Snowflake Stereography and Fallspeed

 

For a live feed of snowflakes from Alta when it’s snowing, please follow this link to the Snowflake Showcase at Alta Ski Area. Otherwise see this gallery. We greatly appreciate any support to continue running the Snowflake Showcase and further develop these cameras. All images on these pages are copyright Tim Garrett, and are freely available for non-commercial or educational purposes. Otherwise, please contact Dr. Garrett through the ACCS link above.


All cold weather forecasting models rely on having an accurate description of the relationships between snowflake mass, diameter and fallspeed. Further, these models need to be able to faithfully describe the complex and rapid processes of snowflake aggregation and droplet riming.

Studies of radar or microwave detection and transmission in the atmosphere rely on having accurate models for how electromagnetic radiation interacts with complex hydrometeor forms.


The physics is complicated enough that it is difficult to arrive at good answers for these problems using theory alone. Rather, the formulas that describe these processes must be based on observations of the real world. But this can be a tremendous  technical challenge because snow and rimed graupel particles are small, fast moving, delicate and prone to evaporate under examination.


To help solve this problem, Cale Fallgatter has designed and built a new instrument, the Multi-Angle Snowflake Camera, or MASC, that takes automated multi-angle images of snowflakes while they are in free-fall and simultaneously measures their fall-speed. Multi-angle views help to refine area, and mass reconstructions. MASC image acquisition software has been developed by Konstantin Shkurko.


The prototype MASC saw its in
augural Alta storm on April 30, 2011. Commercial versions of the MASC shown at right are available through startup company Fallgatter Technologies. The MASC has been sold to the US Army Cold Regions Research Laboratory for avalanche research at Mammoth Mountain, and to the Department of Energy and Vanderbilt University for climate studies in Alaska and Greenland.


Check out the pictures at this gallery or a live feed when it is snowing at Alta's Snowflake Showcase. The MASC has been featured in the news by several outlets, including NBC, Yahoo, Fox News and The WeatherChannel.


During the winter seasons of 2011-2012 and 2012-2013, Tim Garrett led the Wasatch Hydrometeor Aggregation and Riming Experiment (WASHARX), supported by the National Science Foundation. One MASC was placed at our remote site: the High Alpine Research Laboratory for Diversity in Snow (HARo
LDS), located at 10,000' altitude within Collins Gulch at the Alta Ski Area bounds. Alongside the MASC at HARoLDS was an FSSP-100 droplet size distribution probe.


At Alta Base at 8500’ alltitude, we placed a second MASC and, through a collaboration with Sandra Yuter at North Carolina State University,  a vertically-pointing 24 GHz Micro Rain Radar. Meteorological measurements were obtained at 6 locations throughout the depth of Collins Gulch.


We are using this data to obtain an unprecedented long-term database for characterizing frozen hydrometeors and their vertical evolution as they fall through a storm. A summary of our most recent results is presented in:


Garrett, T. J., C. Fallgatter, K. Shkurko, and D. Howlett, 2012: Fallspeed measurement and high-resolution multi-angle photography of hydrometeors in freefall. Atmos. Meas. Tech., 5, 2625-2633, doi:10.5194/amt-5-2625-2012


In previous years we have taken photographs at HARoLDS with a more primitive version of the MASC, a HYVIS from Meisei Inc. in Japan. See a full time-series of an April 2010 storm here.


Alta Ski Area and NoHow Inc, provide essential logistical and technical support for this project