History and Future Directions in Monitoring Natural Ice Nuclei Populations

Modern weather modification research and operations began in the late 1940's. From the beginning, a basic foundation for the conceptual models of precipitation enhancement by cloud seeding in supercooled clouds, and hail suppression by cloud seeding in convective clouds, has been the hypothesis that increasing the concentration of active ice nuclei above that that is normally naturally present will lead to more efficient mixed-phase precipitation processes, and to higher concentrations of smaller hailstones in hailfalls. The technology for monitoring ice nucleating activity of the natural aerosol developed as part of the general weather modification research that began at this time. A variety of instruments have been developed over the years. None has been accepted as universally superior at predicting the activity of the aerosol in clouds. This technology really stopped evolving after the dramatic reduction in weather modification research funding after 1980. Today's weather modification operational paradigm requires customizing seeding materials and seeding rates to specific conditions. Improved quantification of the activity of the natural aerosol as ice nuclei is needed to improve cloud seeding operations. A survey of past measurement technology and a look at future innovations that could lead to improvements will be presented.