Simulated storm lifetime and precipitation production is exquisitely sensitive to the parameterized rate of precipitation formation and condensate removal. Extensive prior research has shown that the achilles heel in our ability to provide accurate weather forecasts lies in how models represent bulk microphysics parameterizations (BMPs), particularly when it comes to mixed and ice phase processes. There are two core questions here: 1) For a given meteorological scenario, how is hydrometeor habit and particle diameter (or area) related to particle mass and fallspeed? 2) How do the relationships between hydrometeor habit, size, mass and fallspeed in a storm evolve due to aggregation and riming processes?

The next generation of BMPs for weather models needs to be informed by new measurement methods that must be capable of detailed characterization of hydrometeor form, three-dimensional structure, and fallspeed, conditioned by detailed information about the local meteorological context. Past research into these problems has been challenged by either a necessity to mathematically idealize ice crystal shapes, imprecise measurement methods, or an element of subjectivity due to a need for direct human participation in field measurement.

Intellectual merit:

This project will remove much of the guesswork in prior observational efforts with an unprecedented combination of meteorological and microphysical measurements. For the winter of 2011-2012, the Wasatch Hydrometeor Aggregation and Riming Experiment (WASHARX) will have as its centerpiece the newly developed Multi-Angle Snowflake Camera (MASC). This is a potentially transformative instrument since it will provide, for the first time, fully-automated 20 ìm-resolution multiply-stereoscopic color photography of hydrometeors, along with concurrent measurement of their fallspeed. Within the bounds of a high-altitude ski resort along the Wasatch Front near Salt Lake City, two of these new instruments will be installed within a steep, highly protected side canyon. The two MASCs will be vertically separated by 410 m. This observing system will also be accompanied by meteorological measurements along the full canyon depth of 760 m, as well as a cloud droplet size distribution probe and the North Carolina State University's vertically-pointing 1.2 cm MicroRainRadar. The expected outcome of this project will be an unprecedented data set that will be used for studying hydrometeor fallspeed relationships and their vertical evolution due to aggregation and riming processes within a storm system.

Broader impacts:

Scientific progress in our field has regularly hinged on broad accessibility of new tools. In addition to providing new BMPs for future integration in weather and climate models, this study will help support scientific development of a new instrument (and manufacture of a replica) that we intend to make available for future scientific field programs. Indeed, initial steps have been made toward commercial production of this instrument for scientific research, environmental safety applications and public interest. The project also has a broad educational component. The 3D steroscopic images obtained at the local ski area will be made accessible in real-time to classrooms and the general public through a website developed in cooperation with Alta Ski Area. Finally, we will work with local K-12 level teachers to develop modules for relating snowflake form to local meteorology.

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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A. Gannet Hallar
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North Carolina State University Raleigh
United States
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