Aircraft Studies of Charge-Enhanced Contact Ice Nucleation

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The Principal Investigators are making fundamental measurements needed for advancing understanding of the mechanisms and conditions that lead to the formation of ice crystals in clouds. One of the major unsolved issues in atmospheric science is the determination of the physical processes that lead to the initial formation of ice particles in clouds. The intellectual merit of this research is that new critical data on the generation of ice in clouds are being obtained by direct, in situ, measurements. Important data on ice formation are being obtained using facilities of the National Science Foundation during the Ice in Cloud Experiment (ICE). Data on the microphysical properties of clouds are being obtained by aircraft equipped with the most advanced cloud physics instruments. The Principal Investigators are using their unique sensitive electrometer to measure the average charge carried by cloud drops and aerosol particles. They are investigating how naturally occurring charges enhance the scavenging of aerosol particles by cloud drops and whether the resulting contact causes cloud drops to freeze. Data on charge are critical because without charge-induced attraction between aerosol and cloud drops contact is unlikely. The measurements made by the Principal Investigators are being used to evaluate the physical processes responsible for initial ice formation and the rates of contact-freezing of cloud drops in stratus and cumulus clouds.Because the conversion of supercooled cloud drops to ice significantly changes the cloud radiative properties, the broader impacts of the Principal Investigators' research will lead to improvements in cloud radiation calculations. Applications include better retrieval of cloud properties from satellite data and more accurate predictions by climate models. In addition to the importance of the research on ice formation in clouds, the Principal Investigators' research will advance understanding in related disciplines such as scavenging of air pollution by clouds. This project is contributing to the development of scientific infrastructure through the creation and utilization of new instrumentation to address unresolved problems in atmospheric science.