Collaborative Research: Secondary Production of Ice in CUmuLus Experiment (SPICULE)

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Clouds can contain liquid droplets, frozen crystals, or a mixture of both. Whether a cloud is mostly liquid or mostly frozen has a significant impact on the potential for precipitation and the interaction of the cloud with radiation. Certain clouds can change from mostly liquid to entirely frozen in a surprisingly short amount of time, a phenomenon known as glaciation. The speed at which clouds glaciate is dependent on the phenomena of secondary ice production, where the freezing of some droplets affects others in a cascading fashion. The exact mechanism for efficient secondary ice production is still up for debate in the scientific community. This project will consist of two research aircraft making measurements of the same cloud at different heights to provide additional data on secondary ice production. The main societal impact of the award will be through the improvement of the representation of ice processes in numerical weather models, leading to better weather forecasts and climate projections. Student involvement will ensure the education and training of the next generation of scientists.The research team will conduct a summer 2020 field campaign in the western Great Plains to improve understanding of the processes involved in ice initiation and secondary ice production in cumulus clouds. The investigators argue that the well-known Hallet-Mossup process is not able to explain the observed rapid glaciation of cumulus clouds, and they offer the alternative hypothesis that the development of supercooled liquid droplets at the -5C level in strong cumulus updrafts leads to a spicule production/drop fracturing secondary ice production and rapid glaciation by the -20C level. The study is designed to provide improved quantitative measurements with dedicated flight profiles that will minimize ambiguity associated with primary nucleation and contamination from older clouds. The NSF/National Center for Atmospheric Research C-130 aircraft would target the below cloud region through the 0C level and the SPEC LearJet would penetrate the cloud from the 0C level and up in altitude. Important instruments include the Colorado State University suite of ice nuclei probes, the SPEC 3V-CPI and the University of Wyoming W-band cloud radar.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.