Measurement of How Air Motions Perturb Snowflake Orientation and Settling

Anyone who has watched snowflakes fall know that their motion is often erratic, moving sideways, swirling, lingering, or being swept towards the surface. These complex actions affect the precipitation rate, which is key for transportation safety and water resources. This project will use an advanced instrumentation suite to make measurements to address the problem of how air motions affect snowflake settling. The work will provide input to the numerical modeling community resulting in improved weather forecasting. The project contains significant public outreach, including continuing a popular data product related to avalanche danger, and will provide workforce training for students at the intersection of meteorology and mechanical engineering. The study will address the problem of how air motions affect hydrometeor settling, with a new hypothesis that horizontal mean wind plays a far more important role determining how fast hydrometeors settle than has been previously recognized. Measurements of snowflakes and atmospheric conditions will take place at a field site in Alta, Utah, equipped with a meteorological tower, Multi Angle Snowflake Camera (MASC) for high-resolution imagery of hydrometeors in free fall and the Differential Emissivity Imaging Disdrometer (DEID) for snowflake properties such as mass, size and density. Snowflake motion and background turbulence will be imaged through a combination of Particle Imaging/Tracking/Streak Velocimetry (PIV, PTV, PSV) techniques. The outcomes of the project will be: 1) Measurement of the effects of winds on hydrometeor settling, 2) Novel datasets for the study of the effects of environmental fluid flows on particle settling, and 3) New parameterizations describing the effects of wind variability on frozen hydrometeor settling. 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. NSF Award ID: 2608968 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Timothy Garrett | Institution: University of Utah, SALT LAKE CITY, UT | Award Amount: $699,464 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2608968 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2608968.html