April 10, 2013
High-Speed Camera Captures Snowflake Geometries In Midair
Brett Smith for redOrbit.com - Your Universe Online
It is said that no two snowflakes are alike and new research from the University of Utah shows just how unique the cold-weather precipitation can be.
Using a high-speed camera system, the researchers were able to capture images of individual snowflakes and determine how fast they were falling to the ground.
"For forecasting the weather, fall speed is the thing that matters," Tim Garrett, an associate professor of atmospheric sciences at the university, said in a statement. "The weather models right now do OK at simulating clouds, but they are struggling to accurately reproduce precipitation: rain or snow, but particularly snow.”
“The problem is that we do not have a very good sense for how the sizes and shapes of snow particles relate to how fast they fall,” Garrett said. “This is important because the lifetime of a storm, and where exactly it snows, depends greatly on how fast snow precipitates."
Besides assisting in weather forecasting, Garrett said its important to understand how falling snow disrupts microwave communications; "the big problem is there is a very poor sense of how microwave radiation interacts with complex snowflake shapes.”
Modern weather forecasting models use complicated formulas to simulate precipitation and predict the evolution of a storm system.
"There has been a huge amount of research into improving these formulas, but their accuracy is limited by how well we are able to measure snow and how fast it falls,” Garrett said.
Forecasting calculations are still based on research performed during the 1970s in the Northwestern US along the Cascade Range. Snowflake fall speed was measured, and then flakes were photographed, collected and melted to determine their mass — all by hand.
"These early researchers got only a few hundred images over two years because they had to collect each snowflake individually by hand," Garrett said. "Our snowflake camera can automatically collect thousands of snowflake photographs in a single night."
Using two multi-angle cameras at Utah's Alta Ski Area located above Salt Lake City, the researchers capture black-and-white images of the snowflake, since color sometimes lowers image definition.
Once the images are taken, the Utah researchers utilize image-analysis software to differentiate snowflakes by form, intricacy, size and estimated mass.
"The complexity is so vast as to almost defy an easy categorization of snowflakes," Garrett said. "Everything lies along a continuum of possible sizes, shapes and extent of riming."
Besides capturing and categorizing the snowflakes, the researcher also use vertically pointed radar that determines the precipitation composition in the air column overhead.
"The radar tells you how strong the storm is, where and when there are layers of rain and snow, and how tall the storm is," Garrett said. "To interpret what we're seeing with the cameras, it helps to know the structure within the storm and how it is changing with time."
He added that the study´s use of radar coincides with industry standards for meteorologists.
"Ultimately, the primary diagnostic tool that weather forecasters use during a storm is radar, and they want to be able to relate what they see on radar to whether or not there is snow or graupel, and how much,” Garret said.
Click here to view an interactive showcase of the snowflakes captured in Garrett's study.