How hail is produced in deep convective storms has been studied for several years, but many questions still remain. It is well-known that hailstones begin their growth around small ice particles which are referred to as hailstone embryos. Results over the last decade have drawn attention to an area in severe storms known as feeder cells. These are small convective clouds that form near the main storm cell and eventually are absorbed ("feed") into the main convective cell. It is speculated that, at least in some types of hailstorms, these feeder cells are the main producers of the embryos that eventually grow into large hail. In conjunction with the National Oceanic and Atmospheric Administration, the National Science Foundation will participate in a field program to study hailstorms. This project, known as the North Dakota Thunderstorm Project, will be held during the Summer of 1989. As part of this research effort, the Principal Investigator intends to study two aspects of embryo production. First, using in situ aircraft measurements, the microphysical characteristics of feeder cells will be investigated. This will include experimental seeding with artificial ice nuclei in the feeder cells to investigate the effects of premature nucleation on microphysical processes. The second area of investigation will focus on a phenomenon known as fine scale reflectivity patterns. These are areas of enhanced radar echo return and have been thought to be a source of hailstone embryos. Through direct sensing, the Principal plans to investigate the hypothesis that these are indeed areas of high concentration of embryos and that these embryos often find their way into the regions of the storm where large hail is produced. //

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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Stephan P. Nelson
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University of Wyoming
United States
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