Passage IV

NATURAL SCIENCE: This passage is adapted from the article “When Research ls a Snow Job” by Sarah Boyle (©2002 by National Wildlife).

The figure is beyond comprehension: Every year, 1,000,000,000,000,000,000,000,000 (I septillion) snowflakes fall worldwide. As the crystals fall, they encounter different atmospheric conditions that produce flakes with unique attributes. The more complex those conditions are, the more elaborate the crystals.

Kenneth Libbrecht is a physicist at the California Institute of Technology. Along with the work of scientists at the U.S. Department of Agriculture’s Agricultural Research Service (ARS), his research is uncovering new information about the magical world of snow crystals—information that has practical applications in such diverse area as agriculture and the production of electricity.

Snow crystals are individual crystals—usually in a hexagonal form—while snowflakes are collections of two or more snow crystals. Beginning as condensed water vapor, a crystal typically grows around a nucleus of dust. Its shape depends on how the six side facets—or faces—grow in relation to the top and bottom facets. If they grow relatively tall, the crystal appears column-like; if the side facets are short compared to the length of the bottom and top facets, the crystal looks platelike.

Currently Libbrecht is trying to crack the problem of why the crystal facets’ growth varies with temperature. He believe this may have something to do with the ice surface’s “quasi-liquid” layer, which affects how water molecules stick to the surface.

By manipulating the temperature and humidity within an incubation chamber (and by adding an electric current or various gases at times), Libbrecht creates “designer” snowflakes in his lab. Such experiments are helping him determine how crystals form.

William Wergin, a retired ARS resear biologist, and a colleague, Eric Erbe, were using scanning electron microscopy to look at biological problems relating to agriculture. To avoid the laborious procedure that using such equipment usually entails, the two scientists decided to freeze the tissue they were working with and look at in the frozen state.

“One day it happened to be snowing,” says Wergin, “and we were looking for a specimen. We imaged some snowflakes and were very surprised to see what we did.” It was the first time anyone had attempted to image snow crystals with scanning electron microscopy, which provides precise detail about the crystals’ shape, structural features and metamorphosed conditions (crystals often change once on the ground depending on the surrounding environment).

Wergin called another ARS colleague, hydrologist Albert Rango, to see if the snow crystal magnifications had any applications for his research. Rango now uses Wergin’s electron microscopy data, along with microwave satellite data, in the Snowmelt Runoff Model to predict the amount of water available in a winter snowpack. For western states such as Colorado, Montana, Utah and Wyoming, about 75 percent of the annual water supply comes from snowmelt. Snowmelt water is critical to crop irrigation and hydroelectric power, as well as recreation and domestic water supplies, fisheries management and flood control.

Before employing the scanning electron microscopy results, the forecasted amounts of snowpack water were inaccurate whenever the size and shape of the snow crystals varied much from the norm. “The more we know about crystals,” notes Rango, “the easier it will be to use microwave satellite data for predictions of the snow water equivalent.”

Currently, forecasts using the model are about 90 percent accurate. A 1980 study estimated that improving the prediction by 1 percent would save $38 million in irrigation and hydropower in the western United States.

Rango is also looking ahead at climate change predictions. “Following the estimates that have been made about what will happen by 2100, things are definitely warming up,” he says. Temperature increases will likely result in a reduction in stream flow as overall snow accumulation decreases, winter precipitation runs off as rain, and water evaporates at a quicker rate. The gap between water supply and demand will magnify even more, greatly increasing water’s economic value, anticipates Rango.

Not only does the crystal research help gauge snowmelt, it is also useful in predicting avalanches, designing artificial snow, and perhaps in the near future, examining air pollution. “You can put snow in a scanning electron microscope and tell which elements are present, such as sulfur and nitrogen,” says Wergin. “You cant hen see what kind of pollution is in the area and possibly track the source.”