprehensive surface in situ observation sites in a boreal forest environment. The station has been measuring atmospheric aerosols, biogenic emissions, and an extensive suite of parameters relevant to atmosphere–biosphere interactions continuously since 1996. Combining vertical profiles from AMF2 with surface-based in situ SMEAR II observations allows the processes at the surface to be directly related to processes occurring throughout the entire tropospheric column. Together with the inclusion of extensive surface precipitation measurements and intensive observation periods involving aircraft flights and novel radiosonde launches, the complementary observations provide a unique opportunity for investigating aerosol–cloud interactions and cloud-to-precipitation processes in a boreal environment. The BAECC dataset provides opportunities for evaluating and improving models of aerosol sources and transport, cloud microphysical processes, and boundary layer structures. In addition, numerical models are being used to bridge the gap between surface-based and tropospheric observations.

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